Food is preserved to keep it fresh, free from bacteria, fungi, and other contaminates. Food preservation was a difficult thing to do until the early 20th century. Until then food had been preserved in "ice rooms" (rooms filled with ice blocks) or "ice boxes" (a smaller version of an ice room). Those methods of storage were only available for the wealthy until the late 19th century. Before then, most foods had to either be pickled (stored in vinegar), or buried in salt (meat only). These methods of preservation led to unbalanced diets, causing diseases such as heart disease, rickets and other such diseases.
Food may also be preserved by drying or canning. Drying is used for herbs and fruits. The fruit is thinly sliced and dried in a low heat for several hours. Herbs may be dried by tying in bundles and hung in a dry, warm place.
Canning (bottling) was discovered in 1809. Food is placed in a glass jar and heated in a water bath. After some time the jar is covered with a metal cap and allowed to cool. This creates a pressure seal seal which prevents contamination, the heat kills bacteria. For some products a layer of melted wax may be used to seal the jar.
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