254 THE PRESERVATION OF FOOD PRODUCTS 
are not specially liable to bacterial action. All such substances 
as fruit 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 impor- 
tant in several directions. Manykinds 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 com- 
pletely 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 
mycelia 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 mycelia 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 Jit 
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 Microtrganisms.—If it were possible to pre- 
vent bacteria, yeasts, and molds from gaining access to food ma- 
