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Alcohol proof (usually termed simply "proof" in relation to a beverage) is a measure of the content of
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
(alcohol) in an
alcoholic beverage An alcoholic beverage (also called an alcoholic drink, adult beverage, or a drink) is a drink that contains ethanol, a type of alcohol that acts as a drug and is produced by fermentation of grains, fruits, or other sources of sugar. The c ...
. The term was originally used in England and was equal to about 1.8 times the percentage of
alcohol by volume Alcohol by volume (abbreviated as ABV, abv, or alc/vol) is a standard measure of how much alcohol (ethanol) is contained in a given volume of an alcoholic beverage (expressed as a volume percent). It is defined as the number of millilitres (mL) o ...
(ABV). The UK now uses ABV instead of proof. In the United States, alcohol proof is defined as twice the percentage of ABV. The definition of proof in terms of ABV varies from country to country. The measurement of alcohol content and the statement of content on bottles of alcoholic beverages is regulated by law in many countries. In 1972, Canada phased out the use of "proof"; in 1973, the
European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...
followed suit; and the UK, where the concept originated, started using ABV instead in 1980. The US code mandates the use of ABV, but permits proof to be used also. The
degree symbol The degree symbol or degree sign, , is a typographical symbol that is used, among other things, to represent degrees of arc (e.g. in geographic coordinate systems), hours (in the medical field), degrees of temperature or alcohol proof. The symbo ...
(°) is sometimes used to indicate alcohol proof.


History

The term ''proof'' dates back to 16th century England, when
spirits Spirit or spirits may refer to: Liquor and other volatile liquids * Spirits, a.k.a. liquor, distilled alcoholic drinks * Spirit or tincture, an extract of plant or animal material dissolved in ethanol * Volatile (especially flammable) liquids, ...
were
taxed A tax is a compulsory financial charge or some other type of levy imposed on a taxpayer (an individual or legal entity) by a governmental organization in order to fund government spending and various public expenditures (regional, local, or n ...
at different rates depending on their alcohol content. Similar terminology and methodology spread to other nations as spirit distillation, and
taxation A tax is a compulsory financial charge or some other type of levy imposed on a taxpayer (an individual or legal person, legal entity) by a governmental organization in order to fund government spending and various public expenditures (regiona ...
, became common. In England, spirits were originally tested with a basic "burn-or-no-burn" test, in which an alcohol-containing liquid that would ignite was said to be "above proof", and one which would not was said to be "under proof". A liquid just alcoholic enough to maintain combustion was defined as 100 proof and was the basis for taxation. Because the
flash point The flash point of a material is the "lowest liquid temperature at which, under certain standardized conditions, a liquid gives off vapours in a quantity such as to be capable of forming an ignitable vapour/air mixture". (EN 60079-10-1) The fl ...
of alcohol is highly dependent on temperature, 100 proof defined this way ranges from 20% at to 96% at alcohol by (ABW); at 100 proof would be 50% AB. Another early method for testing liquor's alcohol content was the "gunpowder method".
Gunpowder Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon (in the form of charcoal) and potassium nitrate (saltpeter). ...
was soaked in a spirit, and if the gunpowder could still burn, the spirit was rated above proof. This test relies on the fact that
potassium nitrate Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ions K+ and nitrat ...
(a chemical in gunpowder) is significantly more soluble in water than in alcohol. While less influenced by temperature than the simpler burn-or-no-burn test, gunpowder tests also lacked true reproducibility. Factors including the grain size of gunpowder and the time it sat in the spirit impact the dissolution of potassium nitrate and therefore what would be defined as 100 proof. However, the gunpowder method is significantly less variable than the burn-or-no-burn method, and 100 proof defined by it is traditionally defined as 57.15% ABV. By the end of the 17th century, England had introduced tests based on
specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...
for defining proof. However, it was not until 1816 that a legal standard based on
specific density Specific density is the ratio of the mass versus the volume of a material. Density vs. gravity Specific density is based upon units of mass and volume, while specific gravity Relative density, or specific gravity, is the ratio of the de ...
was defined in England. 100 proof was defined as a spirit with the
specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...
of
pure water Purified water is water that has been mechanically filtered or processed to remove impurities and make it suitable for use. Distilled water was, formerly, the most common form of purified water, but, in recent years, water is more frequently puri ...
at the same temperature. From the 19th century until 1 January 1980, the UK officially measured alcohol content by proof spirit, defined as
spirit Spirit or spirits may refer to: Liquor and other volatile liquids * Spirits, a.k.a. liquor, distilled alcoholic drinks * Spirit or tincture, an extract of plant or animal material dissolved in ethanol * Volatile (especially flammable) liquids, ...
with a
gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
of that of water, or , and equivalent to 57.15% ABV. The value 57.15% is very close to the fraction . This led to the definition that 100-proof spirit has an ABV of . From this, it follows that to convert the ABV expressed as a percentage to degrees proof, it is only necessary to multiply the ABV by . Thus pure 100% alcohol will have 100×() = 175 proof, and a spirit containing 40% ABV will have 40×() = 70 proof. The proof system in the United States was established around 1848 and was based on percent alcohol rather than specific gravity. Fifty percent alcohol by volume was defined as 100 proof. Note that this is different from 50%
volume fraction In chemistry and fluid mechanics, the volume fraction φ''i'' is defined as the volume of a constituent ''V'i'' divided by the volume of all constituents of the mixture ''V'' prior to mixing: :\phi_i = \frac Being dimensionless, its unit is ...
(expressed as a percentage); the latter does not take into account change in volume on mixing, whereas the former does. To make 50% ABV from pure alcohol, one would take 50 parts of alcohol and dilute to 100 parts of solution with water, all the while mixing the solution. To make 50% alcohol by volume fraction, one would take 50 parts alcohol and 50 parts water, measured separately, and then mix them together. The resulting volume will not be 100 parts but between 96 and 97 parts, since the smaller water molecules can take up some of the space between the larger alcohol molecules (see volume change). The use of proof as a measure of alcohol content is now mostly historical. Today,
liquor Liquor (or a spirit) is an alcoholic drink produced by distillation of grains, fruits, vegetables, or sugar, that have already gone through alcoholic fermentation. Other terms for liquor include: spirit drink, distilled beverage or hard ...
is sold in most locations with labels that state its percentage alcohol by volume.


