240 PHYSIOLOGY OF BACTERIA 



temperature of fermentation was 24°C. at the start, and gradually 

 increased to about 31°C. The acidity of the solution was kept at 

 pH 4.8 to 5.2, and was allowed to increase towards the end of the fer- 

 mentation to pH 5.5 to 5.8; if necessary, it was regulated by H2SO4 

 or Na2C03. 



The wort was allowed to run slowly into the container filling it 

 in five to seven hours, as is the custom in plant procedure. Acid 

 calcium phosphate is added to molasses at the rate of 2.0 gm. 

 P2O5 per 100 gm. sugar; the molasses is diluted, heated to 85°C., 

 acidified with H2SO4, and filtered. Malt sprouts are extracted with 

 hot water. Peanut meal is heated with dilute H2SO4 until about 

 90 % of the nitrogen has become soluble. 



In order to offer equal quantities of assimilable nitrogen, the 

 following assumptions, based upon long experience, were made: 

 Molasses: 0.7-0.8% of the molasses weight is assimilable N. 

 Peanut meal extract: 65-70% of the soluble nitrogen is assimilable N. 

 Malt sprout extract : 65-70 % of the soluble nitrogen is assimilable N. 

 Ammonia, asparagin, urea etc: 100% assimilable. 

 When sucrose was offered in place of molasses, K2SO4 and MgS04 

 were added in appropriate amounts. 



The washed yeast and the wort were analyzed at the end of the 

 experiment, and the yeast was tested for its fermenting capacity 

 because all these experiments aimed at the production of a good 

 bakers' yeast. The volume of CO2 produced by 10 gm. of yeast was 

 determined as described on p. 104, and the time which 5 gm. of yeast 

 required to raise a standard flour dough to a standard volume was 

 measured. The keeping quality was tested by observing the time 

 required for the yeast to soften in a 35°C. incubator. 



In all these experiments, the substrate, i.e., the sugar, 

 is limited, and is used up completely during the nine to 

 twelve hours of the experiment, the initial concentration 

 varying between 1 . 5 and 2.5%. The biochemical problem 

 is then to explain why yeast, with the same energy 

 supply, will give different crops with different building 

 materials. 



The crops vary considerably. The first six experi- 

 ments contain the same amounts of assimilable nitrogen 

 in the wort, 2.4 gm. from molasses and 2.5 gm. from 



