The Complete Technology Book on Starch and Its Derivatives

The Complete Technology Book on Starch and Its Derivatives

Author: H. Panda
Format: Paperback
ISBN: 8178330733
Code: NI81
Pages: 540
Price: Rs. 1,100.00   US$ 125.00

Published: 2004
Publisher: Asia Pacific Business Press Inc.
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Starch is a group of poly saccharides, composed of glucopyranose units joined together by glucosidric linkages. Starch is also metabolized for energy in plants and animals, and is used to produce a large number of industrial products. Starch is processed to produce many of the sugars in processed foods. The biggest industrial non food use of starch is as adhesive in the paper making process. Other important fields of starch application are textiles, cosmetic and pharmaceutical uses. Starch can be obtained from maize, sorghum, roots and tubers such as tapioca, arrow root, potatoes etc. Starch truly serves as a multifunctional ingredient in the food industry. Starch is one of the most present biomaterials has witnessed significant developments over the years. By products are obtained in the manufacture of different types of starch such as maize gluten has a number of interesting possible uses in industry, zein (by product of corn processing) is used in the preparation of stable glass like plastics, modification of zien is used as adhesives and in the preparation of coating compositions for paper, the most important by product from wheat starch manufacture is gluten which is used in preparing diabetic foods, for feeding cattle, thickening agent in textile printing and so on. The Global starch market is likely to get respite from deceleration in its market growth, with growth poised to receive a new lease of life in the next few years.
This book basically illustrates about the properties, structures, manufacturing process explained with flowcharts and diagrams, applications of starch and its derivatives etc. The major contents of the book are structure and chemical properties of starch, chemical composition, molecular structure, starch granule properties, water sorption and granule swelling as a function of relative humidity, factors affecting starch paste properties, the oxidation of starch etc.

This is a unique book, concise, up to date resource offering a valuable presentation of the subject. This book contains processes of starch and its derivatives. This book is an invaluable resource for new entrepreneurs, industrialists, consultants, libraries.

