2.2.1. Fried products
2.2.2. Bottled and canned products
2.2.3. Dried fruits and vegetables
2.2.4. Chutneys, pickles and salted vegetables
2.2.5. Pectin and papain
2.2.6. Sauces
2.2.7. Juices
2.2.8. Squashes, cordials and syrups
2.2.9. Preserves (jams, jellies, marmalades, pastes, purees and fruit cheeses)
2.2.10. Wines, vinegars and spirits
A small number of starchy fruits, including jakfruit, breadfruit and banana are fried and eaten as snackfoods. Heat during frying destroys enzymes and micro-organisms and if sufficient moisture is removed and the product is packaged, it can have a shelf life of several weeks. The most common example of this type of snack-food is banana chips and the process chart (Figure 6) shows their production.
The stages in processing are described in the left-hand column and are split into those steps that are essential for all products (on the right) and those that are only needed for some products (on the left).
Care is needed to control the temperature of the oil used for frying, not only for safety reasons, as very hot oil can splash onto operators when wet fruit is immersed, but also because of financial and quality considerations. When oil is heated too much, it exceeds its smoke point and a blue haze appears above the oil. This is a sign that the oil is breaking down chemically and it will then begin to get more viscous and develop an unpleasant flavour. The flavour is transferred to the product, making it unacceptable. When the oil thickens, more is retained on the product and there is a higher cost in buying more oil than is needed. Too much oil on the product also reduces its shelf life.
Bottling and canning are essentially similar processes in that food is filled into a container and heated to destroy enzymes and micro-organisms. Fruits can be packed into jars with a hot, sugar syrup and vegetables can be packed into a hot brine. The filled jars are sealed and pasteurized so that an internal vacuum forms when they are cool. The sealed container then preserves the food by preventing re-contamination and excluding air and sometimes light. Preservation depends on an adequate heat treatment and an air-tight (or 'hermetic') seal. The process for bottled fruit is shown in Figure 8.
There are three grades of syrup: a light syrup contains 200g sugar per litre, a medium syrup 400-600 g/l and a heavy syrup 800g/l. The concentration of salt in brine is usually 15 g/l. Acidic fruits require relatively mild heating conditions for pasteurization (e.g. 90-100°C for 10-20 minutes) to destroy yeasts and moulds, whereas less acidic vegetables require more severe heat sterilization to destroy food poisoning bacteria (e.g. 121°C for 15-40 minutes, depending on the size of the container). Fruits can also be part-processed and stored until required in sugar syrup or sodium metabisulphite solution (equivalent to 1000 ppm.) to allow production to take place for a larger part of the year.
It is not advisable for inexperienced small scale processors to bottle vegetables unless they are acidified, because of the risk of poisoning from inadequately processed foods. Vegetables can however be processed by pasteurization if the acidity is first adjusted using citric acid or vinegar.
Figure 6. - Process chart for production of fried fruits
Figure 7. - Small scale peeler for fruits
Canning is not suitable for small scale processing for the following reasons: the time and temperature of canning are critically important and must be carefully controlled. If the cans are under-processed, there is a risk of serious food poisoning and even death from a type of micro-organism named Clostridium botulinum. If cans are over-processed, the vegetables lose much of their texture, colour, vitamins and flavour and are not saleable. The establishment of correct heating conditions depends on the type of food, the size and shape of the can and the initial level of contamination of the vegetables. This requires the skills of a qualified food technologist or microbiologist.
When foods are heated in sealed cans during the canning process, the temperature of sterilization is above 100°C and the pressure outside the can must equal that inside, to prevent the cans from exploding. This is achieved using high pressure steam and a strong vessel named a 'retort'. Both steam boiler and retort are expensive and likely to be beyond the means of a small scale processor. Additionally, compressed air is needed to maintain the pressure while cans are being cooled, which together with the necessary controllers, adds to the capital cost of equipment.
Even if cans are available in a particular country, they are usually more expensive than other forms of packaging. Different types of product also require a particular internal lacquer to prevent the metal from corroding when it is in contact with the fruits or vegetables and such lacquers may not always be available. In addition a 'seamer' is needed to seal the lid onto the can and regular checks and maintenance are necessary to ensure that the seam is properly formed. Failures in seams are one of the main causes of spoiled or dangerous canned foods.
It is therefore necessary to ensure that seamer operators are fully trained and experienced in adjusting the machines and a 'seam micrometer' is another necessary capital expense to be able to do this. In summary therefore, canning requires a considerable capital investment, trained and experienced staff, regular maintenance of relatively sophisticated equipment, a regular supply of the correct types of cans and a comparatively high operating expenditure.
Because of the more acidic nature of fruits, a lower processing temperature is adequate and this process is suitable for small scale operations. In all cases, a food technologist should be consulted to advise on process times and conditions for bottled products.
Additional processing notes
Syrup pre-treatment
Types of dryers
Packaging
Drying removes most of the water from fruits and vegetables to extend their shelf life and to increase their convenience and value. The reduction in weight and bulk also makes transport cheaper and easier although many dried foods are fragile and require packing in boxes to prevent them from being crushed. Different categories of dried foods can be described as high-volume, lower-value crops such as staple cereals and low-volume, higher-value foods such as dried fruits, vegetables herbs and spices. This second category offers better opportunities for profitable production by small scale processors.
Air dried products are the most common type of dried fruit and vegetables and other more expensive methods, such as freeze drying, are not considered in this book. Some products may be blanched or sulphured/sulphited to protect their natural colour and help preserve them. Crystallized fruits, peels for marmalade and cake production and osmotically dried fruits (known as 'osmasol' products when dried in a solar dryer) are fruit pieces that are soaked in hot concentrated sugar syrups to extract some of the water before air drying.
