1. SOURCES, UTILIZATION, AND CLASSIFICATION OF OILS AND FATS
Classification of Fats and Oils
Milk Fat Group
Lauric Acid Group
Vegetable Butter Group
Animal Fat Group
Oleic-Linoleic Acid group
Erucic Acid Group
Conjugated Acid Group
Marine Oil Group
Hydroxy Acid Group
2. PHYSICAL PROPERTIES OF FATS AND FATTY ACIDS
Oiliness and Viscosity
Surface and Interfacial Tension
Density in the Solid State
Density and Volume of Plastic Fats Dilatometry
Heat of Combustion
Specific Heats, heats of Fusion or Crystallization
Vaporpressure and Boiling Points. Heat of Vaporization
Thermal Conductivity
Miscibility with Organic Solvents
Solubility in Organic Solvents
Mutual Solubility of Fats and Fatty Acids with Water
solubility of Gases In Fats
Refractive Index
Absorption Spectra
Resistance
Dielectric Constant
3. REACTIONS OF FATS AND FATTY ACIDS
Hydrolysis
Interesterification
Saponification with Alkalies
Formation of Metal Soaps
Hydrogenation in the Carboxyl Group
Formation of Nitrogen Derivatives
Formation of Acid Chlorides
Hydrogenation
Halogenation
Addition of Thiocyanogen
Addition of Maleic Anhydride
Sulfation, Sulfonation
Chemical oxidation Epoxidation and hydroxylation
Atmospheric oxidations Rancidity
Polymerization
Isomerization
Reactions of Hydroxyl Groups
Preparation of Ketones, Aldehydes, and Hydrocarbons from Fatty Acids
Pyrolysis to Produce Motor Fuels
Manufacture of Sebacic Acid
4. VINYL LAURATE AND OTHER VINYLE ESTERS
5. LINOLENIC ACID AND LINOLENYL ALCOHOL
Some Reaction Products
Linolenyl Alocohol
Linolenyl Aldehydes
Miscellaneous
6. FRACTIONATION OF FATS AND FATTY ACIDS
Fractional Crystallization
Winterization of Vegetable Oils
Cold Clearing of Fish Oils
Fractional Crystallization of animal Fats
Crystallization of Vegetable Stearines
Fractional Crystallization of Fatty Acids
Liquid-Liquid Extraction
Solvents for Liquid-Liquid Extraction Liquid-Liquid Extraction In Practice
Theory and General Practice
Purification of Fatty Acids by Distillation
Fractional Distillation of Fatty Acids
Molecular Distillation
Methods Involving Chemical Reaction
Urea Adducts
Chromatography
Countercurrent Distribution
Recovery of Minor Constituents
7. SOLIDIFICATION, HOMOGENIZATION, AND EMULSIFICATION
Plasticizing of lard and Shortenings
Solidification of Margarine
Solidification of Soap Products
Emulsification
Peanut Oil
Milling of Groundnut
Effect fo Storage of Groundut Kernels of the Yield & Quality of Oils and Cake
Effect fo Size Reduction of the Kernels Prior to Crushing
Cooking of Prepared Seed Material
Optimum Quantity of Oils to be left in the First Pressed Cake
Summary of The Results
Olive Oil
Palm Oils
Sesame Oil
Corn Oil
Safflower Oil
Tobacco Seed Oil
Poppyseed Oil
Teased Oil
Kapok Oil
Rice Bran Oil
Sorghum oil
Other Oleic-Linoleic Oils
Rapeseed Oil
OtherErucic Acid Oils
Linolenic Acid Oils
Soybean Oil (91)
Perilla Oil
Hempseed Oil    
Wheat Germ Oil
Horse Fat
Other Linolenic Acid Oils
Conjugated Acid oils
Tung Oils
Oiticica oil
Ises in coating
In Conclusion
Marine Oils
Whale Oil
Sardine or Pilchard Oil
Japanese Sardine Oil
Menhaden Oil
Herring Oil
Fish Liver Oils
Hyrdoxy Acid Oils
Castory Oil
8. KOKUM
Garcinia Indica Chois
Description
Flowering And Fruiting
Distribution
Estimation of Seed Production
Collection of Seeds
Oil
9. MAHUA
Description
Flowering And Fruiting
Distribution
Locaity Factors
Propagation
Estimation of Seed Production
Other Uses
10. NEEM
Description
flowering and Fruting
Distribution
Locality Factors
Propagation
Usefulness in Afforestation
Estimation of Seed Production
Collection And Storage of Seeds
Oil Other Uses
11. PUNNA, UNDI
Flowering And Fruting
Distribution
Locality Factors
Propagation
Estimation of Seed Production
Collection of Seeds
Oil
Uses of the oil
Other Uses
12. KARANJ
Description
Flowering & Fruiting
Distribution
Locality Factors
Propagation
Usefulness in Afforestation
Estimation of Seed Production
Collection and Storage of Seeds
Oil
Uses of the oil
Other uses
13. KUSUM
Description
Flowering And Fruiting
Distribution
Locality Factors
Propagation
Estimation of Seed Production
Collection of Seeds
Oil
Uses of the oil and Cake
14. DHUPA
Description
Flowering and Fruiting
Distribution
Locality Factors
Propagation
Estimation of Seed Production
Collection of Seeds
Fat
Uses of Fat
Other uses
15. NAHOR
Description
Flowering and Fruiting
Distribution
Locality Factors
Propagation
Estimation of Seed Production
Collection of seeds
Oil
Uses fo The oil
Refining of oil
Other Uses
16. KHAKAN, PILU
Description
Flowering And Frutting
Distribution
Locality Factors
Propagation
Usefulness in Afforestation
Estimation of Seed Production
Collection and Storage of Seeds
Fat
Other used
17. PISA
Description
flowering and Fruiting
Distribution
Locality Factors
Propagation
Estimation of Seed Production
Collection and Processing of Seed
Oil
18. TALL OIL
Recovery of Tal oil
Application of Tall oil
19. TALL OIL PRODUCTS IN SURFACE COATINGS
Tall Oil in Alkyd Resing
Tall Oil Formulation in Alkyd Resins
Esters of Tall Oil Products
Other Uses for Tall Oil Products
20. TALL OIL IN THE PLASTICIZER FIELD
Tallate Driers
Esterification of Tall Oil For Plasticizers
Tall oil in Adhesives and Linoleum Cement
Tall oil In Rubber-Based Adhesives
Tall Oil In Hot-Melt Adhesives
Tall Oil Production in Linoleum Cements
Formulation with Tall Oil
Formulation with Tall Oil Esters
Tall Oil in Asphalt Products and Petroleum uses
Tall Oil In Asphalt
Roads
Soil Treatment
Roofing
Adhesives
Antistripping Agents
Plasticizers
Miscellaneous
Tall Oil In Petroleum Application
Oil and Gas Well Fracturing
Drilling Muds
Demulsification Agents
Corroson Inhibitors
Catalyst
Lubricating Oil Additives
21. TALL OIL IN LIQUID SOAPS
Tall Oil In Disinfectants
Tall Oil In Synthetic Detergents & Wetting Agents
Tall Oil In Biodegradable Detergents
22. TALL OIL IN RUBBER
Styrene-Butadiene Rubber
Foam rubber
Tall Oil In Paper Size
Paper Making Process
Rosin Sizing Materials
Forms of Size Available
Paste Size
Dry Size
Methods of Proeparing Liquid Size
Cooking Process
Emulsion Process
Bewoid Process
Delthirna Process
Internal And External Sizing
Effect of Wet Strength Resings and Paper Coating Resins of Sizing
Sizing of Nonconventional paper
Testing of Sizing
23. SOAP AND OTHER SURFACE ACTIVE AGENTS
Commercial Soap Products
Characteristics of Soaps Saponified by different Methods
Effect of Different Factors on Physical Characteristics of Bar Soaps
Types of Commercial Soap
Furface-Active Agents Other Than Soap
Classification of Surfactints
List of Surfactants
Anionic Surfactants
Nonionic Surfactants
Ampholytic Surfactants
Applications
Detergents
Wetting Agents
24. PAINTS, VARNISHES, AND RELATED PRODUCTS
Materials
Unmodified Drying Oils
Modified Drying Oils
Resins and Copolymerizing Materials
Dryers
Thinners
Pigments
Miscellaneous Engredients
Manufactured Products
Oil Paints
Varnishes Adn Enamels
Water-Dispersible Paints
Printing Inks
Manufacturing Operations
Cooking of Varnishes and Resins
Mixing and Grinding
Other Mechanical Operations
25. MISCELLANEOUS OIL AND FAT PRODUCTS
Linoleum
Oiled Fabrics
Putty and Other Sealing or Calking Materials
Rubberlike Materials
Core Oils
Lubricating Greases
Cutting Oils
Oil For Leather Treatment
Textile Lubricants and Softening Agents
Plasticizers
Illuminants and Fuels
Cosmetic And Pharmaceutical Oils
Tinning Oils
Hydraulic Oils
Insecticides and Fungicides
Commercial Stearic and Oleic Acids
Other Fatty Acids
Metal Soaps
26. ISOCYANATE-MODIFIED DEHYDRATED CASTOR OIL
Introduction
Materials and Methods
Analytical Methods
Preparation of Urethane Derivatives
Film Characteristics
Results and Discussion
27. STYRENE COPOLYMERISATION OF ISOMERISED TOBACCO
SEED (NICOTIANA TOBACUM) OIL AND ITS ALKYD
Experimental
Materials used
Isomerisation
Styrenation of tobacco seed oil
Preparation of styrenated alkyds
Post-strenation Process
Results and Discussion
Isomerisation
Styrenation
Drying Characteristics
Flexibility and Adhesion
Scratch hardness
Water resistance
Acid resistance
Alkali Resistance
Conclusion
28. MODIFIED MAROTI OIL (HYDNOCARPUS WIGHTIANA) FOR ALKYDS
Experimental Techniques and Results
Formulation of alkyds
Evaluation of film properties
Discussion
Conclusion
29. IMPROVED ALKYDS WITH EPOXIDISED RUBBERSEED OIL
Experimental Techniques and Results
Formulation of alkyds
Evaluation of film properties
Discussion
Concluion
30. ALKYDS BASED ON BLOWN KARANJA OIL
Experimetal
Formulation of alkyds
Discussion
Conclusion
31. THE PREVENTION OF GELATION DURING THE
MALEINISATION OF DEHYDRATED CASTOR OIL
Experimental
Preparation
Maleinisation
Water solubility
Results and Discussion
Reaction with Acrylonitrile
Reaction with acetic anhydride and phosphorus pentachloride
32. UTILIZATION OF NONCONVENTIONAL OILS
Discussioh
Conclusion
33. CASTOR-UREA RESINOUS OIL
Experimental
Discussion of Results
34. PALMDIESEL AS ALTERNATIVE RENEWABLE ENERGY
Chemistry of The Reaction
Laboratory Evaluation of Alkyl Esters as Diesel Substitutes
Stationary Engine test
Prelminary Field Trial
Porim vehicles
Taxis
Exhaustive Field Trial
Pilot Plant
Recovery of Vitamin E & Other Minor Components from Methyl Esters
Future Development
Reduction of pour points of methyl esters
One Step conversion of the process
More uses of Glycerol
Methylesters as kerosene Substitute
Other uses of esters
Conclusion
Inclusion Compounds
Cage (Clathrate) inclusion Compounds
35. EXTRACTION OF FATS AND OILS
Preparation of Animal Material
Preparation of Oil Seeds
Heat Treatment of Oil-bearing Materials
Rendering of Animal Fats
Cooking of Oil Seeds
Batch Pressing
Mechanical Expression of Oil
Continuous Pressing
Low-Pressure Pressing
Centrifugal Expression
Solvent Extraction
Application
Recovery of Oil from Fruit Pulps
Extraction of Olive Oil
Extraction of Palm Oil
36. REFINING AND BLEACHING
Refining & Bleaching Methods
Effect of Refining & Other Processing Treatment on specific Impurities
Refining Losses
Applications
Desliming or Degumming
Degumming by hydration
Preparation of Commercial Lecithin
Acid Refining
Removal of Break Material by Heat Treatment
Alkali Refining
Reffining with Caustic Soda
Color Standards
Chemical Bleaching
37. HYDROGENATION
Importance of Hydrogenation
Heat of reaction
Diversity of Possible Reactions
Selectivity with Respect to Different classes fo Glycerides
Nickel Alloy or Raney Catalysts
Hydrogenation Equipment
Characteristics of hydrogenated Fats
Hydrogenation of Shortening Stocks
Hydrogenation of Margarine Oils
Hydrogenation of Hard Butter Substitutes
Hydrogenation of Inedible Fats and Fatty Acids
removal of Nickel From hydrogenated oils
Special hydrogenation Processes
Hydrogenation to Produce Fatty Alcohols
Fatty Alcohols by Sodium Reduction
Conjugated Hydrogenation
Hydrogenation of Nitriles to Produce Fatty Amines
Hydrogenation in Solvents
38. DEODORIZATION
Historical
Naturel of Deodorization Process
General Design Features
Batch Deodorization
Continuous Deodorization
39. CUTTING OIL
Manufacture of Soluble Cutting Oil
Soluble Cutting Oil by Sulphonated Oils
Manufactur fo Straight Cutting Oils
Process
Plant Economics
40. RICE BRAN OIL
Introduction
Process of Manufacture
Plant Economics
Manufacturers of Raw Materials
Manufacturers of fatty acids, fatty oils, drying oils & Its derivatives (UK)

