When producing alcoholic beverages, it is important to determine the percentage alcohol by volume (% ABV). This is to inform consumers of their alcohol intake and also to calculate excise. In Australia, an excise tax is applied to the production of alcohol in accordance with the Excise Tariff Act 1921. Depending on the type of beverage produced, excise is charged at different rates. For example, a beer with an alcohol volume exceeding 3.5%, packed in a container over 48 litres, attracts a $33.77 per litre excise.
The American Society of Brewing Chemists (ASBC) outlines an accurate method for determining the %ABV of beer using distillation. A set sample amount of degassed beer is distilled to collect the alcohol as the distillate. The sample is heated until the alcohol vaporises, the vapour then passes through a condenser and is collected in a receptacle. If water is distilled in the process, the final specific gravity step will compensate for this. The distillate is then topped up to a set amount with distilled water. The diluted distillate is then measured for specific gravity with a hydrometer at the temperature specified (temperature of the sample is important as it will affect final result). The specific gravity can then be used to determine the amount of alcohol in the sample and also the % ABV of the beer sample.