Density meter procedures and the official AOAC pycnometer method to measure proof of ethanol-water solutions in the 25-79° proof range were collaboratively studied. Measurement of proof by density meter is simpler, requires less time and smaller samples, and gives more reproducible results than the AOAC pycnometer method. Differences of —0.05 to +0.02° proof between averages of results reported for density meter and pycnometer are acceptable, considering that proof of finished alcohol products is reported to 0.1°. The density meter method has been adopted official first action.
A method is described for determining the ethanol concentration of liqueur-type products containing dissolved solids. The sample is distilled in an allglass still equipped with spherical joints; the proof of the distillate, diluted to known volume, is measured by a Mettler/Paar density meter. Ten collaborators determined proof of 6 different synthetic liqueurs containing ethanol-water-sugar mixtures and 2 alcoholic dairy products. Proof of the samples varied from 33 to 92°. Standard deviations and coefficients of variation for this method varied from 0.069 to 0.278 and from 0.20° to 0.36°, respectively. The method has been adopted official first action.
A procedure using the Mettler/Paar density meter to measure the concentration of ethanol in aqueous solutions has been collaboratively studied. This instrument measures specific gravity to ±0.00001, which corresponds to ±0.02° proof. Fourteen collaborators determined the ethanol concentration in 7 different samples varying in proof from 1 to 190°. The density meter values for these samples are 0.00 to 0.17° lower than true proof as determined by a pycnometer. This is the result of nonlinearity which occurs when the specific gravity of ethanol solutions is plotted vs concentration. A graph or programmed calculator can be used to correct for this difference.
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