The estimation of alcohol in beers and wines is generally made in one of two ways, either by direct distillation and determining the alcohol in the distillate, or, indirectly, by evaporating the alcohol from a sample and obtaining the per cent. from the difference in specific gravity of the sample before and after the alcohol has been driven off. Authorities differ as to the accuracy of the indirect method, some even holding it to give better results than the direct estimation. It is generally recommended to use both methods, as the one gives a check over the other, and it is very easy to carry both on together, as the same sample which is used for the distillation can be used for the determination of the density of the dealcoholized solution, provided no tannin is used. I much prefer the distillation method, and have adopted the results by it in the tables.

I have almost invariably found that during the distillation a precipitation of flocculent albuminous matter takes place in the flask, evidently bodies which are rendered insoluble, either by the evaporation of the alcohol or acetic acid, or by the heating of the solution, and it would seem obvious that this separation of solids from the solution would vitiate more or less the results by the indirect method.

For the distillation method 100cc. of the sample, freed from carbonic acid by shaking, are measured out, rinsed into a flask with about 50cc. water, the latter connected with a Liebig's condenser, and l00cc. distilled off. The sample and distillate should be measured at the same temperature. The specific gravity of the distillate is then obtained by means of an accurately tared picnometer, preferably one carrying a thermometer, so that the weight may be taken at exactly 15.5° C. The per cent. of alcohol in the distillate is then obtained by reference to a table giving the per cent. of alcohol in solutions of different specific gravities, of which tables Hehner's are the best in use. This per cent. multiplied by the specific gravity of the distillate, and the result divided by the specific gravity of the original sample, gives the per cent. of alcohol by weight contained in the latter. The accuracy of the operation is increased by weighing the sample taken, and also the distillate. Then the weight of the distillate multiplied by the per cent. of alcohol corresponding to its specific gravity as found in the table, and the result divided by the weight of the sample taken, gives the per cent. of alcohol by weight contained in the latter.

For the indirect method it is necessary to estimate accurately the specific gravity of the original beer, thoroughly freed of carbonic acid by shaking and standing; then 100cc. or any convenient quantity is measured out, evaporated to half its bulk, cooled, and made up to its original volume with water, taking care to have the solution at the same temperature as the sample when first measured. The specific gravity of the dealcoholized liquor is taken. Then the specific gravity of the original sample divided by the specific gravity of the dealcoholized solution gives the specific gravity of the alcohol evaporated, from which figure the per cent. of alcohol is ascertained by reference to the table. The same sample which is used for distilling can be very conveniently used for this determination as well.

Hehner's alcohol table.