236 THE PRESERVATION OF FOOD PRODUCTS. 



juices, jellies, jams, in short, anything preserved by sugar, are 

 liable to yeast action. Therefore, in their preservation, it is 

 to be borne in mind that we are dealing chiefly with yeasts which 

 are much more easily killed than bacteria. Sterilization of these 

 products is much easier than sterilization of proteid foods. 



By Molds and Higher Fungi. Although these are less impor- 

 tant agents in the spoiling of foods than bacteria, they are important 

 in several directions. Many kinds of food bread, cheese, etc. 

 will support a mold growth if kept rather moist. Molds grow 

 chiefly on the surface, but when they become luxuriant they cause 

 the material to become "musty" and to develop unusual as well 

 as unpleasant flavors. Almost any food might in time be completely 

 spoiled by molds, but usually the bacteria and yeasts act more 

 rapidly than the molds, so that mold action is secondary. In the 

 decay of wood and timber it is the higher fungi that play the chief 

 part (bracket fungi and other tree fungi) . They force their myceiia 

 into the trunk of the solid tree, softening it and beginning the 

 process of decay. The common molds are the primary cause of 

 the decay of fruit, for they force their myceiia through breaks 

 in the skin of the fruit and then through the whole fruit. While 

 yeasts and bacteria may sometimes be concerned in the rotting of 

 fruit the molds are almost universally the cause of this phenomenon. 



PRESERVATION OF FOODS. 



The extremely varied nature of farm products has made it 

 necessary to find many different methods of preservation, since 

 what is well adapted for one may be useless for another. The 

 method of preserving wheat, for example, is not adapted for pre- 

 serving milk or fruit. There are several fundamental methods in 

 use, each of which has numerous modifications. 



Protection from Microorganisms. If it were possible to pre- 

 vent bacteria, yeasts, and molds from gaining access to food materials, 

 *rhe food could be preserved indefinitely. But these organisms or 

 their spores are so abundant everywhere that this is impossible, 

 except by hermetical sealing. Some foods, however, are thus pro- 

 tected. Fruits have a certain amount of protection against the 



