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 



