FRUITS AND THEIR COMPOSITION. 313 



bodies contained in fruit. It consists of one of the lowest members 

 of the vegetable kingdom (Torula cerevisice), and under the micro- 

 scope is seen to be made up of little oval transparent globules, 

 having a diameter of not more than 0.1 millimetre and often 

 adhering in clusters and strings. They are propagated by bud- 

 ding, and die as soon as they have reached their highest state 

 of development. In contact with air and water yeast soon un- 

 dergoes putrefaction. 



The chief products of vinous fermentation are alcohol and car- 

 bon dioxide ; a small quantity of sugar is at the same time con- 

 verted into other products, about 2.5 per cent, being transformed 

 into glycerin and 0.6 to 0.7 per cent, into succinic acid. A 

 further portion of the sugar, about one per cent., is assimilated in 

 the form of cellulose by the yeast and separated. By the simul- 

 taneous formation of these different secondary products about 

 5.5 to 6.5 per cent, of sugar is lost in the formation of alcohol. 

 As they are not always formed in equally large quantity no con- 

 clusion can be arrived at from the content of sugar in the must as 

 to the quantity of alcohol corresponding to theory in the finished 

 wine ; it is, as a rule, supposed that the sugar yields one : half its 

 weight of alcohol, which is sufficiently correct for all practical pur- 

 poses. 



Absolute alcohol, L e., alcohol entirely free from water, is a very 

 mobile fluid, clear as water and almost odorless ; it boils at 173 F., 

 and when it is cooled down to 148 F. it becomes viscid, but 

 does not solidify. Its specific gravity at 32 F. is 0.80625, and 

 at 59 F. 0.79367. It is very inflammable, and burns with a 

 blue, non-luminous flame. It absorbs moisture with great avidity, 

 and is miscible with water in all proportions, the mixture evolv- 

 ing heat and undergoing contraction. 



The methods for determining the content of alcohol in a fluid 

 have already been given on p. 198. 



Succinic acid. No accurate researches have as yet been made 

 in regard to the quantity of this acid in wine, its influence upon 

 the quality of the wine, and the conditions under which more or 

 less of it is formed during fermentation. According to Pasteur, 

 the more succinic acid is formed the slower fermentation pro- 

 gresses; the weaker the development of yeast and the less nour- 



