150 WHAT IS THE PURE YEAST OF PASTEUR? 



methods. It would, therefore, be an error to assume that by 

 substituting another antiseptic for tar tar ic acid, as, for example, 

 carbolic acid, salicylic acid, hydrofluoric acid, &c., it would be 

 possible to destroy not only all bacteria present, but likewise all 

 the species of wild yeasts, so that only the desired species or 

 race of culture yeast would remain, freed from all competing 

 organisms. Such a universal remedy does not exist. It 

 must also be remembered that even if we have got rid of 

 the bacteria and wild yeasts, we are still far from having 

 attained the desired pure culture. There are, namely, a 

 large number of species of good beer yeasts, both high and 

 low, and many of these, although widely different in other 

 respects, exhibit the same behaviour towards antiseptics. 

 The conditions are further complicated owing to the fact 

 that cells belonging to one and the same species may behave 

 differently under the same treatment according to their 

 varying conditions, according to whether they are young or 

 old, well or ill nourished, &c. It is also by no means a 

 matter of indifference whether the pitching yeast consists 

 only of the desired species, or whether this is mixed with 

 other brewery yeasts ; this is shown by the fact that species 

 of culture yeasts, each of which when used alone gives a 

 good beer, may under certain conditions produce disease 

 when mixed (see following chapter). In short, certainty 

 cannot be attained in the manner mentioned above ; it is, 

 in fact, necessary to start from the single cell and from this 

 to prepare the absolutely pure culture. 



It is a known fact that an addition of tartaric acid retards 

 the development of most species of bacteria which occur in 

 pitching yeast and in wort ; from what has been stated above, 

 it will be seen how dangerous this remedy may become. 

 When it is proposed to employ it in breweries, it is, therefore, 

 advisable to add it in only small quantities, and, indeed, to 

 use it with caution. Good breweries are conducted even at 



