1 86 "DISEASES" OF BEER, 



afflicted. The beer at the first-named brewery was attacked 

 by the disease known as yeast turbidity, whilst in the case 

 of the latter brewery, the beer acquired a disagreeable odour 

 and an objectionable bitter taste. Since it was not possible 

 to discover any fault either in the wort or in the fermentation, 

 I had to assume that these objectionable effects were caused 

 by micro-organisms. Tests made with Pasteur's method for 

 the purification of yeast, proved of no avail. By comparing 

 all my observations I arrived at the opinion that the cause 

 of the disease must, without doubt, be sought in the pitching 

 yeast. Although a microscopic examination revealed no 

 foreign organisms in the yeast except a few bacteria, I 

 nevertheless started with the idea that yeast cells which 

 were to all appearance similar, might yet belong to several 

 species, and that some of these might have caused the 

 diseases. The method, therefore, to be adopted was to split 

 up the brewery yeast into its constituents, to prepare a large 

 number of pure cultures of them, and, finally, to carry out 

 fermentation experiments partly with each species separately 

 and partly with mixtures, and in such a manner that the 

 conditions would correspond with those obtaining in the 

 brewery. If the opinion with which I started was correct, 

 I should in this way find out which of my pure cultures 

 contained good brewery yeast, and which of them contained 

 disease yeast. An investigation of this kind can, at the 

 present time, be carried out with comparative ease in any 

 zymotechnic laboratory ; at that time, however, there were 

 difficulties to be overcome. Since then the technique in 

 this field especially has been developed in a high degree. 



The experiments showed that the diseases mentioned 

 were caused by species of yeast which were quite different 

 from the preponderating culture yeasts present in the pitching 

 yeast of the two breweries, and that each of the latter when 

 employed alone gave a good beer. As will be shown in the 

 following pages, the number of species capable of producing 