Figure 8. - Process chart for bottled fruits
Figure 9. - Examples of fruit cutters suitable for small scale production
The preparation procedures needed for dried fruits and vegetables are summarized in Table 6 and production methods are shown in the Process Chart (Figure 10).
Some vegetables and a few fruits such as limes may also be salted before drying. In this case the high salt concentration preserves the food by both drawing out water by osmosis and by the anti-microbial properties of the salt. Salt tolerant micro-organisms begin to grow while the product is sun dried and these produce acids and characteristic flavours, High salt concentrations also prevent the action of some enzymes, which would cause a loss in quality of the dried food during storage. Vegetables must be washed to lower the salt concentration before they are eaten (vegetables that are salted but not dried are described in Section 2.2.4).
Fruits and vegetables must be carefully selected before drying. If fruits in particular are over-ripe they are easily damaged and may be difficult to dry. If they are under-ripe, they have a poorer flavour, colour and appearance. Care and attention to hygiene are essential because any bacteria or moulds that contaminate vegetables before drying are likely to survive on the dried food. The temperature of drying is not high enough to kill them and when the food is re-hydrated, they can grow again and cause food poisoning.
Figure 10. - Process chart for dried fruits and vegetables
Blanching
Blanching destroys enzymes and prevents changes in colour, flavour and texture during storage. However, by itself, it does not preserve the food and vegetables must therefore be further processed by drying to achieve a long shelf life. Vegetables are blanched by heating in hot water or steam for a short time (Table 7) and then cooled on trays. For production at a small scale, vegetables can be placed in a wire basket and immersed in boiling water (Figure 42).
In steam blanching, vegetables are placed in a strainer and this is then fitted over a pan of boiling water and covered with a lid to prevent the steam escaping. Steaming takes a few minutes longer than water blanching, but has the advantage of retaining more nutrients as they are not lost into the water.
There are optional chemical treatments that help to retain the colour and texture of some dried fruits and vegetables. For example, the bright green colour of leafy vegetables, peas etc. can be retained by adding sodium bicarbonate to blancher water and the texture of some vegetables, such as okra and green beans, can be maintained by blanching in a calcium chloride solution. Both chemicals are usually available from pharmacies in major towns.
Sulphuring and sulphiting
For most fruits, 350-400g sulphur are used per 100 kg fruit, burning for 1-3 hours. Sulphur dioxide prevents browning in foods such as apple, apricot and coconut, although it should not be used with red fruits as it bleaches the colour. Sulphuring (using sulphur dioxide gas) is achieved by exposing pieces of cut or shredded fruits to burning sulphur in a sulphuring cabinet. The amount of sulphur used and the time of exposure depend on the type of fruit, its moisture content and limits placed by law in some countries on the residual amounts of sulphur dioxide in the final product (Section 2.4.2) or by commercial limits set by importers. This should be checked with a local Bureau of Standards. There is an increasing consumer resistance to sulphited fruits in some industrialised countries and if the product is considered for export the local Export Development Board or import agents should be consulted.
In sulphiting, the sulphur dioxide is dissolved in water, rather than as the gas used in the sulphuring process. Sodium sulphite, sodium metabisulphite or potassium metabisulphite are made into solutions, either by adding one of them to the blanching water or more often, by soaking the food for 5-10 minutes in a sulphite dip. About two thirds of the weight of sodium metabisulphite is formed as sulphur dioxide when it is dissolved in water. For example, to form a 0.001% solution which is equivalent to 1000 ppm, 1.5g is dissolved in a litre of water to form 1g of sulphur dioxide per litre. At this concentration, sulphiting can also be used as a method of intermediate storage of fruits to spread production over several months throughout the year.
Table 6. - Preparation procedures for fruits and vegetables before drying
|
|
Cleaning |
Sorting/Grading |
Peeling |
Size reduction |
Blanching |
Salting |
Sulphur dioxide treatment |
|
Fruits |
Needed for all fruits |
Important for all fruits |
Required for most products |
Cutting larger fruits for faster drying |
Not usually done for fruits |
Very few |
For some fruits to prevent browning |
|
Vegetables |
Needed for all vegetables |
Important for all vegetables |
Used for some vegetables |
Slicing for larger vegetables or shredding cabbage |
Commonly used for softening and preventing browning |
For some salted vegetable products (e.g. cabbage) |
Used with a few light coloured vegetables to prevent browning |
This method can be used to remove up to half of the water in fruit and is therefore a cheap way of increasing the production rate of a dryer or for part-processing fruits for intermediate storage so that production can be extended throughout the year. In general the method gives good retention of colour in the dried food and produces a sweeter, blander tasting product. However, acids are also removed from fruits during the process and the lower acidity of the product may allow mould growth if the food is not properly dried and packaged.
Table 7. - Blanching times for different vegetables
|
Food |
Blanching time (minutes) using: |
|
|
Steam |
Water |
|
|
Leafy vegetables, |
2 - 2.5 |
1.5 |
|
Sliced beans |
2 - 2.5 |
1.5 - 2 |
|
Squashes |
2.5 |
1.5 - 2 |
|
Cabbage |
2.5 |
5-2 |
|
Peas |
3 |
2 |
|
Carrots |
3 - 3.5 |
3.5 |
|
Cauliflower |
4 - 5 |
3 - 4 |
|
Potatoes |
6 - 8 |
5 - 6 |
In a more complex method to that described in Figure 10, fruit is first boiled in 20% syrup and then soaked overnight. The fruit is then strained from the syrup and transferred each day to 40% and 60% syrups in turn (Figure 11), with optional boiling for 10 minutes at each transfer. After soaking, the syrup is diluted to approximately half of the original concentration. Each day the most dilute syrup (10%) is used for other products and a new 60% syrup is made up. The advantages of this method include reuse of sugar syrups and a softer texture in the final product. In Figure 11, the containers therefore circulate 'backwards' as they contain more dilute syrup. Some producers have even more stages in the process and may transfer fruit into increasing sugar concentrations each day for up to fourteen days. This results in a succulent, soft texture in the final product.
