Relevant for: Alcoholic beverage industry (e.g. wine, spirits, brandy, whisky, etc.), tax and customs laboratories, pharmaceutical industry
The measurement of the alcohol content of alcoholic beverages is indispensable to ensure that the products conform to the label declaration of alcohol content, and to establish the basis for the payment of tax.
1 Densitymeasurementisofficiallyrecognized
An officially recognized method for the determination of alcohol concentrations in alcohol/water mixtures either by weight (%w/w) or volume (%v/v; ABV = alcohol by volume) is the measurement of density followed by conversion into alcohol concentration using official alcohol tables.
Accepted instruments for alcohol determination include pycnometer, hydrometer and Anton Paar density meters.
Pycnometers provide good accuracy, but the method is time-consuming and requires trained personnel to obtain reproducible results.
Hydrometers usually provide less accuracy and require 300 mL to 500 mL of sample, but are easier to use. Careful calibration is necessary.
2 Common units of alcohol concentration
Alcohol %v/v: This unit is influenced by temperature changes, therefore temperature should always be quoted together with the alcohol concentration (example: 41.90 %v/v at 20 °C corresponds to
41.82 %v/v at 15 °C). Results obtained using different density/alcohol tables may be slightly different.
Therefore it is advisable to mention the alcohol table together with the results.
Alcohol %w/w: This unit is not influenced by temperature (example: 40.82 %w/w at 20 °C is identical to 40.82 %w/w at 15 °C).
Grams per 100 mL or per L: The temperature must be quoted together with the results in g/mL (or g/L) as the results are influenced by the temperature.
- Proof: This unit is found in the US and several other °Proof is the alcohol concentration in %v/v at 60 °F (15.56 °C) multiplied by two. Pure alcohol (100 %) therefore corresponds to an alcohol content of 200 °Proof (US °Proof = ABV * 2).
The unit °Proof in Great Britain (UK) is not as common as it is in the US and it is different from the American
°Proof degrees (UK °Proof = ABV * 1.75).
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