1. CARBONATION AND FILLING
Introduction
Carbonation
The nature and effects of carbonation
Properties of carbondioxide
Equilibrium pressure
Measurement of carbonation
Carbonation determination
Carbonators
Designs of carbonators
Air exclusion
Proportioners
Fillers and Filling Valves
Basic filling valve operation
Filling valve development and the
influence of ambient filling
2. EFFECTIVE APPLICATION OF QUALITY CONTROL
Introduction
Evolution of QC in the Soft Drinks Industry
Concept of quality
Evolution of soft drinks QC
The Small-to-Medium-Sized Business
Contract packing
Setting up a cost-effective system for QC
Product and packaging innovation
National Operations with Multiple Plants
Impact of industry concentration
Organisation of QC at plant level
Centralised organisation for quality
Bottling versus canning QC requirements
Equipment selection for quality
Development of in-line quality-monitoring equipment
Potential quality problem areas
Product recall
Water quality and treatment
Statistical QC
Microbiology
Dispensed soft drinks
International QC and QA of Soft Drink Operations
The franchise system
Technical services
The international quality assurance laboratory
Ingredient quality
Packaging quality
Trouble-shooting the theory in practice
The Future
Influence of packaging
New ingredients formulation and sanitation requirements
Role of the soft drinks associations
The final word
3. FLAVOURINGS AND EMULSIONS
Flavourings
Legislation
Creation
Production
Emulsions
Manufacture
Application of Flavourings and Emulsions
Selection
Methods of use
Evaluations
4 SYRUP ROOM OPERATION
Introduction
Syrup Room Design
Wall finishes
Floors and drainage
Ceilings and lighting
Heating, ventilating and air conditioning
Syrup Room Equipment
Storage, mixing tanks and systems
Pipework, fittings and connections
Ingredient flow
Pumps
Measurement of liquid
Filtration of ingredients
Ultraviolet sterilisation
Pasteurisation
Homogenisation
Syrup Room Materials Storage and Handling
Sugar
High-fructose glucose (Corn) syrup
Acids
Sweeteners
Preservatives
Flavourings
Colours
Fruit juices and comminuted bases
Syrup Room CIP Systems and Detergents
Design of a CIP unit
Rate of flow in pipelines for CIP
Calculation of reynolds number
Choice of detergents
Automaton and computerisation in syrup rooms
Typical system description
Typical operating sequence for syrup manufacture
Multiple Component Mixing Plant
Construction
Control and operation
Future Developments
5 ACIDS, COLOURS, PRESERVATIVES
AND OTHER ADDITIVES
Introduction
Acids
Carbonic acid
Citric acid
Tartaric acid
Phosphoric acid
Lactic acid
Acetic acid
Malic acid
Fumaric acid
Ascorbic acid
Colours
Preservatives
Micro-organisms and soft drinks
Sulphur dioxide
Benzoic acid and benzoates
Esters of para-hydroxy-benzoic acid
Sorbic acid and sorbates,
Other Additives
Emulsifiers
Stabilisers
Saponins
Anti-oxidants
The Safety of Food Additives
6. HIGH-INTENSITY SWEETENERS
Introduction
Use of Intense Sweeteners
Current Sweeteners
Acesulfame K
Aspartame
Cyclamate
Saccharin
Stevioside/Stevia
Thaumatin
Dihydrochalcones
Potential New Sweeteners
Alitame
Sweetener Approval and Regulation
Future Use of Intense Sweeteners
7. CARBOHYDRATE SUGARS
Introduction
History
Carbohydrate Sugars
Granulated sugar
Liquid sugar
Glucose syrup: high-fructose syrup
Quality
Trade requirement
Quality assurance management
Sugar analysis
Transportation and Delivery
Bulk delivery of granulated sugar
Bulk delivery of Liquid carbohydrate Sugars
Security of delivery
Storage
Granulated sugar in bags
Granulated sugar in bulk
Liquid carbohydrate sugars
On-site Dissolving of Granulated Sugar
Batch dissolving
Continuous dissolving
High-capacity dissolving
8. PACKAGING SYSTEMS FOR FRUIT JUICES AND
NON-CARBONATED BEVERAGES
Introduction
The Fresh Cold Fill System
The Hot Fill System
Filling Equipment for Gable Top Cartons
Packing Materials for Gable Top Cartons
Product Protection and Product/Pack Interaction
General considerations
Cold filled juices
Hot filled juices
Flavour
Packaging of Frozen Concentrated Juices (FCJ)
Filling in Glass Containers
Plastic Containers and Pouches
9. GRAPE JUICE PROCESSING
History of Grape Juice Processing in North America
Grape Cultivars
The Chemistry of Grape Juice
Carbohydrates
Acids
Mineral content
Phenolic
Volatiles
Modern Grape Juice Processing
Harvesting/ripening
Stemmer/crusher operation
Hot-break process
De-juicing/pressing operation
Coarse filtration
Bulk storage and tartrate precipitation
Enzyme clarification
Polish (fine) filtration
Hot fill
Process Alternatives
Cold-pressing
Aseptic process
Concentration
Sulfur dioxide preservative
10. PROCESSING OF CITRUS JUICES
Introduction
Fruit Harvesting and Transport
Unloading and Storage of Fruit
Fruit Transfer from Storage Bins to Extractors
Juice Extraction and Finishing
Extractors
Finishing
Juice Processing for Pasteurized Single Strength
Juice Processing for Concentrate
Characteristics of 1950s evaporators
Modern evaporators for citrus fruit
Essence Recovery
Chilled Juice from Concentrate
Pulp Wash
Frozen Pulp Processing
Manufacture of Citrus Cold Pressed Oil
Manufacture of Livestock Feed from Citrus Peel
Peel dryer
Waste heat evaporator
11. APPLE JUICE
General Background
Juice extraction
Pomace disposal
Blending and packaging
Natural Style Juices
Clarified Juice and Concentrate
Enzyming
Pulp enzyming
Fining
Concentrates
Hazes and deposits
Authentication and Adulteration
Composition of Apple Juice
Sugars and sorbitol
Starch & pectin
Organic acids
Protein and amino acids
Polyphenols and colour
Minerals
Volatile components
Other flavour aspects
Microbiology
Food Tests
Test for the presence of pectin in clarified Juice
Test for the presence of starch
Test fining with gelatin
Test fining with gelatin/kieselsol
Test for overfining
12. EQUIPMENT FOR EXTRACTION AND PROCESSING
OF SOFT AND POME FRUIT JUICES
Introduction
Modern juice processing methods
Juice Extraction Systems
Fruit storage and handling
Milling
Pressing
Comparison of pressing systems
European grape pressing
Pre-treatment with Pectolytic Enzymes
Post-press Clarification
Decantation
Centrifugation
Earth filtration
Rotary vacuum filters
Sheet filtration
Cartridge filters
Membrane filtration
Concentration/Aroma Recovery
Rising film evaporators
Falling film evaporators
Centrifugal evaporators
Heat recovery from evaporated water
Aroma recovery
Pasteurisation
Flash pasteurisation
Batch pasteurisation
In-pack pasteurisation/hot filling
Fruit Juice Plant Layout
Materials of construction
Fruit reception
Handling and washing fruit
Seasonal problems
Effluent treatment
Juice storage
Summary
13. CHEMISTRY AND TECHNOLOGY OF CITRUS JUICES AND BY-PRODUCTS
Principal Citrus Cultivars
Origin of citrus
Commercial citrus regions
Citrus growing areas
Effect of frost
Effect of soil
Composition and Structure of Citrus Fruits and Juices of Various Cultivars
General relationship
Organic acids
Carbohydrates
Color pigments
Vitamins and inorganic constituents
Flavonoids
Lipids
Operational Procedures and Effects on Quality and Shelf Life of Citrus Juices
Outline of good manufacturing and processing procedures
Concentrate handling for reprocessing and/or
reconstruction
Sanitation or stabilization
Water for reconstitution use
Processing of chilled high and low pulp reconstituted orange juice
Finished product handling and storage
Citrus Juice Flavor Enhancement with Natural Citrus Volatiles
Components of citrus juice flavor
Citrus flavor enhancement technology
Citrus oils and aroma and their recovery
Pectic Substances and Relationship of Citrus Enzymes to Juice Quality
Effect of Time, Temperature and other Factors on Citrus Products
14. LEGISLATION CONTROLLING PRODUCTION, LABELLING AND MARKETING
Fruit Juices, Concentrated Fruit Juices and Fruit Nectars, Introduction
Fruit juice regulations in EEC countries
Fruit juice regulations in the United States and Canada
Fruit juice regulations in other major countries
Fruit juice standards produced by codex alimentarius
Non-Carbonated Fruit Beverages
Introduction
Fruit drink regulations in EEC countries
Fruit drink regulations in other European countries
Fruit drink regulations in the United states and Canada
Fruit drink regulations in other major countries
15. TROPICAL FRUIT JUICES
Introduction
Guava
Mango
Passion fruit
Pineapple
Other Tropical Fruits
Acerola
Banana
Kiwifruit
Lulo
Papaya
Soursop
Umbu
Tropical Fruit Juices in Europe Today
The Future
16. WHISKY 418
Introduction
History of Whisky Production
Outline of the Whisky-producing Process
Individual Operations
Raw materials
Mashing and cooking
Fermentation
Distillation
Maturation and ageing
Blending and colouring
Effluent disposal and spent grains recovery
Organoleptically Important Components of Whisky
Concentrations of organoleptically important compounds
Chemical nature of organoleptically important compounds
Contribution of compounds to organoleptic properties
Origin of organoleptically important compounds
17. BEER
Introduction
Historical Aspects of Brewing
Prehistoric and early historic
Brewing in Europe
Outline of the Brewing Process
Malting
Suitability of barley for brewing
the malting process
Kilning
Mashing
Brewing liquor
Mash-tun ingredients other than malt
Mashing systems
Enzymolysis in the mash tun
Sparging
Direct Conversion of Barley to wort
Wort Boiling and Cooling
General
Hops and hopping
Wort clarification and cooling
Fermentation
Brewing yeasts
Biochemical events during brewing fermentations
Physical behaviour of yeast
Fermentation systems
Beer Treatments
Maturation and conditioning
Haze prevention
Yeast removal
Pasteurization
Post-fermentation bittering
Beer Properties
Colour and clarity
Foam
Flavour and aroma
General composition and dietary value of beer
Beer Defects
Gushing
Microbiological spoilage
Oxidation flavour, stale flavour and other off-flavours
The State of the Industry
Types of beer brewed
18. RUM
Introduction
Production of Rum
Types of rum and the raw materials used
Pretreatment of the raw materials
Fermentation
Distillation
Maturing
Aroma Compounds of Rum and their Formation
Higher alcohols
Fatty acids
Esters
Phenolic compounds
Nitrogenous compounds
Sulphur-containing compounds
Lactones
Carbonyl compounds
19. TABLE WINES
Introduction
Some Economic Aspects of the History of Wine Making
Grapes
Must Treatment
Alcoholic Fermentation
Post Fermentation Operations
Microbiological Stabilization
Malo-lactic fermentation
Microbiological spoilage,
Sulphur dioxide addition
20. CIDER AND PERRY
Introduction
Definition of cider and perry
Outline of the process of cidermaking
Historical aspects
Composition
Juice
Fermentation and storage
Disorders
Technology
Fruit supply
Juice production
Juice treatment
Fermentation and storage
The final cider
Ancillary products

