With regard to the densities of solutions of pale and brown malt, it is interesting to observe that the gravities of the solutions of the two malts agree very closely, and that tlaey occupy a position intermediate between that of the two sugars. That the malt wort is of less density than a solution of atarch sugar, containing the same proportion of carbon, indicates that a portion of the carbon in the wort exists in some other form than that of starch sugar ; for if the whole carbon of the malt wort were present in the form of starch sugar, the gravity of the wort should somewhat exceed that of the pure starch augar solution, since a small proportion of alkaline and earthy salts exists in the malt infusion, and must add to its gravity. The carbon present in the small quantity of albumen of the malt could not affect the result materially. The lesser density of malt wort as compared with a solution of starch sugar containing an equal proportion of carbon is no doubt in part due to the presence in the former of certain proportions of dextrine and caramel, substances which both pro duce solutions considerably lighter than those of starch sugar containing similar amounts of carbon. Both dextrine and caramel are forms of the sugar principle, and the presence of the former in a wort is due to the incomplete saecharization of the starch of the malt during the mashing process. The presence of caramel, or burnt sugar, is no doubt due to the changing of the starch sugar by heat during the process of kiln-drying the malt. It exists in larger quantities in highly dried milt than in the paler kinds, whilst in the case of the black malt used in porter and stout brewing, almost the whole of the soluble portion appears to be caramel.
Graham, Hofmann, and Redwood also point out that a substance greatly resembling caramel is produced during fermentation, owing to the saccharine matter of the wort never being wholly converted into carbonic acid and alcohol, even under the most favourable circumstances. A portion of solid matter always remains which isunfermentable, even if the alcohol is distilled off and fresh yeast used. This residuary has been termed gummy substance, hut when obtained by the fermenta tion of pure sugar it partakes more of the character of caramel, or of glucic acid, particularly in tbe low gravity of its solution in water. Of pure sugar fermented, 4.4,3.72, and 3.70 per cent. was con verted into this substance in three fermentations, in which one and a laalf, three, and six measures of yeast were employed to one hundred measures of solution, containing one-seventh of its weight of sugar. This extractive substance may be obtained in the form of a syrup by evapo rating the liquid after the oompletion of the fermentation. This syrup reddens litmus paper ; gives, like caramel, a transparent blue solution, with sulphate of copper and caustic potash in excess; is not fermentable by yeast even after being boiled with sulphuric acid, whilst it is precipitated by baryta water, and when treated with subacetate of lead gives a brown precipitate more voluminous and of a lighter colour than the precipitate produced by the same means from a solution of pure caramel.
That it is a compound of two or more substances is proved by the fact that a portion of it is precipi tated by the addition of a solution of neutral acetate of lead. Solutions of this extractive substance have densities very closely agreeing with those of caramel containing similar quantities of carbon. The presence of this extractive substance, which is produced during the fermentation of malt worts, as well as sugar worts, appears to exercise a greater influence than dextrine in giving to fermented worts an apparent attenuation without a corresponding production of alcohol, and the more nearly the worts are exhausted by fermentation, the greater is its effect. The indication by gravity of the extractive substance is so much lower than that of starch sugar, that the former substance only indi cates about five-sixths of the saccharine principle that has given rise to it. Hence it is that original gravities cannot be calculated on the assumption that the solid matter in beer is sugar, or a sub etance having the same gravity as sugar. ln the maturing of beer by time, an increase of attenua tion is observed, which is no doubt due to the slow continuation of the vinous fermentation, with the disappearance of sugar and formation of alcohol ; but there is some reason to believe that the attenuation is not entirely due to that cause. Part of the loss of gravity appears to be occasioned by the change in condition of the saccharine principle, from that of starch sugar to that of the extractive substance, a change which involves a loss of speci6c gravity without a corresponding production of alcohol.
During the process of fermentation of a malt wort, a change is produced in the proportion of albuminous matter ; this proportion is diminished in consequence of the formation of yeast, which causes a proportion of the albumen to assume an insoluble form. In a wort made from pale malt with hops, of the gravity of 1088, and containing 21 per cent. of solid matter, it was found tbat the nitrogen amounted to 0.217 per cent., and might be considered as representing 3.43 per cent. of albumen ; whilst after this wort had been fully fermented the proportion of nitrogen was reduced t,o 0.134 per' cent., corresponding to 2.11 per cent. of albumen. Solutions containing 2.11 and 3'43 per cent. respectively of egg-albumen, have been ascertained to have tbe sp. gr. 1003.1 and 1004.2, therefore the loss of albumen which took place during the fermentation of the wort corresponded to a. reduction of gravity from that cause alone of 1°.1. In the same wort, the mineral constituents, consisting of soluble salts of the earths and alkalies, amounted to 0.443 per cent. before and 0.463 per cent. after fermentation, a variation of no practical importance.