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Related Books


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1. Structure and Chemical Properties of Starch
Structure and Properties
Chemical Composition
Molecular Structure
Starch Granule Properties
Water Sorption and Granule Swelling as a
  Function of Relative Humidity
Factors Affecting Starch Paste Properties
2. The Swelling And Gelatinisation of Starch
The Swelling of Starch
The Gelatinisation of Starch
The Use of Swelling Agents to Study Gelatinisation
Methods of Following the Course of
  Gelatinisation of Starch : Optical Methods
Methods Depending on Viscosity
The Effect of Injury to Starch Granules before
  Gelatinisation on the Properties of the Pastes
Viscosity and Structure
The Rigidity of Starch Pastes
3. The Role of the Minor Constituents of Starch
The Role of Phosphorus in Starch
The Formation of 'Werner Complexes'
The Adsorption Theory
The Amylophosphoric Acid Theory
The Significance of Nitrogen in Starch
The Coacervation Theory
Fatty Acids Present in Certain Starches
Other Acids Present in Starch as Esters
4. The Retrogradation of Starch
'Retrogradation' of Starch by Freezing
'Retrogradation' by Solvents
Monomolecular Dispersion
Complete Retrogradation
The Explanation of Retrogradation
Practical Significance of Retrogradation in Industry
The Prevention of Retrogradation
Reactions with Formaldehyde
5. Starch and the Hydrogen Bond
6. The Reaction of Starch with Iodine
The Effect of Heat
Sensitivity of the Reaction
An Abnormal Starch-Iodide Reaction
The Composition of Starch Iodide
Use of Starch Iodide
The Starch-Iodide Reaction in the Spectro-photometric
  Determination of Starch
7. Root Starches
Manufacture of Potato Starch
Refining the Starch
Drying the Starch
Some Difficulties Occurring in the Manufacture of Potato Starch
Cassava Starch or Brazilian Arrowroot
The Manufacture of Sweet-Potato Starch
8. Cereal Starches
The Manufacture of Wheat Starch
Manufacture of Maize Starch
Early Process. Extracting the Starch
Treating the Starch
Modern Process
Rice Starch
9. The Oxidation of Starch
Oxidation by Nitric Acid
Oxidation by Ammonium Nitrate
Oxidation by Chromic Acid
Oxidation by Permanganates
Oxidation by Hydrogen Peroxide
Oxidation by Halogens
Oxidation by Oxy-halogen Acids
Oxidation by other Per-compounds
Oxidation by Oxides in Acid Solution
Oxidation by Irradiation
Oxidation by Air in Acid Solution
Oxidation by Ozone
Oxidation by Hypohalites
Oxidation by Alkaline Chlorite
Oxidation by Alkaline Aktivin
Oxidation by Alkaline Permanganates
Oxidation by Alkaline Peroxides
Oxidation by Air in Alkaline Solution
Electrolytic Oxidation
Oxidation by Alkaline Mercuric Oxide
Oxidation by Alkaline Persulphates
Oxidation by Bromine
Oxidation by Iodine
10. Glucose and Maltose
The Manufacture of Glucose
Raw Materials
Earlier Process
The More Recent Process
The Crystalline Forms of Anhydrous Dextrose and
  Dextrose Hydrate
Producing Anhydrous Dextrose
Uses of Glucose
The Manufacture of Maltose
11. Ethyl Alcohol and Acetone
The Manufacture of Ethyl Aclohol
The Amylo Process
The Production of Acetone
12. Dextrin and British Gums
Methods of Manufacture
Raw Materials
The Choice of Acid
Pre-treatment of Starch before Torrification
Main Steps in Dextrin Manufacture
Addition of Catalyst
Maturing the Starch
Drying the Starch before Roasting
The Roasting Process
Cooling and Re-moistening the Dextrin
Grinding and Bagging-off Operations
Conversion of Starch to Dextrin by the Wet Process
Acid Conversion in the Wet Process
The Conversion using Enzymes
13. Modified Starches
Physical Treatment to Modify Starch
14. Adhesives from Starch and Dextrin
Purpose and Applicability
The Application of Adhesives
Theoretical Considerations
Flour Pastes
Adhesives from Starch
Treatment with Caustic Alkalies
Treatment with other Alkaline Substances
Treatment with Acids
Treatment with Salts
Treatment with Oxidising Agents
Treatment of Starch with Swelling Agents
Addition of Various Compounds to Starch Adhesives
Dextrin Adhesives
15. The Foodstuff Industry
Potato Products in the Food Industry
Importance of the Storage History of Potatoes
Colour of Potato Chips
Cooking other then Frying
The Gelatinisation of Starch
The Effect of Various Factors on Gel-Strength of Starch Pastes
Uses of Starch on Various Foodstuff Preparations
Starch in the Baking Industry
Moisture Absorption by Dough
The Influence of Other Physical Properties of
  Starch on Baking Quality
The Diastatic Activity of Flours
The Chemistry of certain Baking Faults
16. The Paper Industry
Tub Sizing
Coated Papers
17. The Textile Industry
Sizing of Yarns
Considerations influencing Sizing
  Mechanical Properties of Starch Films and
  Sized Cloths Arranged in Order of Decreasing Magnitude
The Effect of Auxiliary Agents on the
  Properties of Sizes and Finishes
The Use of Enzymes in Desizing
The Finishing of Textile Fabrics
Adhesive Dressings
Characteristics of Individual Starches
Wheat Flour
Tinting and Blueing Agents
The Suitability of Starches and Dextrins
The Printing of Textile
Function of the Thickener
Colour Value
Starch Products used for Thickenings
Disadvantages attendant on the Use of Starch Thickenings
Thickenings of British Gums
18. Miscellaneous Uses of Starches and Dextrins
The Soap Industry
Laundry Starches
Cosmetic and Pharmaceutical Uses
Horticultural Uses
Fire-Proofing Preparations
Explosives and Fuels
Some Unclassified Uses
19. Utilisation of the By-Products of Starch Manufacture
20. Antiseptic Agents and Preservatives
21. General Features and Nomenclature of Amylases
22. Preparation of Enzymes used in the Starch Industry
Enzymes from Malt
Preparation of Individual Malt Enzymes
Enzymes from Moulds or Fungi
Enzymes from Animal Juices
Bacterial Enzymes
23. The Action of -Amylase on Starch
Soluble Starch
Erythro Bodies
- and   -Glucosides
The Mode of Action of -amylase
24. Analysis of Starch and its Derivatives
General Methods of Analysis
Saccharide Contents of Acid-Converted Starch Hydrolyzates
Reducing Sugars
Schoorl Method : Conversion of Titer Difference to Reducing Sugar
Assay by Specific Gravity
Conversion of Commercial Degrees Baumé to % Dry
  Substance for Commercial Corn Syrups and Dextrose Solutions
Trace Components
Crude Fiber
Lactic Acid
Iodine Value
Peroxide Value
Free Fatty Acids
Cold Test
Smoke Point
25. List of Material Suppliers
List of Chemical Suppliers