The higher value of dried fruit and vegetable products, compared for example to cereals crops, may justify the higher capital investment in a fuel-fired dryer or electric dryer and the extra operating costs for the fuel or electricity. These types of dryer allow higher drying rates and greater control over drying conditions than do solar or sun drying and they can therefore result in a higher product quality. However it is necessary to make a careful assessment of the expected increase in income from better quality products compared to the additional expense, to make sure that this type of dryer is cost-effective (see also Section 2.3).
Sun drying is only possible in areas where, in an average year, the weather allows foods to be fully dried immediately after harvest (see Figure 3, seasonality chart). The main advantages of sun drying are the low capital and operating costs and the fact that little expertise is required.
Figure 11. - Process for making crystallised (or candied) fruits
The main problems with this method are as follows:
· contamination, theft or damage by birds, rats or insects· slow or intermittent drying and no protection from rain or dew that wets the product, encourages mould growth and may result in a relatively high final moisture content
· low and variable quality of products due to over- or under-drying
· large areas of land needed for the shallow layers of food
· laborious because the crop must be turned, moved if it rains and animals must be kept away
· direct exposure to sunlight reduces the quality (colour and vitamin content) of some fruits and green vegetables.
The quality of sun dried foods can be improved by reducing the size of pieces to get faster drying and by drying on raised platforms, covered with cloth or netting to protect against animals and insects (also Section 1.2.1).
Solar drying has been studied in detail by scientists in many countries for many years (see Bibliography), but it is not yet widely used commercially. The main applications to date are in Bangladesh for desiccated coconut, in Guatemala for herbal teas and in Uganda for dried fruits for export. Details of equipment for solar drying and fuel-fired drying are given in Section 2.5.4.
If the climate is dry, it may not be necessary to package dried foods as they will not pick up moisture from the air. However a humid climate is likely to result in dried foods gaining moisture and going mouldy. The stability of dried foods depends not only on the humidity of the air at which a food neither gains nor loses weight (the 'Equilibrium Relative Humidity'), but also on the type of food. Different foods can be grouped according to their ability to absorb moisture from the air. The two groups are hygroscopic, which absorb moisture easily and non-hygroscopic, which do not absorb moisture. The classic example is salt and pepper, where salt is very hygroscopic and pepper is non-hygroscopic, but similar examples exist for fruit and vegetable products. This difference determines the packaging requirement for different fruit and vegetable products. The moisture content at which a food is stable is known as the Equilibrium Moisture Content and examples of this for different fruits and vegetables are shown in Table 8, together with the packaging requirement for different groups of foods.
Dried fruits and vegetables are usually packaged in one of the many different types of plastic film. The selection of the correct type of packaging material depends on a complex mix of considerations which include:
· the temperature and humidity of the air in which the product is stored
· the capacity of the product to pick up moisture from the air
· reactions within the product caused by air or sunlight during storage
· the expected shelf life
· marketing considerations (Section 2.8.3)
· cost and availability of different packaging materials.
In general, although thin polythene film is usually the cheapest and most widely available material, it is only suitable for storing dried fruits and vegetables for a short time before they pick up moisture, soften and go mouldy. Polypropylene has better barrier properties and therefore gives a longer shelf life, but it is usually more expensive and it may not be available in many countries. Other more complex films, such as laminated films made from polythene and aluminium foil, offer much better protection to dried foods, but are considerably more expensive and more difficult to find in developing countries. Details of this complex area are given in publications in the bibliography and discussed further in Section 2.5.5.
Table 8. - Moisture contents at which selected foods are stable and packaging requirements for each group
|
Food |
Moisture content (%) |
Degree of protection required |
|
Fresh fruit and vegetables |
75-85 |
Package to prevent moisture loss |
|
Marmalade |
35 |
Non-hygroscopic: - Minimum protection or no packaging required |
|
Raisins |
7 |
|
|
Fruit sweets |
3 |
Hygroscopic: - Package to prevent moisture uptake |
|
Potato crisps |
1.5 |
|
(Adapted from Food Processing Technology by Fellows)
Most dried foods also need a sturdy box or carton to both prevent crushing and to exclude light which causes loss of colour and development of off-flavours during storage. The properties of different packaging materials for dried foods are shown in Table 9.
From the table, it can be seen that some types of packages provide good protection against air and moisture pickup for example, whereas other protect against light, crushing, etc. It is therefore common for dried foods to be packed in airtight and moisture-proof bags, which are then placed in an outer container to protect against light, crushing, etc.
