FERMENTATION 



347 



The gravity of the wort is called the original gravity that of the beer, beer-gravity. 

 The report of Graham, Hofmann, and Kedwood, upon ' original gravities/ may bo 

 Bupposed to be in tho hands of every brewer ; but as some of the points examined 

 ma&rially explain many of the phenomena of vinous fermentation, we have trans- 

 ferred a fow paragraphs to our pages-: 



' As tho alcohol of tho beer is derived from tho decomposition of saccharine 

 matter only, and represents approximately double its weight of starch-sugar, a 

 speculative original gravity might be obtained by simply increasing the extract- 

 gravity of the beer by that of the quantity of starch-sugar known to be decomposed 

 in the fermentation. Tho inquiry would then reduce itself to tho best means of ascer- 

 taining the two experimental data, namely, the extract-gravity and the proportion of 

 alcohol in the beer, particularly of tho latter. It would bo required to decide whether 

 tho alcohol should be determined from the gravity of the spirits distilled from the 

 beer ; by the increased gravity of the beer when its alcohol is evaporated off; by the 

 boiling-point of the beer, which is lower the larger the proportion of alcohol present ; 

 or by tho refracting power of the beer upon light various methods recommended for 

 the valuation of the spirits in beer. 



1 Original gravities so deduced, however, are found to be useless, being in error 

 and always under the truth, to an extent which has not hitherto been at all accounted 

 for. The theory of brewing, upon a close examination of the process, proves to be 

 less simple than is implied in the preceding assumption ; and other changes appear to 

 occur in worts, simultaneously with the formation of alcohol, which would require to 

 bo allowed for before original gravities could be rightly estimated. It was found 

 necessary to study the gravity, in solution of each by itself, of the principal chemical 

 substances which are found in fermented liquids. These individual gravities defined 

 the possible range of variation in original gravity, and they brought out clearly for 

 tho first time the nature of the agencies which chiefly affect the result. 



' The use of cane-sugar is now permitted in breweries, and the solution of sugar 

 may be studied first as the wort of simplest composition. The tables of the specific 

 gravity of sugar solutions, constructed by Mr. Bate, have been verified, and are con- 

 sidered entirely trustworthy. The numbers in the first and third columns of Table I., 

 which follow, are however, from new observations. It is to be remarked that these 

 numbers have all reference to weights, and not to measures. A solution of cane- 

 sugar, which contains 25 grains of sugar in 1000 grains of the fluid, has a specific 

 gravity of lOlO'l, referred to the gravity of pure water taken as 1000 ; a solution of 

 50 grains of cane-sugar in 1000 grains of the fluid, a specific gravity of 1020'2, and 

 so on. The proportion of carbon contained in tho sugar is expressed in the second 

 column ; tho numbers being obtained from the calculation that 171 parts by weight 

 of cane-sugar (C^H^O 11 ) consist of 72 parts of carbon, 11 parts of hydrogen, and 

 88 parts of oxygen ; or of 72 parts of carbon combined with 99 parts of tho elements 

 of water. It is useful to keep thus in view the proportion of carbon in sugar so- 

 lutions, as that element is not involved in several of the changes which precede or 

 accompany the principal change which sugar undergoes during fermentation, and which 

 changes only affect the proportion of the oxygen and hydrogen, or elements of water, 

 combined with the carbon. The proportion of oxygen and hydrogen in the altered 

 sugar increases or diminishes during the changes referred to ; but the carbon remains 

 constant, and affords, therefore, a fixed term in the comparison of different solutions. 



TABLE I. Specific gravity of solutions of Cane-sugar in water. 



' When yeast is added to the solution of cane-sugar in water, or to any other sac- 

 charine solution, and fermentation commenced, tho specific gravity is observed to 