^ Top

Carbonation and filling

Introduction

In any bottling or canning operation, the filling machine is the interface between the container and the product. For the majority of carbonated soft drink installations, the final product does not exist until a point immediately prior to the filler. The processing operation involves combining finished syrup, treated water and carbon dioxide gas in the correct proportions, and normally this is carried out on a continuous basis, with the beverage being produced at a slightly faster rate than the requirement of the filler. Although there are many plants still operating on the old method of pre-dosing the empty bottle with the requisite amount of syrup and then topping-up with carbonated water, the modern process of pre-mix filling, where the carbonated, finished product is transferred to the container in one filling operation, is now predominant. The accuracy of the syrup/water proportioning and the control of the degree of carbonation are vital to the commercial success of carbonated soft drink production. This chapter details some of the latest advances in the processing equipment. The filling machine is unable to improve the standard of the beverage and the correct function of the processor plays a major role in predetermining the ultimate quality of the product and the overall success of the filling operation.

In the last ten years filling units have continued to increase in complexity and price. Filling valves have been developed in three main areas: to encourage a streamline pattern of liquid flow into the container (vital to successful ambient filling); to improve the control of fill height in the container; to adapt to changes in container design. The introduction of the large PET bottles (2-, 3- and, recently, 5-litre sizes) has necessitated the production of fillers with appropriately wide filling valve centres to accept these containers; hence, although filling machines have increased in the multiplicity of filling valves, they have also increased in physical size owing to wider valve centres. At the time of writing, Krones AG of Neutrabling, West Germany, claim the largest filler of 176 valves and in excess of 6 metres in diameter; the fastest filler would appear to be the 120-head can filler from Holstein and Kappert GmbH of Dortmund, West Germany, capable of speeds over 2000 cans per minute.

The advances in filler design have coincided with the development of ambient filling facilities and the almost total replacement of glass by PET plastic in the large bottle sector. The inexorable progress of the latter material casts a shadow over the future of glass for carbonated soft drinks as PET bottles become larger and, more important, are breaking into the less-than-1-litre range. The possible success of a returnable PET bottle is a fascinating scenario with its effect on bottling line composition and design, together with the added complications in the areas of distribution and return.

The filling machine still holds pride of place in the production line; the individual handling of containers at current outputs cannot fail to be impressive-although it is recognised that the modern, high-speed labelling machine is a tribute to engineering excellence in dealing with bottles, labels and adhesives at speeds never contemplated twenty years ago. At the filler, the formulated product is introduced into the prepared container, and the management of this operation is crucial; high outputs of large bottles demand huge quantities of product, and flow rates of 50,000 litres per hour through fillers are commonplace. Inaccuracy, malfunction or human error can have disastrous effects on yields and operating efficiencies, and the production technologist must be aware of how the equipment is intended to function so that, in the event of failure, corrective actions may be speedily taken before substantial losses are incurred.

Carbonation

The artificial inclusion of a dissolved gas in a soft drink beverage was developed from the popularity of natural occurring mineral waters, which are discharged in a slightly carbonated form from rock formations in many of the well-known spa resorts around the world. The medicinal advantages of spa products have been panegyrised to the point of exaggeration and the ingestion of the dissolved carbon dioxide has always been considered an important part of the therapeutic process. What cannot be denied is that the addition of carbon dioxide makes any soft drink more palatable and visually attractive.

1. The nature and effects of carbonation

Carbonation may be defined as the impregnation of a liquid with carbon dioxide gas (CO2). When applied to a soft drink product, the result is a beverage which sparkles and foams as it is dispensed and consumed. This escape of CO2 during consumption of the drink should complement and enhance the flavour, and will add an exciting tingle that stimulates the palate. The amount of CO 2 gas producing the carbonation effect is usually specified as ‘volumes’–meaning, in broad terms, the number of times the total volume of dissolved gas may be divided by the volume of the liquid. For example, a 3.0 volume drink will contain CO2 to the extent of three times the volume of the beverage. A more accurate definition involving the parameters of pressure and temperature will be explained later in this chapter.

The organoleptic effects are not the only benefits of the CO2 content; at carbonations above 3.0 volumes the CO2 has a preserving property, the extent of which is dependent upon pH, sugar, initial microbial load and the nature of the micro-organisms. This desirable attribute of carbonation should be considered as an added ‘bonus’ and must not be a substitute for other precautions taken to ensure the safety and extended shelf-life of a product.

Each soft drink formulation requires a particular degree of carbonation so that the effervescence is appropriate to the flavour and nature of the beverage. Fruit drinks–such as orange, bitter lemon, etc.–should contain low levels of carbonation whereas juice-based drinks–colas, ginger beer and cream soda–should be in the medium-to-high range of CO2 content. Mixer drinks, so-called as they are used mainly to mix with spirits, require high carbonations since the addition to other still (non-carbonated) liquors dilutes the original carbonation level. Drinks in this category would be tonic water, ginger ale and soda water. Soda water filled into syphons contains the maximum degree of carbonation usually encountered in the industry. These particular containers rely upon internal pressure to dispense the contents and, as the syphon empties, this pressure is replenished from the carbon dioxide dissolved in the product.

In practical terms, carbonation levels vary between 1 volume of CO2 in fruit drinks to 4.7 volumes in mixers and up to 6.0 volumes in soda syphons. Figure 1 shows typical carbonation values for a range of well-known drinks; a degree of latitude is indicated since individual recipes require their particular carbonations. The increasingly popular, large PET bottles constitute a special case; not only does the CO2 gradually escape through the permeable polymer material producing a marked reduction in the carbonation of the contents over a period of time, but the repeated opening and closing of the container for occasional consumption can result in the final 25/30% of the contents having an unacceptably low carbonation. This latter problem arises because each time the bottle is resealed, CO2 gas escapes from the residual product to pressurise the headspace volume and most of this gas then escapes to atmosphere on the next occasion the bottle is opened. These large containers are not really intended for intermittent consumption and to compensate for the future loss of carbonation, the product is carbonated to a slightly higher level than would be appropriate for the particular drink.

2. Properties of carbon dioxide

Carbon dioxide is a colourless gas with a slightly pungent odour; when dissolved in water the resultant carbonic acid mixture has an acidic and biting taste which is not unpleasant. CO2 does not support combustion and is used extensively in fire extinguishers. High concentrations in the atmosphere will quickly suffocate respiratory animals and since the gas is 1.53 times heavier than air at 70 °F, great care must be taken when entering vessels that have contained CO2 and may not have been sufficiently vented and purged; in these circumstances, residual CO2 will lie in the base of the tank to trap the unwary entrant. Carbon dioxide is usually present in atmospheric air at a level of approximately 300 ppm by volume and it is dangerous to breathe atmospheres containing more than 5% by volume; it has been postulated that workers may be safely exposed to a maximum concentration of 5000 ppm CO2 by volume for 8 hours per day.

CO2 is one of the very few gases suitable for providing the effervescence in soft drinks. It is non-toxic, inert, virtually tasteless, readily available at moderate cost and may be liquefied at reasonable temperatures and pressures, allowing convenient bulk transportation and storage. The solubility of CO2 in both water and soft drink product allows an acceptable retention of the gas in solution at atmospheric pressure and room temperature, although slight agitation will promote an evolution of gas bubbles from the body of the drink which creates the attractive sparkling effect.

The bulk storage of liquid CO2 in soft drinks plants is now commonplace all over the world; pressurised and insulated tanks holding CO2 at 20 bar. and maintained at a temperature of –17ºC by a small refrigeration unit, are available in various sizes from 5 to 50 tonnes in both horizontal and vertical modes. In order to obtain a sufficient supply of dry gas to feed the carbonation equipment, etc., it is necessary to utilise a suitable vaporiser unit which may be heated by water, steam or electricity.

Small-scale production plants still use thick-walled cylinders containing approximately 25 kg of liquid CO2 at 60 bar and these are usually connected in banks to allow a reasonable off-take rate without recourse to additional heating. In the more remote areas of the world, carbon dioxide is still generated on site by the chemical action between an acid and a carbonate -e.g. sulphuric acid and sodium bicarbonate: alternatives would be the combustion of fuel oil or the extraction of CO2 from the flue gas of a boiler operation or similar heating facility.

