212 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX. 
mass to remain over the period of rest until the growing time comes 
again (Fig. 47). Other kinds of food contain a large amount of 
water, and the farmer must find some means of protecting such food 
from bacterial action. This is accomplished in a variety of ways, 
but may best be considered under two heads: i. The agency of 
microorganisms in preparing the crop. 2. The methods of pro- 
tecting the crop from the attack of mischievous. organisms. To a 
certain extent the two subjects overlap, since in several cases the 
methods adopted for preserving the material furnish it with flavors 
or other characters which distinctly add to its value. 
THE ALCOHOLIC FERMENTATION. 
The fermentation of sugar into alcohol and carbonic acid is due 
to yeast. Among the various aspects of farm life there are quite a 
number based upon this type of fermentation. We have seen that 
yeasts are especially related to sugars, and that any product which 
contains much sugar is more likely to undergo alcoholic fermenta- 
tion than putrefaction. Yeasts, when dry, may remain alive for a 
long time and float around in the air. The air at all times and in 
almost all places is, therefore,, sure to contain these living yeast 
plants, ready to begin to grow and produce a fermentation whenever 
they fall into a sugar solution. These air yeasts are sometimes 
called wild yeasts in distinction from the cultivated yeasts that are 
now articles of commerce. But whether from the air or from a 
package of commercial yeast, the organisms are essentially the same 
and their action the same. 
The chief products of our farms which are liable to direct alcoholic 
fermentation are the fruit juices. Alcoholic fermentation is also 
the foundation of the gigantic distillery and brewery industries, which 
make use of grains and other farm products. But these hardly 
belong to our immediate subject. There are, however, a few forms 
of fruit-juice fermentations more or less common on our farms. 
Wines. The name wine is given to the fermented juice of 
fruits. The most common fruit used for this is the grape, whose 
juice is rich in sugar and easily pressed from a mass of the fruit, as a 
