Way back in late nineteen sixties, Indian food industry was excited about the import of several dehydration plants from Bulgaria with many features lacking in the locally fabricated driers. These were used mainly to dehydrate onions, largely for export as domestic market for dried foods was limited to some dry fruits and nuts. Amongst fruits grapes, dates and a few high value products were popular,most of which were imported. As for vegetables the only product commanding some market was dehydrated peas, probably because of the short season when fresh peas could be obtained. To day the market for dehydrated products has shrunken to a very low volume because of the arrival of many new technologies which are better suited to give a product of superior quality. Freezing technology which can preserve almost all foods with very little change in the original quality has become the new mascot of food industry in many countries and it is a question of time before it gets established nation-wide in India also.
It is true that human beings were using for hundreds of years the drying process utilizing the abundantly available sun light to preserve many high moisture foods for long time. These included fruit, vegetables, nuts and meat which are all dried to keep them stable and usable for consumption when their growing is not possible due to unfavorable weather conditions. In northern India farmers preserve their surplus potato crop by slicing and sun drying and the dried slices with low moisture content can keep well for an year, being consumed as and when needed by frying. The two major steps involved in sun drying are well known, viz blanching and drying in thin layers under the sun till the moisture level comes down to safe level. Water activity in a food determines its vulnerability to microbial spoilage and low moisture products have low water activity making them safe for storage under clean environment without exposure to moisture and insects.
One of the main constraints in marketing dried foods is the loss of texture during drying and inability of dried foods to regain the original weight on reconstitution. This naturally affects the eating quality, with many consumers preferring not to patronize them. Even Freeze Drying technology could not deliver a product without adversely affecting the texture, though the flavor quality of the final product was superior. No wonder this technology is largely restricted to manufacture of soluble coffee and tea products with high flavor profile.
Dried foods, especially sun dried ones are relatively less expensive though quality wise mechanical drying has better controls. If horticulture produce materials like Chilli, Black Pepper, Turmeric, Ginger, Cardamom and many spices and herbs are still dried in the field it is because of economic considerations. Attempts in the past to use automated/continuous driers were not successful because of cost considerations. It is often claimed that sun dried products are brighter in color because of the action of ultraviolet rays in the sun light. Conventional drying also uses sulfite to protect the color and sulfite allergy is becoming increasingly becoming common place forcing the industry to preclude this chemical. Advent of freeze drying process gave the dehydration industry a short respite but both capital investment in the plant and the exorbitant processing cost made it some what irrelevant for the main stream food industry. If texture and taste can be compromised to some extent, sun drying is still the most affordable preservation technique but increasing affluence amongst the population in many emerging developing countries makes dried foods some what unpopular. It is because of the food ingredients industry, which is supporting dried foods for use in products like soups, baked foods and low cost curry mixes, that dehydrated food industry is still surviving..