3. Equilibrium pressure

In common with other gases, carbon dioxide increases in solubility as the liquid temperature decreases, and for every combination of (I) the amount of CO2 in solution and the temperature of the liquid there is a finite minimum pressure that is necessary to retain the gas in solution. This is a condition known as ‘equilibrium’ where, owing to molecular movement, the gas leaving solution is equalled and balanced by the gas entering solution. At equilibrium pressure the gas/liquid mixture is just stable but any decrease in pressure or increase in temperature will render the mixture metastable (or supersaturated) in that the pressure/temperature combination is insufficient to keep the CO2 in solution. In this circumstance, gas will be spontaneously released (particularly if there is some agitation of, or irritant applied to, the solution) — a condition known as ‘fobbing’ or ‘foaming’ and usually apparent when a bottle of carbonated product is opened to atmospheric pressure. The inability of a carbonated beverage to retain its full CO2 content in solution at atmospheric pressure gives rise to the attractive ebullience observed during the act of pouring the drink into a glass and the liberation of further CO2 during the actual consumption.

Carbonated product held in a container that is open to the atmosphere will gradually lose carbonation as the gas is liberated and escapes from the liquid. In a closed container, this evolution of gas proceeds to fill the headspace volume and gradually increases the pressure, quickly at first and then more slowly as the equilibrium condition is approached. The actual rate of the transfer of gas from product to headspace depends not only on the proximity of the headspace pressure to equilibrium pressure but also on the temperature of the liquid, the nature of the beverage and the extent of any agitation or irritation imposed on the liquid. A quiescent, stable product not subjected to vibrations or movement may take many hours to reach equilibrium—whereas the same product, roughly shaken, will, take only seconds to attain the equilibrium state. The CO2 gas leaves the beverage and collects in the headspace volume to provide the necessary equilibrium pressure to keep the remaining gas in solution—at a slightly lower carbonation than the original value. This condition applies to all bottles and cans that have been filled with carbonated beverage and then sealed with the appropriate closure.

4. Measurement of carbonation

Since the degree of carbonation is such an important factor in the formulation of a soft drink, it is imperative that a standard form of measurement of carbonation should be available; this would allow the production of particular products at different times and in different locations and yet ensure that the carbonation of these products meets the required, agreed standard. Previously, it has been mentioned that carbonation may be quantified in ‘volumes’; a volume of gas is indeterminate unless the parameters of pressure and temperature are specified and two scales are in current use. In the UK the term ‘volumes Bunsen’ is popular where the gas volume is measured at atmospheric pressure (760mm of mercury) and the freezing point of water (32ºF or 0°C); an alternative scale used in the USA (and therefore followed by many franchise bottlers throughout the world) is ‘volumes Ostwald’, where measurement is also carried out at atmospheric pressure but any temperature adjustment is ignored. A third method, used on the European continent, measures carbonation in grams per litre and since one volume (Bunsen) is equivalent to 1.96 grams CO2 per litre, doubling the volumes of carbonation will give an acceptable approximation of the grams of CO2 per litre of product.

5. Carbonation determination

An obvious method of gauging the degree of carbonation would be to extract the total CO2 content from a known volume of product, adjust the gas volume to atmospheric pressure and, where desired, mathematically convert this volume to 0°C; the ratio of gas volume to original beverage volume will give the figure for carbonation.

This procedure is used in some QC laboratories but is usually restricted to low carbonation products as the routine is somewhat cumbersome.

A superior procedure (and still used extensively in the industry despite the introduction of later, sophisticated techniques) makes use of the equilibrium phenomenon described earlier. If the temperature and equilibrium pressure of a product are known, then there must be a fixed carbonation level based on these two factors. From laboratory measurements of the maximum amounts of CO2 dissolved in water at various pressures and temperatures and by the application of Henry’s Law, a graph may be produced of the three-way relationship between dissolved volumes, temperatures and equilibrium pressures. Figure 2 shows the maximum volumes of CO2 (adjusted to 760 mm Hg and 0°C) which may be dissolved at various temperatures and pressures. Fitting a pressure gauge to a container of carbonated beverage and shaking vigorously until the pressure stabilises will give the equilibrium reading; having also noted the temperature of the product, these two readings may be applied to the graph and the degree of carbonation determined. For example, an equilibrium pressure of 2 bar at a temperature of 6°C would indicate a carbonation of 4.0 volumes.

Unfortunately, this simple procedure is prone to inaccuracy owing to the possible inclusion of air in the beverage. (The presence of air in a carbonated product will radically affect the future quality and shelf-life of the drink since the oxygen element of the air promotes aerobic spoilage and oxidation of certain constituents.) A further complication is that air is roughly one-fiftieth the solubility of carbon dioxide, and although it may be considered that this small fraction renders the presence of any air inconsequential, the opposite is actually the case; any air contained in the product will exclude approximately fifty times its own volume of CO2. In fact, air in its normal composition of 21% oxygen and 79% nitrogen (ignoring trace gases and water vapour) does not dissolve in liquids to produce dissolved oxygen and nitrogen in these same proportions; owing to the differing solubilities and proportions of the two main constituents, the dissolved ‘air’ is actually 35% oxygen plus 65% nitrogen. This enrichment of the oxygen proportion is unfortunate since it is this particular component that is responsible for many of the spoilage problems associated with ‘air’ contamination.

When measuring the equilibrium pressure of a sample of carbonated product, other gases (such as oxygen and nitrogen dissolved from atmospheric air), if present, will also exert partial pressures dependent upon the individual presences and solubilities. In the case of oxygen and nitrogen, although the proportions may be small, the solubilities are much lower than that of CO2 and therefore the partial pressures necessary to keep the foreign gases in solution will be higher. In this eventuality, the total equilibrium pressure (being the summation of the partial pressures of CO2, O2 and N2) will be greater than that produced by the carbon dioxide content alone. This enhanced pressure, gauge reading during the carbonation test will indicate a higher carbonation level than is actually present. A high ‘air’ content not only produces a false reading of the carbonation level but also imparts a ‘flatness’ or lack of sparkle to the beverage and results in a stale flavour.

In order to avoid a distortion in the carbonation reading produced by dissolved oxygen and nitrogen, a simple modification applied to the pressure/temperature procedure previously described will allow a more accurate determination of the CO2 content: when the container is shaken to equilibrium, the first pressure is allowed to escape slowly to atmosphere and the container then agitated again to the equilibrium condition, which is the pressure used to compute the carbonation level from the graph in Figure 2. This adaptation is often referred to as the ‘second shake’ method and eliminates the misleading effect of any dissolved ‘air’ since the latter, being less soluble than CO2, will leave solution during the first shake and will be vented-off as the container is de-pressurised.

The equipment used to determine the equilibrium pressure in a container will vary according to the supplier, but basically consists of a hollow piercer (or lance) which enters the bottle cap or can lid and is connected to a pressure gauge and a release valve. Glass bottles should always be enclosed in a metal cylinder during the agitating operation but plastic bottles and cans may be held in an open frame as shown in Figure 3.

When a filled bottle or can is selected for a carbonation test it may have been obtained directly from the production line, or it may have been extracted from warehouse stock, or it may have been delivered to a central laboratory from a satellite factory; in the last two instances, the containers will have attained equilibrium pressure but bottles and cans taken from the production line will not have reached that condition and require special attention before being tested. The container should be wrapped in a cloth dampened with cold water and shaken vigorously for at least 30 seconds and then allowed to rest undisturbed for another 5 minutes; this procedure will ensure that equilibrium conditions have been obtained for all gases in the package, i.e. the gases will have been distributed between the headspace and the product according to their solubilities and presences.

The test may now proceed as follows:

(1) Check that the release valve is tightly closed.

(2) Place the bottle or can in the apparatus and puncture the crown, cap or can base with a firm movement to ensure that a seal is made.   

(3) Check that the pressure gauge has registered and record this reading for possible comparison with the second-shake pressure.

(4) Open the release valve slightly and allow the top pressure to escape in a controlled manner until the gauge reads zero or bubbles escape from the beverage.

(5) Firmly close the release valve.

(6) Shake the container and tester vigorously until the pressure gauge rises to a maximum reading and no further shaking will increase it; record this pressure.

(7) Release the pressure, remove the container from the tester and immediately measure the temperature of the product - taking care to do nothing that would raise this temperature.

(8) Using the pressure reading obtained in (6) and the temperature obtained in (7), determine the carbonation from the chart in Figure 2 where the vertical pressure line meets the horizontal temperature line.

If the point of intersection of these lines lies between particular carbonation curves, it is usually satisfactory to estimate the actual carbonation level; to obtain greater accuracy, the proportion of the horizontal (pressure) values may be used for interpolation of the exact carbonation. Instruments should be carefully maintained and regularly checked; any inaccuracies in measuring temperatures and pressures will obviously produce imprecision in the carbonation reading.

The difference between the ‘first shake’ and the ‘second shake’ pressures is significant. If the beverage is completely free of all gases except carbon dioxide and the headspace volume is of the order of 5% of the total container capacity (as is usual in most bottles and cans), then the percentage fall in equilibrium (gauge) pressure between first and second shakes will be approximately 5%; if the process is repeated several times, the pressure will reduce by 5% each time until all the carbonation is lost. Taking into account the CO2 lost between shakes and the internal volume of the apparatus plus pressure gauge, etc., a reduction of 7-8% between first and second shakes could be considered acceptable; results in excess of this figure will indicate that dissolved ‘air’ is probably present and the cause should be investigated and rectified if reasonably air-free (and oxygen-free) products are to be produced.

Effective application of quality control

Introduction

Although the organoleptic qualities of soft drinks and some of their major ingredients present specific problems in the attainment of consistent high quality, this challenge has been successfully met by the introduction of comprehensive quality control (QC) and quality assurance (QA) systems incorporating advanced laboratory and in-line instrumentation aided by the application of statistical and microbiological techniques relevant to high­speed packaging operations.

The effects of increasing legislation, added to the growing consumer insistence on safer products and higher quality standards in a competitive market, have augmented the prime objective of the modern quality technologist - the achievement of consistent product quality within company standards. Supportive expertise must now be provided to reduce manufacturing costs by tighter controls on raw material quality and utilisation, and to improve production line efficiencies.