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Sample Chapters

(Following is an extract of the content from the book)
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Cereal Starches

The Manufacture of Wheat Starch

In the manufacture of wheat starch the chief problem lies in the separation of the starch from gluten. Gluten consists of two protein substances, glutenin and gliadin, and in water swells to a sticky mass which retains the starch. Schhukin has examined the chemical composition of hard and soft wheats (Table 11). To separate the starch, the gluten may be destroyed by fermentation, as in the older processes, or mechanically kneaded in flowing water, by which the starch is liberated and carried away. Processes based on the mechanical separation are in general use today, as the gluten can be recovered and is a valuable by-product.

In the old fermentation method (v.s.), often known as Hale's method, the grain is steeped until it is soft enough to be coarsely crushed in a mill, the temperature of the steeping water playing a large part in determining the time of steeping. This preliminary steeping may, however, be omitted. A mash is made of the crushed grain and left to ferment. The period of induction of fermentation can be shortened if liquor from a previous fermentation is introduced into the mass. The period of fermentation required to bring the mass to the required state varies with climatic conditions. In the summer about 7 to 10 days are required, and in the winter the process may take as long as 30 days. Proteins and other nitrogenous matter decompose during the fermentation, and acids are produced which in turn help to dissolve the gluten, the latter becoming more soluble as its degradation proceeds. Gases, chiefly carbon dioxide, ammonia, and hydrogen sulphide, are evolved in the early stages of the process, and the whole mass has an offensive, putrefying odour, which constitutes a drawback to the process. As the fermentation proceeds, the mass becomes acid from the formation of acetic, butyric and lactic acids, and clots of moulds appear on the surface. The fermentation should not be carried to the stage at which the liquid becomes viscous, as it has then proceeded too far and difficulties will be encountered. At the desired stage, supernatant liquor is run off and the remaining sludge transferred to washing drums. The suspension of starch flows out through the wall of the drum, which may be made of cloth or fine metal-gauze. By revolving the drum horizontally and passing in water through the central shaft the mass may be washed until very little starch remains. The starch-milk is run off by means of troughs to settling tanks, where it is washed several times by agitation, settling, and decantation. The mass of starch is then removed to draining-boxes lined with flannel, or it is spread upon porous draining-floors, after which it is sent to the drying room.

The fermentation process is rarely, if ever, used at the present time. Not only is the valuable gluten lost, but the process is a lengthy one, offensive in operation, and gives rise to effluents, the disposal of which offers difficulties.

