SPECIFIC GRAVITY AND FERMENTATION. 



89 



ing liquor. However, these readings can not be implicitly relied upon 

 because of the variable quantity of nonfermentable solids. No one 

 lias yet been able to devise a method by which gravity determinations 

 can be made to indicate composition with chemical accuracy, but the 

 table published on page 89 of Bulletin 71, Bureau of Chemistry, seems 

 to come within such reasonable bounds of accuracy that it may be 

 used as a guide in the fermentation room. 



With a view to illustrating the use of this cellar table all the 

 hydrometer readings taken during fermentation of the ciders made at 

 this station, the chemical analyses made at the several stages of fermen- 

 tation, and the approximate percentages of sugar and alcohol deter- 

 mined theoretically, have been arranged in parallel columns in Table 

 VII. In those instances where only a hydrometer reading is given 

 there is of course no comparison, but where alcohol and sugar deter- 

 minations were made the comparison is direct and interesting. In a 

 considerable number of instances. the calculated or approximate per- 

 centages are close indeed to those actualh T determined by analysis, but 

 in several instances they are wide apart. The peculiarities of yeast 

 races has to do with this matter, as we have definitely proved that cer- 

 tain yeasts are able to produce a higher percentage of alcohol in 

 identical musts than others. Also, when the theoretical table was com- 

 piled it was assumed that the nonsugar solids always exceeded 2 per 

 cent in normal must and ciders, but this does not appear to be alwa} T s 

 true, as shown by the analyses of the special ciders made with pure 

 yeasts at this station. 



TABLE VII. A comparison of gravity determinations and analyses made at various stages 

 of fermentation, with the percentages of sugar and alcohol calculated from gravity read- 

 in r/s alone. a 



WORK OF 1901-2. 



For table of hydrometer readings, see page 89, Bui. No. 71, Bur. of Chem., U. S. Dept. of Agr. 