This chapter reviews the evolution and growing importance of both QC and QA in the soft drinks industry. Particular emphasis is accorded to the practical problems of establishing and operating effective quality systems in three types of business, viz. small-to-medium, national and international: not surprisingly, the wider scale of quality supervision demanded by both national and international operations receives principal attention, although the particular issues relevant to smaller companies are also highlighted.

As production speeds increase and equipment becomes more complex, it is particularly important that the QA systems are geared to prevent defectives as distinct from the QC systems applied in-plant in order to detect defectives.

Finally, the chapter examines some of the important technical factors that are likely to influence the industry’s growth and development, emphasising the contribution required from quality technologists both now and in the future and stressing the prospect of challenging and exciting careers for newcomers to the soft drinks industry.

Evolution of QC in the soft drinks industry

1. Concept of quality

Before beginning to describe the development and increasingly important role of QC in soft drinks manufacture, it is important to first lay down the ground rules for achieving consistent first-class quality, as this requires a multidisciplined approach within each company in order to be successful. Put simply, manufacturers produce their various product flavours to formulations which incorporate predetermined quality standards governed by consumers’ expectations of a consistent, good-flavoured and refreshing drink, at a reasonable price. We therefore have three critical areas of quality to consider.

• Quality of design - what we believe our consumers want;

• Quality of manufacture - our best efforts at making it;

• Quality of marketing - what the consumer actually gets.

These shall now be examined in more detail.

Quality of design. This is an R&D and marketing responsibility, to quantify what the consumer wants (no mean task) and develop formulations that match this expectation. Raw material sourcing, costs and availability, compositional legislation and processing requirements all feature in this important development stage. As there continue to be many notable failures with ‘new’ soft drink products, it must be assumed that this area of quality continues to prove most difficult to quantify accurately. QC input at this stage is normally limited to establishing the necessary tolerances for the quality parameters to be used in production control and verifying that the processing requirements can be met.

Quality of manufacture. The bulk of this chapter will be devoted to the application of QC during the manufacturing process for carbonated soft drinks, requiring the combined disciplines of chemistry, physics, engineering, statistics, microbiology - and common sense! With high-volume production and using statistical sampling methods, the achievement of 100% product fully within specification is not normally possible. A more practical target is to ensure the maximum expected quality according to the process capability of the production line, which should have been selected to meet the company’s quality standards.

Quality of marketing. In addition to their role in the development of new products (or re-formulation of existing products), the marketing function has an important responsibility for ensuring that their company’s product range reaches the market in the same condition as it was when produced. Through co-ordination and liaison with sales, production and distribution, marketing can help ensure that products reach the consumer well within shelf-life and are competitively priced and packaged. The effects of age, heat, sunlight and dampness during storage before sale, the interaction of some ingredients plus possible microbiological activity in the product, all combine to reduce the ‘factory-fresh’ product quality. Although soft drinks suffer far less from these factors than many other products and have, in most cases, a shelf-life of up to one year, products containing light- or heat-sensitive ingredients such as ascorbic acid, quinine, aspartame and certain food colours, can deteriorate appreciably and lose their palatability and attractive appearance. This can be a significant problem in certain overseas markets.

These three key areas of quality must be borne in mind when setting up a comprehensive quality system extending from raw material supplies right through to final point of sale.

2. Evolution of soft drinks QC

A number of key factors in the development of the industry after the Second World War helped to accelerate the evolution of soft drinks technology and the need for in-plant QC. These included

• Increased demand for international branded soft drinks- particularly colas

• Introduction of soft drinks legislation covering product composition, contents (volume), labeling, ingredients and prescribed container sizes

• Significant new product and package developments, including the introduction of comminuted fruit drinks, low-calorie drinks and one-trip containers - particularly PET bottles.

These factors brought in train the introduction of the pre-mix filler design (where the finished product and not carbonated water, is handled in the filler bowl) and the coagulation chemical treatment of the raw water, which required more technical supervision in-plant. Although, initially, laboratories were staffed by either qualified chemists (who tended to be laboratory, rather than plant, oriented) or trained production personnel (as in the USA), evaluation of the procedures and QC approach used by the major inter­national franchisors enabled these to be selectively applied in the industry, demanding the employment of multi-disciplined technologists with direct plant experience. As their contribution to the business increased, so did their status in the industry. The following sections review the application, in practice, of quality systems in three different levels of business:

• The small-to-medium business

• The national manufacturer with multiple plants

• The international (franchise) business.

The small-to-medium-sized business

Many of these were family owned businesses supplying local sales and with strong brand loyalty. After many years of heavy dependence on experienced, reliable production personnel for quality supervision, the need for closer technical control of production became increasingly apparent as production speeds increased, formulations became more complex and one-trip packa-ging was introduced. These companies were also competing with the high-quality branded products supplied by national companies and had to reassess their quality of design, manufacture and marketing to stay fully competitive. With increasing dependence on the new QC function and its vital contribution in the control of raw material utilisation and costs, QC became more firmly established in the management team and progressively assimilated the necessary techniques to apply the new skills of microbiology and statistics in their quality plan. Where two or more plants were operated, a central QC co-ordinating role became necessary to ensure common standards, procedures and quality performance, and these responsibilities were coupled with product and packaging development. QA systems began to be developed to prevent production of defectives as well as further improvement in QC procedures and equipment for the detection of defectives.

1. Contract packing

As larger companies turned to contracting out production as an alternative to building new, expensive plant, this development became an important catalyst for smaller businesses with latent expansion plans. The high plant and product standards demanded by the contractors frequently required up-grading of plants, resources and, in particular, the QC function. Marks and Spencer have provided a good example of the growth potential for their suppliers through contract packing in the UK - provided that the packers recognise the critical role of quality in this type of operation.

2. Setting up a cost-effective system for QC

As close control of overheads became increasingly necessary in the highly competitive drinks market, there were major constraints in the smaller companies on the introduction and expansion of QC and progress was somewhat slower than in larger companies. Basic tests for Brix, carbonation and contents were initially introduced, but as product development became increasingly important, more experienced chemists were engaged to handle both QC and product/packaging development. This also enabled a more professional approach to be taken and prime attention was given to the principal sources of substandard quality by setting tighter Brix and carbonation standards and by checking these key quality parameters at regular intervals throughout production. Similarly, procedures for ingredient processing and accuracy were improved through the introduction of Brix and acidity standards and closer laboratory supervision of flavoured syrup preparation.

Finally, the introduction of benzoate-preserved comminuted bases for fruit drinks, replacing juice-based drinks preserved with the more effective sulphur dioxide, highlighted the need for more stringent hygiene procedures and routine microbiological control.

It is interesting to note that until QC had proved itself in many organisations, initial reporting relationships were to production management and this is still the norm in many US plants where trained production personnel handle the QC responsibilities. Independent reporting to general management developed as the value of effective QC became more apparent.

In summary, therefore, with limited resources available, the operating costs of QC were more than off-set by the savings in ingredient utilisation during processing, i.e. through less waste and by tighter control of the syrup/water proportioning during the pre-filling blending and carbonating process. Reductions in line rejects and in consumer complaints were other areas of cost benefit through the introduction of QC.           Finally, elimination of trade spoilage (which could affect considerable quantities of stock in the trade) was achieved through more frequent intensive sanitation procedures, including the introduction of hot sanitation techniques before and after production of the more sensitive beverages containing comminuted fruit bases.

3. Product and packaging innovation

Companies in this category had a significant advantage over larger companies in being able to launch new products or packaging more quickly and with less investment risk. This greater flexibility enabled the more alert companies to capitalise on current consumer trends with minimum advertising spend, i.e. through local launches. Where necessary, the company’s own technical resources could be augmented by specialist consultancy support and a number of examples exist of impor-tant innovations to the industry introduced in this way and adopted later by larger companies. A major contribution to the success of such innovations was made by the chief chemists, quality managers or technical managers of these smaller operations.

Some companies also had the good fortune (or wisdom) to have acquired natural spring or well-water sources which could be more fully exploited with the dramatic growth in bottled waters.

Although the soft drinks industry’s concentration in recent years has sadly led to the closure of many smaller businesses, those that have survived through shrewd marketing, contract packing, or by becoming low-cost producers, have also contributed to the industry’s technological development and owe this, in some measure, to the efforts of their QC staff.

National operations with multiple plants

1. Impact of industry concentration

The increasing concentration of the international beverage business, through acquisitions, joint venture and equity share, has significantly reduced the number of soft drinks manufacturers in Europe and the USA. In the UK, for example, there are less than a dozen major carbonated drink manufacturers operating high-speed, low-cost production units - generally on a multi-shift basis. This has required some adjustment in approach to the control of quality through up-dating of test procedures, sampling plans and use of in-line inspection equipment. Through improved plant design, both processing and filling plant have increased reliabilities but the sheer scale of the operation can mean major cost penalties when things go wrong. With 1000 bottles per minute (bpm), bottling lines capable of producing over eight million cases of product per annum and canning lines now operating much faster than this, QC response to line problems has to be immediate, the problem rapidly assessed and remedial action implemented without delay.

Reduction in operating plants has, however, eliminated some of the problems of product quality variability between plants - a significant issue in the past in some organisations.

2. Organisation of QC at plant level

A key requirement for plants operating shift systems is the achievement of equal quality performance on all shifts. This is normally a people-related problem requiring considerable company effort in the selection, training, motivation and supervision of key line personnel - particularly as automation reduces the number of line operators, all of whom make some contribution towards product quality.

Basic requirements for an effective QC system include

• Comprehensive raw material, processing and finished product specifications;

• A quality plan (endorsed in a company technical manual) identifying the sampling frequency and source, tests required and test equipment to be used;

• Well-equipped laboratory facilities, ideally located close to both production floor and key processing operations and including separate microbiological laboratory;

• A clear understanding of the QC function’s responsibilities and level of authority by both plant and central management;

• A positive, planned programme for the training, re-training and motivation of the QC team.