Table 9 - Properties of packaging materials for dried fruits and vegetables
|
Type of Packaging |
Protection provided against: |
|||||||
|
Moisture |
Light |
Air & odours |
Heat |
Micro-organisms |
Dust |
Crushing |
Animals & insects |
|
|
Clear glass |
3 |
1 |
3 |
2 |
3 |
3 |
3 |
3 |
|
Coloured glass |
3 |
2 |
3 |
2 |
3 |
3 |
3 |
3 |
|
Ceramic pot |
1 |
3 |
3 |
3 |
3 |
3 |
3 |
3 |
|
Metal tin |
3 |
3 |
3 |
1 |
3 |
3 |
3 |
3 |
|
Metal foil |
2 |
3 |
2 |
1 |
2 |
3 |
1 |
1 |
|
Plastic pot |
3 |
3 |
3 |
2 |
3 |
3 |
2 |
2 |
|
Wooden chest |
2 |
3 |
1 |
3 |
1 |
3 |
3 |
2 |
|
Paper board (cardboard) box |
1 |
3 |
1 |
3 |
1 |
3 |
2 |
1 |
|
Fibreboard drum |
1 |
3 |
1 |
3 |
2 |
3 |
3 |
2 |
|
Paper bag |
1 |
2 |
1 |
1 |
1 |
2 |
1 |
1 |
|
Polythene film |
2 |
1 |
1 |
1 |
2 |
3 |
1 |
1 |
|
Cellulose film |
3 |
1 |
3 |
1 |
2 |
3 |
1 |
1 |
|
Polypropylene film |
3 |
1 |
3 |
1 |
2 |
3 |
1 |
1 |
|
Cotton or Jute sack |
1 |
2 |
1 |
1 |
1 |
2 |
1 |
1 |
Notes: It is assumed that all packs are properly sealed. 1 = poor protection, 2 = fair protection, 3 = good production.(Adapted from Food Processing Technology, by Fellows and Appropriate Food Packaging, by Fellows and Axtell)
Chutneys
Additional processing notes
Pickles
Salted vegetables
Additional processing notes
Chutneys are thick, jam-like mixtures made from a variety of fruits and vegetables, sugar, spices and sometimes vinegar. Any edible sour fruit can be used as a base for a chutney, to complement the sweet taste from the sugar. The high sugar content has a preservative effect and vinegar addition is not always necessary, depending on the natural acidity and maturity of the fruits that are used. Most products are boiled, which not only produces a caramelised syrup and alters the taste, colour and thickness, but also pasteurises the product and thus adds to the preservative action of the sugar and acids. Other products are allowed to ferment naturally and the acids produced by a mixture of bacteria preserve the product. Depending on the types of spices that are added, these may also have a preservative effect, in addition to their contribution to flavour. Fruits can also be sulphited as a method of intermediate storage to spread production over several months throughout the year. The process chart (Figure 13) uses a formulation for mango chutney as a typical product of this type.
Figure 12. - Using a hand-held refractometer to check sugar content
(Courtesy of Midway Technology Ltd.)
Natural acids from the fruit, from vinegar or those produced by fermentation, together with the high sugar content, are used to preserve the chutney after a jar has been opened. A correct balance between the levels of sugar and acid is required to prevent mould growth and a Preservation Index can be used to calculate the amounts of ingredients to be added. Alternatively, when sugar is the main ingredient or the product is boiled, a refractometer (Figure 12) can be used to check that the final sugar content of the syrup is 68-70%. Sugar is added before heating if a dark product is required or towards the end of boiling to produce a light coloured product.
The Preservation Index is a measure of the preserving power of combinations of acid and sugar (sugar is measured as 'total solids'). This is used to assess whether a chutney or pickle is safe from food spoilage and food poisoning micro-organisms. The value can be calculated as follows:
Details of how to measure acidity and total solids are given in Section 2.7.2. However, if a manufacturer has no access to basic laboratory equipment or is not sure how to carry out the calculation, it is best to take a sample of product to a Bureau of Standards, University Food Science Department or food testing laboratory which can analyse it and recommend adjustments to the recipe if necessary.
Vegetables such as cucumber, cabbage, olive and onion are fermented by lactic acid bacteria which can grow in low concentrations of salt. The bacteria ferment sugars in the food to form lactic acid, which then prevents the growth of food poisoning bacteria and moulds or other spoilage micro-organisms. The amount of added salt controls the type and rate of the fermentation. If for example 2-5% salt is used, a natural sequence of different types of bacteria produce the lactic acid. If higher concentrations of salt (up to 16%) are used, a different product called 'salt stock' pickle is produced, which is preserved by the salt and not by fermentation. Fruits and vegetables can be preserved in this way as a method of intermediate storage to spread production over several months throughout the year.
Sometimes, sugar is added to increase the rate of fermentation or to make the product sweeter. Alternatively, vegetables may be packed in vinegar (acetic acid), salt and sometimes sugar to produce a variety of pickled products. Because these vegetables are not fermented they have a different flavour and texture. They are usually pasteurised. Sweet pickles are made from single fruits or mixtures of fruits and vegetables. They are preserved by the combined action of lactic or acetic acid, sugar and in some cases added spices. A summary of the different types is shown in Table 10 and a process chart (Figure 14) describes their production.
Figure 13. - Process chart for chutney (e.g. mango chutney)
Salted vegetables are made by building up alternate layers of chopped or shredded vegetable such as cabbage, with layers of salt in a sealed drum (see also Section 1.2.1). The salt has two preservative actions: it draws out water from the vegetables by osmosis to form a concentrated brine in the base of the drum; and salt also has a direct anti-microbial action. The high levels of salt are reduced by washing the products before they are eaten.
Table 10. - Examples of different types of fruit or vegetable pickles
|
Product |
Salt |
Sugar |
Vinegar |
Process |
|
Fermented sweet pickle |
5% then 3% |
1-2% then 3% |
0 then 5% |
Fermented for 1-2 weeks then repack in vinegar + salt + sugar (optional pasteurization) |
|
Fermented sour pickle |
5% then 3% |
0 then 0 |
0 then 5% |
Ferment for 1-2 weeks then repack in vinegar + salt (optional pasteurization) |
|
Unfermented pickle |
3% |
1% |
5% |
Pack straight away and pasteurize |
|
Salt-stock pickle |
15% |
0 |
0 |
Store until required. Then wash out salt and repack as unfermented pickle |
Pickles which have an adequate Preservation Index do not need to be pasteurised. However as an additional measure to prevent spoilage, they can be pasteurised or the sugar/salt/vinegar mixture can be heated, added to the vegetables and the jars filled while product is still hot. In this way the hot product forms a partial vacuum in the jar when it cools and further aids preservation.
