METHODS OF STUDYING THE YEASTS 



163 



Klocker's Method for Estimating Alcohol in Fermented Solutions: 

 Klocker l has modified the Pasteur drop reaction for the determina- 

 tion of alcohol in fermented solutions and claims to be able to deter- 

 mine the presence of alcohol in 0.002 per cent by volume. Five cubic 

 centimeters of the solution are used in a vessel 180 mm. long and 24 

 mm. in diameter. The solution is slowly 

 warmed over a wire gauze by means of a 

 gas flame taking care to prevent bumping. 

 Characteristic oil drops accumulate in the 

 glass tubing, higher up or lower, depending 

 on the concentration of alcohol. By this 

 method it was demonstrated that small 

 amounts of alcohol were formed in yeast 

 water on standing. Other substances, such 

 as acetone, may give the reaction but it is 

 necessary that they be present in large 

 amounts. As a control iodoform may be 

 formed by the following method: A small 

 amount of sodium carbonate (2 grams per 

 10 c.c. of product) and iodine (0.1 gm.) may 

 be added and the temperature brought to 

 60 C. until the iodine has disappeared. On 

 cooling, crystals of iodoform will be formed 

 which may be examined under the micro- 

 scope. 



Determination of Efficiency of Yeast : It 

 is often convenient to have information con- 

 cerning the efficiency of yeasts especially if 

 it is necessary to select, from among a 

 number of these organisms, one which will 

 cause the maximum amount of change in the 

 shortest time. Different methods may be 

 used. Any of the products of fermentation ^atus for ~L 



in 



Presence of Alcohol 



may be measured quantitatively. The alcohol 



may be determined at any time during the 



process of the fermentation but has this disadvantage that consider- 



able time would be used if many determinations were necessary. 



Probably the most convenient method which has been devised is to 



measure the amount of carbon dioxide which is formed and from this 



to determine the extent of the fermentation. 



This may be carried out either volumetrically or gravimetrically. 



1 Klocker, A. The determination of traces of alcohol in fermenting solutions. 

 Cent. Bakt. Abt. II, 31, 108-111; Chem. Absts. 6 (1912), 136. 