3. Centralised organisation for quality

In a multi-plant operation, co-ordination and standardisation of quality systems are fundamental to the achievement of consistent quality standards. This responsibility may be vested in a quality controller or manager, with a small support team for statistical data processing, development of new test procedures and a hygiene specialist (or microbiologist) for plant sanitation audits. Regular auditing of all company plants will be a key responsibility of the central quality function to assure senior management that quality is. indeed, under control. This is therefore a quality assurance responsibility, rather than one of quality control and helps to differentiate the respective roles within the quality organisation.

In a larger organisation, the central quality function may be included with engineering and R&D, and be placed under a technical director with full board authority. Clear functional and reporting responsibilities of the plant QC manager with both plant and central management must be defined. One favoured structure is for the QC manager to report to the factory manager with functional responsibility to the central quality controller.

The central quality function would also have responsibility for the preparation and updating of all technical manuals, for liaison with both R&D and marketing in the development and introduction of new products, packaging and ingredients and with R&D and engineering in the development of new process systems.

4. Bottling versus canning QC requirements

Although a number of routine tests are common to both canned and bottled products (e.g. Brix, carbonation, pH or acidity, fill contents and microbiological status) there are certain important differences in either test procedure or emphasis that need highlighting. Owing largely to the design and material of the modern can, higher production efficiencies are generally obtained on canning lines than on glass-bottling lines and, with fewer stoppages, quality tends to be more consistent. The quality integrity of the can and its contents depend heavily, however, on close control of the end seaming operation and effective headspace air removal through flushing with CO2 or nitrogen immediately prior to can end application. Nitrate levels in process water must be low as can corrosion may develop with high nitrate content. Sugar for canning must be free from sulphur dioxide preservative (still used in some parts of the world) and it is essential that any proposed change in the design, composition or specification of the can or end component is advised to the canner by the supplier and, where considered necessary, thoroughly checked out before adoption. This is particularly relevant to the internal lacquering system used and the PVC compound on the end component. Can contents are normally checked by an in-line fill-height inspector which employs a radioactive isotope source.

In bottling operations, high-quality glass or PET containers are vital for good line performance. While crown-closure application is quite simple and presents few quality problems, close control of cap application (both plastic and aluminium caps) is necessary for good carbonation retention yet easy consumer removal. Contents variability between bottles can occur with low-calorie and some foaming products at the narrow neck fill-point of the bottles, making it difficult to balance equipment settings to provide both good fill and standard carbonation.

Efficient utilisation of ingredients through tight control of fill contents and Brix (or acidity for low-calorie drinks) is a significant QC responsibility in both canning and bottling and will avoid major cumulative losses on high-speed units particularly. Consistent high quality normally means maximum raw material conversion with minimum wastage.

5. Equipment selection for quality

In view of the major investment involved for modern high-speed bottling and canning lines (e.g. £4 million for a 1000 bpm returnable bottle line) the capability of the line to meet all of the company’s quality standards must be carefully assessed before purchase. Each equipment component contributes to the final product and package quality, and it is important for QC to participate in equipment selection from the outset through to commissioning and final assessment of the plant’s process capability against the quality tolerances demanded by the company.

6. Development of in-line quality-monitoring equipment

Following the major increase in production speeds in recent years, periodic on-line sampling followed by laboratory testing proved to be inadequate as action response to substandard quality was too slow. Development of in-line test equipment has accelerated in both Europe and the USA and alternative equipment is now available to monitor key parameters such as Brix, carbonation, pH, colour, clarity, etc. Although earlier equipment was designed to monitor the appropriate quality parameters, the latest designs transmit the test results to the process control mechanism, ensuring that any out-of-standard situation is rapidly corrected. Prime interest in Brix and carbonation has provided equipment available from a range of manufacturers including Terris, Anacon and GAC in the USA and also Maselli and Embra in Europe. Density monitoring in-line, as an alternative to Brix, is preferred by some soft drinks manufacturers and equipment is available from Paar Scientific Ltd, London. Increased popularity of diet drinks (containing no added sugar) has required alternative control parameters such as acidity, and in-line instrumentation using infrared spectroscopy is now available.

In addition to the basic tests for carbonated products, water-treatment plant control can be readily exercised by the use of various types of in-line instrumentation for monitoring pH, total dissolved solids, alkalinity, residual chlorine, etc. Other well-established systems include in-line empty-bottle inspection (after washing) utilising new camera techniques, bottle washer detergent strength monitoring by conductivity and fill-height inspection for both bottles and cans.

Recent developments include multiple-label inspection (an increasingly important requirement on high-speed bottling lines as manning levels are reduced) and in-line microbiological sampling linked to rapid test methods for evaluation of finished product stability before release to the trade. Clearly, this has become a major feature in the quality control of high-speed soft drink production lines demanding familiarisation of QC personnel with the operating principles and techniques of this equipment.

7. Potential quality problem areas

The prime sources of variable product quality in a typical large production plant will now be examined in detail. These problems tend to stem from five principal sources:

• Poor material quality

• Process malfunction through either equipment failure or human error

• Ingredient omission through either equipment failure or human error

• Inadequate sanitation

• Malfunction or inadequate control of filling/carbonating/proportioning equipment.

Raw material quality.   From the range of ingredients used, chemical additives produced to BP or equivalent standards are unlikely to provide quality problems and the quality plan should therefore focus on sugar, CO2 and fruit materials. Although these particular ingredients should be tightly specified and quality-controlled during manufacture, they are more likely to provide problems in some parts of the world compared with other ingredients. The quality plan should, therefore, include batch sampling and at least physical examination of the fruit materials, taste and odour checks on CO2 and Brix, colour, taste and micro checks on each batch of sugar. Water, as a prime ingredient and liable to seasonal quality variation, requires particular QC attention in respect of both incoming water quality and control of treatment used. See Section which covers this vital area in more detail. Packaging materials can present short, sharp, serious problems on the production line and inspection policies differ from one company to another. Some companies develop a comprehensive vendor rating scheme which includes regular inspection visits to suppliers’ plants by QC staff from the bottling or canning plant, with free access to the suppliers’ quality records. Alternatively, incoming goods inspection schemes can be established for statistical sampling and examination of incoming packaging for approval (or rejection) before use. Selection of the best system will depend on the reliability of the supplier and availability of the packaging - a real problem in certain countries: In view of the critical importance of container dimensions for good filling and handling on the production line, spot sampling (at least) for dimensional checks is a worthwhile insurance before the containers are filled. Unfortunately, in many countries, serious packaging defects continue to be discovered either on the production line or, worse still, in the trade, through lack of appreciation of the value of pre-use inspection schemes.

Process malfunction. Although a malfunction or operator error can occur at any time in either water treatment or flavoured syrup preparation, morning start-up (particularly Mondays or after holiday shut-down periods) tends to be the most vulnerable period when QC needs to be on guard against unusual problems developing. Coagulation water treatment plants can be notoriously unreliable after shut-down periods and when they are subjected to peak early morning demands. In flavoured syrup preparation, some products require special processing such as filtration, pasteurisation or homogenisation which, under peak pressure conditions, can be inadequately processed with disastrous effects on the finished product in the trade. Each important stage or the ingredient processing operations has to be highlighted in the Quality Plan, with appropriate supervisory checks by QC staff and the status of the process logged for each day’s production.

Ingredient omission. Although effectively part of the previous section on process malfunction, omission of vital ingredients continues to be a costly vulnerable area of processing operation in many companies. This is recognised by the major international franchisors who normally supply their bottlers with a ‘unit pack’ which includes all the key ingredients for flavoured syrup preparation except sugar, making the syrup process much simpler and more reliable. Where unit packs are not used, formulae need to be clear and unambiguous, with the ingredients added in an optimum sequence - as certain, ingredients can interact. Various systems are used to verify the accurate addition of all the ingredients, including operators double-checking each other’s measurement and addition of every ingredient and logging these in a batch report. While the successful application of modern laboratory techniques such as HPLC has enabled analytical verification of Ingredients such as saccharin, benzoate preservative and caffeine, other ingredients such as flavour (essence) content, fruit juice or comminuted fruit content, quinine, aspartame, sodium citrate, etc., cannot be readily checked before the syrup is required for production. Fortunately, more advanced syrup or finished product blending systems are being developed and are already operating with apparent high reliability, including in-line monitoring instrumentation. In most world-wide plants, heavy dependence continues on reliable operator processing, backed up by independent QC checking. In addition, the important organoleptic check on the flavoured syrup prior to bottling creates a related problem, particularly in large operations producing flavoured syrups on a batch basis as the considerable number of batches produced daily places a heavy load on the sensory capacity of the QC staff. The industry continues therefore to seek a suitable instrumental ‘sniffer/taster’ to deal with this problem, although development of highly reliable processing  plant is clearly a better option. Until then, it remains important for QC laboratories to include adequately trained, skilled tasters for the vital test.

Inadequate sanitation. Major soft drinks companies operate comprehensive plant sanitation programmes to ensure good product shelf-life without trade spoilage. The use of fruit juices or comminuted fruit bases, and the growing trend away from the use of chemical preservatives, demands the consistent application of stringent hygiene procedures. Hot sanitation methods using programmed ClP systems have proved most effective employing, for example, 1% caustic solution at 80 °C or, alternatively, an initial cold detergent treatment followed by hot water sterilisation at 80 0C, for 20-30 min. In certain equipment systems, temporary removal of refrigerant is necessary before the hot treatment.

Suspect areas of plant cleaning tend to be pipeline ‘dead-legs’, pump rotor faces, filler-head springs and valves, i.e. where fruit-juice pulp can rapidly accumulate and provide a source of infection. QC monitoring of plant hygiene must, therefore, include periodic physical dismantling and inspection of plant after sanitation, followed by microbiological swabbing. As it is normally impracticable to hold finished product stock until micro clearance by QC (i.e. 3-5 days after production), the recent development of rapid micro methods using impedance and luminescence techniques has enabled results to be available in 12-24 hours (depending on the degree of contamination) and before stock is despatched to the trade.

