12 PURE CULTURES OF 



solution. According to Pasteur's experiments, it was the 

 bacteria which gave rise to the diseases of beer, and he 

 accordingly commenced experiments on the purification of 

 yeast. Of the various means which he made use of for this 

 purpose, he and his associates, Duclaux and Velten especially, 

 recommended treatment with a solution of cane sugar to 

 which a little tartaric acid had been added. There was thus 

 no question here of a true pure culture, but merely a supres- 

 sion of the bacteria present in the yeast. My experiments 

 have shown, however, that this method is unsuitable for the 

 purification of brewery yeast, as it favours the development of 

 the disease yeasts. The result attained is thus the opposite of 

 what was desired (see p. 130). That Pasteur should recom- 

 mend such a method is readily explained, for at that time 

 there was no evidence as to what a good brewery yeast and 

 what a disease yeast is. Under these circumstances it is 

 evident that his method could not secure an introduction 

 into practice. 



Several writers before Pasteur often expressed the opinion 

 that there are different species and varieties of yeast which 

 produce different fermentations and impart different characters 

 to the beer. Similar views occur in the writings of the earlier 

 zymotechnologists, e.g. Bail in 1857. The most common 

 view was that the brewery yeast could rapidly change its 

 character, and even merely through employment in different 

 breweries ; some, indeed, even stated that it could change into 

 mucor yeast and into a number of mould forms. Another 

 view, advocated especially by Reess in 1870, was that the 

 yeasts have a very limited sphere of development, and in 

 accordance with this, species were named merely from the 

 form of the cells : the sausage-shaped cells being named Sacch. 

 Pastorianus, the small oval cells, Sacch. ellipsoideus, and the 

 larger oval cells, Sacch. cerevisice, &c. We now know, however, 

 that this view is also quite incorrect, and that Reess's system 

 has no true basis. In short, opinions were thrown out in all 



