The use of ice to refrigerate and thus preserve food goes back to prehistoric times.Through the ages, the seasonal harvesting of snow and ice was a regular practice of most of the ancient cultures: Chinese, Greeks, Romans, Persians. Ice and snow were stored in caves or dugouts lined with straw or other insulating materials. The Persians stored ice in a pit called a yakhchal. Rationing of the ice allowed the preservation of foods over the warm periods. This practice worked well through the centuries, with icehouses remaining in use into the 20th century. In the 16th century, the discovery of chemical refrigeration was one of the first steps toward artificial means of refrigeration. Sodium nitrate or potassium nitrate, when added to water, lowered the water temperature and created a sort of refrigeration bath for cooling substances. In Italy, such a solution was used to chill wine and cakes. (责任编辑:admin) |