PRODUCED BY ALCOHOLIC FERMENTS. 175 



out such decisive experiments is that the methods which were 

 then at their command, did not enable them to do so. 



The confused ideas which prevailed even in 1876 with 

 regard to the two great questions of pure cultivated brewery 

 yeast and the diseases of beer produced by alcoholic fer- 

 ments, are also seen from the fact that Pasteur recommended 

 the method described above (cultivation in a solution of cane 

 sugar containing a little tartaric acid) for the purification of 

 yeast. So far as it is a question of suppressing the bacteria, 

 his method is irreproachable ; but since brewery yeast, as a 

 rule, contains also wild yeast in greater or less amount, the 

 treatment with tartaric acid will, as my experiments have 

 shown, in most cases cause the suppression of the good 

 brewery yeast, whilst the development of the wild yeasts will 

 be promoted (see " What is the pure yeast of Pasteur ? " 

 Chapter II., p. 130). In order to properly judge Pasteur's 

 standpoint, it must, however, be regarded in the light of his 

 time. It can then scarcely be conceived that it was even 

 possible at that time to clearly appreciate these fundamental 

 questions. As we shall see, no further progress had been 

 made even six years later. 



A method such as that proposed by Pasteur must 

 naturally soon be found to be quite unsuitable in the brewery, 

 and in fact it was quickly given up wherever it was tried. 



Pasteur constructed a special form of apparatus (pp. 326- 

 340) for cultivating yeast, and it was also his intention to do 

 away with the open coolers in breweries, and to substitute 

 closed vessels in which the boiling wort from the hop-back 

 could be cooled and aerated without becoming infected. He 

 also constructed a suitable form of apparatus for this purpose 

 (pp. 371-378). These forms of apparatus were shortly after- 

 wards adapted by Pasteur's associate, Velten, to the practical 

 requirements of the brewery. If on this account Velten has for 

 some years appeared as the discoverer of something quite 

 new, he forgets that the principle and also the apparatus 



