PRODUCED BY ALCOHOLIC FERMENTS. 169 



organisms which induce different kinds of fermentation, 

 alcoholic, lactic, acetic, butyric, &c. Therefore, if it is desired 

 to bring about a pure alcoholic fermentation, free from the 

 formation of objectionable acids it is evidently necessary to 

 keep out those micro-organisms which produce these acid 

 fermentations. Pasteur drew this conclusion, and first made 

 use of its application to wine.* 



It was known long ago that wine is subject to different 

 changes, which may seriously affect both its taste and its 

 appearance ; for instance, it may become sour, bitter, viscous, 

 cloudy, &c. It was Pasteur, however, who first discovered 

 the causes of these disagreeable changes (diseases} ; he 

 showed, namely, that they were produced by different bac- 

 teria. As a remedy for such diseases, he recommended the 

 employment of heat in accordance with the method of 

 Scheele and Appert already described. This must, of course, 

 be carried out at an early stage of the disease, before the 

 bacteria have been able to develop to any considerable 

 extent ; when the wine is once spoilt, it is of no avail to kill 

 the disease germs. 



As regards the alcoholic fermentation of wine, Pasteur 

 considered that, on account of the favourable composition of 

 the grape juice, it can, without danger, be left to the yeast 

 fungi which happen to be present on the surface of the grapes 

 and in the air. Subsequently he also gave expression to this 

 view in his work, ' Etudes sur la biere,' p. 4. 



In his book on the alcoholic ferments,f Reess gives a 

 systematic description of various yeast forms, and he starts 

 with the view that the form and size of the cells, taken alone, 

 constitute specific characters. The large oval yeast cells are, 

 accordingly, classed as Saccharomyces cerevisice, the smaller 

 oval cells as Sacch. ellipsoideus, the sausage-shaped cells as 

 Sacch. Pastorianus, and so forth. As will be recollected from 



* Pasteur, ' Etudes sur le vin,' Paris, 1866. 



t Rcess, ' Botanische Untersuchungen ubcr die Alkoholgarungspilze,' 1870. 



