Alcohol by Volume (ABV)
Alcohol by volume is a standardized measure of how much alcohol (ethanol) is contained in any alcoholic beverage (expressed as a percentage of total volume).
ABV is defined as the number of milliliters of pure ethanol present in 100 milliliters of solution at 20°C. The number of milliliters of pure ethanol is the mass of the ethanol divided by its density at 20°C, which is 0.78924 g/ml. The ABV standard is used worldwide. In some countries, alcohol by volume is referred to as degrees Gay-Lussac (after the French chemist Joseph Louis Gay-Lussac), although there is a slight difference since Gay-Lussac used 15°C.
Mixing two different strength alcoholic beverages, usually causes a decrease in volume (although if both are low strength it may be an increase).
ALCOHOL BY WEIGHT
Alcohol by Weight is a measurement term used in the United States to legally regulate and tax alcoholic beverages.
It is expressed as a percentage of total mass. In some localities, breweries print the abw (rather than abv) on beverage containers, particularly on low-point versions of popular domestic beer brands.
Because alcohol is less dense than the water component of the beverage, alcohol percentage by weight is only ⅘ of the alcohol percentage by volume (e.g., 3.2% abw = 4.0% abv), which has caused confusion among consumers more familiar with the worldwide standard of Alcohol by Volume. It is possible to convert ABW to ABV by dividing ABW by 0.079.
JOSEPH LOUIS GAY-LUSSAC
Joseph Louis Gay-Lussac (born December 6, 1778, Saint-Léonard-de-Noblat, France—died May 9, 1850, Paris), was a French chemist and physicist, known mostly for two laws related to gases. His work on alcohol-water mixtures (1824), definitively proves that ethanol and CO2 are the main products of the decomposition of sugar by fermentation, which led to the degrees Gay-Lussac (°GL), used to measure alcoholic beverages in many countries.
His name is one of the 72 names inscribed on the Eiffel Tower.
ABW VS. ABV
Typically beverages sold in the United States (US) had expressed alcohol content in ABW however from 2003 Federal regulation has required all liquor labelling to state ABV. In the United Kingdom and Europe the display of the ABV on labelling has been a legal requirement since 1980, following the recommendations of the International Organization of Legal Metrology (OIML). Prior to this legislation the Sikes system (percentage proof) had been in use for over 160 years. In Europe and Canada all beverages containing 1.1% ABV or more must display the actual ABV on the packaging.
The term alcohol proof was originally used in the United Kingdom and was defined as 7/4 times the alcohol by volume (ABV). In the United States, alcoholic proof is defined as twice the percentage of ABV.
The measurement of alcohol content and the statement of this content on the bottle labels of alcoholic beverages is regulated by law in many countries. The purpose of the regulation is to provide pertinent information to the consumer.