The Alsatian Process dispenses with fermentation, and is occasionally employed on the Continent. The grain is steeped until soft and the steeping water is changed frequently to avoid acid-formation and fermentation. The grain is then roughly crushed and the mass kneaded in a continuous stream of water supplied from sprinklers over the trough. The process is slow, as about 10 hours are required for the treatment of 1 ton of wheat. It has the advantage, however, that good-grade gluten is recoverable if the steeping is not too prolonged. A temperature of 30oC is recommended by Rehwald to hasten this step of the process. One ton of wheat yields about 750-1000 lb. of first-quality starch and about 220-450 lb. of starch of second quality.

Martin's Process is the one most generally used now, partly owing to the low initial outlay for plant, and partly to the good yields of first- quality starch obtained. About 45-55 per cent. of good starch on the weight of wheat, 10-20 per cent. of inferior starch, and 10-15 per cent. of good-grade gluten free from husks may be obtained. The disadvantages of the process are the higher-priced starting materials and the relatively large yield of second-grade starch, contaminated with gluten, that is produced. This, however, can be utilised as a good basic material for sizes and adhesives. It is a fairly rapid process. Wheat flour, the starting material, is made into a dough with about 40 per cent its weight of water and allowed to stand for 1 hour. The gluten swells, and the mass is transferred in lumps to the washing-machine, in which the dough is kneaded by means of a grooved roller on a grooved bed flanked by sieves, while a constant stream of water is supplied by means of sprinklers. The starch-milk is collected in troughs beneath the machine and is led into settling-tanks. The remaining gluten is removed after each operation.

Fesca's Process also uses flour as the raw material, and separates the starch from the gluten by means of a centrifuge. A suspension of flour in water is made and centrifuged, using a non-perforated drum. In this way a layer of starch is obtained on the wall of the drum, whilst the gluten forms a layer on the inside, a certain amount of gluten also remaining in suspension. Knives or scrapers, that may be set at a required distance from the centre of the centrifuge drum, are used for scraping off the gluten layer. The liquid from this process is rich in nitrogenous material and mineral salts and is incorporated in feeding-stuffs, which are then dried. To obtain a sharper separation of the starch from the gluten, Klopfer has suggested several modifications of this process, namely, the use of a 1 per cent solution of sodium bicarbonate, or of sodium chloride, or of green malt extract in the making of the flour suspension. The addition of these substances is claimed to improve the separation without destroying the nutritive value of the gluten.

This process is economical; it requires very little plant and water, and has low overhead charges. About 50 per cent of the flour solids appears in the gluten layer, which contains about 22 per cent protein, 67 per cent starch, and other solids; this by-product finds a valuable outlet in the manufacture of feeding-stuffs, and is used in the preparation of macaroni, semolina, and similar products.

In all the above processes the starch obtained requires purification before being used for a number of purposes, and this is carried out by washing with water, sieving, and sedimenting. The percentage of small starch grains present is determined by the rate of flow of the starch liquor over the tables or through the vats. When the centrifuge method is employed in the purification process it is usually carried out after the primary purification in order to avoid trouble due to the gluten particles choking the filter cloth; or, again, the centrifuge may be of the non-perforated type. After successive washings and sedimentation the starch cakes are filter-pressed or centrifuged in a perforated drum, and dried at 30oC, this temperature being increased to 60-70oC. later, when most of the moisture has been driven off. The cakes so obtained have a brownish discoloured layer on the outside, which is scraped off and may be used for low-grade work and for adhesive-making.

In some cases the treatment of glutenous starch to obtain pure starch is carried out with water containing a small amount of acid, usually acetic acid, which exerts a dispersing action on the gluten. Sulphuric acid is sometimes used, but suffers from the disadvantage that the acid is non-volatile, whereas if acetic acid is used, any remaining traces are driven off in the drying process. Caustic soda is another excellent but non-volatile dispersing agent for gluten. If crystal starch is required, the acid treatment is often omitted, as the presence of small amounts of gluten improves the coherence of the product, whereas with very white starches containing practically no gluten it is sometimes necessary to add a small amount of white dextrin to obtain the necessary binding effect. Good crystals of maize starch (v.s.) may, however, be prepared even when all the gluten has been removed and no dextrin added.

