162 0. A. WATK1NS ON YEAST AND OTHER FERMENTS. 



same material as the cellular tissue of other vegetables— in the 

 interior of which is a highly complex gelatinous substance allied to 



albumen. 



The appearance of Yeast under the microscope varies con- 

 siderably with its condition ; when at rest, that is, when fermenta- 

 tion is arrested, its form varies from globular to ovoid, frequently 

 with an uneven outline, as if the cells were very partially empty ; 

 but when they are put into a fresh solution of sugar they swell out, 

 and during active fermentation appear globular or nearly so, and 

 more transparent than before. 



When Yeast is added to brewer's wort it increases rapidly, and 

 grows to six or eight times its original quantity during fermenta- 

 tion ; the wort being a solution which contains in abundance the 

 elements required for its development, namely, grape sugar and 

 some albuminous substances derived from the malt and hops. 



During fermentation these albuminous matters disappear from 

 the solution in proportion to the development of the Yeast, and the 

 sugar also disappears in the same ratio. When the fermentation 

 is complete, we find that in place of the complex albuminous 

 matters in the wort we have simpler chemical combinations, such as 

 salts of ammonia, and in place of the sugar we have alcohol. These 

 chemical changes take place simultaneously ; but with this impor- 

 tant difference, that the amount of nitrogen in the original wort is 

 reduced by about one-half, while the alcohol and carbonic acid 

 nearly correspond to the weight of the sugar, the remainder being 

 converted into lactic acid, &c, a small quantity of which is always 

 formed during vinous fermentation. But the Yeast consisting 

 almost entirely of albuminous matters, and having increased to 

 several times its original quantity, fully accounts for the disappear- 

 ance of so large a proportion of the nitrogen from the wort. 



Thus it will be easily understood, that Yeast, in order to grow, 

 must be supplied with some soluble azotised matter, such as 

 albumen ; and it is as easily proved that it will not grow without. 



To ferment 100 parts of sugar, one part of yeast is required ; 

 when the fermentation is complete, the yeast is exhausted, and in 

 its place ammoniacal salts and cellulin are found. As the vinous 

 fermentation takes place only during the growth of the yeast, it 

 may be said that it will grow in simple saccharine solutions. In a 

 certain sense this is correct, but such growth is degenerate and ex- 

 haustive, and not the healthy growth which increases and multi- 