Malfunction or inadequate control of filling/carbonating/proportioning equipment. This is frequently the most common source of variable product quality through a combination of equipment maintenance inadequacies or poor operator control. As described earlier, it is important to know the process capability of the plant (which may vary between products) before defining the quality tolerances to be applied. The frequency of sampling must be determined according to output speed and expected machine performance and, in some companies, the line operators are made responsible for the start­up of the plant to the necessary Brix and carbonation standards and for checking output quality at regular intervals. The QC checks are therefore confirmatory but include more comprehensive product analyses and packaging examination. Critical periods demanding close operator and QC attention are flavour or package changes and start-up/shut-down of plant, as errors are more likely to occur at these times.

Flavourings and emulsions

Flavourings

Although flavourings are normally used in extremely small quantities in a carbonated soft drink, their impact can make the difference between a tasty product and one that is bland and uninteresting. If follows, therefore, that many flavourings are highly concentrated and their application dose rate must be optimised with great care.

1. Legislation

The use of flavourings is controlled in most countries by the Food Regulations, which should be checked very carefully. Flavourings are normally classified into three categories:

• Natural flavourings, in which the components are obtained by an appropriate physical process (including distillation and solvent extraction) or an enzymatic or microbiological process from material of vegetable or animal origin, either in the raw state or after processing for human consumption by traditional processes of food preparation (including drying, torrefaction and fermentation).

• Nature identical flavourings, which are produced by chemical synthesis or isolated by a chemical process, and are chemically identical to a substance naturally present in material of vegetable or animal origin.

• Artificial flavourings, which are produced by chemical synthesis but are not chemically identical to a substance naturally present in material of vegetable or animal origin.

To illustrate this, consider bitter almond oil or, as it is commonly known, benzaldehyde. When it is extracted totally from almonds, it is natural. When it is produced by either the oxidation of benzene carbinol or by chlorinating toluene to produce dichlorotoluene and then saponifying with lime water, it is nature identical.

In some instances, the use of an artificial ingredient may be preferable, because it contains no impurities. Analysis can be undertaken with such accuracy that traces

of undesirable components can easily be detected. Some of these impurities may be harmful and too costly to remove. However if the trace components are not harmful, the material may be used.

Although many flavourings will contain ingredients from two or even all three of these categories, it is normal for the status of a flavour to be given as that of the lowest percentage component. This can often mean that a flavouring that contains 99.5% of natural components and only 0.5% artificial ones will be given the status artificial.

2.Creation

The creation of new flavourings is a skilled job and can only be undertaken by someone with several years’ experience. A flavourist will have a wide range of raw materials available, arranged on an ‘organ’ from which the appropriate ingredients will be selected. A flavouring will often consist of over 25 individual ingredients. For example, raspberry can be broken down to several basic types - top notes, fruity, green, berry, background, woody, pippy, and sweet - the whole of which will combine to give a full round flavouring.

3. Production

The production of flavourings can be as simple as mixing two or three ingredients together. In most cases, however, the use of sophisticated and specialised equipment is necessary. Below is a brief description of some of the various techniques used by the flavour industry.

Distillation. A typical example of this method uses soft fruit. The fruit is crushed and at the point of fermentation pure alcohol is added. The flavour and aroma pass into the solvent. The alcoholic solution is then filtered and by fractionated distillation the alcohol is recovered (for further use) leaving the concentrated flavouring behind. This is done under vacuum conditions so as not to harm the delicate flavour which may be damaged by excessive heat.

Extraction. Probably the best-known extraction process is in the manufacture of separation flavourings. In this method, a citrus oil can be washed with-a-mixture of solvent and water to extract the oxygenated (flavour-containing) compounds from the insoluble terpenes. The resulting soluble flavouring can be boosted with other ingredients to give the desired finished flavouring.

Maceration. As the word implies, this method involves soaking the raw material. It is commonly used for citrus peel, herbs, such as basil and mint, or spices such as ginger or chillies. The material is ground and placed in a tank with solvent to extract the flavour. A period of time may be allowed to elapse for full extraction, and this may vary from a few hours to several months. Eventually, the liquid is separated by decantation and is filtered. The use of ultra-waves can speed up this process and is now being used successfully on large-scale production.

Carbon dioxide extraction. Carbon dioxide can exist as a solid, liquid or gas, and is easily isolated in any of these forms. At normal atmospheric temperature and pressure, the solid form becomes gas without passing through the liquid phase. However, when solid carbon dioxide is heated under pressure, the liquid form is produced. The use of liquid carbon dioxide is becoming increasingly important for the extraction of delicate natural products.

Natural products usually contain a large number of different chemical compounds, which, with different solvents, can be extracted to a greater or lesser extent depending on their solubility in that solvent. The use of carbon dioxide can be very important with delicate compounds as extractions are normally carried out at low temperatures (- 20 °C to + 20 °C) thus ensuring that the material is not damaged by excessive heat.

The use of materials produced by carbon dioxide extraction is growing, enabling the flavour industry to develop flavourings more true to nature than previously.

Emulsions

An emulsion can be described as a dispersion of one liquid in another in which it would not normally be miscible. Most emulsions used in carbonated soft drinks consist of two phases, which are homogenised under positive pressure. The following indicates some of the ingredients used in beverage emulsions.

Although a wide range of materials is used to produce these emulsions, the ingredients are normally controlled by the Food Regulations which specify not only the flavourings but also the emulsifiers and stabilisers that can be used.

The main use of emulsions in carbonated soft drinks is as a clouding agent. When considering the organoleptical features of a soft drink, the visual appearance is extremely important as the ‘eye appeal’ can often be the determining factor in deciding which drink is actually purchased.

Syrup room operation

Introduction

It is possibly true to say that the design of any syrup room depends upon the desired end product. This chapter attempts to detail some of the equipment and materials that are necessary for a modern syrup room operation. In designing a syrup room, there are many considerations to be taken into account. These may be grouped as follows.

Hygiene-related. The design of infrastructure, tanks and pipework must ensure sterility and safeguard the end product from future spoilage. The choice of detergent and type of CIP (Clean-in-Place) system is important.

Product-related. To do with the raw material, its storage, handling and treatment, all of which affect the future quality of the drink.

Process-related. Plant and equipment. From the humble origins of the syrup rooms of the 1930s and 1940s (when syrup batches of 100 and 250 litres were commonplace and 1000-litre batches were unusual), the concept has evolved to the present-day syrup room being considered as a ‘mini-factory’ within the main soft drinks complex - clinically designed, staffed and operated by qualified technicians assisted by modern plant and sophisticated instrumentation.

Present developments include the automated and computeri-sed systems currently available, and the latest advances where a multiple component mixing plant prepares finished product as opposed to the conventional preparation of syrup. These areas, together with the storage and handling of raw materials, are discussed to give an appreciation of the size, complexity and importance of any syrup room operation.

Syrup room design

1. Wall finishes

An elaborate interior is not necessary, but a critical area of any syrup room is the finish on the walls as these are constantly exposed to harsh cleaning compounds as well as the acid components of the product; for wall surfaces to last, they must be impervious to this kind of treatment. With continual use of water and inevitable sugar deposition, these surfaces are extremely prone to mould growth. Ceramic tiling has generally been used but tends to be expensive and spray tile finishes may be used as an alternative; this finish is applied directly to masonry blocks and consists of several layers of epoxy enamel paint covered with a glaze coating.

2. Floors and drainage

A surface coating capable of resisting strong acid and alkaline solutions is necessary; unprotected concrete surfaces offer little resistance to these types of solutions. Quarry tiling is an excellent surface but, again, can be very expensive; several less costly products have now been introduced, based on epoxy finishes that have been developed to resist the corrosive effects of specific compounds. Proper drainage must be installed to allow fast flow of waste to reduce contact time of corrosive products on floor areas, and drains should always be designed to allow adequate cleaning.

3. Ceilings and lighting

A concealed or dropped ceiling system is generally used and is supplied as lightweight panels; the surface should be resistant to the type of products used in a syrup room since vapours are often carried upwards and deposits can occur. Fluorescent lighting systems are most commonly used and should be waterproof to reduce the effects of corrosion and prevent ingress of insects.

4. Heating, ventilating and air conditioning

Environmental conditioning is preferable but is not installed in many factories in the UK. The advantages of these types of systems are:

1. They reduce relative humidity which, in turn, reduces condensation on equipment and piping that could support mould growth.

2. They reduce airborne contamination by filtering out dust, etc.

3. They reduce ambient syrup temperatures which could affect filling performance.

4. They improve equipment performances by permitting them to operate at cooler temperatures.

Syrup room equipment

1. Storage, mixing tanks and systems

Tanks are used for a number of purposes and can vary from a small vessel for dissolving purposes to large storage tanks. Some factories are equipped with syrup tanks of capacities greater than 30000 litres, although many factories still use tank sizes of 5000 to 20000 litres and consider such batches economical. The number and sizes of tanks are determined by many factors:

• Number of hours in a working day

• Line filling speed

• Variety of products and flavour changes

• Filtration requirements of syrup

• Sterilisation requirements between critical flavours

• Ageing or maturation time of syrups

• De-aeration of syrups after mixing

Traditional syrup rooms had tanks with open tops and the only form of agitation was manual, often using a wooden paddle. Modern syrup room tanks are now designed to be fully enclosed and are fitted with manholes, inspection lamps, agitators, high- and low-level probes and full CIP spray-ball assemblies: level indication is often by sight glass or the use of load cells.

Mixing systems. The correct amount of agitation in a tank is very important; the agitation should be smooth since violent agitation leads to aeration which is difficult to remove and causes problems at the filler. A comprehensive range of mixers is now available and can vary from propeller-type mixers to high shear mixers. The positioning and type of mixer to be used should be carefully selected depending upon the size of tank and the nature and viscosity of product to be mixed.

Mixers can be attached to the tops of tanks or by more permanent mountings at the bottom or side entries. Variable-speed motors can be fitted to ensure that excessive aeration does not occur when low levels of syrup are mixed in large tanks. One of the major problems encountered in mixing syrup is the exclusion of air; it is good practice when preparing syrup to first add water to the tank.