^ Top

Extraction of Fats and Oils

The separation of oils and fats from oil-bearing animal and vegetable materials constitutes a distinct and specialized branch of fat technology. The widely differing characteristics of fatty materials from diverse sources have given rise to extraction processes such as rendering, pressing, and solvent extraction. All extraction processes, however, have certain objects in common. These are, first, to obtain the fat or oil uninjured and as free as possible from undesirable impurities; second, to obtain the fat or oil in as high a yield as is consistent with the economy of the process; and third, to produce and oil cake or residue of the greatest possible value.

Fatty animal tissues consist largely of fat and water which may be separated from the solid portions of the tissue and from each other with relative ease by one of the rendering processes. The extraction of vegetable oils is a more difficult matter. Vegetable materials, and in particular some of the oil seeds, contain a large proportion of solid material associated with the oil. Here, careful reduction of the material, followed by heat treatment, and the application with the oil. Here, careful reduction of the material, followed by heat treatment, and the application of heavy pressure, is required to obtain an efficient separation of the oil from the solids.

Even after the most efficient pressing, an oil cake will retain an appreciable amount to absorbed oil, usually amounting to 2.5 to 5% by weight. In the case of seed or other materials initially high in oil and low in solids content, the un-extracted residue will contain only a small fraction of the total oil. However, in seeds of low oil content, for example, soybeans, it may contain as much as 15% to 20% of the total oil. For the processing of low-soil seeds solvent extraction is particularly valuable, since it will reduce residual oil in the extracted seeds to less than 1%. The chief disadvantages of solvent extraction are the high initial seeds to less than 1%. The chief disadvantages of solvent extraction are the high initial cost of the equipment and the fact that some oil seeds disintegrate under the influence of the solvent and consequently are difficult to handle.

A number of more-or-less critical operations in oil milling are auxiliary to the actual expression or extraction. Wherever possible it is desirable to decorticate oil seeds before the oil is removed in order both to increase the capacity of the extraction equipment and to avoid loss of oil through absorption by the hulls. The seeds must then be rolled, g round, or otherwise reduced to fine particles. After they are reduced, they must be given heat treatment to make the walls of the oil cells permeable to the oil and to render the oil free-flowing, except where solvent extraction is used; then heat treatment is not generally necessary. In processing cottonseed, special attention must be given to the inactivation of gossypol or other toxic constituents.

In extracting oil from oil seeds there are some major differences between common American and common European practice. They result from basic differences in the supply of raw materials. Most American mills operate on domestic oil seeds, and they are usually located close to producing areas. Frequently only one type of oil seed is processed. The quality of the seed is generally high, with relatively little variation in seed characteristics through the processing season or from one season to another. European mills, on the other hand, process imported raw materials almost exclusively, and each mill must be prepared to handle a variety of oil seeds differing widely in quality and processing characteristics. As a result, American milling practice has become highly specialized, with the object in each case being to perform a specific operation with the highest possible efficiency. In European mills it has been necessary to sacritice some operating efficiency in favour of flexibility of operation. This accounts for the greater use in Europe of cage-type as opposed to open-type batch presses; and for the employment of multistage continuous pressing, as compared to single-stage high-pressure pressing in America.

Table 1.

Average yield of oil from commercial processing of common oil seeds (Percent oil from seed of normal moisture content)a

Babassu (kernels)	63	Perilla seed	37
Castor beans	45	Roppyseed	40
Coconut (copra)	63	Rapeseed	35
Corn (germs)	45	Rice bran	14
Cottonseed	16	Safflowerseed	28
Flaxseed	34	Sesam seed	47
Hempseed	24	Soybeans	18
Kapok seed	20	Sunflowerseed	25
Oiticica (kernels)	60	Teaseed	48
Plam, African (kernels)	45	Tung	35
Peanuts	35

The average yields of oil obtainable by commercial extraction methods from a number of common oil seeds are summarized in Table 1. Certain comparative data on whole seeds and kernels are found in Table 2. For information on yields from fruit pulps and animal sources, reference should be made to the specific fats and oils in other portions of this chapter and in other chapters.

It is probable that the first methods of fat extraction were rendering procedures practiced by primitive man, following cooking techniques developed for the preparation of meats for food. The pressing of oil from olive pulp probably antedated the pressing of oil seeds, although seeds were processed by the Chinese and others at an early date using mechanical presses operated by wedges or levers. On the other hand, the more efficient hydraulic operation of mechanical presses was not adopted until early in the nineteenth century. The continuous screw press is a modern development, and the solvent extraction of oil seeds on a large scale was not a reality until after World War I.

*Soyabeans are now being dehulled at many mills so as to produce a 50% protein soybean meal especially suitable where low fiber content is important in a feed.

The residues from the processing of oil seeds or animal tissues for fat are generally high in protein content and are in good demand as animal feedstuffs. They have a limited use as a source of human food (soybean or cottonseed flour), or as a source of industrial proteins (for example, for making glues). The residues from castor beans and tung nuts are toxic unless specially treated; hence they are used only as fertilizer, etc.

Mechanical Pretreatment

PREPARATION OF ANIMAL MATERIAL

Fatty animal materials, as compared with oil seeds and other vegetable materials, require comparatively little preparation prior to the rendering operation. Fatty stock destined for the production of neutral, low-temperature-rendered fats, such as oleo stock or neutral lard, is carefully trimmed and washed before it is charged to the rendering units. Ordinary stock, such as that used in making prime steam lard, is always washed and is less carefully trimmed.

In the larger establishments the stock to be rendered is sorted into different classes of material, partly to avoid mixing high-quality materials with those of low quality, and partly because some stocks, such as those containing large bones, require more severe rendering than others.

In either dry rendering or steam rendering, separation of the fat is more rapid if the fatty stock is first cut into small pieces, although this operation is ordinarily omitted in steam rendering. Prolonged wet rendering under pressure will disintegrate even large bones or whole carcasses, so that the preparation of stock for this process is not critical.

Rotary hashers, similar in principle to ordinary household food choppers, are used for the reduction of stock which is free from bones. The degree of reduction is usually much coarser than that employed in the processing of oil seeds; the dimensions of the hashed pieces may be measured in large fractions of inches or even in inches. Most animal materials disintegrate quite readily. Whale blubber is particularly tough and requires more drastic treatment. Blubber presses, consisting of heavy corrugated rolls, are now in use. Passage of large chunks of blubber through these rolls reduces them to semi fluid condition and decreases the rendering time.

PREPARATION OF OIL SEEDS

Cleaning. The first step in the processing of oil seeds is cleaning to separate foreign material. Sticks, stems, leaves, and similar trash are usually removed by means of revolving screens or reels. Sand or dirt is also removed by screening. Permanent or electromagnets installed over a conveyor belt are used for the removal of tramp iron. Specialm "stoners" are employed for taking out heavy stones and mud balls from shelled peanuts. As stated previously, the cleaning of oil seeds is preferably carried out before the seeds are placed in storage. Often, however, it is not, since adequate cleaning capacity is costly.

Dehulling and Separation of Hulls. Wherever practicable, oil seeds are preferably decorticated before they are extracted. The hulls of oil-bearing seeds are low in oil content, usually containing not more than about 1%, although contamination with kernels will, of course, increase the oil content with resultant loss of available oil. If the hulls are not removed from the seeds before the latter are extracted, they reduce the total yield of oil by absorbing and retaining oil in the press cake and, in addition, reduce the capacity of the extraction equipment.

The hulling machines used for the decortication of medium-sized oil seeds with a flexible seed coat, such as cottonseed, peanuts, and sunflowerseed, are of two principal types: bar hullers and disk hullers.

The rotating member of a bar huller is a cylinder equipped on its outer surface with a number of slightly projecting, longitudinally placed, sharply ground, square-edged knives or "bars." Opposed to the cylinder over an area corresponding to about one-third of its surface is a concave member provided with similar projecting bars. The seeds are fed between the rotating cylinder and the concave member, and the hulls are split as the seeds are caught, between the opposed cutting edges. The clearance between the cutting edges may be adjusted for seeds of different sizes.

The disk huller is more or less similar in principle to the bar huller except that the cutting edges consist of grooves cut radially in the surfaces of two opposed and vertically mounted disks, one of which is stationary and the other rotating. The seeds are fed to the center of the disks and are discharged at their periphery by centrifugal force. With either type of huller the condition of the seed is somewhat critical. Wet seed are difficult to split cleanly and may clog the huller, particularly if it is of the disk type. On the other hand, if the seeds are very dry, the kernels may disintegrate excessively.

