156 BACTERIA, YEASTS, AND MOLDS 



of the water from the leaves lowers the temperature. In 

 warm climates this principle is made use of to cool drinks 

 by keeping them in earthenware receptacles the surfaces 

 of which are constantly moistened. The evaporation of 

 the water on the outside cools- the inclosed liquids. 



Cooling may be used for any kind of food. Three 

 general rules should always be followed where food is 

 put aside for preservation at a low temperature. 



1 . Cool the food as quickly as possible. This should 

 be done before covering and setting aside for keeping. 



2. Use every possible device for avoiding moisture. 



3. Use food quickly after taking it from its place of 

 storing, for such food when warmed decays rapidly. 



The Use of Heat 



The easy destruction of bacteria by heat suggests a 

 means for increasing the keeping properties of many 

 foods. Liquid foods may first be boiled and then cooled 

 as quickly as possible, after which they may be put away 

 in cold places for preservation. It is necessary that the 

 material should actually be boiled, since a lower tempera- 

 ture is not only useless but frequently detrimental. If a 

 putrescible material is simply steeped in warm water and 

 then put away, it will spoil rapidly ; if it is boiled it may 

 be preserved for some time. Boiling is useful for such 

 materials as soups, stews, or any liquid not injured by 

 boiling. It must be remembered, however, that boiling 

 will not preserve the material indefinitely ; it simply delays 

 the spoiling. 