Glass jars are the most commonly used packaging material, but if a shorter shelf life is expected, pickles may also be packed in small quantities in polythene pouches and sealed with an electric heat sealer. To avoid seepage of product, which can damage paper labels and make the package unattractive, a double pouch can be used comprising an inner pack that contains the product and an outer pouch with a label between the two.
Figure 14. - Process chart for pickled vegetables
Pectin is a component of nearly all fruits and vegetables and can be extracted and used in food processing to form the characteristic gel in jams and marmalade. The richest sources of pectin are the peels of citrus fruits such as lime, lemon, orange and passion fruit or the pulp of apple (known as 'pomace' after juice has been extracted). Commercially, pectin is available as either a light brown powder or as a dark liquid concentrate. It is stable if stored in cool, dry place and it will lose only about 2% of its gelling power per year.
Figure 15. - Process chart for pectin extraction
There are two main types of pectin:
1) high methoxyl (HM) pectins that form gels in high solds jams (above 55% solids) in a pH range of 2.0-3.5; and2) low methoxyl (LM) pectins, which do not need sugar or acid to form a gel, but instead use calcium salts.
These form a gel with a wide range of solids (10-80%) within broader pH range of 2.5-6.5. They are used mainly for spreads or for gelling agents in milk products. However, there are a large number of different types of pectin within each group, such as 'rapid set' and 'slow set' pectins, that are made for different applications and it is necessary to specify carefully the type required when ordering from a supplier.
It is difficult to make specific grades of pectin or the powdered products at a small scale. Where attempts have been made to set up small commercial pectin units, the process has not been financially viable due to the expense of recovering solvents that are used to precipitate the pectin before drying. However, it is possible for jam-makers to increase the amount of crude (unrefined) pectin in their products by extracting it with water without using solvents (Figure 15). This is useful if the producer is making jam from fruits such as melon that are naturally low in pectin. When using pectin to make set preserves, such as jams, jellies etc., it is important that the pH is within the range of 3.0-3.5 and that they are boiled to at least 68% solids content. Powdered pectin is added to fruit pulp at 3-6g per kg of final product, but it should first be mixed with about five times its weight of sugar to prevent lumps forming when it is added to the pulp or juice (see also Section 2.2.9).
Papain is an enzyme that is found in the skin of unripe papaya fruits. It breaks down proteins and finds widespread applications in industrialised countries for meat tenderising and in brewing. Advances in biotechnology during the last twenty years resulted in a synthetic papain that was cheaper than the natural enzyme and as a result there was a decline in the market for natural papain. However, in recent years, there has again been increasing interest in the natural product and it can now achieve a higher value than before.
For profitable production, it is usually necessary to plant papaya trees in orchards, rather than collecting it from widely scattered trees which increases collection costs. Crude (unrefined) papain is normally produced because the refining technology is too expensive for most small-scale entrepreneurs. The process of papain extraction involves making shallow cuts in the skin of unripe fruits while they are still on the tree. The skin then oozes a white, sticky liquid which is collected by scraping the fruit each day for several weeks. This 'latex' is then spread out in shallow trays and sun-dried until it becomes brittle. The crude papain is packaged and exported to refiners. Because papain is an enzyme that attacks proteins, the crude latex should be handled with gloves to avoid damage to the operator's skin.
Sauces are thick viscous liquids, made from pulped fruit and/or vegetables with the addition of salt, sugar, spices and vinegar. They are pasteurised to give the required shelf life, but the basic principle of preservation is the use of vinegar, which inhibits the growth of spoilage and food poisoning micro-organisms. Other ingredients such as salt and sugar contribute to the preservative effect and the correct Preservation Index (Section 2.2.4) ensures that the product does not spoil after opening and can be used a little at a time. Some may contain a preservative such as sodium benzoate, but this is not necessary if an adequate Preservation Index is achieved. Sauces can be made from almost any combination of fruit or vegetables, but in practice the market in many countries is dominated by tomato sauce, chilli sauce and to a lesser extent, mixed fruit sauces such as 'Worcester' sauce, which contains apples and dates in addition to tomatoes. Depending on the scale of production, pulping and sieving out seeds and skins can be done by hand or using special pulper-finisher machines (Figure 16). The process for making sauce is outlined in the process chart below (Figure 17), using tomato sauce as an example.
Similarly, at a small scale, sauces can be made using simple open boiling pans, provided that care is taken to heat slowly with constant stirring to avoid localised burning of the product, especially at the end of heating. At a larger scale, processing is done using steam heated, stainless steel 'double jacketed' pans (Figure 18).
Figure 16. - Pulper-finisher used to extract fruit pulp without seeds or skins
Figure 17. - Process chart for tomato sauce
Additional processing notes
Acidity
Pulping
Pasteurisation
Filling
The beverage market is divided into products that are intended to quench thirst, such as juices, nectars and carbonated drinks and those that are drunk on special occasions, such as wines and spirits, where religion or custom permit. Competition from large scale manufacturers is among the fiercest in beverage manufacture and considerable amounts of money are spent on advertising, packaging and sophisticated distribution systems in this sub-sector. Thus beverage manufacture is one of the most difficult for small scale producers to become established and successful. However there is a growing trend in urban centres of some developing countries towards increased juice consumption and this market may become larger in future years.
In this Section, the process for making juice is described first. In subsequent processes for other drinks, the base material, fruit pulp, is used as the starting point in the process. The description of juice manufacture (Figure 19) should therefore be read in conjunction with other sections.
