134 MICRO-ORGANISMS AND FERMENTATION. 



By means of these experiments Hansen has adduced an 

 important character for the determination of the Saccha.ro- 

 mycetes. 



A new distinctive characteristic for the species has been 

 discovered by the same author in the different anatomical 

 structure of ike spores. Both these characters and others 

 which are described in the following pages (e.g., film formation, 

 etc.,) must necessarily be considered in a complete examination 

 of a Saccharomyces species. 



The method given below for the analysis of low breivery- 

 yeast from, a practical standpoint was based by Hansen on 

 certain observations of the temperature curves for the 

 development of spores and on the structure of the spores. 

 Thus it was found that at certain temperatures the species 

 employed in the brewery, the so-called cultivated yeasts, 

 develop their spores later than the so-called wild yeasts, 

 several species of which also occur as disease-germs in the 

 brewery. Hansen also found that the structure of the spores 

 in these two groups is generally different, in that the young 

 spore of a cultivated yeast has a distinct wall or membrane, and 

 the contents are not homogeneous, are granular, and exhibit 

 vacuoles ; in the case of wild yeast, on the other hand, the 

 wall of the young spore is most frequently indistinct and the 

 contents are homogeneous and strongly refract light. It 

 should also be added that the spores of cultivated yeasts are 

 usually larger than those of wild yeasts. 



1. For the continual, daily control of brewery-yeast as 

 regards contamination with wild species, the following very 

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

 primary fermentation, a small quantity of the fermenting 

 liquid is removed from the fermenting-vessel in a sterilised 

 flask ; this is set aside for some hours until the yeast has 

 settled to the bottom, and the sediment is then spread upon 

 a gypsum block in the manner described on page 126. This is 

 then introduced into a thermostat maintained at a tempera- 

 ture of 25 C. or 15 C. 



