ALCOHOLIC FERMENTS. 135 



It was found namely and it has been subsequently con- 

 firmed by the elaborate investigations of Holm and Poulsen 

 that the species of cultivated yeasts employed in low-ferment- 

 ation breweries can be divided into two groups. One group 

 yields spores later than wild yeast when a temperature of 

 25 C. is maintained ; the other group, on the contrary, gives 

 spores in about the same time as wild yeast at the above 

 temperature, but at a temperature of 15 C. the cells of wild 

 yeast show spore-formation considerably sooner than the cells 

 of these cultivated yeasts. 



The cultures maintained at 25 C. are examined after an 

 interval of 40 hours, and those maintained at 15 C. after an 

 interval of three days. 



Experiments of my own show that high breiuery-y easts can 

 be analysed in a similar manner. 



By means of experiments which were undertaken with the 

 view to determine to what extent Hansen's analytical method 

 can be relied on for technical purposes, Holm and Poulsen 

 came to the conclusion that a very small admixture of wild 

 yeast, about \-2QOth of the entire mass (Carlsberg bottom- 

 yeast No. L), can be detected with certainty in this manner. 

 Hansen's previous researches had shown that when, for in- 

 stance, the two species, Sacch. Pastorianus III. and Sacch. 

 ellipsoideus //., 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, that Sacch. Pastorianus 7., which 

 imparts to beer a disagreeable odour and an unpleasant bitter 

 taste, can, under the same conditions, scarcely exert its 

 injurious influence 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 gives ample information as to the 

 presence of these disease ferments. 



This method likewise possesses the advantage that the 