All drinks in this Section contain pulped fruit or juice from a single fruit or a mixture of fruits. Carbonated drinks, which do not contain fruits are not included in this book. Drinks can be divided into those that are drunk immediately after opening and those that are diluted before use. The first group should not contain any preservative but the second group may need a preservative such as sodium benzoate to have a long shelf life after opening. Unopened bottles of both types should have a shelf life of 3-9 months, depending on the storage conditions.
Fruit juices should be pure juice, with nothing added (see Section 2.4.2), except in products such as some types of melon juice, in which the level of acidity needs to be increased by addition of citric acid to give a pH below approximately 3.5-4.0. Preservation is due to pasteurisation and the natural acidity of the juice. The process for juice production is shown in Figure 19.
A wide range of drinks can be made from pulped fruit or juice and production can be spread over a larger part of the year by processing a sequence of fruits or by part-processing pulps and storing them in 1000-2000 ppm. sodium metabisulphite solution.
pH paper is useful for checking the acidity of some less acidic juices (e.g. melon juice at pH 4.0-5.0). The optimum range is 3.0-4.0 and it may be necessary either to blend juices or adjust the pH with citric acid, to prevent spoilage of less acidic juices.
Figure 18. - 'Double jacketed' pan for larger scale boiling
Soft fruits such as berries, passion fruit and papaya can be pulped by hand, whereas harder and more fibrous fruits such as pineapple and mango require mechanised pulping. Manually operated pulpers are available for places where there is no electricity and there are also a wide range of powered pulpers and blenders. At higher production rates, pulper-finishers brush fruit through a sieve and separate seeds, skins etc. from the pulp. Juice can also be extracted from fruit using a fruit press or fruit mill or by steaming the fruit. Citrus fruit juices are extracted by reaming the fruit and again comparatively simple equipment is available for this purpose (Figure 45).
Drinks need to be pasteurised if they are to have a shelf life of more than a few days. The time and temperature required for pasteurisation depends on the type of product and the bottle size, but is typically 10-20 minutes at 80-90°C. They can either be pasteurised and then hot filled into pre-sterilised bottles, or cold filled and then pasteurised in sealed bottles using a large pan of simmering water with the water level around the shoulder of the bottle. Because the pasteurisation temperature does not exceed 100°C, there is little risk of the bottles bursting. However, as with all glass containers, the temperature difference between the glass and the product or hot water should not exceed 20°C. A water cooler can be constructed to speed up the rate of cooling of filled containers. Hot bottles and cool water pass in a counter-current way through a trough to minimise 'heat shock' to the containers. In order to prevent contamination by dust, insects etc., all bottles must be cleaned properly using hand-held bottle brushes or mechanised brush cleaners. If bottles are re-used, they must be thoroughly washed with detergent to remove any residual material that may have been stored in the bottle and then sterilised by heating to boiling in a water-bath for at least 10 minutes.
Figure 19. - Process chart for fruit juice production
Hand filling from a jug is often too slow for the required throughput and fillers can be constructed by fitting one or more taps to the base of a stainless steel or food grade plastic bucket. More sophisticated fillers measure and control the volume of liquid filled into each bottle (Figure 47).
Waxed cartons have become popular because of their lower cost compared to bottles, together with savings in time and money for collection and washing of re-useable bottles. However, the cost of equipment to form and seal the cartons is too high for most small scale producers and cheaper alternatives including plastic pots with sealed foil lids are becoming more popular in some countries.
These are drinks that are diluted to taste with water and are thus used a little at a time. The container must therefore be re-closeable (Figure 20) and these products may contain a preservative, usually sodium benzoate, to prevent spoilage after opening. Squashes are made from at least 30% fruit juice mixed with sugar syrup (Figure 23). Cordials are simply crystal-clear squashes. Although food dyes are used by some processors, these are not necessary for most products. Regulations on the composition of squashes are in force in some countries (see Section 2.4.2).
Syrups are filtered juices that are concentrated by boiling until the sugar content reaches 50-70%. The heat and high solids content preserves the syrup and it is used in place of sugar or honey. Syrups can be made from a wide range of fruits, but the most common type is made from grapes.
Figure 20. - A range of squashes from different manufacturers
Figure 21. - Process chart for squashes and cordials
Jams, jellies and marmalades
Pastes and purees
Fruit 'cheeses'
Additional processing notes
Jam is a solid gel made from fruit pulp or juice from a single fruit or from a combination of fruits. The composition is controlled by law in some countries (Section 2.4.2). In mixed fruit jams, the first named fruit should be at least 50% of the total fruit content. The sugar content is normally 68-72%, which will prevent mould growth after opening the jar.
Jellies are crystal-clear jams that are produced using filtered juice instead of fruit pulp. Marmalades are produced mainly from clear citrus juices (including lime, orange, grapefruit, lemon and orange) and have fine shreds of peel suspended in the gel. Ginger may also be used alone or in combination with the citrus fruits. The fruit content should not be less than 20% citrus fruit and the sugar content is similar to jam. The correct combination of acid, sugar and pectin is needed to achieve the required gel structure and rapid boiling is necessary to remove water quickly, to concentrate the mixture before it darkens and loses its ability to form a gel. The process chart for jams, jellies and marmalades is shown in Figure 22 and a summary of common faults in jam making is shown in Table 11.
In principle, pastes and purees can be made from any fruit or vegetable. The most common types are tomato and garlic, which are widely used in cooking. These products can be made at a small scale by carefully evaporating water to concentrate the pulp, with constant stirring to prevent darkening or localised burning. The concentration of solids in the paste is normally around 36%. The high solids content and natural acidity are sufficient to preserve the product for several days but pasteurisation in bottles or cans is needed for a longer shelf life. In some preparations, sugar, salt and vinegar are added to assist in preservation.
