FERMENTATION 



349 



may be attained with even a more serviceable expression for the result, by measuring 

 exactly a certain quantity of the beer, such as four fluid ounces, and boiling it down 

 to somewhat less than half its bulk in an open vessel, such as a glass flask, so as to 

 drive off the whole alcohol. The liquid when cool is made up to four fluid ounces, 

 or the original measure of the beer, and the specific gravity of this liquid is observed. 

 It has already been referred to as to the extract-gravity of the beer, and represents a 

 portion of the original gravity. Of a beer of which the history was known, the original 

 gravity of the malt wort was 1121, or 121; the specific gravity of the beer itself 

 before evaporation, 1043 ; and the extract-gravity of the beer 10567, or 567. 



' The second observation which can be made with sufficient facility upon the beer, 

 is the determination of the quantity of alcohol contained in it. This information may 

 be obtained most directly by submitting a known measure of the beer to distillation, 

 continuing the ebullition till all the alcohol is brought over, and taking care to con- 

 dense the latter without loss. It is found in practice that four ounce-measures of the 

 beer form a convenient quantity for the purpose. This quantity is accurately 

 measured in a small glass flask, holding 1 750 grains of water when filled up to a mark 

 in the neck. The mouth of the small retort containing the beer is adapted to one end 

 of a glass tube-condenser, the other end being bent and drawn out for the purpose of 

 delivering the condensed liquid into the small flask previously used for measuring the 

 beer. The spirituous distillate should then be made up with pure water to the 

 original bulk of the beer, and the specific gravity of the last liquid be observed by the 

 weighing bottle, or by a delicate hydrometer, at the temperature of 60 Fahr. The 

 lower the gravity the larger will be the proportion of alcohol, the exact amount of 

 which may be learned by reference to the proper tables of the gravity of spirits. The 

 spirit- gravity of the beer already referred to proved to be 985*25 ; or it was 14'05 

 of gravity less than 1000, or water. The "spirit-indication" of the beer was there- 

 fore 14-05 ; and the extract-gravity of the same beer 567. 



' The spirit-indication and extract-gravity of any beer being given, do we possess 

 data sufficient to enable us to determine with certainty the original gravity ? It has 

 already been made evident that these data do not supply all the factors necessary for 

 reaching the required number by calculation. 



' The formation of the extractive matter, which chiefly disturbs the original gravity, 

 increases with the progress of the fermentation ; that is, with the proportion of 

 alcohol in the fermenting liquor. But we cannot predicate from the theory any rela- 

 tion which the formation of one of these substances should bear to the formation of 

 the other, and are unable, therefore, to say beforehand that because so much sugar 

 has been converted into alcohol in the fermentation, therefore so much sugar has also 

 been converted into the extractive substance. That a uniform, or nearly uniform 

 relation, however, is preserved in the formation of the spirits and extractive substance 

 in beer brewing, appears to be established by the observations which follow, Such 

 an uniformity in the results of the vinous fermentation is an essential condition for 

 the success of any method whatever of determining original gravities, at least within 

 the range of circumstances which affect beer brewing. Otherwise two fermented 

 liquids of this class, which agree in giving both the same spirit-indication and the 

 same extractive gravity, may have had different original gravities, and the solution 

 of our problem becomes impossible.' 



The following table, one of several of equal value, gives the results of a particular 



TABLE II. Fermentation of Sugar-Wort of original gravity 1055-3. 