Different seeds very considerably in the readiness with which they fall out of the split hulls. Peanuts, for example, are loose in the shell and separate readily. Cottonseed kernels or "meats : are more adherent to the hull; consequently, the hulls are customarily passed through a hull beater to detach small meat particles after the first separation of hulls and meats by screening. The separation systems used for cottonseed, peanuts, etc., consist of various combinations of vibrating screens and pneumatic lifts. It is necessary not only to separate the hulls from the meats but also to separate and recycle a certain proportion of uncut seeds which escape the action of the huller. In the case of cottonseed the following separations are commonly carried out: (a) separation of large meat particles from hulls and uncut seed screening: (b) separation of hulls from uncut seed by an air lift: (c)separation of small meat particles from hulls by beating and screening; and (d) separation of hull particles from meats by air.

In practical mill operation, especially on cottonseeds, the greatest yield of oil is obtained by nicely balancing the degree of separation attained. If an attempt is made to separate hulls from the meats too cleanly, there will be a loss of oil due to meats being carried over into the hulls. If an excessive proportion of hulls is left in the kernels, there will likewise be an undue loss of oils from absorption by the hulls. Under certain condition, there may be an appreciable loss of oil due to absorption by the hulls. Under certain condition, there may be an appreciable loss of oil due to absorption by the hulls an the latter come into contact with the oily meat particles during the separation operation. It is generally advisable to effect the separation of kernels and hulls as quickly as possible after the seeds are hulled, in order to avoid excessive contact between hulls and kernels or kenel particles.

Cottonseed are invariable delivered to the mills from the gins without removal of their coating of short fibers or linters, and must be delinted before they are hulled. Delintering machines (known as "linter") are similar in principle and appearance to cotton gins, consisting essentially of a revolving assembly of closely spaced circular saws which pick the lint from the seed. The fibers are removed from the saw teeth by a revolving cylindrical brush or by an air blast that suspends them in an air stream in which they are conveyed through pipes to collection equipment. The lint is not ordinary removed from the seed in a single operation but is taken off in two or three cuts. Each successive cut is of lower grade than the cut preceding it since increasing quantities of hull material are removed by the saws as delinting proceeds and fiber length is decreased.

Previously soybeans were seldom decorticated before processing for oil (except where the meal was destined for human consumption) because of mechanical difficulties and because the hull constitutes but a small part of the seed and is relatively nonabsorbent. Today, dehulling is increasingly common. It is usually accomplished by first cracking the beans on cracking rolls and then separating the hulls from the kernels in two stages :

1. Hulls are secreened from kernels and uncracked beans and aspirated at the end of the top deck of a double-deck shaking screen. Uncracked beans are returned to the cracking rolls while the kernels are put on a second deck of finer mesh screen at the end of which hulls are again aspirated. Fines are joined to the whole kernel flow.
2. Hulls which have been aspirated contain some kernel particles. Therefore, these are subjected to an air separation using a gravity table to separate the light hulls from the heavier kernels. Depending on the degree of separation required, a "middling" fraction may be taken and this broken down on another gravity table.

A somewhat different system makes use of simultaneous grinding and aspiration to dehull the beans and separate the hulls. In general, the choice of system, depends on the processor, who may use many modifications of general techniques for his purposes.

Small oil seeds, such as flaxseed, perilla, rapeseed, and sesame, are usually processed without decoration. In some cases it would be desirable to hull the small seeds if this could be done economically; but so far the process has been considered impracticable. Owen has reported a series of experiments in the dry decortication of flaxseed and other small oil seeds using an experimental machine of unspecified design. He concludes that hulling of linseed is impracticable because a large portion of the total oil is contained in the separated hull, but he suggests that it might prove advantageous in the case of certain other small seeds, for example, hampseed.

The various palm kernels, such as oil palm or Africa palm kernels, babassu kernels, and cohune kernels, constitute a special class of oil seeds, since they are of relatively large size and are surrounded by a particularly hard, thick shell. Because of the low cost of labor in the producing regions, the large size of the nuts, and the refractory nature of the shells, these nuts are often cracked and the kernels separated by hand. The entire production of Brazilian babassu kernels, amounting in some seasons to 25,000 tons, has in the past been separated in this manner.

In Africa, nuts of the oil palm, which are less thick-shelled than most of the American palm nuts, are apparently hand-cracked to some extent; but on the plantations of Indonesia and Malaysia they are usually machine-cracked. In one type of machine the nuts are fed to the center of a rotor provided with curved baffles, along which the nuts are flung out against a heavy steel housing and broken by impact Another type of machine is simply a special type of hammer mill. The rotor consists of a frame supporting four heavy steel paddles; the nuts are dropped into the path of the paddles and cracked by impact.

After the nuts are cracked they are dropped to rotary screens where some separation of kernels and shells is obtained. A considerable proportion of shell fragment, however, cannot be separated by screening. Owing to the high density of the shells, air separation like that used on cottonseed and peanuts, etc., is likewise ineffective in producing a further separation. Here are two methods in vogue for separating palm kernels from shell fragments of a size comparable to that of the kernels. The dry method takes advantage of the fact that the kernels are founded and roll easily, whereas the pieces of shell are flat and sharp edged, and hence do not roll as readily on an inclined surface.

Dry separators consist of inclined belts provided with sharp projections which move continuously upward. When a mixture of kernels and seeds is fed onto the surface of the belt the kernels roll down the belt and are collected at the lower end, whereas the fragments of shell are caught on the projections and carried over the top of the belt into a separate bin. Means must be provided for recycling of material after both the cracking and separating operations, since neither cracking nor separation is complete after one passage of the material through the machines.

The alternative method of separation consists of floating the kernels from the more dense shells in brine solution. This method has the advantage of producing a clean separation of kernels and shells, but the separated kernels must be dried before they can be stored or shipped.

The American palm nuts of the Attalea family, including the babassu and cohune, are excessively thick-shelled and extremely difficult to decorticate by machinery. The babassu is particularly troublesome because it contains several kernels, each of which is enclosed in a separate cavity within the shell. Whereas the splitting of an oil palm nut or most cohune nuts along a single plane of cleavage will usually free the kernel, the similar splitting of a babassu nut may not release a single one of its four to eight kernels.

Recently, a number of different machines have been devised for cracking American palm nuts. The machines designed for round nuts of the coyol type have either been of the centrifugal or hammer-mill design or have utilized the positive action of mechanically or hydraulically operated hammers striking against the nut as it is confined against a stationary anvil member. Some of the machines designed for cohune or babassu nuts employ chisel-like cutting edges which split the nut into a number of segments, like those of an orange. Other machines for cohune and babassu nuts employ the hammer-mill principle. These machines break up the kernal rather badly, and thorogh drying of the kernels is relied upon to inhibit excessive enzyme action in the broken kernels during shipment.

In the case of any variety of palm nut, adequate drying of the nuts prior to cracking is mandatory to ensure that the kernel will not adhere to the shell. Green or undried kernels fill the shell cavity tightly and adhere very strongly. In Malaysia the general custom is said to be to expose oil palm kernels to the air in layers 4 to 5 feet deep in roofed sheds equipped with concrete floors. A month's drying under these conditions suffices for reasonably good cracking and separation, and 6 week's drying ensures good separation. Some factories use steam-heated drying rooms in which the nuts, contained on wire trays, are adequately dried in 3 days. Another effective drying method is to treat the nuts with live steam in a revolving drum for 1 to 2 hours, after which they are air-dried for a few hours. Because of their thicker shells, American palm nuts, such as the cohune and the babassu, would be expected to dry more slowly. Aside from the fact that it is necessary for efficient decortication, thorough drying of the nuts will, of course, minimize the danger of deterioration in the kernels from enzyme action.

Reduction of Oil Seeds. The extraction of oil from oil seeds, either by mechanical expression or by means of solvents, is facilitated by reduction of the seed to small particles.

Opinion is divided as to whether the grinding or rolling of oil seeds actually disrupts a large proportion of the oil-bearing cells. The assumption of extensive cell breakage has in the pas been based chiefly upon the fact that seed flakes yield a large fraction of "easily extractable" oil upon treatment with solvents, and a smaller fraction (usually 10-30%) of oil that is extracted with much greater difficulty. The former fraction was presumed to come from broken cells. It has been shown, however, that seeds (soybeans) that are cracked rather than rolled, with a minimum of crushing, likewise yield a large fraction of oil that is easily washed out with solvents. Further more, Woolrich and carpenter could observe little disruption of cells in rolled cottonseed flakes examined under the microscope.

As an argument against extensive cell destruction they pointed out that the cells of conttonseed are only 0.001-0.0015 inch in diameter, whereas the thickness of rolled cottonseed particles is not less than 0.005 inch. On the other hand, Shchepkina's rather high estimates of the proportion or broken cells were made from a count of free aleurone grains in flake samples.

In any event, it appears that many oil cells remain intact after even the most careful reduction, and that the walls of these cells are made permeable to the oil only by the action of heat and moisture in the cooking operation. However, the cell walls will be more readily acted upon by heat and moisture if the seed particles are small.

Obviously, rolling seed or seed particles into thin flakes will facilitate solvent extraction both from the disruptive effect of rolling and by reducing the distances that solvent and oil must diffuse in and out of the seed during the extraction process. Early work indicated that the rate-controlling factor in the solvent extraction of seed flakes was probably the internal resistance of the flakes to the molecular diffusion of solvent and oil.

Hammer mills attrition mills, and other devices are sometimes used for the preliminary reduction of large oil seeds, such as copra and palm or babassu kernels; but for the final reduction it is the almost invariable practice in the United States to use milling rolls. These are generally considered to be more economical to operate than other types of mill. Also, thin flakes to which oil seeds are reduced by smooth rolls are more satisfactory for hydraulic pressing than the irregularly shaped particles obtained by grinding. Flaking rolls are essential for preparing oil seeds for continous solvent extraction since no other form of mill is capable of forming particles which are thin enough to extract readily yet large enough and coherent enough to form a mass through which the solvent will freely flow.

A roll assembly commonly used for the reduction of cottonseed, flaxseed, and peanuts in the mills of the southern United States consists of a series of five rolls placed one above the other. The seed is introduced by a feeding mechanism between the two top rolls. It passes back and forth between adjoining pairs of rolls as it travels from the top to the bottom of the assembly; hence it is rolled four times. Each roll supports the weight of all the rolls above it, so that the seed particles are subjected to progressively increasing pressure as they pass from one pair of rolls to another. Although the lower rolls are smoothy, the top roll is commonly corrugated to insure that the seed will be "nipped" as fast as they are fed to it. A popular five-high roll assembly consists of four upper rolls each 14 inches in diameter by 48 inches in width, and a bottom roll 16 inches by 48 inches in size, operating at a peripheral speed of about 630 ft./min. This unit has a rated capacity of 80 short tons of cottonseed or 300 bushels of flaxseed in 24 hours. However, the actual capacity in any case depends upon the flake thickness that is obtained. Detailed data on the capacity and efficiency of cottonseed flaking rolls have been published.

Cottonseeds are usually rolled to a thickness of between 0.0005 and 0.010 inch where mechanical pressing is to be used. With solvent, flake thickness is seldom under 0.008 to 0.010 inch. The repeated passage of the material through the rolls results in considerable breaking up of the individual flakes but this is not particularly disadvantageous in the case of seed which are to be mechanically expressed. Small oil seeds, such as flaxseed and sesame, are usually rolled in preparation for expression.

