Nowadays most foods are dried mechanically; the conventional method of such dehydration is to put food in chambers through which hot air is blown at temperatures of about 110oC at entry to about 45oC at exit. This is the usual method for drying such things as vegetables, minced meat, and fish.

      Liquids such as milk, coffee, tea, soups and eggs may be dried by pouring them over a heated horizontal steel cylinder or by spraying them into a chamber through which a current of hot air passes. In the first case, the dried material is scraped off the roller as a thin film which is then broken up into small, though still relatively coarse flakes. In the second process it falls to the bottom of the chamber as a fine powder. Where recognizable pieces of meat and vegetables are required, as in soup, the ingredients are dried separately and then mixed.

      Dried foods take up less room and weigh less than the same food packed in cans or frozen, and they do not need to be stored in special conditions. For these reasons they are invaluable to climbers, explorers and soldiers in battle, who have little storage space. They are also popular with housewives because it takes so little time to cook them.

The word “they” in paragraph 5 refers to _______________.

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