Manufacture of Maize Starch

The largest producer of maize starch is the United States of America, where it is generally known as 'corn starch', and is widely employed.

The amount and quality of the starch produced from maize depend upon the conditions of cultivation in a similar manner to the variations in potato starch, but between narrower limits.

In manufacture the starch has to be separated from the associated nitrogenous substances quickly to prevent deterioration being brought about by fermentation or acid formation. Centrifugal methods have been employed for this separation. The protein matter, or gluten, which is present to the extent of about 8-10 per cent consists of water-soluble albumins, alkali-soluble glutelins, the globulins that are soluble in dilute salt solutions, and prolamines, which are soluble in aqueous alcohol and occur only in the grains. Most of the nitrogenous substances are separated as the substantially water-insoluble gluten, but some of the more soluble globulins, together with the water-soluble albumins, are removed from the corn when it is steeped at the beginning of the process. This steeping-water also contains soluble salts, which form some 33 per cent of the solid matter removed at this stage. The gluten consists of about 50 per cent protein matter, 5 per cent oil, and 35 per cent starch, together with fibre and a little mineral matter. The starch, which constitutes 55-65 per cent of the dry weight of the grain, is contained in the endosperm, from which it is removed by crushing and maceration. In the old process the whole grain was treated, but present-day procedure is to separate the embryos and treat them to recover the oil they contain. Baines has protected a process whereby the grain is heated with five to fifteen times its weight of water in a closed vessel at 85-95oC, and a somewhat similar method is employed by Wildsmith. The by-products from the manufacture of maize starch are of commercial value, and are dealt with on page 360.

Early Process. Extracting the Starch

Williams have described the earlier processes. In these the whole grain was steeped in water for several days at about 60oC, the water containing 0.25 per cent sulphur dioxide or 0.3 per cent calcium bisulphite to retard excessive fermentation. It was then lightly ground between Buhr-stones to disintegrate the grains, and the mass well washed on sieves. After re-grinding and washing the mass a second time, to extract any residual starch, the two lots of starch-milk were mixed and concentrated by tabling, the gluten and fibre being carried off by the water and collected by sedimentation in large tanks.

Treating the Starch

The starch was next washed from the tables into a tank where it was treated with about 1 per cent. caustic soda, calculated on the weight of starch in suspension. This treatment caused the residual gluten to swell and at the same time facilitated the removal of the fatty material. The starch-milk, after further dilution, was again tabled, and the raw starch, which then contained about 0.1 per cent. alkali, again mixed with water. After sieving to remove impurities, this starch-milk was passed to washing vats where, during the sedimentation, some fermentation took place and the acid formed neutralised the residual alkali. After several washings, followed by sedimentation, the starch was passed to draining boxes, as in the present-day process. The draining was followed by drying, which is carried out today on similar lines and which may conveniently be considered at this point.


In the draining boxes the moisture-content is reduced in a few hours to 45-55 per cent., approximately. The blocks are then transferred to a warm chamber, where more moisture is lost, and the surface of the block form a crust which is discoloured by soluble impurities coming to the surface. This discoloured starch is scraped off and returned to another batch being processed. The blocks of scraped starch are treated according to the type of product required; for lump starch they are broken and air-dried, for crystal starch they are wrapped in paper and dried slowly at 30-40oC. It is preferable to allow the blocks to remain at room-temperature for several days before heating, and then to raise the temperature to about 35oC over two to three weeks. Pearl starch is obtained by drying at 71-80oC. for 18-20 hours.

The starch produced by the older methods has not, in general, such a good colour as that obtained in the present-day sulphurous acid process. The starch from the latter is largely used in glucose-syrup manufacture, and tends to give more fluid solutions; starch from the alkali process finds a big outlet in laundry work.