In the preparation of oil seeds for expression in expellers* or screw presses, the production of thin particles is not essential as for hydraulic pressing since heat is generated and seed particles are broken up by the intense shearing stresses developed in the barrel of the expeller. Soybeans to be processed in expellers are usually cracked by corrugated cracking rolls into particles averaging 10 to 16 mesh in size and are then expressed without rolling or further reduction. Plam kernels, copra, peanuts, etc., are handled in expeller plants both with and without rolling. Cottonseed are usually rolled before expeller processing.

The rolls used for flaking soybeans or other oil seeds for solvent extraction are normally somewhat different in design from those described above. Since large, coherent flakes are desired, the flaking operation is commonly carried out by a singly passage of the whole or cracked seeds through the rolls. Therefore only one pair of rolls is provided; the rolls are mounted side by side rather than being superimposed and are equipped with heavy springs to maintain the pressure of one roll against the other. Since the clearance between rolls of this type is adjustable, flakes of quite uniform thickness are produced.

A reasonable high moisture content is required in oil seeds which are to be formed into thin, coherent flakes. Very dry seeds do not flake well. For solvent extraction, cracked soybeans are adjusted to a moisture content of 10-11% and flaked while still; hot and slightly plastic, that is, while at a temperature of 160-170° F. In some cases the cracked beans are steamed for a short time prior to flaking.

Heat Teatment of Oil-Bearing Materials

The heat treatments given oil-bearing materials may be divided into two categories according to whether they are alone productive of oil or merely serve to facilitate the subsequent expression of oil by mechanical means. The term "rendering" is generally applied to treatment designed to remove all or most of the fat from fatty animal tissues or other materials with a high ratio of fat to solid matter. The heat treatment applied to oil seeds and similar materials prior to pressing is more commonly termed "cooking". Some methods of processing are a combination of rendering and cooking.

In the case of either rendering of cooing, the principal object of the heat treatment is the same; that is, to coagulate the proteins in the walls of the fat-containing cells and make the walls permeable to the flow of oil. The flow of oil from the oil-bearing material is also assisted by the lowered viscosity of the oil at elevated temperatures. Since oil-containing materials are never completely dry, heat treatment is inevitably associated with various effects due to the presence of moisture, even when water is not added in the processing operation. Water must be present for the above-mentioned protein coagulation to take place. Anhydrous proteins do not readily coagulate or exhibit other evidences of heat denaturation. In some cases water also assists in the displacement of oil from the surfaces of solid materials through superior physiochemical affinity for the latter.

RENDERING OF ANIMAL FATS

Fatty animal tissues free from muscle or bone are usually 70-90% fat; the remainder consists of water plus a small amount of connective tissue. The latter is made up largely of proteins; hence, the residue from rendering ("tankage", "craklings", "stick", etc.) like the residue from the processing of oil seeds, is essentially a protein concentrate which is used principally as an animal feed.

The product of highest fat content (92-95%) obtained in meat packing establishments is leaf fat from hogs. The internal fat from cattle used for the manufacture of oleo stock contains 60-80% fat. A considerable amount of lard and tallow is obtained, however, from bone stock and other low-fat material, which may; not contain more than 10-15% fat. Under certain circumstances, whole carcasses of large animals may be rendered for inedible fat recovery and conversich of the residue to tankage.

Most of the fish oil produced comes from the rendering of whole small oily fished, such as sardines and herring, which contain 10-20% oil. Whales, however, which give an average oil yield in the neighborhood of 30,000 pound per animal are trimmed of their fatty tissues or blubber, which contains about 70% fat and is rendered separately from bones or flesh.

Methods of rendering are dictated by the nature of the fatty stock, as well as the characteristics desired in the rendered fat and the rendering equipment available.

Dry Rendering. "Dry" rendering is one of the simpler methods of fat extraction. It is distinguished from "wet" rendering in that the expulsion of fat is accompanied by dehydration of the fat and fatty tissues, so that the latter are essentially dry at the end of the operation. The drying of bacon, to cite a familiar example, is essentially a dry-rendering process.

Dry rendering is normally carried out in horizontal steam-jacketed tanks with a large charging opening in the center of the tip and an agitator. The agitator has paddles attached by arms to a horizontal shaft. After the charge (5,000 to 10,000 pounds) is dried to the desired moisture level, the contents are discharged into a steel box equipped with a perforated liner and all possible free liquid drained off. The residue is pressed, and the fat obtained is combined with the drained fat. After settling, centrifuging, or filtering, it is ready for market. The residue is ground as a protein supplement for animal and poultry feed.

The cooking or drying operation may be carried out at atmospheric, superatmospheric, or reduced pressures. Best yields are obtained under vacuum, but most plants operate at atmospheric pressure. Recent development in cooking includes increased agitation (34 to 40 r.p.m. versus 15 to 20 formerly), permitting a decrease for animal and poultry feed.

The cooking or drying operation may be carried out at atmospheric, superatmospheric, or reduced pressures. Best yields are obtained under vacuum, but most plants operate at atmospheric pressure. Recent development in cooking includes increased agitation (34 to 40 r.p.m. versus 15 to 20 fomerly), permitting a decrease in cooking time of about 25%.

Dry rendering is preferred for inedible products where flavor and odor are secondary and the production of large quantities of high quality residue is important.

Wet Rendering. Wet rendering is used for edible products where color, flavor, and keeping qualities are of prime importance and the relative percentage of residue is mall. It is carried out in the presence of a large amount of water. Separated fat was formerly removed by skimming, but centrifugal methods are widespread today. There are two varieties of wet rendering: low-temperature, which is conduced at temperatures up to the boiling point of water, and high-temperature or steam rendering, which is carried out under pressure in closed vessels.

Most of the animal fat produced in the United States is rendered by the steam process. The lard produced by this method of rendering is known as "prime steam lard". In addition to lard, tallow and whale oil are also usually steam rendered.

The apparatus used in United States packing houses is a vertical cylindrical steel autoclave or digester with a cone bottom, designed for a steam pressure of 40 to 60 pounds per square inch and a correspondingly high temperature. The vessel is filled with the fatty material plus a small amount of water, and steam is admitted to boil the water and displace the air. The vessel is then closed except for a small vent, and the injection of steam is continued until the operating temperature and pressure are attained; then digestion is continued for a variable time depending upon the temperature and also the nature of the charge. The usual digestion time is 4 to 6 hours. Under the influence of the high temperature employed, the fatty materials in the digester disintegrate to some extent; there is very efficient separation of the fat, which rises to the top of the vessel, leaving a layer of solids (tankage), and "stick water" in the bottom. Pressure is then slowely relieved, and the fat-water interface is adjusted to the level of a draw-off cock on the side of the vessel. The fat is drawn off and purified from traces of water and solid material by settling or occasionally by centrifuging. Eventually it may be filtered.

In the steam rendering of high-fat stock, 99.5% or more of the fat in the raw material is ordinarily recovered. The fat that is not recovered consists of a small residue in the tankage plus a very small amount which remains in the "stick water". The usual packing house "killing" and "cutting" fats yield about 80% and 70% lard, respectively, plus 2 to 3% each of dry tankage and dry "stick" or solid residue from the evaporation or "stick water". The dry tankage and stick will ordinarily contain about 10 to 12% and 1.5% to 2% of fat, respectively. Both are high in protein content; tankage from good stock may analyze as high as 70 to 72% protein, and stick may be as high as 90% or more.

The advantages of steam rendering are that an efficient recovery of fat is obtained in relatively simple equipment and that it is adaptable to a wide variety of material. There is little tendency for proteins, etc., to dissolve or disperse in the fat in the presence of water; hence the fatty stock may contain a large proportion of nonfatty tissue. Bony stock can be handled by this process since it is effectively disintegrated by prolonged treatment with steam under an elevated pressure.

Steam rendering is less rapid and less efficient than dry rendering from the standpoint of heat consumption, however, and a large amount of water must be evaporated in order to recover the non-fatty residue in a concentrated from. Some hydrolysis of fat occurs during steam rendering; the free fatty acids content of prime steam lard is seldom less than about 0.35%. At 47 pounds pressure development of free fatty acids is at the rate of about 0.06% per hour. The acidity in any case depends upon the rendering time and temperature and the storage temperature and duration of storage of the fatty stock before it is processed. By careful scheduling of operations, killing fats may be rendered reasonably soon after the animals are slaughtered, but carcasses are chilled to 32-36°F before cutting fats are available. The stability of lard towards oxidation bears no relation to the acidity and appears to depend principally upon processing and handling subsequent to rendering.

One of the major recent developments in rendering has been the discovery that antioxidants added before rendering greatly enhance the stability of the fat produced. Sims and Hilfman studied the stabilization of lard and edible beef fats during pressure steam rendering. Antioxidants tested included butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate and citric acid combinations, and a mixture of BHA and BHT. Poorer results were obtained with the mixtures in propylene glycol.

There are several modifications of continuous wet rendering operations in which attempts are made to obtain a better product and a better protein residue than the usual pressure tank products. These include.

1. KINGAN PROCESS. This process is based on the release of oil from tissue through comminution to subcellular dimensions. Raw material is finely ground, pumped through an appropriate heat exchanger, and reground in a hammer mill, and the fat is then separated from the protein and waste by a special type of centrifuge.
2. TITAN EXPULSION SYSTEM. The fat stock is quickly minced and rendered in a combined mixer-boiler apparatus ("Expulsor"). It is then strained (to remove tissue, which is subsequently pressed) and the strained emulsion pumped to continuous three-phase separators where a low-moisture clarified oil is drawn off and separated sludge is intermittently discharged.
3. DELAVAL CENTRIFLOW PROCESS. Cell rupture is accomplished by mechanical disintegration (first minimizing temperature as required) in a specially designed disintegrator. Then cracklings are removed from the fat mass by a "desludger" centrifuge, after which the liquid phase is heated, deodorized, and centrifuged to produce purified oil and glue water.
4. SHARPLES PROCESS. This is based on the mechanical rupturing of the fat tissue, followed by two-stage centrifugal separation. A "Super-D-Canter" separated the protein tissue from the liquid fat and discharges it as a dry meaty solid. A second centrifuge called an "Autojector Clarifier" removes protein and water from the fat, intermittently discharging sludge. By suitable low temperature (115 to 120°F.) a non-coagulated protein material is produced as one of the products, it is claimed, and this product appears to have possibilities as an edible meat product.
5. IMPULSE RENDERING. This process is used mainly for preparing and defatting bones for glue. Fat stock, especially crushed bones, is continuously disintegrated in a high-speed hammer mill under an excess of flowing cold water. The intense impact sets the fat free. The discharge from the mill is allowed to settle in a cold water tank from which the fat is continuously skimmed off. The ground bone is continuously removed from the bottom and transferred to another tank containing hot waster (70-95°F), where more fat is separated. It is claimed that better-quality fat and higher protein residue are obtained by this process.

The production of marine oils is rather similar to animal fat rendering. It varies with the type of fish processed and whether vitamin A and D oils or high-quality fish meal is the prime objective. With the synthetic production of vitamins D2 and D3 as well as vitamin A, the current trend is to fish meal and dissolving the connective tissue.

