Explain about the Drying - methods of food processing?

Drying is the oldest and probably the simplest way of preserving food. It is usually accomplished by the removal of water. Dried foods are preserved because the available moisture level is so low that the microorganisms cannot grow and enzyme activity is controlled. Moisture from food may be removed by a number of methods: drying by the Sun's rays and by the modern artificial ones. Grains and nuts were the first foods to be dried under the sun and air. However, sun-drying is a slow process, risk of contamination and spoilage and is limited to climates with a hot Sun and a dry atmosphere and to certain fruits such as grapes (raisins), figs, dates, apricots, raw mangoes (amchur), pears and peaches.

Vegetables like beans, peas, cabbage, cauliflower, lady fingers, garlic, onions, chillies, turmeric and all leafy vegetables can also be dried by sun-drying. Drying of fruits and vegetables involves washing, peeling, preparing and spreading on flat bottom trays and drying under Sun. Fish (Bombay duck) and shrimps are dried by exposing them to the Sun on the seashore. The word dehydration usually implies the use of controlled conditions of heating, with the forced circulation of air or artificial drying (mechanical drier) as compared with the use of sun-drying. Using mechanical driers, fruits, fruit leathers, banana chips, tea, coffee, milk, soups, fish, meat, eggs and vegetables can all be dried year-round. Dried foods are compact and lightweight; do not require refrigeration and last much longer than the fresh foods. Dried foods should be stored in airtight containers to prevent moisture from rehydrating the products and allowing microbial growth.