The agitators should not be set in motion until they are well covered with liquid. All ingredient pipework should be directed to run additions down the side of the tank instead of allowing them to splash into the bulk of the liquid. Some tanks have inlet points of the bottom feed type and these help in reducing splashing, foaming and aeration. Syrup batches should generally be allowed to stand to de-aerate before filling to allow any entrapped air to escape; it is usual to allow at least one hour minimum or two hours ideally for sugar-based syrups.

High-shear mixers. High-shear mixers are often employed in the soft drinks industry to disperse stabilisers, e.g. xantham gum and sodium carboxymethyl-cellulose; these can be very difficult to dissolve unless the correct technique is employed. The high-shear mixer should be started in water and the powder added as quickly as possible; the use of a venturi to pre-wet the particles is particularly useful. The powder is sucked down into the disintegrating head and dispersed before the viscosity has developed. It is important that the powder should never be added slowly since it will mean that the last of the powder is added to a mix that is already of high viscosity and will inevitably form lumps that will be difficult to disperse.

Liquid jet mixers. These offer an alternative to conventional agitators and have been used successfully for the production of finished syrup. The system provides a homogeneous mixture with very little entrained air; this is due to the short mixing time as the mixing process starts while the vessel is being filled. The application for liquid jet mixers is determined by the viscosity of the liquid to be mixed; generally these mixers can be used where centrifugal pumps are capable of transferring the liquids to be circulated.

Jet mixers are normally installed at the lowest point possible in a tank to ensure adequate and efficient blending in the event of a low liquid level; the installation of a jet mixing nozzle in the base of a mixing tank and the circulation of liquid is illustrated in Figure 1.

The jet of liquid flowing out of the diffusion nozzle at high speed generates a reduced pressure in the inlet cone of the diffuser which causes a liquid stream to be sucked out of the vessel and carried along; the diffusion jet mingles with the drawn-off liquid, increasing its velocity. The turbulence in the diffuser produces a homogeneous liquid mixture and the entire contents of the vessel are blended in a short time without creating circular movement.

2. Pipework, fittings and connections         

The majority of pipework is stainless steel and if suspended ceilings are used the pipework can be run above the ceiling. All pipework to the syrup-manufacturing area should be marked or colour coded; this helps to eliminate mistakes and promotes safety.

Various fittings and valves are used to connect pipes; e.g. bends, tees and reducers; sight-glasses and instrument ports; and valves for directing and regulating the flow and the pressure.

Permanent joints are sometimes used by welding or expansion. Where disconnection of pipework is required the pipe coupling is in the form of a threaded union which has a seal or gasket in between. Swing bends are often used where a piping run needs to be switched from one line to another,  e.g. connecting CIP line to the syrup line. All pipe connections should be tightened firmly to prevent air being sucked into the system and to prevent leakage of syrup. Sight-glasses are often located in the pipeline where a visual check on the ingredient is required. Connections may be provided to allow the mounting of measuring instruments such as thermometers, pressure gauges, conductivity probes (to detect liquid). Sampling ports can be included, but it is essential that the sampling port does not allow contamination to occur to the ingredient.

Valves. Many designs of valves are available for process systems and can, vary from manual operation to air-operated types. The choice of valve is important for a number of reasons:

•Valves should be leaktight against known line pressures.

• Air valves should close on air failure.

• Diaphragms should be of approved food grade material.

• Valves should be resistant to harsh corrosive products, should be reliable and should be designed for minimum maintenance.

Shut-off and changeover valves have distinct positions. A regulating valve allows the passage or flow of liquid to be controlled gradually and is used for the fine control of flow and pressure at various points in the piping system.

Check Valves are fitted where it is necessary to prevent product from flowing in the wrong direction; the valve is normally kept open by the flow of liquid in the right direction. If the pressure on the downstream side of the valve becomes greater than the flow pressure, the valve disc is forced against its seat by the back pressure and the valve is effectively closed against reversal of the flow.

Pressure relief valves are used for regulating the pressure of the product in the piping. If the pressure is too low the spring presses the plug against its seat; when the pressure reaches a certain level, the force of the plug overcomes the spring and the valve opens. Spring tension is adjusted to set the desired opening pressure.

3. Ingredient flow

Pipework should be designed to prevent any pockets occurring along the line where the product or cleaning detergent can collect; this could lead to microbiological spoilage or contami-nation of the syrup by a detergent. It is also desirable to ensure that low points are designed into pipe work so that full drainage may be obtained via a valve at that point.

It is essential to design the pipe sizes to give adequate flow but ensure that mechanical bruising of the product does not occur. Flow resistance will occur in pipework due to friction in straight pipe lengths, changes in direction of flow due to bends, valves and other fittings. The flow resistance is expressed in terms of the column or ‘head’ of water necessary to compensate for loss of pressure due to resistance.

Traditional syrup rooms had tanks on a floor above the filling lines and the pressure arising from the head of syrup was usually sufficient to transport it to the production line at the required flow rate. In modern factories, which are designed on high output, it is more difficult to gravity feed and so pumps are therefore used to generate the pressure required.

The resistance to the flow of a liquid results in a loss of pressure and the component is therefore said to cause a pressure drop in the pipe. The pressure drop is measured in terms of head and is equivalent to the resistance of the ingredient, the size of pressure drop being governed by the velocity of the flow, i.e. flow rate and size of pipe. If the velocity exceeds a certain value (dependent upon the nature of the liquid) then not only does the frictional head increase (requiring a more powerful pump) but the flow in the pipe becomes turbulent and disturbed, producing a possible adverse effect on the syrup.

4. Pumps

Nowadays, with high throughput operations, it is necessary to convey large quantities of liquid through pipelines often with large numbers of bends, valves, etc.. and through pasteurisers, homogenisers and other associated equipment which could all possibly contribute to pressure drop. Pumps need to be fitted at various points in the line to convey the liquid and compensate for the loss of head; however, pumping agitates the product and it is essential that the correct pump is chosen. Many different types are available from the range of centrifugal, diaphragm, peristaltic, gear and positive displacement pumps.

Centrifugal pumps. These are often used since they can be manufactured to a sanitary design, are suitable for CIP and are not capable of producing accidental over-pressure. A centrifugal pump comprises an impeller rotating in a casing, a delivery chamber and an electrical drive. Liquid entering the pump at the centre of the casing is carried round by vanes. If the liquid has to be pumped up to a tank at a higher level, the pump discharge pressure must be sufficient to raise the liquid to that height. This type of head is known as a static delivery head. The pump characteristics supplied by a manufacturer usually relate to water; the viscosity of a product makes a difference. When highly viscous liquids are pumped, the pressure losses in the pump are higher and so the energy of the product leaving the impeller will be lower than for water.

During pumping, liquid is carried from one side of the pump to the other, creating a partial vacuum in the space once occupied by the liquid. This space on the suction side is then refilled with more liquid.

Cavitation on a pump can occur when the pressure at the suction falls below the saturation pressure of the liquid (varies with temperature) and dissolved oxygen comes out of solution; this can be avoided by reducing the pressure drop on the suction line, e.g. large pipe size. fewer valves, raising liquid level above pump inlet, etc.

Flow controllers are often used to maintain a constant flow rate; an effective method of flow control is to vary the speed of the pump, which can be achieved mechanically, hydraulically or electrically. The centrifugal pump can be used to handle a wide range of liquids provided the viscosity is not too high; the pump is not self-priming and the suction line and pump easing should be filled with liquid before switching on.

Positive displacement pumps (rotary). There are many types of self-priming positive-displacement pumps. The rotary pumps work on the principle of two synchronised driven lobed rotors, which have a very close clearance but do not actually touch each other. As the rotors turn, the volume between the lobes at the suction port increases and the partial vacuum created causes liquid to enter the pump. The liquid is carried in the space between the lobes and the pump casing to the outlet; as the volume between the lobes is reduced, the pressure increases and the product is discharged.

In order to prevent excessively high pressures, positive-displacement pumps usually have some form of relief valve, which automatically returns some of the liquid to the inlet if the pressure becomes too great. Flow is normally regulated by varying the speed of the pump. Positive-displacement pumps are generally used for handling high-viscosity liquids.

5. Measurement of liquid

The contents of tanks may be measured using meters, dipsticks, sight-glasses or load cells. The use of load cells is a common method for monitoring ingredients; these, however, have some disadvantages in that all additions need to be converted to weight.

Reliable sanitary meters have been developed for measuring liquids. Accurate meters are the most practical method of measuring quantities of liquid into a tank.

Registering meters are normally fitted with shut-off valves which automatically close at a predetermined setting, shutting off the flow of liquid. Meters do have an advantage in that multiple additions may be made simultaneously, thus saving time and often aiding mixing. In the absence of meters, the dipstick method of measuring liquid is reliable and has been widely used for many years. These are made from stainless steel and have a hooked end to facilitate hanging the strip from a specially marked spot on the side of the tank. With the use of dipsticks, each tank must be calibrated individually. Using an accurate meter or calibrated measure, water is introduced into the mixing tank: the dipstick is then calibrated to this level and marked. The mark is checked by repeating the process several times, being certain to hang the dipstick from the same point each time. Once the calibration has been accurately esta-blished, the level is scribed permanently into the stainless steel.

A sight-glass, mounted on the side of a syrup tank with sanitary mountings, is another means of measuring contents in a tank. The sight-glass should be accurately calibrated and marked. Unless careful cleaning is employed, sight-glasses can offer hiding places for contamination.    

6. Filtration of ingredients

A number of ingredients in syrup manufacture - and, indeed, in certain instances, the syrup itself - require some form of filtration, which could range from a simple mesh filter to a more sophisticated plate-and-frame or cartridge-type system. Micro-filtration is nowadays a safe and efficient method of removal of unwanted particles and other turbidity components. Where high carbonation mixer drinks are concerned, it is preferable to ensure all active centres are removed to aid good filling: the syrup itself can be filtered typically through a nominal 50mm cartridge for this purpose.