Deatherage has described in detail laboratory and pilot plant experiments on the alkali rendering of lard and beef fats. The best results are obtained when the fat is digested at 85-95°C for 45 minutes to an hour with a 1.75% sodium hydroxide solution. After digestion is complete, the fat is sepatrated from the aqueous liquid, which contains a small amount of undigested solids, by centriguging, and washed, first with 2-5% salt solution, and then with water. Fat recovery is equivalent to or better than that obtained by steam rendering without significant hydrolysis or darkening of the fat or production of the typical cooked flavor of steam lard. The process is best adapted to reasonably fresh fat; stocks in which any considerable amount of hydrolysis has occurred are difficult to process because of the excessive formation of soap in the aqueous phase. Soap is derived only from free fatty acids in the fat; under the mild conditions of the digestion, there appears to be no appreciable saponification of neutral fat. The fat is, of course, alkali-refined as it is rendered; hence it is produced substantially free of acidity. A typical lard has a free acids content of 0.01% and a Lovibond color of 2 yellow and 0.3 red.

Rendering slaughterhouse waste by ammonia plus ammonium diacid phosphate under pressure for peptonization and separation into aqueous and fat phases has been patented.

A recent publication reports reduced "fruitiness" and free fatty acids in olive oil from adding alkaline materials to olive pulp during grinding or working. Also the manufacture of a good quality olive oil has been claimed by drying olive pomace to 5% moisture, mixing with soda ash, and extracting with carbon disulfide.

Alkali rendering has been found better than steam, water, or acid digestion for recovering vitamin A from fish livers with an oil content of 30% and upwards. Partial removal of antioxidants does not impair the stability of the vitamin.

The use of proteolytic enzymes in rendering is described in a number of patents. It does not however, appear to have been used commercially, expect perhaps in the recovery of fish liver oils. The patent of Parfenjev covers the digestion of fish livers with pepsin at a low pH and a low temperature. The process of Keil for the recovery of lard or other animal fats involves digestion of the fatty stock with a proteolytic enzyme of vegetable origin; for example, 0.005-0.020% papain at a pH of 6.0-7.5, followed by heating to 140-185°F to separate the fat. Halmbacher has patented the use of an enzyme, such as papain or ficin, with a cysteine activator, to decrease digestion time while increasing yield. Other publications deal with treatment of eggs with papain, fish rendering (40), and rendering of coconut meats.

COOKING OF OIL SEEDS

General Considerations. It is university recognized that oil seeds yield their oil more readily to mechanical expression after cooking, but a complete explanation of why this is so is lacking. It is certain that the changes brought about by cooking are complex and that they are both chemical and physicochemical in nature.

The oil droplets in a cottonseed or similar oil seed are almost uctramicroscopic in size and are distributed throughout the seed. One effect of cooking is to cause these very small droplets to coalesce into drops large enough to flow from the seed. An important factor in this phase of the process is the heat denaturation of proteins and similar substances. Before the proteins become coagulated through denaturation, the oil droplets are virtually in the form of an emulsion. Coagulatio causes the emulsion to break, after which there remains only the problem of separating gross droplets of oil from the solid material in the seed. Since the surface of the seed particles is highly extended, surface activity figures prominently in the displacement of the oil. Cooking, in turn, has a profound influence upon the surface activity of the material. The primary objects of the cooking process may, therefore, be summarized as follows : (a) to coagulate the proteins in the seed causing coalescence of oil droplets and making the seed permeable to the flow of oil; and (b) to decrease the affinity of the oil for the solid surfaces of the seed so that the best possible yield of oil may be obtained when the seed are subsequently pressed.

Important secondary effects of cooking are drying of the seeds to give the seed mass the proper plasticity for efficient pressing insolubilization of phosphatides and possibly other undesirable impurities, destruction of molds and bacteria, increase of the fluidity of the oil through increase in temperature, and, in the case of cottonseed, detoxification of gossypol or related substances.

One factor that obviously effects the affinity between the seed and the oil and is amenable to control in the cooking operation is the moisture content of the seed. Very dry seeds cannot be efficiently freed of their oil. However, it is impossible to say just how moisture inhibits wetting between the seed and the oil. It may be that the cooking process produces a film of adsorbed liquid water on the seed surfaces which displaces the oil. On the other hand, the water may be in a more nearly "bound" state, and its presence in the seed in this condition may serve to make the seed surface relatively lipophobic. The optimum moisture of cooked seed varies widely according to the variety of the seed and the method to be used for expression. On cottonseed, for example, 5 to 6% moisture is best for hydraulic pressing, whereas about 3% is optimum for expellers or screw presses; this level needs to be closely controlled for best results. At moistures of 4% and higher, excessive amounts of oil are left in the cake. Soybeans are ordinarily dried to 2½ to 3% moisture before pressing in expellers; copra and sesame seed require moistures of about 2%.

Many substances in oil seeds are surface active, such as phosphatides and free fatty acids, and the degree to which they are present or become active during cooking doubtless influences the tendency of the seed to adsorb and retain oil. It is generally observed that damaged oil seeds give lower yields of oil than undamaged seeds of equivalent oil content. The tendency of damaged seed to retain oil tenaciously is probably due to their high content of free fatty acids or other surface-active agents.

Effect on Quality of Oil and Oil-Cake. In addition to its effect upon the yield of oil, the method of cooking also markedly determines the quality of both the oil and the oil-cake. Cooking is particularly important in its relation to the refining loss of the oil. A large part of the oil lost in caustic refining consists of neutral oil, which is emulsified in the foots. Certain surface-active agents naturally present in the oil favor this emulsification; others appear to inhibit it. The relative proportions of the two classes of substances in the oil depend to a great extent upon the operation of the cooker. There is little published information on the identity of the surface-active agents in crude oils, but is appears that the substances. The presence of gossypol in cottonseed oil is generally assumed to contribute to the production of hard foots and a low refining loss. However, in mill-scale experiments by Wamble and Haris conducted at five different screw-press mills, it was concluded that there was no apparent relation between the gossypol content of the crude oil and the refining loss or refined color.

Normal cooking variations have little effect on oil color or refining loss, although with widely varying cooking conditions considerable differences are noted. Thus, Eaves showed that oils prepared by solvent extraction from raw, tempered, or cooked cottonseed flakes varied in yield of crude oil but that the yield of neutral oil was virtually unaffected. Crude oil from raw flakes was highest in impurities and lowest in neutral oil, crude from tempered flakes was lower in impurities and higher in neutral oil, and crude from cooked flakes was outstandingly low-refining-loss oil. That is, unless oil penalties are sufficient to counteract any change in crude oil yield, it may be to the processor's advantage to avoid partially refining the oil during preparation for extraction.

King have studied the effect of pH during cooking of cottonseed on the properties of the meals and oils. They concluded that oils made from meats cooked at low pH were high in gossypol and were subject to color reversion during storage, while oil from meats cooked at high pH levels had a lower refining loss, were low in gossypol, and were not subject to color reversion on storage.

In good cooking practice flaked cottonseed meats are brought to approximately 12 to 15% moisture by the time they are in the tip kettle of the cooker. There the temperature is increased rapidly to 190°F or higher in order to inactivate the enzyme systems and prevent free fatty acid rise during cooking. Heating should be continued in the presence of not less than 12% moisture until the temperature reaches about 220°F. After this the object is to reduce the moisture content to a suitable value for efficient pressing. This normally requires temperatures from 240 to 270°F, depending upon the amount of venting used. An average final temperature is probably 260°F.

Overcooking of oil seeds has been recognized as undesirable for some time since it may produce abnormally dark oil and cake. There is also evidence that prolonged or drastic cooking tends to be injurious to the nutritive properties of the cake. With cottonseed, for example, it has been shown that increasing maximum cooker temperature or cooking time decreases the feed efficiency for chicks and the relative protein efficiency for rats. Likewise, soybean meal has been shown to lose nutritive value for chicks as heating time is increased.

On the other hand, the nutritive value of soybean meal is definitely improved by moderate cooking. This is due to the coincident inactivation of specific heat-labile factors (trypsin inhibitor, hemagglutinin, saponin, goitrogenic factor, anticoagulant factor, diuretic principle, and lipoxidase). This subject has been recently summarized by Liener.

To improve their palatability and nutritive value, solvent-extracted soybean flakes intended for animal feeding are invariably toasted before they are shipped from the extraction plant. Until fairly recently this was done by adding moisture and cooking in a conventional "stack" cooker after the solvent was removed. With improved desolventizing techniques, desolventizing and toasting are largely accomplished simultaneously by injecting live steam into the solvent-laden flakes as they leave the extractor them steam condenses on the cooler flakes, thus furnishing heat to boil off solvent while at the same time adding moisture. Thus by the time all of the solvent is removed there has been sufficient moist heat to boil off solvent while at the same time adding moisture. Thus by the time all of the solvent is removed there has been sufficient moist heat treatment largely to inactive the heat-labile anitinutritional factors mentioned above. If the oil seed residue is destined for industrial protein use, this type of desolventizing is avoided and a quick heat treatment just sufficient to remove the solvent is carried out, often using superheated solvent vapor or reduced pressure.

One of the prime purposes of cooking cottonseed is to bring about destruction or deactivation of a principal toxic to certain animals (particularly swine and poultry) which has in the past been generally identified as the complex polyphenolic compound, gossypol. Boatner and coworkers have shown that gossypol is associated in the seed with several related compounds and that one or more of these may be actually responsible for the bulk of the observed toxicity, in as much as separated whole pigment glands are much more toxic than purified gossypol. At the present time, most people attribute all the toxicity of cottonseed to free gossypol. At the present time, most people attribute all the toxicity of cottonseed to free gossypol. At the present time, most people attribute all the toxicity of cottonseed to free gossypol, possibly because no one has seen a low free-gossypol meal that was toxic. On the other hand, there have been numerous cases of nontoxic meals containing levels of free gossypol above that normally considered toxic. A partial explanation for this may be the method of analysis for gossypol. Besides the number of other materials closely resembling gossypol in chemical nature, it has now been established that gossypol that is chemically combined may be partially liberated in the analytical procedure, giving abnormally high free-gossypol figures. Thus a special method is now offical for aniline-treated cottonseed meal.

The toxic principle, whatever it may be, is contained in the cottonseed pigment glands, from which it may be extracted by either, acetone, butanol, and other polar solvents. Hexane and similar non-polar solvents will not extract it from the intact pigment glands, but if these glands are ruptured by moisture, wet heat, or polar solvent, the liberated "gossypol" is readily extracted. The toxic principle is quite stable to dry heat.

Lyman and coworkers, who have made a special study of the cooking of cottonseed in relation to detoxification recommend for hydraulic pressing that meats be brought to a moisture content of at least 14.5% before cooking, that the cooking period be at least 90 minutes, and that the final temperature be not less than 115°C (239 °F). A review of the work of many other investigators, however, indicates that for expeller processing the initial moisture content may be lowered somewhat (to about 12%) and the cooking time greatly reduced. In this connection it is important to bear in mind that the term "cooking" usually is used to cover wet cooking plus a drying to moisture levels around 3%. Actually, these are two distinct processes, as Dunning has pointed out, and after the wet-cooking step is completed, subsequent drying may be done instantaneously (by flashing) or very slowly. In normal practice, however, both processes are accomplished in a stack cooker where these is a rather gradual reduction in moisture content and, thus, a gradual transition from cooking to drying. Final cooking temperature is thus considerably dependent upon the amount of venting or aeration of the cooked flakes. For example, a final cooking temperature is thus considerably dependent upon the amount of venting or aeration of the cooked flakes. For example, a final cooking temperature of 240°F or 260°F will yield the same final moisture content if adequate venting is used with the lower temperature.

