130 PUBLIC HEALTH CHEMISTRY 



Addenda. A pint of good beer contains roughly i fl. oz. 

 of alcohol, 1-5 oz. of sugary extract, 20 grains of free acid, 

 14 grains of salts, and 1 pint of CO 2 gas in solution. The 

 extract may be got from the sp. gr. of the de-alcoholized 

 beer by dividing the excess over 1000 by 3-86. The 

 difference between the sp. gr. of the beer and the sp. gr. 

 of the de-alcoholized beer may be taken as the approximate 

 spirit indication in calculating the original gravity of the 

 beer wort, and deducted from 1000, gives sp. gr. of alcoholic 

 water of same alcoholic strength as beer. 



WINE. 



Wine is the fermented juice of the grape, but much 

 of it is made otherwise. The grapes are pressed or 

 trodden (mechanical pressure extracts an excess of tannin 

 and colouring matter from red grapes), and the juice or 

 " must " ferments spontaneously from the yeast existing 

 naturally on the skins, the glucose or grape sugar being 

 converted into alcohol and C0 2 . When fermentation has 

 ceased, the wine is run off from the residue or " lees," 

 composed mainly of yeast cells and cream of tartar (KHT). 

 The wine is kept in casks in which a further fermentation 

 takes place, resulting in the deposition of more KHT. It is 

 then put into casks to mature or " age." In making white 

 wine the must is separated from the skins and stalks, while 

 for red wine the skins of purple grapes are fermented with 

 the must. In grapes the relative amount of sugar and 

 albuminous matter varies. The yeast fungus lives on the 

 latter, and if it is used up before all the sugar is fermented 

 a sweet wine results ; if the contrary happen, a non-sweet 

 or " dry " wine is obtained. The grape juice also contains 

 tartaric acid and its salts, and the proportion of acid to 

 sugar best adapted for wine production is 1 to 40. In some 

 parts, if the acid is in excess, the must is diluted, and sugar 

 (glucose or cane sugar) added in the necessary amount. 

 To make dry wines, white of egg, gelatin, or isinglass is 

 added to feed the fungus until it ferments all the sugar. 



Analysis. 



Specific gravity : varies. Extract. 2-4 per cent. 



Alcohol. By distillation : 6 to 17 per cent. 