It will have been noted that in the preparation of wheat and maize starch the chief problem is to separate the gluten. The differences in manufacturing procedure for wheat and maize starch arise from the differences in the properties of the gluten in the two materials. Gluten from wheat can be kneaded into a tough, elastic, coherent mass, whereas that from maize remains in a finely dispersed state, necessitating special treatment to separate it effectively from the starch.

Modern Process

The sulphur-dioxide process was probably introduced by Wagner in 1886; it is superior to the alkali process in that the oil from the embryos is recovered and the starch more easily purified. Kaufmann has described the modern process, the first stage of which, after any necessary pre-washing, consists in steeping the corn in water for some 30-40 hours at 40-60oC to soften the grains. The water contains 0.3 per cent of sulphur dioxide. The grain is steeped in a battery of vats on the counter-current principle, and then crushed with rollers or in a Fuss mill with sufficient water to maintain the proper gravity; the embryos are set free, together with a small amount of starch, and the germs are separated by flotation in a V-shaped tank having a screw-conveyor at the bottom. After grinding the germs, the oil is expelled by hydraulic presses or removed by solvent extraction. The coarse solid matter removed from the V-shaped tank by the screw and conveyor, and freed from the germs, is ground with water in a Buhr-stone mill, the liquid being delivered into inclined shaking sieves (No. 9 gauze or 90 meshes to the linear in.), and then passes through a series of finer sieves (160 linear in., No. 17) or bolting cloth of 200 mesh, in which the fibrous and cellulosic matter is largely retained. The matter retained in the first sieve is generally re-ground and passed through the sieves again to obtain all the starch possible from it.

The starch is then concentrated by deposition on wooden tables which are 100-130 ft. long, 1-2 ft. wide, and 6-10 in. deep, with a fall of about 4 in. between the ends, the fall being greatest in the first 50 ft. The liquor is adjusted to 6-7o Bè and fed by a pipe, 3-6 in. in diameter, or by a perforated box, to the tables, which are arranged in parallel. Here more fibrous and glutenous matter is removed in suspension, the starch sinking to the bed of the tables owing to its greater specific gravity. The 'green' starch on the tables contains approximately 50 per cent of water, together with 0.5 per cent. of protein matter, and is removed when a depth of 8-9 in. is attained at the head of the table. Any slight surface deposition of gluten is first squeegeed off the starch, which is then flushed with water from the table over rotary filters. In this state the starch may be used directly for the manufacture of glucose syrup, but to obtain the starch for marketing it must be further purified by deposition, either with or without treatment with alkali. If the alkali treatment is omitted the protein-content remains around 0.5 per cent, but by treatment with alkali the figure is lowered to 0.3 per cent, as the alkali causes the gluten to swell and facilitates its removal. The fat is saponified and more easily carried away in the washing.

Recent patents, make use of the fact that gluten and impurities are more strongly absorbed at an air/water interface than starch, so that air blown through raw starch liquor causes the formation of a froth which contains only about 10 per cent by weight of starch but very appreciable quantities of gluten. By this process it is claimed that, after sweeping away the foam, the protein-content of the starch has been lowered from 0.5 to 0.3 per cent The paste is next made up to 22o Bè with water, and pumped into cloth-lined boxes, where it is dried as described above in the account of the old process.

Rice Starch

The production of rice starch offers similar problems to the production of maize starch because the gluten in the rice grain does not form a coherent mass as does wheat gluten. One of the earliest methods was due to Jones and this, with unimportant modifications, is used today. Rice grains are rich in starch, and each granule is coated with a very compact layer of gluten that has to be softened before it can be removed. Granules of rice starch are very small, and take a long time to settle, hence many factories use centrifugal methods of separating the partially purified and the purified starch. Where settling methods are used, as much as six weeks may elapse from the time the grain enters the factory to the time the starch is ready for marketing, so that the use of centrifugal methods, although more expensive, economises both space and time.