Cooking for Hydraulic and Continuous Pressing. The cooking of oil seeds is usually carried out in "stack cooker". These consist of a series of four to eight closed, superimposed, cylindrical steel kettles each usually 72 to 100 inches in diameter and 1.5 to 2.5 high. Each kettle is normally jacketed for steam heating on the bottom (and sometimes on the sides), and is equipped with a sweep type stirrer mounted close to the bottom and operated by a common shaft extending through the entire series of kettles. There is an automatically operated gate in the bottom of all but the last kettle for discharging the contents to the kettle below; the bottom kettle feeds into a cake former or continuous press. The top kettle is provided with spray jets for the addition of moisture to the seed, and each of the lower kettle is provided with an exhaust pipe with natural or forced draft for the removal of moisture. Thus it is possible to control the moisture of the cooking seed, not only with respect to final moisture content, but also at each stage of the operation.

In practice, the rolled meats are delivered at a constant rate to the top kettle by means of a conveyor. After a predetermined period of cooking in that kettle, the charge of meats is automatically dropped to the kettle below so that there is a continuous progression of meats downward through the cooker. The gates which govern the flow of meats from on kettle to another are normally opened and closed automatically by a mechanism which engages the meats at a specific level in each kettle. Thus, the time that the meats charge remains in each kettle is determined by the meats levels for which the kettles are set. An 85 inch, five-high cooker, a common size, has a rated capacity of about 90 tons of cottonseed (calculated upon the basis of the whole seed per 24 hours.

Steam pressure on the upper stacks of a stack cooker is usually maintained at a relatively high value, for example, 70 to 90 pounds per square inch, in order to provide quick heating. On the lower stacks it is usually reduced somewhat, since there it is only necessary to maintain the heated meats at cooking temperature. Cottonseed meats are usually kept in the cooker for 30 to 120 minutes and leave at a temperature of 230-270°F. Seed of good quality are normally cooked longer than poor seed, which tend to darken on prolonged cooking. Peanuts are often cooked for a shorter period.

In continuous operation of a stack cooker, material first in is not always first out. This has been noted by Alderks and can be easily demonstrated by the use of added corn kernels, salted flakes, dyed flakes, etc. So-called "cooking time" represents an average cooking time, with some material remaining in the cooker much longer and some material only a fraction of the average time. However, this does not appear to affect efficient mechanical pressing adversely.

Oil seeds are usually moistened before cooking, or during the early stages of cooking, unless they are initially fairly high in moisture, and their moisture content is then reduced in the cooker. An initial moisture content of 9 to 14% is common in the top kettle of the cooker. This stays relatively constant in the top two to four kettles where the actual "cooking" takes place. In the bottom kettles drying is the objective with increased temperatures and venting commonly employed. The final moisture content depends on the material processed and on whether cooking is to be followed by hydraulic pressing or expeller or screw pressing. For the former, 5 to 6% is used for cottonseed; for the latter, a dryer product, around 3% moisture, is preferred.

Pressure cooking appeared promising at one time and equipment was installed in several mills. Today, however, this type of cooking is not believed to be in use in any commercial installation in this country.

Another specialized type of cooking, the Skipin process, was developed in Russia about twenty-five years ago but has had no acceptance in this country, where quality and efficiency standards are apparently much higher.

It should be noted that although cooking in a stack cooker has been stressed here, it is also possible to accomplish the same objective using horizontal jacketed tubes ("conditioners") through which the material is conveyed by suitable means. In general, these are more commonly used in conjunction with some stack cooking rather than as a substitute for the latter.

Mechanical Expression of Oil

BATCH PRESSING

In recent years increased mechanization and higher labor costs have made hydraulic pressing of oil seeds uneconomical in practically all cases. Today there is no appreciable volume of soybeans hydraulically pressed, and even with cottonseed, where efficiency is better, volume is rapidly decreasing to a point where the end is in sight. Pressing of other oil seeds appears doomed to the same fate.

The oldest method of oil extraction comprises the application of pressure to batches of the oil-bearing material confined in bags, cloths, cages, or other suitable devices.

Levers, wedges, screws, etc., have been used us a means of applying pressure in the more primitive styles of presses, but modern presses are almost invariably actuated by a hydraulic system. Thus the term "hydraulic pressing" is often used in reference to batch pressing in general. There is a limited use of mechanically operated presses for special purposes where only a relatively light pressure is required, as in the pressing of partially solidified oleo stock or lard to yield oleo oil or lard oil.

Batch presses may be divided into two main classes: the "open" type, which requires the oily material to be confined in press cloths; and the "closed" type, which dispenses with press cloths and confines the material in some species of cage. Open-type presses may be subdivided into plate presses and box presses, and closed types may be subdivided into plate pressure and box presses, and closed types may be classified as pot presses or cage presses.

The completeness with which the oil is recovered by mechanical expression is influenced by a number of factors related to the affinity of the oil for solid material in the seed. These include the moisture content, the method of cooking, and the chemical composition of the seed, damaged seed generally retain oil more tenaciously than seed of good quality. With a given lot of seed, cooked and ready for pressing, the oil yield will depend upon the rate at which pressure is applied, the maximum pressure attained, the time allowed for oil drainage at full pressure, and the temperature or the viscosity of the oil.

Attempts have been made to establish a correlation between oil recovery from different seeds and such factors as pressure, pressing time, and temperature or viscosity. Koo and Baskerville et al. proposed empirical equations designed to permit a calculation of the fraction of oil extracted from seed from data on the pressing time, pressure on the cake, viscosity of the oil, etc. all other factors being assumed constant. Later work, however, indicated that factors are involved, all of which are not mutually independent, so that it may not be possible to develop single equation which will correlate all the processing variables.

Hickox has summarized four years of work in this connection at the Engineering Experiment Station of the University of Tennessee, Including data from some millscale tests. He concludes that for hydraulic pressing of cottonseed:

1. The hull content of meats to be pressed should be kept as low as possible since increased hulls lower extraction efficiency and press capacity;
2. Pressure should be applied slowly at first, more slowly than is customary;
3. The total pressure on the cake need not be increased over 2000 pound per square inch unless the final cake thickness is over 1 inch. For thin cakes, increasing the pressure had no effect on the residual oil;
4. The cake should be kept as thin as economical considerations and throughout of the mill will permit.
5. The moisture content of the cake should be controlled carefully (that is, wihin a few tenths of 1%) in order to obtain minimum residual oil;
6. Since the top and bottom cakes in the press are cooler than the middle cakes, it is desirable to raise their temperature by appropriate means in order to obtain maximum extraction efficiency; and
7. Preferably, pressing should be carried out at temperature of 205°F, about 30° higher than typical mill operation.

Open-Type Presses. The frame of an open or Anglo-American press consists of four heavy, vertical steel columns fastened at the top and bottom to heavy end blocks. Within the open cage formed by the columns, and suspended from the top of the press, are a series of horizontal steel plates. These plates closely fill the space enclosed by the columns. They are equally spaced at intervals the entire assembly to become compressed in the pressing operation. Below the plate assembly and attached to a ram operated from below is a heavier bottom plate. The material to be pressed is formed into rectangular cakes which are placed between the various suspended plates. Raising the ram compresses the series of cakes and causes the oil to fall into a drip pan resting upon the bottom block. The stress created by the application of pressure is directed against the top block and is transland into longitudinal stress upon the four columns.

In ordinary plate presses the oil seed flakes are completely wrapped in press cloths and placed between the plates without the use of accessory devices to restrain the cake mass as it is pressed. The surfaces of the plates, however, are usually either corrugated or covered with hair mats to assist in the drainage of the oil and to overcome cake cree page. Box presses are provided with a special boxlike arrangement which encloses the cake on its two long sides and simplifies the wrapping of the cake. The complete press box includes a corrugated drainage rack, a perforated and corrugated steel drainage mat which rests upon the drainage rack and underneath the cake, and steel "angles" which project from the underside of each plate to from the sides of the box enclosing the cake below. With this arrangement, if is only necessary for the press cloth to enclose the cake on the top, bottom, and ends. Thus folding of the press cloth in two directions is avoided, and very heavy, durable cloths may be used. Standard size press boxes are about 2 inches deep, 35 inches long, 14 inches wide at the back, and 14 inches wide at the front, being slightly widened from back to front to facilitate insertion and removal of the cake. Presses are usually constructed with either 15 or 16 boxes. Plate presses of an equivalent size have 24 plates and hence have a greater capacity than box presses.

Presses similar to those described above are generally provided with a 16-inch ram operating at a pressure of 4000 to 4500 pounds per square inch; hence to pressure on the cake is between 1650 and 1850 pounds per square inch. It is important to build up pressure upon the cakes gradually. In order to conduct the initial state of compression more rapidly than the later stages, the hydraulic system operating the presses is provided with automatic valves which delivers oil at 500 pounds pressure to the ram until an equivalent pressure is built up on the cake, and thereafter delivers the maximum pressure of about 4000 pounds. The time allowed for drainage of the oil after the maximum pressure is reached is somewhat variable among deferent mill operators. However, a typical press cycle is as follows: for charging the press, 2 minutes; for attaining maximum pressure, 6 minutes; drainage time, 26 minutes; for discharging the press, 2 minutes; total, 26 minutes. The capacity of a 15-box press operated under these conditions is approximately 11 short tons of whole cottonseed or whole peanuts per 24 hours.

According to Baskerville and Wamble the average press cycle in mills processing cottonseed in the Unites States is probably 30 minutes or less; their calculations indicate that the economically optimum cycle is approximately 50% longer.

An essential accessory to the operation of either plate or box presses is a cake former for automatically delivering a proper quantity of flakes from the cooker and forming the flakes into a cake of the proper size and shape within the press cloth. Cake formers are designed to press the flakes into a coherent mass without the application of sufficient pressure to start the oil from them. They are hydraulically operated. Mechanically operated cake strippers are also provided for removing the somewhat adherent press clothes from the spent press cake. Charging and discharging the presses is carried out entirely by hand, however. An operator is also required for both the cake former and the cake stripper, as neither is fully automatic.

The edges of the cake coming from an open-type press are soft and higher in oil content than the remainder of the cake. Consequently, it is the usual practice to slice or beat off these edges in a mechanical cake trimmer and rework the trimmings through the presses.

Plate presses are usually preferred for flaxseed, whereas box presses are standard equipment in cottonseed or peanut mills. The press cloths used with box presses are woven from human hair, camels; hair, or nylon. A wide variety of materials are used for the cloths used in plate presses, including cotton, wool, and hair.

Closed-Type Presses. Cage presses confine the oil-containing materials within a strong perforated steel cage during the pressing operation, and thus largely dispense with the use for press cloths. They may be operated at higher pressures than are practicable with open presses. They are particularly suitable for the expression of copra, palm kernels, and other oil seeds which are high in oil content and low in fiber and hence are inclined to flow and burst the press cloths of open presses. Castor beans or other seeds which it is desired to process without heat treatment can be pressed satisfactorily only in presses of this type as very high pressures are required to extract the oil efficiently from cold seeds. They are desirable for mills that process many varieties of oil seeds because they can be used on practically any oil seed or other oily material.

