312 VINEGAR, CIDER, AND FRUIT-WINES. 



is advisable to use an alcoholic extract of grape-stones, which are 

 uncommonly rich in tannin. 



Inorganic constituents. The inorganic constituents of the dif- 

 ferent varieties of fruit are very likely the same, namely, potash, 

 lime, magnesia, sulphuric and phosphoric acids; they vary only 

 in the proportions towards one another and in the total quantity 

 of all the substances. Moreover, their quantity is too small to 

 exert an influence upon the quantity of the wine to be produced, 

 being of interest only in regard to the exhaustion of the soil. 

 Though lime and sulphuric acid in sufficient quantity occur 

 almost everywhere in the soil, this cannot be said of potash and 

 phosphoric acid. Unfortunately there are no accurate statements 

 regarding the amount of these substances which is withdrawn 

 from the soil by the crop of one year, but there can be no doubt 

 that it is very large, and that consequently fruit-trees from time to 

 time require a certain amount of manure in order to return to the 

 soil what has been taken from it. 



Fermentation. Fermentation is a chemical process which is 

 always caused by the presence of a ferment or a substance in a 

 peculiar state of decomposition. Although to induce fermentation 

 the presence of a ferment is necessary, it does not take part in the 

 decomposition of the fermenting substance. The products of fer- 

 mentation vary according to the nature of the fermenting body, 

 as well as according to the nature of the ferment. Each peculiar 

 kind of fermentation requires a certain temperature, and it is 

 nearly always accompanied by the development of certain living 

 bodies (infusoria or fungi). 



When yeast is added to a dilute solution of dextrose or another 

 glucose, vinous fermentation speedily sets in; whilst a solution of 

 cane-sugar undergoes fermentation but slowly, the cause being 

 that this sugar must first be converted into inverted sugar before 

 fermentation can commence. Vinous fermentation proceeds most 

 rapidly at 77 to 86 F., and does not take place below 32 or 

 above 95 F. The presence of a large quantity of acids or alkalies 

 prevents fermentation, while if the liquid has a faint acid reaction, 

 fermentation proceeds best. 



The yeast which is formed in the fermentation of the juice of 

 grape and other kinds of fruit is produced from soluble albuminous 



