10 FERMENTING POWER OF PURE YEASTS. 



or smaller quantity of the organism introduced into the bottle or 

 flask. Also it is equally important to sow only from cultures in 

 active growth, otherwise the promptness with which fermentation 

 follows may be very much influenced and unreliable results obtained. 

 Ordinarily, yeast cultures in 10 cc of liquid culture medium in test 

 tubes will be ready to use in three days and will remain strong for ten 

 days. While the yeast in these tube cultures remains alive for 

 many months, cultures from three to ten days old are necessary for 

 the tests under consideration. 



When all is ready for the test of the chemical activity of the 

 yeast, the bottle or flask is sown with a drop of the fluid culture 

 taken direct from a tube in fermentation. The flask is then carefully 

 closed and waxed over the stopper about the opening, so as to prevent 

 the entrance or escape of air or gas except through the control appa- 

 ratus. For this purpose warm paraffin wax is very serviceable and is 

 cleaner to handle than prepared wax. Ordinarily, a number of organ- 

 isms will be sown in separate flasks to be tested at the same time, or 

 the same organism may be tested in various musts and artificial sac- 

 charine solutions. The flasks designated for comparison should all 

 be kept together in a culture oven at a temperature varying from 20 

 to 25 C., as this is thought to be the best range of temperature for 

 yeast organisms. 



Each flask should be labeled as sown. A record of the yeast sown 

 and the medium used in each bottle is kept for identification. Each 

 bottle or flask is weighed as soon as sown, then once each day at the 

 -a me hour each flask is reweighed and these data are entered in the 

 records. The form of record prepared for use in this laboratory (see 

 p. 11) gives the history of the test and the daily weights, the daily 

 loss caused by the escape of gas from the fermenting substance, ;md 

 the temperature readings, together with analyses, etc. Such a record 

 comprises the biological and chemical data of the test, and, in connec- 

 tion with the critical notes giving the appearance of the liquor, the 

 characteristics of the foam and of the bouquet or odor, taken as the 

 gas escapes, the subsidence of the deposit, and other memoranda, fur- 

 nishes a basis for judging of the value of a yeast. Upon these data, 

 if obtained under proper conditions, one may base a conclusion as to 

 whether any particular yeast promises to be valuable for practical 

 work. Such tests <!<> not, however, settle the question. In fact, the 

 value of a yeast for vinous fermentation is not conclusively estab- 

 lished until it has been used in normal must, in regular cellar work. 

 on a sufficiently large scale to give practical results. This chemical 

 test is most essential, however, and should precede the practical test 

 if definite results are to be obtained. 



Many yeasts produce quite similar amounts of alcohol when sown 

 in the same must and leave liquors when fermentation is complete, 