Cages for this type of press are built in both round and square forms. They are usually made up from a number of closely spaced steel bars or slotted steel plates, supported inside a heavy frame or ringed with heavy steel bands. The channels through which the oil escapes increase in size from the interior of the cage outward to minimum any tendency for them, to become clogged with solid particles. The cages are operated in a vertical position in a frame similar to that of the Anglo-American press. Oil is expressed from the charge by forcing a closely fitting head up into the cage from below by means of a hydraulically operated ram. The upper end of the cage may be closed solidly; then pressure is allied only to one end of the charge. Alternately, the cage may float between the lower ram and an opposed head entering from above. In the latter case, pressure is applied to both ends of the seed mass. Cage presses are designed to attain pressures of 6000 pounds per square inch or more.

Since there is a marked tendency for the oil flow in the compressed cake to be longitudinal rather than radial, the cage cannot be packed solidly with the oil seed but must be charged with layers of seed separated by drainage plates and press cloths. Auxiliary equipment is required for filling the cages and discharging the cake. This, and the rather elaborate and heavy design of the cages, makes the initial cost of this type of pressing equipment relatively high. In large installations the cages are usually made removable from the presses, and filling and discharging presses are provided, in addition to a number of finishing presses. A cage carriage is provided for transferring the heavy cages from one press to another.

The pot press is a special form of cage press used for the extraction of cocoa butter or other fats which are solid at ordinary room temperature. In this press the cage is replaced by a series of short, superimposed, steam-heated cylinder sections or "pots". The walls of the pots are solid, and drainage takes place through perforated plated and filter mats in the bottom of each section. Pot presses are usually designed for pressures intermediate between those employed in open presses and cage presses, although they can be built for virtually any desired pressure. The advantages of pot presses are that they can be heated and that they can handle very soft, non-fibreus material, such as fruit pulp, at high pressures without forcing large quantities of solid material into the oil. Their capacity is small, however, in relation to their size and cost, and they require more hand labor to operate than other types of press.

Some oil seeds of high oil content, such as copra, are difficult to express satisfactorily in batch equipment by a singly pressing. In some places it is customary to break up the oil cake derived from the first pressing and subject it a second pressing with or without intervening moisture or heat treatment for the recovery of residual oil. Such practice, of course, requires a double reduction of the seed and also yields an oil of inferior quality from the second pressing. In American practice, the double pressing of oil seed is generally considered obsolete. Oil seeds that cannot be reduced to a low oil content by a singly pressing in hydraulic presses are preferably processed in continuous screw presses or expellers.

CONTINUOUS PRESSING

Continuous expellers or screw presses are now used to the almost complete exclusion of hydraulic presses for the mechanical extraction of soybeans and flaxseed in this country and are of major importance for cottonseeds and peanuts. They are also used extensively throughout the world for the expression of copra, palm kernels, peanuts, cottonseed, flaxseed, and almost every variety of oil seed.

The continuous presses used on oil seeds in the United States are mostly high pressure machines designed to effect oil recovery in one step. They are usually modified to suit a particular material. In Europe various oil seeds are ordinarily handled by the same equipment, and it is common practice to press the seeds in two or even three stages at increasingly higher pressure in each state. The low-pressure presses are also often used for "prepressing" prior to solvent extraction.

Continous presses effect a large saving in common labor over hydraulic systems and completely eliminate the need for press cloth. They are adaptable to a wide variety of materials, and in most cases they produce a much higher yield of oil. Their principal disadvantages are that power requirements are relatively high, they require fairly well-skilled labor for both operation and maintenance and they are not well adapted to intermittent operation.

The first successful mechanical screw press, called an "expeller" (Model No. 1), was made by V.D. Anderson in 1900. I was soon used to express the oil from flaxseed and whole cottonseed. About 1910 the Krupp Works was licensed to manufacture these machines in Germany, where they were used primarily as a for press unit ahead of hydraulic presses. In the United States interest was gimarily in expressing as much oil as possible from seed in the operation, so improvements were made resulting in an "RB" (roll bearing) expeller in 1926 and later the "duo" and "Super Duo" types. In 1933 a "screw press" was introduced by the Bench Oil Machinery Company. Today these two companies are the leading manufacturers of continuous screw press in this country.

The Anderson machines (expellers) utilize a vertical cage to express the most easily removable oil, followed by a horizontal cage for attainment of the high pressure necessary for removal of most of the remaining oil. The French "screw presses" use only a horizontal cage where pressure is gradually built up to a maximum. Another point of difference in machines of the two manufactures is in the method for cooling. Expellers are cooled by product oil, after removal of "foots" in a screening tank and cooling in heat exchangers to reduce the temperature to approximately 120°F. Screw presses, on the other hand, are equipped with ;water-cooled shafts and water-cooled ribs in the bar cages.

Originally, expellers operated on flaked raw materials which were cooked in a horizontal cooker while screw presses employed the stack cooker used for hydraulic pressing. Currently, stack cookers are commonly used with either type of machine, sometimes with preliminary cooking in a horizontal cooker. The trend in the newer installations is to use one large cooker to feed two or more presses.

In both types of machine the pressure necessary to force the oil our of the cooked flakes is obtained by means of continuously rotating worm shafts and worms, with a choke mechanism by means of which cake thickness is controlled. The main worm shaft and worms and designed to exert a pressure of 5 to 15 tons per square inch on the seed being processed and at the same time to convey the seed through and out of the pressure chamber. Several different worm shafts may be employed, depending upon the ; material to be processed and whether or not expression is to be complete or merely pre-pressing preliminary to later solvent extraction.

The drainage barrel is made up of rectangular bars which fit into a heavy barrel bar frame. The individual bars in the drainage barrel are separated by bar spacing clips, the specific spacings depending upon the type and preparation of the material being processed. For example, in an expeller processing cottonseed, the spacing of bars in the main barrel may be 0.010 inch in the feed section, 0.0075 in the center section, and 0.010 in the discharge section. The same sections processing copra may have bar spacings of 0.030, 0.020, and 0.010 inch. The spacing of the bars not only permits the drainage of oil from the material being processed but also acts as a coarse filter medium for the solids.

Within the last few years extraction efficiency with expellers and screw presses has materially improved as a result of machine improvements. The French screw press modifications began with a 9-inch extension of the shaft and cage, soon increasing this to as 11-inch extension, and finally to a 22 inch water-cooled extension. This resulted in lowering oil in meal about 1% without loss in capacity. Anderson expellers, on the other hand, were modified in the vertical section and the horizontal section was increased in length (from 33 to 55 inches), resulting in comparable extraction improvement. Cottonseed cake containing 3 to 3½ % oil is not uncommon now as a result of these new development sin expellers and screw presses.

With adequate preparation and cooking of raw material to be processed, the capacity of an expeller or screw press is a function of the shaft arrangement and the shaft speed. For example, the meats from 25 to 100 tons of cottonseed per day can be expressed leaving cakes containing 3.0 to 9% oil, depending upon the shaft speed and worm arrangement. Moreover, as a rule, no loss in extraction efficiency is experienced in going from the old capacity of about 20 to 25 tons of cottonseed per day to the much higher rate of 45 to 50 tons.

Despite the use of special alloys and manufacturing techniques designed to make expeller parts as hard as possible, shafts do wear with usage and tonnage normally drops. Some modern machines are manufactured with provisions for rapid gear change, making it possible to increase the revolutions per minute and the tonnage with only a very short down time. New or newly built-up shafts may be expected to process the meats from about 1 ton of cottonseed per minute with high efficiency. Where only a pre-pressing action is desired, 100 tons per day can be obtained with approximately 45 r.p.m.

Tonnage may also be increased without loss in efficiency by having a minimum amount of hulls in the expeller feed. Since the expeller appears to handle a certain volume of feed, removal of hulls makes it possible to increase capacity by removing essentially non-extractable material from the feed. This also minimizes wear from the highly abrasive hulls. This increased tonnage with high efficiency naturally increases the power requirements with motor horse powers up to 125 now being used as compared to 40 to 60 of a few years ago. Suitably strengthened gear boxes, etc., are also required. With the high capacity and efficiency thus possible, coupled with lower installed equipment cost as compared to solvent extraction, expeller operations compare favorably in many cases with the more efficient solvent extraction.

In addition to the general literature references on the continuous pressing of oil seeds, there are also references dealing specifically with screw presses expellers, and product quality.

LOW-PRESSURE PRESSING

For the pre-pressing of oil prior to extraction, ordinary high-pressure screw presses may be operated at low pressure and at increased capacity. Specially designed machines are much more satisfactory, however, in new installations these are normally used.

In this country, most of the plants solvent-extracting cottonseed do so via the prepress route. At first this was probably the result of problems in handling "fines" and difficulties in detoxifying the extracted flakes when direct extraction was used. Other advantages of pre-pressing include the need for only a minimum-size solvent plant, since most of the oil is removed in the pre-pressing step, and the production of meal of high protein quality. Disadvantages are high initial equipment costs if, for example, soybeans must also be processed in equivalent tonnage in the same plant and, normally, higher power requirements and repairs.

Expellers and screw presses of the same design as those used for oil seeds are sometimes used for pressing whale or seal flesh or fish, and for processing meat scraps, but these materials are more commonly handled in screw presses specially designed for the purpose. These are generally of lighter construction than the machines built for oil seed extraction and are operated under low pressure.

CENTRIFUGAL EXPRESSION

The removal of oil from an oil-Bearing material by centrifugation has been a standard method only in the case of palm fruit. However, recent developments in the rendering of animal fats make full use of centrifugal separation of oil. The centrifugal recovery of palm oil will be discussed in a later Part of this chapter.

Solvent Extraction

APPLICATION

While extraction with solvents constitutes the most efficient method for the recovery of oil from any oil-bearing material, it is relatively the most advantageous in the processing of seeds or other material low in oil. The minimum oil content to which oil cake can be reduced by mechanical expression is approximately the same for all oil seeds, that is, about 2 to 3%. Consequently, the oil unrecoverable by mechanical expression, in terms of percentage of the total oil, increases progressively as the oil content of the seed decreases. Comparative yields of oil from representative seeds of low, medium, and high oil content by the two methods or processing are shown in Table 15.4. Substitution of solvent extraction for pressing methods increases the yield of oil from soybeans by 12.1%, where as in the processing of cottonseed the increase in 11.5% and in the case of flaxseed only 5.3%. These figures, it should be noted, are industry-wide averages. The increase of oil yield for soybeans and cottonseed by solvent extraction over the most efficient mechanical processing today is appreciably less.

Cottonseed flakes disintegrate more readily and occasion more trouble from the production of fines, whereas peanuts and flaxseed disintegrate very badly. By "pressing" or "forepressing" the seed in low-pressure screw presses to remove a portion of the oil it is possible subsequently to solvent-extract high-oil-content seeds that are difficult or impossible to handle in their original from in conventional equipment. In Europe and where European practices have prevailed, it is the general practice to extract whole soybeans nut to prepress other oil seeds. In the United States pre-pressing is used commercially on cottonseed, flaxseed, peanuts, and corn germ.

