ANALYSIS OF YEAST, 311 



for the development of spores. Thus, it was found that at 

 certain temperatures the species employed in the brewery, 

 the culture yeasts, develop their spores later than the wild 

 yeasts, several species of which occur as disease germs in the 

 brewery. It is also important to note that the structure of 

 the spores in these two groups is usuaUy different. The 

 young spore of culture yeast has a distinct wall or membrane ; 

 the contents are not homogeneous, but are granular, and exhibit 

 vacuoles. In the case of wild yeast, on the other hand, the 

 wall of the young spore is usually indistinct, the contents are 

 homogeneous and strongly refractive. It should also be added 

 that the spores of culture yeasts are usually larger than those 

 of wild yeasts. 



1. For the continuous daily control of low brewery yeast, 

 as regards contamination with wild yeast, the following very 

 convenient method is made use of : At the conclusion of the 

 primary fermentation, a small sample of the liquid is transferred 

 from the fermenting vessel to a sterilised flask; this is set 

 aside for some hours until the yeast has settled to the bottom, 

 when the sediment is transferred to a gypsum block. It is then 

 placed in a thermostat at a temperature of either 25 C. or 15 C. 



It was shown that the species of culture yeasts employed in 

 low-fermentation breweries can be divided into two groups. 

 This has subsequently been confirmed by the elaborate in- 

 vestigations of Holm and Poulsen. At 25 C., one group 

 yields spores at a later period than wild yeast, the other 

 group produces spores in about the same time as wild yeast, 

 but at a temperature of 15 C. the cells of wild yeast show 

 spore-formation much sooner than the cells of either group of 

 culture yeasts. 



The cultures maintained at 25 C. are examined after an 

 interval of forty hours, and those maintained at 15 C. after 

 an interval of three days. 



The author has shown that high brewery yeasts can be 

 analysed in a similar manner. In the case of some species, 

 however, the analysis is best made at 10- 12 C., because a 

 well-marked difference of time between the beginning of 

 spore-formation in culture yeast on the one hand and wild 

 yeast on the other can only be observed at this temperature. 



