Dehydration

Dehydration, removal of water from substances, usually as part of an industrial process or in the preservation of food. Water may be removed in drying chambers through which hot air or gases are passed. A vacuum may be used instead of hot air or gas to evaporate the water at lower temperatures. In chemical processes, gases are dried by passing them through tubes containing drying agents such as calcium chloride. Substances can be dried and kept away from moisture by placing them in a desiccator—an airtight chamber containing a drying agent such as silica gel. Dehydration is an important method of food preservation. Since most food spoilage is caused by bacteria, which can only function in the presence of moisture, dehydration inhibits their activity. Freeze drying, in which foods are frozen and ice removed by sublimation in a vacuum, is increasingly used as it does less damage to the texture and flavor of the food. Dehydration also refers to a serious physiological condition in which the body's tissues lose too much water. It is caused by repeated vomiting, diarrhea, bleeding, or exposure to a hot environment without an adequate water supply.