PURE YEAST AND BREWING OPERATIONS. 291 



known to be in the main a mixture of different races of 

 yeast. 



The employment of single race yeast in high fermenta- 

 tion breweries advanced more rapidly abroad than in this 

 country, and the Hansen system soon gained some pro- 

 minent advocates in this branch of the brewing- industry. 

 In this country, on the other hand, brewers have been slow 

 to benefit by Hansen's investigations and it is only in very 

 few breweries that a fair trial of pure single race yeast has 

 been made. An argument that is frequently urged against 

 the application of the Hansen system in high fermentation 

 breweries is that ordinary brewers' yeast contains different 

 races, certain of which bring about the principal or primary 

 fermentation, whilst others induce the secondary or cask 

 fermentation, and that a single species of yeast is incapable 

 of exercising this double function. 



It is contended, and no doubt with truth, that the suc- 

 cess of single race yeast in low fermentation brewing cannot 

 be regarded as in any way proving that single race yeast is 

 capable of giving equally good results in high fermentation 

 breweries. In the first case the fermentation is carried out 

 at a very low temperature and the beer is also stored at a 

 low temperature, and under these conditions sufficient car- 

 bonic acid gas will be retained to render the beer brisk. 

 In the case of high fermentation, on the other hand, much 

 higher temperatures prevail and a true cask fermentation 

 becomes absolutely necessary. Otherwise the beer will 

 be flat and will be in a condition in which it is very readily 

 attacked by bacteria and wild yeasts, which can never be 

 absolutely excluded under the present conditions of brewing. 

 It is clear, therefore, that the question of the application of 

 Hansen's system to high fermentation brewing must be 

 considered as distinct from that of its employment in lager 

 beer brewing. 



With regard to the actual evidence for and against the 

 use of single race yeast in English breweries it will be seen, 

 from what has been stated above, that the facts which have 

 been established can refer only to a very limited number of 

 breweries. 



