Introduction to the General Principles of Agro-Processing:

Faced with the current economic realities, farmers worldwide are searching for new options of surviving, as well as expanding their business. One of the many opportunities to grow markets, turnover and profits, is by adding value to farm produce through further processing. Most value added food products available to consumers have been processed in some way or other, even if the processing is as simple as cleaning produce before it is packed in plastic or net bags. Two types of processing methods may be performed on raw materials:

  • Primary processing: This type of processing includes the simplest of processes such as washing, peeling, chopping, ageing, the milling of wheat for flour production, and the processing of sugarcane;
  • Secondary processing: This type of processing includes the conversion of primary processed products into more complex food products and includes procedures such as mixing, depositing, layering, extruding, drying, fortifying, fermentation, pasteurisation, clarification, heating, etc.


Agro-Processing of Deciduous Fruit:

The deciduous food group include a large number of crops such as apples, apricots, grapes, peaches, pears, plums and figs.

  • Apples:

Apple cider vinegar: Apple vinegar is produced from alcoholic fermentation and acetous bacterial oxidation of apple juice. Apple vinegar contains between 5-12% acetic acid.

Apple sauce: Apple sauce is the cooked, pulped product prepared from misshape or small sized fruit. It is mainly used as a side dish (condiment) or in bakery products.

Dried apple rings: Dried apple rings are semi-dried or intermediate moisture products containing between 22-25% moisture. It is produced by artificial drying of peeled, sliced apples. Dried apple pieces are mainly used as confectionary ingredients or as a fruit snack.

Apple cider: The beverage is obtained by complete or partial fermentation of apple juice with or without the addition of potable water. It should have a minimum alcohol content of 5% (v/v).

  • Apricots:

Dehydrated apricot pieces: Dried apricot halves (with 15-20% moisture) are further dried to reduce the moisture content to below 5%. Dehydration is performed under vacuum conditions. Dehydrated apricot pieces are used in instant cereal or muesli mixes as well as cocktail nut-and-fruit mixes. It can also be ground to produce a powder.

Sun-dried apricots: Apricot halves or pieces are placed on perforated racks/trays and dried by exposure to sun in hot, dry climates.

  • Grapes:

Naturally dried raisins: The word “raisin” is French for dried grape. By usage, however, the term has become limited mainly to the dried grapes of a few cultivars. Natural drying makes use of sunlight to dry the grapes.

Grape seed oil: This oil is extracted from the pips of grapes after the juice has been expressed. The pips contain 12% oil. It is mainly used for coating raisins to improve the appearance and keep them pliable, the unrefined oil has other industrial uses, including soap and paint manufacture.

Grape vinegar: Grape vinegar is the sour liquid obtained by naturally fermenting grape juice. Wine is used as the starting material to which the vinegar plant (yeast culture) is added. The wine undergoes an acetic fermentation by micro-organisms of the Acetobacter spp. which converts the alcohol to acetic acid.

  • Peaches:

Dried peaches are eaten as a fruit snack or used as an ingredient in recipes. It has a soft, chewy texture and characteristic peach flavour. Freestone peaches with a deep orange colour are used for drying, both sun/solar and artificial air-drying can be used to dry fresh peaches to a final moisture content of between 15-20%.

Peach chutney is a sweet, tangy condiment that is served with curries, hot and cold meats and savouries. Peach chutney may be prepared from both green and ripe peaches, along with other fruit/vegetables (e.g. onion and green pepper), sugar, vinegar and various spices and thickening agents.

Peach jam is produced from peaches harvested at the firm-ripe stage to ensure maximum flavour, colour and pectin development that is essential for successful jam.

  • Pears:

Dried pears are a seem-dried or intermediate moisture product containing 18-22% moisture. Dried pear halves are mainly used as confectionary ingredients or eaten as a fruit snack. The shelf life of this product is about 90 days at ambient temperatures. Storage temperatures of below 7°C will extend the shelf life. Ten tons of fresh pears will yield between 1-1 ½ tons of dried product.

Pear puree is prepared from peeled and cored pear halves through a pulping and screening process. It is preserved by freezing or canning. It may also be concentrated. The puree is a semi-processed product that is used to prepare pear nectar (juices), syrups, sauces, toppings and jams. Optimum processing produces a puree containing 12% soluble solids and a yield of 89%.

Pear relish: A relish is a sweet-n-sour condiment that comprises of preserved fruit/vegetable pieces and spices. It is served with curries, hot & cold meats and savouries. Pear relish is usually prepared from firm mature or green pears.

  • Plums:

Canned prunes: Dried prunes are canned in a sugar syrup to produce a soft, ready to eat product.

Dried prunes are produced from firm-ripe plums with a high solids content and full-bodied flavour. The final product has a moisture content of 18-20%, soft chewy texture and sweet taste. It is an excellent source of fibre. The yield is generally between 25-35%. A prune is produced from a plum variety that can be dried without removal of the pip.

  • Figs:

Small-Scale Fig Preserve: Preserves are similar to jelly with the exception that whole or large pieces of fruit are used in making the preserve. The figs used for the preserve should be firm-ripe instead of soft-ripe and should be uniform in size.

Solar Dried Figs: Figs are usually sun (solar) dried, but mechanical drying is also used in order to produce a low-moisture product. Fig varieties used for drying include Calimyrna, Adriatic, Kadota, Black Mission, and Smyrna. The processing methods for solar dried figs differ from variety to variety although general drying procedures apply to all varieties.