848 FERMENTATION 



fall, owing to the escape of carbonic acid gas, and the formation of alcohol, which 

 is specifically lighter than water; 171 grains of sugar, together with 9 grains of 

 water, being converted into 92 grains of alcohol and 88 grains of carbonic acid 

 (C 1 -H I1 11 + HO = 2C 4 HK) 2 + 4C0 2 ). But if the process of fermentation bo closely 

 watched, the fall of gravity in cane-sugar will be found to bo preceded by a ili.ri.l I 

 increase of gravity. Solutions were observed to rise from 1055 to 1058, or 3 u 

 of gravity, within an hour after tho addition of the yeast, the last being in the usual 

 proportion for fermentation. When tho yeast was mixed in minute quantity only, 

 such as TJ~ of tho weight of tho sugar, tho gravity of tho sugar solution rose gradually 

 in four days from 1055 to 1057'91, or also nearly 3 degrees ; with no appearance, at 

 the same time, of fermentation or of any other change in the solution. This remark- 

 able increase of density is owing to an alteration which takes place in tho constitution 

 of the cane-sugar, which combines with the elements of water and becomes starch- 

 sugar : a change which had been already proved by H. Rose and by Dubrunfaut to 

 precede the vinous fermentation of cane-sugar. Tho same conversion of cane-sugar 

 into starch-sugar, with increase of specific gravity, may bo shown by means of ai-i-ls 

 as well as of yeast. A solution of 1000 parts of cane-sugar in water, having tho specific 

 gravity 1054'64, became with one part of crystallised oxalic acid added to it 105 1'7 ; 

 and, being afterwards heated for twenty-three hours to a temperature not exceeding 

 128 Fahr., it was found (when cooled) to have attained a gravity of 1057'63 an 

 increase again of nearly 3 degrees of gravity.' 



The difference between the gravities of solutions of cane-sugar and starch-sugar 

 are of great practical value, but these must bo studied in the original ; tho result, how- 

 ever, being ' that the original gravity of a fermented liquid or beer must be different, 

 according as it was derived from a wort of cane-sugar or of starch-sugar.' 



The gravity of malt wort was determined to be intermediate between that of pure 

 cane-sugar and starch-sugar, and solutions containing an equal quantity of carbon ex- 

 hibited the following gravities : 



Cane-sugar- 1072'9 Pale malt - 1074'2 Starch-sugar - 1076-0 



Two other substances were found to influence the original gravity of the wort : 

 dextrin, or the gum of starch, and caramel. Tables are given of the specific 

 gravities of these, from which the following results have been deduced : 



Starch-sugar 1076 



Dextrin 1066*9 



Caramel . , . . .1062-3 



Caramel is stated to interfere more than dextrin in giving lightness or apparent 

 attenuation to fermented worts, without a corresponding production of alcohol. 



' Another constituent of malt wort, which should not be omitted, is the soluble 

 azotised or albuminous principle derived from tho grain. The nitrogen was deter- 

 mined in a strong wort of pale malt with hops, of tho specific gravity 1088, and con- 

 taining about 21 per cent, of solid matter. It amounted to 0'217 per cent, of the 

 wort, and may be considered as representing 3'43 per cent, of albumen. In the same 

 wort, after being fully fermented, the nitrogen was found to amount to 0'134 percent., 

 equivalent to 2 - ll per cent, of albumen. The loss observed of nitrogen and albumen 

 may bo considered as principally duo to tho production and growth of yeast, which is 

 an insoluble matter, at tho cost of the soluble albuminous matter. Solutions of ep:g- 

 albumen in water, containing 3'43 and 2'11 per cent, respectively of that substance, 

 were found to have tho specific gravities of 1004'2 and 1003'!. Honco a loss of 

 density has occurred during fermentation of I'l degree on a wort of 1088 original 

 gravity, which can be referred to a change in tho proportion of albuminous matter. 

 It will bo observed that tho possible influence of this substance and of tho greater or 

 less production of yeast during fermentation, upon tho gravity of beer, are restricted 

 within narrow limits.' 



Tho reporters proceed : 



' Tho process required for tho determination of tho original gravity of beer must 

 be easy of execution, and occupy little time. It is not proposed, in tho examination 

 of a sample, to separate by chemical analysis the several constituents which, havo 

 been enumerated. In fact, wo are practically limited to two experimental observa- 

 tions on tho beer, in addition to the determination of its specific gravity. 



'One of these is the observation of tho amount of solid or extractive matter still 

 remaining after fermentation, which is always more considerable in beer than in the 

 completely-fermented wash of spirits. A known measure of tho beer might be 

 rated to dryness, and the solid residue weighed ; but this would bo a troublesome 

 operation, and could not indeed bo executed with great accuracy. Tho same object 



