Тема 20: methods of food preservation

Active Vocabulary

to preserve, preservation, preservative; refrigeration, freezing, heating, pasteurization, sterilization, canning, drying, salting, pickling, smoking, irradiation; to treat, treatment; to process, processing; spoilage agents; to contaminate, contamination; disease; to seal; to retard; to hasten; to render; to prolong; to extend; to immerse; perishable; wholesome; technique, techniques

Notes

1. medium (–a) – среда

2. freeze drying – сублимационная сушка

3. to reconstitute – восстанавливать влагосодержание (высушенных продуктов)

4. stockpiling – запас; накопление

5. freezing facilities – морозильное оборудование

Part 1

As the principal spoilage agents are normally present in food, to destroy them or to prevent their development becomes the chief problem of food preservation.

Any condition opposed to the development of these organisms, whether by retarding their growth or by entirely destroying them, aids in the preservation of food. Methods commonly used include refrigeration, freezing, canning, the use of preservatives, heating, drying, and common storage under suitable conditions. Cold sterilization or irradiation by beta and gamma rays to prolong the keeping quality of food is being widely studied experimentally. The possibilities of this method of food preservation are great.

Heating. Food is commonly preserved through the application of high temperatures. A temperature considerably above that of the body may result in either a pasteurized or sterilized product. Foods are commonly pasteurized by being held at a temperature of from 60° to 66° for thirty to forty minutes, during which time most of the organisms, although not all, are killed.

Sterilization of a food or a substance destroys all life in or on it, and involves heating for a longer time or at a higher temperature than it is necessary for pasteurization.

Canning. After pasteurization and sterilization the material thus treated must be protected from fresh contamination by microorganisms.

Before the discovery of canning it was impossible to keep perishable foods for any great length of time. Today highly efficient machinery and improved containers make possible the production of immense quantities of canned foods for both home and commercial use.

Refrigeration is widely used as a means of maintaining the low temperatures found satisfactory in the storage of perishable foods. Fresh milk, meat and similar foods keep best just above the freezing point. Certain fruits and vegetables also keep better when cold.

During cold storage foods may undergo changes in flavoury texture and nutritive value. The extent of these changes depends upon the length of storage time and the conditions under which they are held.

Freezing, like cold storage, does not destroy the microorganisms and enzymes present in foods. It makes them more or less inactive, however, so that frozen foods, when held at the proper temperature, undergo changes slowly. This applies to the nutritive value as well as to other chemical and physical characteristics.

Part 2

Using Chemical Preservatives. Certain chemicals are helpful in preserving foods either by retarding or preventing the growth of microorganisms. These may be either added to the product or produced in it by fermentation. Sugar is often used in such quantities as to increase the concentration of the food and make it an unfavourable medium for the organisms. Salt and acids, in the form of vinegar or lemon juice, are other substances added for their preservation action.

Drying. Removal of moisture is of benefit in preserving food. Although it is difficult to dry foods to the point of destroying microorganisms, it is comparatively easy to dry foods so that no spoilage takes place. Drying of foods to prevent spoilage does not necessarily mean complete removal of the water, but it does mean concentration to such a point that the liquid is denser than the body fluid of the microorganisms. When food is dried body processes are delayed or prevented.

Freeze Drying. This relatively new process is achieved by freezing under very low pressure so that the ice sublimes, leaving a spongelike (губчатообразный) form without moisture. Hence, the product retains its shape, but the total weight is reduced, often by more than 50 per cent. Product is usually canned or wrapped in foil to keep out moisture. This product requires no refrigeration, because microorganisms cannot grow at such a low moisture content. Reconstitution is achieved by immersion of the sublimated product in water before cooking. There is little change in the product because of chemical or enzymatic action. Reconstituted products clearly resemble the original fresh products in flavour and colour. Stockpiling can be achieved without freezing facilities.