dehydration

Process to preserve food. Moisture content is reduced to 10–20% in fresh produce, and this provides good protection against moulds. Bacteria are not inhibited by drying, so the quality of raw materials is vital.

The process was developed commercially in France about 1795 to preserve sliced vegetables, using a hot-air blast. The earliest large-scale application was to starch products such as pasta, but after 1945 it was extended to milk, potatoes, soups, instant coffee, and prepared baby and pet foods. A major benefit to food manufacturers is reduction of weight and volume of the food products, thus lowering distribution cost.

dehydration

In chemistry, the removal of water from a substance to give a product with a new chemical formula; it is not the same as drying.

There are two types of dehydration. For substances such as hydrated copper sulphate (CuSO4.5H2O) that contain water of crystallization, dehydration means removing this water to leave the anhydrous substance. This may be achieved by heating, and is reversible.

Some substances, such as ethanol, contain the elements of water (hydrogen and oxygen) joined in a different form. Dehydrating agents such as concentrated sulphuric acid will remove these elements in the ratio 2:1.

dehydration

Shortage of water in the body tissues. Symptoms include nausea, thirst and exhaustion. It may arise from inadequate fluid intake or from excessive fluid loss (through sweating, vomiting, diarrhoea). It is treated by drinking plenty of fluid or by saline infusion (replacing lost salts along with water intravenously).