14 FERMENTING POWER OF PURE YEASTS. 



explanation which seems most reasonable is that only weak yeasts 

 occurred in this flask of juice, and at the comparatively high tempera- 

 ture at which it was held in the culture oven other organisms grew 

 to such an extent as to prevent the completion of alcoholic fermenta- 

 tion. This is clear from the analysis, which shows that the vinegar 

 ferment was well developed at the close of the test, as 1.36 per cent 

 of acetic acid was found. 



Flask No. 2, unsterilized, but sown with a pure-yeast culture, 1 

 part to 400 of juice, nearly completed the alcoholic fermentation 

 before it was overtaken by the growth of the vinegar ferment. Flasks 

 3 and 4, sterilized and sown with pure-yeast cultures, show that alco- 

 holic fermentation ran its normal course without any occurrence of 

 acetic fermentation. 



The notes on progress of fermentation and appearance of the 

 material in each flask, are even more instructive than the analytical 

 data. The juice used in these tests was not filtered, but taken just 

 as it ran from the press, hence the notes on formation of " head" 

 and clearing of the liquor have value. A filtered must does not 

 form a " head," in the practical sense of the term. Flask No. 1 was 

 especially slow in starting, and not until forty-two hours had elapsed 

 did it show a well-defined appearance of yeast growth, while No. 2 

 showed active fermentation in eighteen hours, with " head " already 

 forming. Nos. 3 and 4 showed slight fermentation in eighteen hours; 

 No. 2 showed a well-formed " head," liquor beginning to clear in 

 forty-eight hours, while Nos. 3 and 4 showed active fermentation, 

 with only a trace of light, frothy " head." The sterilized juice in 

 flasks 3 and 4 did not take on at all the characteristic appearance of 

 the juice that had not been heated. 



After three days the liquor in flask No. 2 was a bright amber color, 

 nearly clear, with a strong sediment at bottom, and " head " com- 

 pletely formed. The high temperature, together with the strong 

 yeast sown, hastened the completion of the first, or tumultuous, fer- 

 mentation in this flask, and if the liquor could have been properly 

 drawn off at this time and finished at a lower temperature it is prob- 

 able that the acetic fermentation shown by the analysis would not 

 have developed. No. 1, after three days in the culture oven, was in 

 strong fermentation, with "head" forming, but the liquor had a 

 muddy and unpromising appearance. Nos. 3 and 4 were in strong 

 fermentation, with frothy " head;" the liquor was milky and dirty in 

 appearance. After four days' time the " head " on No. 2 was falling, 

 but the liquor was still bright amber. No. 1 showed a fairly good 

 " head " and sufficient deposit, but the liquor was far from clean and 

 unsatisfactory in color. In the case of Nos. 3 and 4 the frothy 

 " head " continued, but the liquor was not clearing. 