Fruit cheeses are fruit pulps that are boiled until they have a final sugar content of 75-85%. They set as a solid block without the need for added pectin, but they do not have the same gel structure as jams and marmalades. They can be cut into bars or cubes to eat directly or they can be used in small pieces in confectionery or baked goods (see also 'fruit leathers' Section 2.2.3)
Figure 22. - Process chart for jams, jellies and marmalades
Batch preparation
A simple way of calculating the amounts of sugar and juice that should be mixed together for squashes and jams is to use the Pearson Square (Figure 23). If for example, a squash having 15% sugar is required, made from orange juice having a 10% sugar content, mixed with 60% sugar syrup, the Pearson Square can be used as follows: draw a square, writing the juice and syrup concentrations on the left side and the product concentration in the middle, as shown in Figure 23.
Subtract the smaller amount from the larger amount diagonally to find the quantities that should be mixed together (in the example, 45 litres of orange juice should be mixed with 5 litres of sugar syrup). Similar Pearson Squares can be drawn to find the amounts that should be used when any two components are mixed together.
Figure 23. - Using a Pearson Square to calculate the amounts of two ingredients in a mixture. (From: Food Chain, N° 17, p15, March 1996)
Boiling
Boiling is done using a stainless steel pan. If other materials are used there is the risk that fruit acids will react with the pan and cause off flavours to develop. At higher production rates, a steam jacketed pan is preferable (Figure 18) as it gives more even and faster heating. If whole fruit is used, there are two heating stages in jam manufacture: initially fruit is heated slowly to soften the flesh and to extract pectin; then the mixture is boiled rapidly until the sugar content reaches 68-72%. This change in heat output requires a sufficiently large and easily controllable heat source. There are three ways to test for the correct point to stop boiling: using a hand-held refractometer (Figure 12) reading 68-70% sugar, a sugar thermometer reading 104-105°C or by placing a drop of the product in cold water to see if it sets.
An alternative method to concentration by boiling, when making products such as tomato paste, is to hang the pulp in a sterilised cotton sack for an hour. During this time the thin watery juice leaks out and the pulp loses half its weight. Then 2.5% salt is mixed into the concentrate and it is re-hung for a further hour, during which time the weight falls to one third of the original. The product can then be packaged and pasteurised or further concentrated. This method is reported to produce a product which has a natural flavour using considerably less fuel than concentration by boiling.
Preserves should be hot filled into new or re-used glass jars, which are then sealed with a new lid. In some countries, plastic containers have been introduced but they are not easy to hot fill (they melt) and the seals are often inadequate, causing product leakage and insect infestation problems as well as a shorter shelf life.
The temperature of filling should be around 85°C. If it is too high, steam condenses on the inside of the lid and water falls onto the surface of the preserve. This dilutes the sugar at the surface and results in mould growth.
If the temperature is too low, the preserve thickens and is difficult to fill into containers. Filling can be done using jugs and funnels, but for higher production rates, small hand-operated or semi-automatic piston fillers are available (Figure 47). In all cases the jars should be filled to approximately 9/10ths full, to assist in the formation of a partial vacuum in the space above the product as it cools. This can be checked using a 'headspace gauge' (Figure 57). The jars are kept upright until the gel has formed during cooling.
Wines are produced by fermentation in which the sugars in the fruit juice/pulp plus added sugar are converted into alcohol and carbon dioxide by varieties of the yeast Saccharomyces cerevisiae, named 'wine yeasts'. Producers need to select one variety that works well in their process and then continue to use it to produce a consistent product. Wines are preserved by the raised levels of alcohol and their natural acidity. Almost any fruit can be used to make wine, but the most popular in many developing countries are pineapple, papaya, grape, passionfruit, banana, melon and strawberry (or strawberry flavoured wine). Typically, the alcohol content of wine is 6-12% and in 'fortified' wines, such as sherry, ginger wine etc., it is usually 15-20%. The main problems are concerned with adequately cleaned fermentation vessels, to prevent contamination by other micro-organisms that spoil the wine and adequate sedimentation or filtration to produce a crystal-clear product. A special licence to sell alcohol is needed in most countries.
Vinegar is produced by a second fermentation in which acetic acid bacteria (Acetobacter species) convert the alcohol in wine to produce acetic acid, (spoiled wine is often due to the unwanted presence of acetic acid bacteria). Whereas in wine production, air is excluded from the vessel by an air lock (Figure 24), in this second fermentation it is important for the bacteria to be in contact with air as much as possible. This is done traditionally by allowing the wine to trickle over a stack of wood shavings or twigs that are held in an open framework, named a 'generator' which allows free circulation of air. The wood becomes covered in the bacteria and the process either operates continuously, re-circulating the wine a number of times until the acetic acid levels rise sufficiently, or part of a batch is retained to inoculate the next batch. Typically, vinegar contains 6-10% acetic acid, which preserves the product for many months/years provided that it is sealed in an airtight container to prevent the acetic acid from evaporating. More modem vinegar fermenters pump air into the wine and are sufficiently expensive to be beyond the reach of most small scale producers.
