A simple, rapid, and accurate method is described for determining the concentration of alcohol in ethanol solutions using a density meter. With this instrument, the U-tube is suctionfilled with 0.7 mL sample, and the results are displayed on a digital read-out in specific gravity units. These values are converted by tables to per cent ethanol or proof. For samples under 40° proof, the instrument is standardized on air and water. When testing samples between 40 and 193° proof, the instrument is standardized on air and an ethanol standard having a proof within ±30° of the sample tested. Thus, large corrections for the nonlinearity of the plot of the specific gravity of ethanol vs. proof are avoided. An equation is presented that corrects for this non-linearity, and the result is obtained in per cent ethanol rather than specific gravity. Proof results obtained with this instrument are in good agreement with the values obtained by a pycnometer and/or refractometer for 1–190° proof ethanol-water solutions, vodkas, whiskeys, brandies, and liqueurs.
A method for measuring color intensity of whisky was developed to replace the present AOAC method, which has become obsolete. The new method was collaboratively studied by 20 persons. Color intensity of whisky was measured as absorbance by a spectrophotometer, using a 1 cm cell, a bandwidth ≤10 nm, and a wavelength of 525 nm. Water was used as reference. Collaborator results appear acceptable for whisky samples that vary in color intensity from 29 to 374 CIU (absorbance X 1000 = Color Intensity Units (CIU)). The maximum standard deviation and coefficient of variation were 5.8 CIU and 6.68%, respectively. The method has been adopted official first action.
A comparison is presented of color intensity values of aged and caramel-colored distilled alcoholic products obtained with spectrophotometers and colorimeters operated at different wavelengths. Absorbances measured by a narrow (≤1 nm) and an 8 nm bandwidth spectrophotometer at 430,525, and 610 nm are compared. Colorimeters evaluated include the Klett-Summerson equipped with Nos. 42, 54, and 60 regular filters and 520, 540, and 560 nm narrow bandpass filters and a Coleman Nepho-Colorimeter, equipped with a 525 nm filter. A conversion chart can be used to convert colorimeter units to absorbance units. The procedure suggested uses an instrument with a bandwidth ≤10 nm at a wavelength of 525 nm; results are reported in absorbance units.
An HIAC particle counter is used to measure clarity of distilled alcoholic products. The number of particles is measured in 5 size ranges from 2 to 90 μm. Average data are given for whiskies, brandy, rum, white gin, and vodka. The highest counts are obtained for aged products and most of the particles are 2–5 μm. The particle counts of different brands of blended whiskies varied from 62 to 5265 particles/ml in the 2–90 μm range. There is no apparent relationship between nephelometer values and particle counts.
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.
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