312 MICRO-ORGANISMS AND FERMENTATION. 



According to the author's researches, distillers' yeast may 

 be analysed in the same way. Lower temperatures are to 

 be preferred for this analysis. Often, however, the investi- 

 gation into the construction of the spore in the selected yeast- 

 type must form the chief part of the analysis, the difference 

 of time for spore-formation in culture yeast and wild yeast 

 frequently proving inadequate. 



Aderhold has established the fact that wine yeast, like beer 

 yeast, may be analysed by Hansen's method. 



By means of experiments undertaken to determine to what 

 extent Hansen's analytical method can 1 be relied on for tech- 

 nical purposes in low-fermentation breweries, Holm and 

 Poulsen concluded that a very small admixture of wild yeast, 

 about ^ihyth of the entire mass (Carlsberg bottom -yeast 

 No. 1), can be detected with certainty. Hansen's previous 

 researches had shown that when the two species, Sacch. Pas- 

 torianus III. and Sacch. ellipsoideus II. which are capable 

 of producing yeast-turbidity in beer are present to the 

 extent of only 1 part in 41 of the pitching yeast, the disease 

 is not developed, provided that the normal conditions of 

 fermentation and storage have been maintained. Further, 

 Sacch. Pastorianus I., which imparts to beer a disagreeable 

 odour and an unpleasant bitter taste,, can scarcely exert 

 its injurious influence under the same conditions when the 

 admixture of this yeast amounts to less than 1 part in 22 of 

 the pitching yeast. Consequently, Hansen's method for the 

 analysis of yeast by means of ascospore formation is sufficient 

 to establish its purity.* 



When the object of the analysis is to characterise the 

 different species present in the sample with greater accuracy, 

 a number of cells are isolated by fractionation, and each of the 

 growths obtained is separately examined. 



In an investigation of bottom yeast in the different stages 



* It is obvious that such an analysis from the vat does not enable direct 

 conclusions to be drawn regarding the predominant biological conditions existing 

 during secondary fermentation in the cask. If, for instance, the beer is run off 

 with a very small quantity of yeast, even if the infection is a small one, the wild 

 yeast will chiefly be found floating in the liquid, and will be carried over into the 

 cask, whilst the greater part of the culture yeasts will have sunk to the bottom 

 of the vat. 



