Alcohol by volume

Change in volume with increasing ABV

Mixing two solutions of alcohol of different strengths usually causes a change in volume. Mixing pure water with a solution less than 24% by mass causes a slight increase in total volume, whereas the mixing of two solutions above 24% causes a decrease in volume.[lower-alpha 1] The phenomenon of volume changes due to mixing dissimilar solutions is called "partial molar volume". Water and ethanol are both polar solvents. When water is added to ethanol, the smaller water molecules are attracted to the ethanol's hydroxyl group, and each molecule alters the polarity field of the other. The attraction allows closer spacing between molecules than is usually found in non-polar mixtures.

Thus, ABV is not the same as volume fraction expressed as a percentage. Volume fraction, which is widely used in chemistry (commonly denoted as v/v), is defined as the volume of a particular component divided by the sum of all components in the mixture when they are measured separately. For example, to make 100mL of 50% ABV ethanol solution, water would be added to 50mL of ethanol to make up exactly 100mL. Whereas to make a 50% v/v ethanol solution 50 mL of ethanol and 50 mL of water could be mixed but the resulting volume of solution will measure less than 100 mL due to the change of volume on mixing, and will contain a higher concentration of ethanol.[5] The difference is not large, with the maximum difference being less than 2.5%, and less than 0.5% difference for concentrations under 20%.

Details about typical amounts of alcohol contained in various beverages can be found in the articles about them.

During the production of wine and beer, yeast is added to a sugary solution. During fermentation, the yeasts consume the sugars and produce alcohol. The density of sugar in water is greater than the density of alcohol in water. A hydrometer is used to measure the change in specific gravity (SG) of the solution before and after fermentation. The volume of alcohol in the solution can then be estimated. There are a number of empirical formulae which brewers and winemakers use to estimate the alcohol content of the liquor made.

Specific gravity is the density of a liquid relative to that of water, i.e if the density of the liquid is 1.05 times that of water it has a specific gravity of 1.05. In UK brewing usage it is customary to regard the reference value for water to be 1000, so the specific gravity of the same example beer would be quoted as 1050. The formulas here assume that the former definition is used for specific gravity.

Wine

The simplest method for wine has been described by English author C.J.J. Berry:[11]

$${\displaystyle {\text{ABV}}\approx 136\times \left({\text{Starting SG}}-{\text{Final SG}}\right)}$$

Beer

See also: Beer measurement § Strength

One calculation for beer is:[12]

$${\displaystyle {\text{ABV}}=131\times \left({\text{Starting SG}}-{\text{Final SG}}\right)}$$

For higher ABV above 6% many brewers use this formula:[13]

$${\displaystyle {\text{ABV}}={\frac {105}{0.79}}\times \left({\frac {{\text{Starting SG}}-{\text{Final SG}}}{\text{Final SG}}}\right)}$$

• Apparent molar property
• Excess molar quantity
• Standard drink
• Unit of alcohol
• Volume fraction

• "How do brewers measure the alcohol in beer?". HowStuffWorks. 12 December 2000.
• Jayes, Wayne. "Alcohol Strength and Density". sugartech.co.za. The Sugar Engineers.