SYSTEMATICALLY SELECTED YEASTS. 21 



An objection which has been frequently raised against my 

 efforts is the following: A pure culture was introduced by 

 way of trial into a brewery at a time when all went well with 

 the old impure yeast, and a careful comparison was made 

 between the beers obtained with the two sorts of yeast. As 

 a result it was found that nothing had been gained by the 

 employment of the new yeast. Why not continue then with 

 the old method ? By all means if it really were a method ; 

 but this is exactly what is wanting. It affords brewers no 

 certainty, but exposes them to great variations and to un- 

 known dangers. The only novelty which pure yeast introduces 

 is certainty and rational working. It is a complete mistake 

 to imagine that a better product will result than the brewer 

 can obtain under the most favourable circumstances with his 

 old impure yeast. When the pure yeast has been properly 

 selected, the latter is the result which it gives, and, contrary 

 to the impure yeast, it gives it always, provided it is always 

 cultivated under the same conditions. 



One and the same yeast does not suit all breweries. As 

 was previously mentioned, it has been found, namely, not only 

 that there are several species or races of culture yeast, but 

 also that these give beers dissimilar in their character, in 

 their stability and in their flavour, and which also behave 

 differently in the fermenting and lager cellars. Every brewer 

 therefore must select, according to a definite plan, a species which 

 suits his brewery, and one of the most essential advances which 

 my investigations have brought about is that this can now be 

 carried out with certainty. That there are species which are 

 suitable for a large number of breweries has already been 

 shown by experience. Such species are especially adapted 

 for preservation as stock forms in zymotechnic laboratories. 

 It would be going too far, should it come about that every 

 brewery wished to have its own species of yeast. At the 

 present time there is a tendency in this direction, and my 

 object therefore is to warn against this. 