Solvent extraction finds some use in the recovery of animal fats. The tankage or cracklings from dry rendering are often solvent extracted, usually in batch extractors. The recovery of fat from garbage is frequently carried out by means of solvent extraction since the low fat content of this material makes of the methods of recovery difficult. Garbage is extracted in batch equipment of special design.

Materials containing scarce of expensive oil are often solvent extracted even when the operation is relatively difficult. Examples are castor oil, olive oil, and wheat germ oil residues from mechanical pressing. Solvent extraction may be used to itstain a fat free residue or a residue in which proteins are not heat denatured rather than for the primary purpose of improving the yield of oil. Thus, for example, cocoa is solvent extracted in order to produce a residue which may serve as a source of theobromine. Solvent extracted meal is preferred for the manufacture of protein adhesives, fibers, or plastics, since there is much less denaturation of the protein in this ;meal than in that obtained by cooking and mechanical pressing.

Since minimum heat treatment is involved, oil produced by solvent extraction is of maximum quality, and the meal contains protein subjected to a minimum of damage due to the effects of heat. On the other hand, there are several disadvantages:

1. Solvent extraction equipment is relatively expensive compared to other extraction systems;
2. Except where nonflammable solvents can be used, there is the ever-present danger of fire and explosion;
3. Low-oil-content meal tends to be dusty, with attendant problems; and
4. As in the case of cottonseed, unheated flakes from the direct extraction of raw flakes may contain material that is toxic to non-uminants and is not removed or inactivated by the relatively mild processing, thus requiring further treatment.

Batch Extractors. Batteries of batch extractors are still in use in Europe for the recovery of oil seeds or mechanical press residues. In modern plants, however, batch equipment is used principally in the form of small units fir the recovery of pharmaceutical oils or other expensive oils; for the extraction of spent bleaching earth; for the processing of meat scraps, cracklings, and garbage; or for other purpose where the tonnage of material handled dose not justify the expense of installing continuous extractors. The largest single use of batch extractors in the United States at the present time is probably for the processing of castor pomace remaining from the cold-cage pressing of castor beans.

Batch extractors vary greatly in design. An extractor which is popular in the castor oil industry consists of a large horizontal drum (18 by 8.5 ft.) mounted on rollers by means of which the drum can be rotated on its longitudinal axis. Inside the drum is a horizontal, perforated, metal strainer covered with a filter mat of burlap, which extends the length of the drum and divides it into two compartments, one much smaller than the other. The large compartment receives a charge of 10 to 12 tons of solid material through which solvent is percolated during the drainage period. Four to six successive extractions suffic to reduce the oil content of castor pomace from about 15% to 1.5%. A common European extractor, some what similar, but of a stationary vertical design with internal mixing arms, has been described.

The extractor commonly used for the extraction of garbage consists of a vertical cylindrical kettle, with a large ratio of diameter to depth, equipped with a vapor-tight cover, a steam jacket, and a vertical low speed agitator. The most popular unit is about 4½ feet high and 10 feet in diameter, and takes a charge of 3 to 5 tons of material. This extractor is suitable also for the extraction of other relatively wet materials, as the material may be dried and extracted in the same vessel.

Solvent systems are used to some extent fir the attraction of fish liver oils, as well as fish oil. A number of other types of batch extractor have been described. The extraction of miscellaneous oil-containing materials, as well as oil seeds, has been developed to a much higher degree in Europe than in the United States.

Continuous extractors. The oldest successful continuous oil seed extractor, and one that many still consider the best type is the Bollman or Hansa-Muhle extractor, otherwise known as the paternoster or basket type. This extractor was designed and first built in Germany the American-built Blaw-knox and French extractors are very similar.

The basket type extractor (Figure 14 and 15) has the appearance of an enclosed bucket elevator. Unlike the various type of continuous extractors to be described later, it does not immerse the oil seed flakes in the solvent but extracts by percolation of solvent through the flakes while they are held in a series of baskets with perforated bottoms. To ensure uniform percolation and drainage, the width and depth of the baskets are usually fixed and the length is varies according to the capacity of the extractor, common dimensions are 20-28 inches deep, 30-40 inches wide, and 40-85 inches long (114). The baskets (usually 38 in the earlier models) are supported on endless chains, within a zastight housing. The flaked oil seeds are conveyed by a screw into a closed charging hopper at the top of the housing, the completely filled conveyor tube serving as an effective vapor seal against the solvent vapor inside the extractor. The baskets are continuously and very slowly raised and lowered at the rate of about I revolution per hour. As each basket starts down the descending side of the apparatus, a charge of seed is automatically dropped into it from the charging hopper. Extraction is effected by the percolation of solvent through the seed during their passage from the top of the bottom and again to the top of the apparatus. As the baskets containing the spent and drained flakes ascend to the top of the housing on the opposite side from the charging hopper, they are automatically inverted and the contents are dumped into a discharge hopper from which they are conveyed by means of screw conveyors to the meal driers.

Fresh solvent at the rate of approximately I pound of solvent per pound of seed its sprayed into a basket near the top of the ascending line if baskets, from which it percolates by gravity through the lower baskets, in counter current flow. The miscella from this side, termed the "half-miscella," is collected in a sump in the lower part of the housing. A pump continuously withdraws it from the sump and sprays it into the topmost baskets of the descending line. From this baskets it percolates downward through the lower baskets like the fresh solvent introduced on the other side of the system and is collected in a separate sump as "full-miscella." The full-miscella is freed from fine seed particles and solvent, to yield the finished oil, by means which will be described later.

Detailed operating data on a modified 400-ton per day Hansa-Muhle plant processing soybeans have been published by Kenyon. Kruse, and Clark. Commercial hexane at a temperature of 136°F is used as the solvent at the rate of 960 pounds per 1000 pounds of flakes (9.5% moisture content) to reduce the oil content of the finished meal (containing 8.0% moisture) to 0.6-0.7% and produce a full-miscella containing 25-28% oil. The extracted and trained flakes leaving the extractor retain about 35% of their own weight of entrained solvent. Most of basket-type extractors built thus far have been large, with capacities of the order of 200-1000 tons of flakes per day.

In recent years the basket extractor has been modified into square and rectangular (horizontal) types where, in addition to solvent or miscella draining vertically from one basket to another, it may be pumped to individual baskets in the horizontal sections. In this way re-circulation of miscella can be used with generally improved efficiency. The horizontal extractor also permits one-floor operation and can be housed at minimum cost.

Basket filling has also been improved with respect to vapor seals and may be adapted to preslurrying of flakes with miscella before dumping into the baskets.

The Blaw-Knox Rotocel extractor is similar in principle to the basket extractors described above; however, the baskets are carried in a rotary motion in a single horizontal plane, and miscella percolating through the baskets and falling into compartments in the bottom of the extractor housing is picket up by a series of pumps and recirculated counter-currently to the flakes. The first commercial unit placed in operation on soybeans in early 1950 employed 18 cells and six stages of extraction. It operated in a housing 12 feet high and 22 feet in diameter and had a capacity of 250 tons per day. Extractors approximately four to seven times this capacity are now in operation. These are reported to have all the advantages of the conventional basket type extractor without some of its disadvantages, being more compact and more flexible in operation. The French Oil Mill Machinery Company has recently announced a stationary basket extractor in which flakes and major machine parts remain stationary throughout the entire extraction cycle.

The principal advantage of the basket type extractors that it yields a very clean miscella with a minimum content of distance the flakes are not subjected to mechanical disturbance during the extraction period and the descending baskets form on effective of filter beds for the half-miscella from the ascending baskets…. Most of the fines production occurs. Its principal disadvantage are that it permits the possibility of channeling solvent flow through the seeds and that some oil seeds tend to pack in the baskets are home relatively impervious to percolation, with the result that the extraction rate becomes slow and the size of extractor required … given capacity becomes unduly large. It should be noted however that materials difficult to process in the basket-type extractor …. Complicate the operation of extractors or other types.

Another early German extractor, the Hildebraus (124), consists essentially of two vertical tubes interconnected …. Bottom by a third horizontal tube, with motor-driven screws …. The flakes down one tube, across, and up the other tube ….. current to the flow of solvent. Because of the working given ….. by the screws, flake disintegration and fines production are relatively extensive; for this reason it is unsuitable for seeds such as cottonseed although it has been reasonably successful in processing soybeans. A number of installations are in operation in this country and … but the trend appears to be away from this type of equipment. The original Hildbrandt extractor is no longer manufacture …… the modified design with screw propulsion of the flakes found…… extractor or the modern counterpart of the latter …… the Detrex extractor. A variation in design consis ……. Substitution of a drag-link conveyor for the flake-propelling. All of these latter extractors were designed for the ….. solvent and were intended primarily for the …… extraction of soybeans, for example, at the rate of about 25 ……. A number of these extractors, manufactured by the …….. Works, Minneapolis. Minnesota are in service in …………

The Bonotto extractor …… divided into a number of sections by a revolving ass ……. Horizontal plates attached to a cenral shaft. The plates are .……. a series of staggered slots through which the flakes, introducing the top of the column, proceed downward by gravity, counter ……. A rising flow of solvent. Stationary Scraper arms placed just …… plate provide gentle agitation of the flake mass to prevent…… or bridging and assist in moving the flakes through …….. The original Bonotto extractor employed a screw discharge ……. Mechanism to compress the spent flakes and seal the bottom of the column against the escape of solvent. Discharge of the flakes through such a mechanism has the advantage of squeezing out most of the entrained solvent. With some seeds, however, it is not mechanically reliable; hence, in extractors of the Bonotto type operating on seeds other than soybeans it has generally been replaced with an inclined side tube, up which the spent flakes are carried by a Redler or draglink conveyor, through a set of squeezing rolls.

An improved Bonotto design uses a Redler conveyor within a closed loop to feed the column and filters the miscella from the column through the flakes in a portion of the loop before it is discharged. This assists in clarifying the miscella and also extracts considerable oil from the flakes before they enter the extractor proper.

The Allis-Chalmers and Anderson extractors are modifications of the Bonotto apparatus; each employs stationary plates or partitions and moving scraper arms within the column rather than moving plates and stationary arms, and there are other structural differences, as well as differences in auxiliaries. The Anderson extractor for soybeans uses a choke or plug-forming flake discharge and has a built-in mechanically operated device for settling fines out of the miscella; the allis-Chalmers extractor uses an inclined side tube discharge for all oil seeds. In present installations this type of extractor is commonly used with pre-pressing, thus minimizing the problem of "fines" in the miscella.

The Kennedy extractor is built in the form of a long, enclosed trough divided into a number of sections, each of which has a rounded bottom. An impeller wheel carrying four curved and perforated blades revolves in each section, with the blade tips closely following the contour of the rounded bottom. Material introduced into the first section is transferred the contour of the rounded bottom. Material introduced into the first section is transferred the length of the trough, from section to section, by the scooping action of the impeller blades as the solvent flows through the bottom of each section in a counter direction. As the material is lifted up the curved section wall aboe the liquid level, to fall into the succeeding section, it is compressed slightly between the impeller blade and the wall; this squeezes out some of the entrained solvent and serves to decrease the carryover of solvent from one section to another by the flakes. From