PRESERVATION BY DRYING 141 



housewife may be confident that some device for preser- 

 vation has likely been used in their preparation. The 

 modern city is possible only because we have learned 

 methods of food preservation. 



It is of course not always possible to use all kinds of 

 food in a fresh condition, and it becomes quite necessary 

 to have some means devised for their preservation. The 

 means adopted for preservation are always to subject the 

 food to conditions unfavorable for bacteria growth. 



Drying 



Since bacteria require a considerable quantity of water 

 for their growth and multiplication, they will not develop 

 at all in foods that are even moderately dry. Molds will 

 grow upon a food that has only a small amount of water, 

 but bacteria require from 25^ to 30^6 of water in their 

 foods in order that they may grow. Molds will grow 

 upon damp floors, damp cloth, or paper, but bacteria can 

 attack these materials only when soaked with water. 



A practical application of this fact is drying, — one of 

 the most widely used methods of preserving food. This is 

 adopted by nature for the purpose of preserving many 

 food products, like corn, wheat, oats, rye, etc. Nature 

 wants to keep such seeds from decaying for some time, 

 perhaps during the winter season, in order that they may 

 be in good condition for the growth of the young seedlings 

 in the spring. To accomplish this the seed, when it ripens, 

 is deprived of its moisture, so that when fully ripe and 

 ready to be shed from the plant it has become a dry, 

 hard, tough mass, forming the grain of wheat or corn, or 



