All foods begin to deteriorate, or spoil, as soon as they are harvested or slaughtered. Most spoiling is caused by microorganisms such as bacteria or mold, or by chemical changes within the food itself due to enzyme action or oxidation. The purpose of food preservation is to stop or slow down the spoilage. Ways of preserving food have been practiced since ancient times, although knowledge of what actually causes food to spoil has been gained only in modern times. Ages-old food preservation techniques include drying, salting, smoking, fermenting, pickling, cooling, and freezing. Modern methods include canning, mechanical refrigeration and freezing, the addition of chemicals, and irradiation.

One of the most ancient methods of food preservation is sun- or air-drying. Drying removes much of the food's water; without adequate water, microorganisms cannot multiply and chemical activities are nearly halted. Dried meat was one of the earliest staple...