In contrast to the conventional filter plate systems the modern cartridge housing concept has numerous advantages.

• Completely enclosed, sanitary and leak free

• Quick change out of filter media

• Short cleaning and sterilisation times

Some cartridges can be cleaned in forward flow with hot water and significantly reduce costs by prolonging cartridge life. Typical cartridge systems feature a polypropylene centre core, outer cage and end caps and either a cotton wound cartridge or often a charged nylon membrane. The components are thermo-welded to eliminate the use of glue or resins, which may impart unwanted off-flavours.

Acids, colours, preservatives and other additives

Introduction

The commercial success of a soft drink formulation depends upon a number of factors. A strong, well-placed advertising campaign will bring the consumer to purchase the new product but, thereafter, the level of repeat sales will reflect the degree of enthusiasm with which the new drink has been received.

Taste panelling and market trials are also preliminaries to a successful launch, yet continuity of sales will ultimately depend upon the product itself, primarily its appearance and taste, as assessed by the consumer, and then, perhaps, the reproducibility of quality in both manufacture and storage -these latter being the major concerns of the producer and soft drinks retailer, who must maintain a regular turnover to survive.

It is hardly surprising that the development of a new drink product can take many months, while all aspects of its appearance, organoleptic properties and stability are tuned to requirements. In the final analysis, organoleptic properties are paramount, and the aroma, taste and mouth-feel must be complementary in their contribution to the resulting drink. However, the immediacy of colour and its importance to the success of the product cannot be underestimated.

In recent years, the use of synthesised ingredients has frequently been under attack by the media and, as a result, market forces in many countries have initiated a rapid move in the direction of natural ingredients.

We have seen an influx of various natural colour extracts to the food industry which, being largely pH dependent and light sensitive, have found limited use in soft drinks. A few have found acceptance, but even so are still open to scrutiny in terms of adverse metabolic effects. Many have no reco-mmended ADI (Acceptable Daily Intake in mg/kg body weight) values, while others have values allocated which are not far removed from those of the synthetic colours they have replaced.

Preservatives also show signs of being phased out, as improved methods of pasteurisation and aseptic filling are

devised. The ability of carbon dioxide to act as a preservative places carbonated drinks in a strong position for future develop-ment.

A typical carbonated soft drink comprises carbonated water, sugar, citric acid, flavouring, acidity regulators (e.g. sodium citrate), colouring, preservative and artificial sweeteners, if used. The flavour component is presented against a finely tuned backcloth of the other ingredients, providing the right degree of sweetness, bitterness, sourness, and acidity (pH) to enhance drink palatability.

Acids

Following water and sugar, the acid component is third in terms of concentration. Its presence tends to be taken for granted, yet, without its contribution, the other formula components are left lacking in character. Because of the general tartness or sourness in taste, acidity is useful in modifying the sweetness of sugar. It will increase the thirst-quenching effect of the drink by stimulating the flow of saliva in the mouth and also, because of a reduction in pH level, tends to act as a mild preservative. While the majority of soft drinks contain acids, it is the carbonated drinks that have the additional effect of dissolved carbon dioxide. Not officially recognised as an acid addition, the presence of carbon dioxide under pressure certainly provide that extra sparkle to mouth-feel, flavour and sharpness (or bite) to the drink, so it has been included here under the identity given to its soluble form.

1. Carbonic Acid

The solution of carbon dioxide in water exploits weakly acidic properties. Neither liquefied nor dry gaseous carbon dioxide affects dry blue litmus indicator paper, but if the paper is moistened it will provide an acid reaction in contact with the gas. There is little doubt that in solution some of the gas forms carbonic acid by combination with water.

Potassium and sodium carbonates can be used in the production of ‘dry’ carbonated drink mixes, where a blend of sugars, fruit acid crystals, spray-dried flavourings and other additives such as stabilisers is formulated to produce a drink which, when dissolved in water, has a carbonation level of about 1-1½ volumes carbon dioxide. In its more regular role, during the production of carbonated drinks, carbon dioxide is introduced as part of the bottling sequence, being dissolved under pressure before or after dilution of the bottling syrup with water. Measured in volumes of dissolved gas per unit volume of water at a specified temperature and pressure (usually ‘Volumes Bunsen’ at 0°C and 1 atm), the average level employed is in the region of three volumes although extremes of perhaps one volume and six volumes are sometimes encountered where highly specialised flavoured products are required.

2. Citric acid

This is by far the most widely used acid in fruit-flavoured beverages. It has a light fruity character that blends well with most fruits and, in fact, is found as a major constituent in many of them, e.g. unripe lemons contain 5-8% of the acid. It is also the chief acid constituent of currants, cranberries, etc., and is associated with malic acid in apples, apricots, blueberries, cherries, goose­berries, loganberries, peaches, plums, pears, strawberries and raspberries, with isocitric acid in blackberries and with tartaric acid in grapes.

It was originally obtained commercially from lemons, limes or bergamots by pressing the fruit, concentrating the expressed juice and precipitating citric acid as its calcium salt by running in, with constant stirring, a slurry of chalk and water. The crude calcium citrate was then filtered off, filter pressed and washed prior to treatment with sulphuric acid to yield the free citric acid, which was then filtered from the precipitated calcium sulphate, and finally isolated by concentration of its solution by boiling, from which crystals of the monohydrate formed.

It was noted at the time of Dr Martin’s Treatise on Industrial and Manufacturing Chemistry that a known organism existed Mucor Piriformis (C. Wehmer, German Patent 72,957) - that could ferment sugar directly into citric acid. Owing to the low market prices of Sicilian lemon juice, no wide technical application of this early enzyme process had been made. However, citric acid is now produced by the action of specific enzymes upon glucose and other sugars.

Citric acid is a white crystalline solid and can be purchased in its powdered form or as the monohydrate. This latter state is more convenient in terms of storage, as it does not have a tendency to absorb moisture, as does the anhydrous form.

3. Tartaric acid

This acid occurs naturally in grapes as the acid potassium salt and, during fermentation of grape juice, will be seen to deposit from solution as its solubility decreases with increasing alcoholic content of the wine. The acid can be obtained in four forms: dextro, laevo, meso-tartaric and the mixed isomer-equilibrium, or racemic acid. Commercially it is usually available as the dextro-tartaric acid. The acid possesses a sharper flavour than citric and, as such, may be used at a slightly lower rate to give an equivalent palate acidity. (Note that palate acidity is a purely subjective measurement and it is generally agreed that a number of acids may be used at a concen-tration different to that indicated by their chemical acid equivalent).

Tartaric acid may be isolated from the crude deposit of tartrates obtained from the wine fermentation process in a similar manner to that originally used for citric acid - by leaching the deposit with boiling HCl solution, filtering clear and re-precipita-tion of the tartrates as the calcium salt. Further treatment with sulphuric acid is used to liberate the acid, which can then be purified by crystallisation.

Tartaric acid (dextro form) exists as a white crystalline solid mp 171-174°C. If used in beverage production, the acid must be perfectly pure and guaranteed for ‘food’ use. It has disadvantages in that its salts are of a lower solubility than those of citric, particularly the salts of calcium and magnesium. When using hard water, it is therefore advisable to use citric acid to avoid unsightly deposition of insoluble tartrates.

4. Phosphoric acid

The acid is derived from mineral and not vegetable sources although occurring naturally in some fruits, e.g. limes, grapes, in the form of phosphates. It is used in some beverages as a substitute for, or in addition to, citric and tartaric acids, having a sharper and drier flavour than either of the above acids. Its taste is of flat ‘sourness’, in contrast with the sharp fruitiness of citric acid, and it seems to blend better with most non-fruit drinks. In the UK, it is not allowed in drinks claiming the presence of fruit juices and comminuted fruits. Its main use is in cola-flavoured beverages, where its special type of acidity complements the dry, sometimes balsamic, character of the cola drinks.

Pure phosphoric acid is a colourless crystalline solid (mp 42.35 °C) but is usually used in solution as a strong, syrupy liquid, miscible in water in all proportions. It is commercially available in concentrations of 75,80 and 90%. The syrupy character is the result of hydrogen bonding, which occurs at concentrations greater than 50%, between the phosphate molecules. It is corrosive to most construction materials and rubber-lined steel or food-grade stainless steel are recommended for holding vessels.

5. Lactic acid

Sometimes used for the acidification of beverages, lactic acid possesses a smoother flavour than any of the foregoing acids. It is supplied commercially as an odourless and colourless viscous liquid and is obtained from the fermentation of sugars by lactic acid bacillus.

6. Acetic acid

As in the case with phosphoric acid, under UK legislation this acid is limited to use in non-fruit juice drinks and really only qualifies where its vinegary character can contribute to a suitable flavour balance. Pure glacial acetic acid is a colourless, crystalline solid of mp 16 °C and is one of the strongest of the organic acids in terms of its dissociation constant and displacing carbonic acid from its carbonates.

7. Malic acid

This is the natural acid found in apples and other fruits. A crystalline white solid (mp 100°C), it is highly soluble in water. Being less hygroscopic than citric acid it possesses improved storage and shelf-life properties.

Malic acid is slightly stronger than citric in terms of perceived palate acidity and imparts a fuller, smoother, fruity flavour. It is of course, first choice for apple-flavoured drinks.

Unlike tartaric, its calcium and magnesium salts are highly soluble and the acid presents no problems in hard-water areas.

8. Fumaric acid

Not permitted under UK soft drinks legislation, fumaric acid is widely used in other countries as an acidulant, notably in the US market.

In terms of equivalent palate acidity it can be used at a lower rate than citric acid and typical replacement can be employed at two parts fumaric per three parts citric in water, sugar water and carbonated sugar water. Its main drawback is a reduced solubility compared with the citric acid and special methods need to be employed in getting it into solution.

9. Ascorbic acid

This acid (known as Vitamin C) is not only used as a contributory acidulant but rather as a stabiliser within the soft drinks system and its anti-oxidant properties improve the shelf-life stability of the fl