Solar Dehydration

The process of dehydration in foodstuffs is simply that of reducing the internal water content and in certain instances the intracellular water content of the food. Effectively when heat is applied to the food it induces evaporation of the water, which results in the water within the food first migrating to the periphery of the food, and then undergoing a phase change from liquid to gas, in other words water to water vapor.

The reduction in water content results in reduced water activity with a consequent reduced growth of microorganisms. Each microorganism has a maximal, optimal and minimal water activity at which it grows, and generally bacteria require more moisture than yeasts and yeasts require more moisture than molds. Dehydration of foods is an excellent method of preserving the foods and is practised extensively in the modern age. Solar dehydration is using the sunshine and consequent heat of the sun, to induce evaporation and dry the food.

Solar dehydration can sometimes be limited to climates with hot sun and dry atmospheric conditions and tends to work best with certain select food types, for example prunes, figs, apricots, pears and peaches, and in the case of meat, beef jerky and certain fish species. Whilst in certain instances this can literally be achieved by placing the foodstuff in a single layer in the direct sunshine on a container or tray and turning the food on a regular or semi-regular basis, the technique is generally facilitated by using a solar dehydrator.

A classic example of solar dehydration using a simple tray technique is the kapenta fishing industry in Lake Kariba in the Zambezi Valley in Zimbabwe, where 20 tons of kapenta (Tanganyika sardine) are caught each year during the evening. The small fish are then mixed with coarse salt (1lb salt for 12 lbs of fish) on the fishing boats and subsequently transported to land where the kapenta are sorted and placed on large, flat trays and dried in the sun. The fish remain an extremely important source of protein for the local population.

A solar dehydrator, also referred to as a solar dryer, is a solar appliance that is designed to dry foods using the power of the sun and nothing else. Solar dehydrators function to extract moisture from foods, while preserving color and flavor.

Once adequately dried, store the food in clean, sterile plastic bags at between 40-70 ? F (5-20 ? C). The food should be fairly brittle once properly dried. If you want to apply a degree of science to the process you could analyze the actual moisture content of the food, per individual food type or category, and through a process of trial and error you could determine exactly what your targeted final moisture contents should be per individual food type and what the normal solar application would be to achieve those levels.

A further enhancement to the dehydration process would be to either vacuum pack the dried foods or even package the foods using gaseous nitrogen flush to eliminate oxygen, thereby extending the shelf life of the food, although both of these add-on techniques will have an associated cost.