(introduction...)

PRODUCT/PROCESS DESCRIPTION

Types of Fruit Products

Drinks

All drinks contain pulped fruit or juice from a single fruit or a mixture of fruits. They can be divided into those that are drunk immediately after opening and those which are stored and used gradually. The first group should not contain any preservative but the second group need preservatives 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. Different types include:

i) Fruit juice (with nothing added).

ii) Nectars (which contain at least 30% fruit pulp and are drunk immediately after opening).

iii) Squashes (which contain at least 25% fruit pulp mixed with sugar syrup). They are diluted to taste with water and contain preservatives.

iv) Cordials (crystal clear squashes).

v) Syrups (which are boiled, filtered juices with a sugar content of 50-70%). They are used in the concentrated form and do not usually contain preservatives.

Fermented Juices

These include a range of fruit wines, vinegars and spirits. Yeasts ferment sugars in the juice to alcohol, which together with the natural acidity preserves the products when the concentration is high enough (more than 6% alcohol). Some low alcohol drinks are pasteurised to prevent spoilage. Vinegars are produced by a two-stage fermentation - first by yeast to produce wine and then by acetic acid bacteria to produce vinegar (acetic acid). Vinegars are normally standardised at 6-10% acetic acid, which preserves them from spoilage.

Fruits in Syrup

Fruits are packed into jars with a 30-50% sugar syrup. The filled jars are pasteurised and then sealed tightly while hot so that an internal vacuum forms when they are cool. Preservation depends on an adequate heat treatment and air tight (or "hermetic") seals.

Preserves (jams, jellies and marmalade)

Preservation depends on a high sugar content (68-72%) combined with the acidity of the fruit to prevent spoilage. The setting qualities and strength of the gel depend on the sugar content, the fruit content, the acidity and the amount of pectin (an extract from fruit skins) added. A careful balance is needed between the sugar, acid, pectin and fruit to achieve a good quality product. Jellies are clear filtered gels. Marmalades, which are generally made from citrus fruits, are gels which contain shreds of peel. Jams can contain whole fruit pieces, juice or fruit pulp.

Confectionary Products

Fruit cheese (e.g. guava cheese) is a jam type mixture that is further boiled to give a sugar content of 75-85%. It sets as a solid block. The high sugar level combined with the natural acidity prevents spoilage.

Dried Fruit Products

These include dried fruit pieces, fruit leathers and osmo-sol dried fruit. They are described in detail in the drying chapter. In general fruit products do not form a staple part of the diet but add variety and choice to staple foods. They are low cost raw materials, which are usually widely available in rural areas and different types are available throughout the year. Many of the methods of processing are relatively low cost and simple to use at a small scale and a wide variety of products are possible. Finally valuable extracts such as pectin or citrus oil may be produced as ingredients for other large scale manufacturers. However fruits (and vegetables) are bulky raw materials and incur high transport costs. In addition markets can be a long way from the growing areas which increases transport costs for what are relatively low value products. A demand for the products may not exist as people may prefer to eat fresh foods and do not worry if the food is not available for a short season each year. This is especially so if there is an alternative fruit or vegetable for them to eat. Do not attempt to use a surplus simply because it exists - the demand for the products must be demonstrated.

Types of Vegetable Products

Dry Salted Vegetables

The high salt concentration preserves the food by both drawing out water from the food and by the anti-microbial properties of the salt. Salt also interferes with the action of enzymes. Vegetables must be washed to lower the salt concentration before they are eaten. Dry salting does not need fuel, is simple to do and the food quality is well retained.

Brined Vegetables

A solution of salt (brine) is used to preserve vegetables. There are many different types of brine containing 2-16% salt, often with added sugar. However, higher concentrations require the vegetables to be washed before use. Those which have lower concentrations of salt may also be pasteurised to aid preservation.

Pickles and Sauces

Vegetables (for example 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 lactic acid. In vegetable products the lactic acid 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 fermentation. If 2-5% salt is used a natural sequence of different bacteria produce the lactic acid. If higher concentrations of salt (up to 16%) are used, a different product called 'salt stock' pickle is produced. Sometimes, sugar is added to increase the rate of fermentation or to make the product sweeter. (The different types of pickles are shown in Table 1.)

Table 1: Types of Pickled Vegetables

Alternatively vinegar, salt and sometimes sugar are used to acidify vegetables and produce a variety of products but because the vegetables are not fermented they have a different flavour and texture. Sweet pickles and sauces are made from single fruits or mixtures of fruits and vegetables. They are preserved by the combined action of acetic acid, sugar and in some cases, added spices.

Dry vegetables (These are discussed in detail in Chapter 1 Dried Foods)

In general many vegetables have a longer harvest season and a longer shelf life in the raw state than fruits, and production can therefore continue for a larger part of the year. Many vegetables form the staple food in the diet or are used in soups and stews and they therefore have high demand. Some extracted products (e.g. sugar and starch) are valuable staples, which also have a high demand. In general vegetable processing is more difficult on a small scale than fruit processing because of the low acidity and hence the risk of food poisoning.

Most fruit products are acidic and are not spoiled by bacteria. They do not therefore carry the risk of food poisoning. Spoilage is by yeasts or moulds. Most vegetables are less acidic and are spoiled by bacteria and moulds. Some of these bacterial can cause food poisoning. In addition naturally occurring enzymes rapidly change the colour, flavour and texture of fruits and vegetables after harvest. These factors produce a characteristically short shelf life and rapid processing after harvest is therefore necessary. Preservation is achieved by either destroying enzymes and micro-organisms using heat (blanching, pasteurisation), or preventing their action by:

1) removing water (drying, boiling to make concentrated syrups or jam, using concentrated solutions of salt or sugar to draw out water from the food),

2) by increased acidity or chemical preservatives (acidity can be changed by adding acids (for example lemon juice or vinegar), or by fermentation. Examples of preservatives include sulphur dioxide and sodium benzoate).

3) by using low temperatures (freezing, chilling or cooling).

In this Chapter the use of low temperatures is not considered due to the high capital costs of equipment and the need for refrigerated distribution and storage. Canned fruit products are produced in a similar way to the bottled products described below, but canning is not described due to the high costs of equipment and cans. Technical advice is also needed to find the correct processing rime and temperature time as it varies with different foods and different containers. This type of processing is not recommended for vegetables on a small scale due to the risk of food poisoning.

Details of the production of the above products are shown in the process flow diagrams (1-17).

PROCESS FLOW DIAGRAMS