8 



FERMENTING POWER OF PURE YEASTS. 



pure yeast has been isolated it is necessary to subject it to scientific 

 and practical tests. The measurement of the yeast's activity as a 

 chemical reagent in breaking down sugars in solution has been the 

 scientific test used. This test is so devised as to obtain a direct time 

 measure of the fermenting power of the yeast and to determine the 

 products resulting from its growth in the liquor fermented. Only 

 those yeasts which have been isolated in accordance with correct 

 technique and have shown good characteristics, such as vigor, bright- 

 ness of resultant liquor, etc., and thus warrant further investigation, 



are subjected to the chemical 

 test in culture flasks. 



CULTURE FLASK. 



This test is accomplished by 

 sowing the yeast cultures into 

 flasks so prepared that the 

 growth activities of the yeast 

 may be observed, the loss of 

 carbon dioxid estimated, and, 

 after fermentation is com- 

 pleted, the resultant products 

 determined by analysis with- 

 out complication of the results 

 by the growth of other organ- 

 isms. A flask prepared for 

 this work is shown in fig. 1. 

 It consists ordinarily of a 

 stout, clear bottle, or of an 

 Erlenmeyer flask of 800 cc 

 capacity. In this flask are 

 placed 400 cc of a filtered 

 must or other prepared cul- 

 ture medium, the composition 

 of which has been determined 

 by analysis. The flask or bot- 

 tle is then stoppered with a 

 I M if orated rubber stopper, through which is fitted the ventilating 

 tube, shown in fig. 2. The stem of the tube, inserted through the 

 stopper, should not extend down near the liquor, as when fermenta- 

 tion is active the slightest agitation will tend to throw the foam 

 through the ventilating tube and the test will be lost. The outer end 

 of the tube is curved down onto the neck of the bottle or flask and 

 carries a control apparatus consisting of a flask-like enlargement <>f 

 the tube, with a small inner tube which dips down into the control 

 liquid contained in the enlarged outer portion of the ventilating 



Fio. 1. Culture flask for fermentation tests. 