Table 11. - Common faults in making preserves
|
Fault |
Possible cause |
Prevention |
|
1. Gel does not set or is not firm |
Incorrect pectin type dissolved |
Select correct type of pectin |
|
Too little pectin |
Check formulation |
|
|
Solids content too low |
Add more sugar |
|
|
Incorrect pH value |
Check pH, adjust with citric acid |
|
|
Pectin not fully |
Mix with sugar before dissolving |
|
|
Boiling for too long |
Produce smaller batches |
|
|
Pectin solution too old |
Use new stock |
|
|
Pre-setting |
Increase filling temperature |
|
|
Holding at high temperature for too long (pan too big) |
Lower filling temperature, make smaller batches or use slow-setting pectin. |
|
|
2. Gel too firm |
Too much pectin |
Check formulation |
|
Solids content too high |
Heat less, add less sugar or add more water |
|
|
pH too low |
Adjust pH |
|
|
3. Pre-setting |
Filling temperature too low |
Increase filling temperature or choose slow-setting pectin |
|
Filling time too long |
Produce smaller batches or use slow-setting pectin |
|
|
Solids content too high |
See above |
|
|
pH too low |
See above |
|
|
4. Fruit floats |
Filling temperature too high |
Lower filling temperature |
|
Pectin sets too slowly |
Choose rapid-set pectin |
|
|
Gel not strong enough |
See (1) above |
|
|
Solids content too low, giving slow setting |
See above |
|
|
pH too high, giving slow setting |
Adjust pH |
|
|
5. Syneresis (cracked gel with oozing liquid) |
Pre-setting due to low filling temperature |
See (3) above |
|
pH too low |
Adjust pH |
|
|
Solids content in fruit and in gel are different |
Pre-mix fruit and sugar syrup and hold overnight or cook longer |
Figure 24. - An air lock used in wine making
Alcohol has a lower boiling point than water and distillation (vaporising the alcohol and then condensing it) is used to concentrate the alcohol in spirit drinks. Distillation is carried out in a still which is a clean drum, fitted with a safety valve and a pipe to carry away the vapour. Wine or other alcoholic liquor is placed inside the drum and heated. The alcohol vapour is passed through cooled air or cool water and the distillate condenses and is collected. Note: distillation is illegal in many countries without a government licence.
There are a large number of traditional methods for distillation. One such method in East Africa involves filling fruit wine or beer into an oil drum and placing it at a shallow horizontal angle over a fire (this angle prevents any liquor from being sucked over with the distillate during boiling). A hollow bamboo pipe, approximately 10 cm in diameter, is fitted to the opening of the drum and sealed with a pulp made from the inner layers of a banana trunk. Five hollow bamboo pipes, approximately 2 cm in diameter, are fitted vertically down from the larger pipe and sealed in a similar way. Each pipe leads to a baked clay pot of approximately 20 litres capacity, submerged in a pit of slow-running water, diverted from a stream. The pots are held below the surface of the water by wood branches that are bent over them and fixed into the soil at each end (Figure 25).
Distillation is controlled by sampling each pot at intervals to determine its alcohol strength and adjusting the rate of heating by adding or removing firewood. As the strength declines with continued distillation, the end point is determined by the desired alcohol strength in the product, usually 35-40%. Distillation is continued for 3-4 hours and 40 litres of spirit are filled from the pots into clean bottles and sealed with a stopper made from banana or papyrus leaves. The spirit is preserved by the high alcohol content and has a shelf life of several years.
Figure 25. - Traditional distillation of spirits from banana juice
(Courtesy of Midway Technology)
Modem stills are made entirely of copper or stainless steel and larger ones are fitted with thermostatically controlled heaters. These are too expensive for most small scale producers, but small copper stills for making essential oils have been used for making small amounts of alcohol.
Figure 26. - Process chart for fruit wine
Figure 27. - Process chart for vinegar
Sugar may be added to fruit juice to raise the level to about 20° Brix and after inoculation with about 3% yeast, it is held in a fermentation vessel, made from food grade plastic or glass, for about ten days. It is important to keep the vessel closed to prevent bacteria and mould from infecting the batch. After ten days the fermenting wine is 'racked' (filtered) by passing it through a muslin or nylon straining cloth into narrow necked fermentation vessels, plugged with cotton wool or fitted with a air lock (Figure 24).
The fermentation is then continued for between three weeks to three months, depending on the temperature and the strain of yeast being used. The end of the fermentation is seen when there are no more bubbles rising to the surface.
Figure 28. - Process chart for spirits
|
Stage in process |
Quality Assurance |
Equipment Required |
Notes |
|
|
Essential |
Optional |
|||
|
Fermented juice |
|
|
|
See Figure 26 for production of wine. |
|
|
Filter |
|
Coarse muslin cloth. |
Filter through coarse muslin cloth to obtain juice. |
|
Heat |
|
|
Distillation equipment. |
Distil the liquor into clean containers (e.e. Figure 25). |
|
Standardize |
|
Check alcohol content. |
Alcohol hydrometer. |
Adjust the alcohol content to that declared on the lable by blending with previous batches or adding clean water to achieve 30-40% alcohol. |
|
Fill & Seal |
Bottles/caps |
Check fill-weight and correctly sealed pack. |
|
Cold fill into pre-sterilized bottles. |
|
Label and Store |
|
Check that label and storage conditions are correct. |
|
Store on racks, in boxes with a cool dry atmosphere. |
It is then siphoned into clean containers and allowed to clear and mature before it is siphoned into bottles and sealed with sterilised cork stoppers or roll on pilfer-proof (ROPP) screw caps. Some fruit wines, such as pineapple, are difficult to clear because of natural gums in the fruit. These can be removed by heating the juice and allowing the gums to precipitate out before the juice is fermented. This can be a particular problem when waste fruit from other processes (e.g. drying or bottling) is used for wine making. Great care should be taken to ensure that only the fermented liquor is used for distillation. Any suspect liquor or other materials should not be distilled because of the risk that they may contain methanol. This is a type of alcohol which if consumed causes blindness and in sufficient amounts, death.
The information given in this Section is intended to enable producers to select a product for manufacture. Once a potential product has been chosen, it is then necessary to determine the feasibility of operating a small enterprise to make it and this is described in the following Section.