Rice starch is generally made from the broken white grains which have been rejected for use in the foodstuffs industry, or from 'cargo rice', which is the grain still enclosed in the outer brown cuticle. The by-product from the latter type of raw material is of value for cattle food, as it contains phosphorus compounds and rice oil.

The grain is fed by gravity into cement or iron vats, provided with air-agitation and fitted with perforated false bottoms. Caustic soda solution of sp. gr. 1.005 is run in until the level of the liquid is 12 to 24 in. above the grain. After standing for 24 hours, with periodic air-agitation, the liquid is withdrawn, the grains washed with water, and fresh liquor added. The steeping is continued for a further 36 to 48 hours, and then the grains are soft enough to squash by gentle pressure between thumb and finger, or the mass may have started to disintegrate. The mass of soft grains is ground with caustic soda solution of such a strength that the outflow liquor from the disintegrator has sp. gr. 1.240. Ammonia solution may be used instead of caustic soda solution; it saves half the time but is more costly.

The mass is now passed to the settling tanks, or in some factories to the centrifuges, in which case the amount of solids in suspension is kept higher than if it is to be settled. The imperforate-drum type of centrifuge is used, and after the operation has been completed any heavy fibrous matter is found against the outer wall, followed by a layer of starch containing some fine fibrous matter, whilst the last and inner layer consists of gluten admixed with some starch. The inner layer is scraped off before the main bulk of the starch is discharged.

The wet starch is agitated with water, to which is often added 0.25 per cent. of formaldehyde solution (35 per cent. strength) to inhibit fermentation, and either settled or centrifuged, and after removing the gluten layer the washing and separation processes are repeated. In some factories a bleaching process is introduced at this stage, and in others a blueing agent is added in order to improve the colour of the final starch.

There is no set rule for the order in which operations for purifying the starch are carried out. In some factories screening precedes, and in others it follows the centrifugal separation. Centrifuging the starch before screening saves wear on the silk screens, as the material passing through is much less alkaline than if the order of operations is reversed. With centrifugal separation the amount of alkali present is double that used when settling is employed, and the concentration of starch is also greatly increased.

The starch liquor is adjusted to sp. gr. 1.210 and passed into draining boxes, which have perforated bottoms and are lined with cotton fabric. In many modern plants, suction can be applied to the bottom of the boxes and, to hasten draining, air-pressure may be applied through covers fitted on the top. As it is important that no air bubbles should form in the mass, the sides of the boxes are tapped while the liquor is still free enough to liberate entrapped bubbles. When the starch has drained sufficiently to set to a solid block the boxes are discharged, and the blocks of moist starch are cut into four pieces and placed on porous plates in a crusting-stove.

In the crusting-stove the starch blocks are dried for about 48 hours at 50-60oC, then removed, and the brownish discoloured outer layer of starch scraped off and returned to one of the washing tanks. The starch-block is now ready for the final drying operation.

The drying process is very important, and must be strictly controlled, as the characteristic appearance of crystal or lump rice starch depends upon the attainment of correct drying conditions. If crystal starch is to be prepared, the blocks, after crusting and scraping, are wrapped in paper. For the first 48 hours the temperature is kept at 35oC, and the humidity of the air circulated in the drying-stove is not allowed to fall below 14 grains per cubic foot. At the end of 48 hours the temperature is raised by 3oC in each succeeding 24 hours, and the humidity of the circulated air is allowed to fall until, when the temperature of 50oC has been reached, practically dry air is being used. The temperature is then raised to 57-60oC for 36-58 hours, after which the starch is removed from the stove and the paper removed. For ordinary purposes, where crystal starch is not required, a shorter drying-time and higher initial temperature may be used, as the careful drying described above is carried out solely with the object of obtaining the starch in compact lumps.

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