342 MICRO-ORGANISMS AND FERMENTATION. 



(b) Distillery and Pressed Yeasts. 



To solve the problem whether distillery and pressed yeasts 

 are capable of forming endogenous spores, a possibility denied 

 by Wiesner and Brefeld, the author, in 1884, undertook an 

 exact examination of a number of samples of such yeasts, 

 and in the same year, together with Hansen, published the 

 results in Dingler's Polytechnic Journal, showing that there ia 

 no possible difficulty in obtaining an abundant and rapid 

 spore-formation from these species. At the same time the 

 author was able to arrive at certain conclusions regarding the 

 composition of such yeast. By the help of fractional cultures, 

 it was found that both top and bottom fermentation species 

 occur in ordinary distillery and pressed yeast. Further 

 investigations showed that in one and the same mass of yeast 

 two morphologically different types may frequently occur, 

 one chiefly giving isolated cells in a fully-developed state, the 

 other, budding colonies of many cells. It was impossible, 

 therefore, to trace any connection between this and the fer- 

 mentation phenomena brought about by the two species. 

 The two morphological types remain unaltered after being 

 preserved for years. 



Detailed researches further showed that both pressed yeast 

 and the top yeast used in distilleries include a multitude of 

 clearly distinguishable types, and a few years later pure 

 selected races from the author's laboratory were first intro- 

 duced into yeast factories, and then into the distilleries of 

 Northern Europe and into Molasses factories. 



Owing to the physiological state of the species, due to the 

 dissimilar composition of the nutritive fluids, very important 

 differences are exhibited with respect to propagating power, 

 yield of alcohol, character of the alcohol, etc. These are 

 retained throughout many years, so that it is necessary 

 in many cases to instal an absolutely pure culture of a 

 suitable yeast in each individual factory. By expert applica- 

 tion of such cultures, and particularly by a rational lactic 

 acidification, which arrests the development of foreign organ- 

 isms found in the mash, it is possible to secure a higher yield 

 and a better quality both of alcohol and of yeast. Rayman. 