Governmental regulation


European Union

The
European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...
(EU) follows recommendations of the
International Organization of Legal Metrology The International Organization of Legal Metrology (french: Organisation Internationale de Métrologie Légale - OIML), is an intergovernmental organisation that was created in 1955 to promote the global harmonisation of the legal metrology procedu ...
(OIML). OIML's International Recommendation No. 22 (1973) provides standards for measuring alcohol strength by
volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). The de ...
and by
mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...
. A preference for one method over the other is not stated in the document, but if alcohol strength by volume is used, it must be expressed as a percentage of total volume, and the water/alcohol mixture must have a temperature of when measurement is done. The document does not address alcohol proof or the labeling of bottles.


United Kingdom

On 1 January 1980, Britain adopted the ABV system of measurement prescribed by the European Union, of which it was a member. The OIML recommendation for ABV used by the EU states the alcohol by volume in a mixture containing alcohol as a percentage of the total volume of the mixture at a temperature of . It replaced the Sikes
hydrometer A hydrometer or lactometer is an instrument used for measuring density or relative density of liquids based on the concept of buoyancy. They are typically calibrated and graduated with one or more scales such as specific gravity. A hydrometer ...
method of measuring the proof of spirits, which had been used in Britain for over 160 years.


United States

In the United States, alcohol content is legally required to be specified as an ABV percentage. For bottled spirits over containing no solids, actual alcohol content is allowed to vary within 0.15% of ABV stated on the label. Proof (the term ''degrees proof'' is not used), defined as twice the percentage of alcohol by volume, may also be stated. For example, whisky may be labeled as 50% ABV and as 100 proof; 86-proof whisky contains 43% ABV. The most typical bottling proof for spirits in the United States is 80 US proof, and there is special legal recognition of 100-proof spirits in the
bottled in bond Bottled in bond is a label for an American-made distilled beverage that has been aged and bottled according to a set of legal regulations contained in the United States government's Standards of Identity for Distilled Spirits, as originally laid ...
category defined since 1897. The
Code of Federal Regulations In the law of the United States, the ''Code of Federal Regulations'' (''CFR'') is the codification of the general and permanent regulations promulgated by the executive departments and agencies of the federal government of the United States. ...
requires that liquor labels state the percentage of ABV. The regulation permits, but does not require, a statement of the proof, provided that it is printed close to the ABV number. In practice, proof levels continue to be stated on nearly all spirits labels in the United States, and are more commonly used than ABV when describing spirits in journalism and informal settings.


Canada

Beverages were labelled by alcohol proof in Canada until 1972, then replaced by ABV.


See also

*
Liquor Liquor (or a spirit) is an alcoholic drink produced by distillation of grains, fruits, vegetables, or sugar, that have already gone through alcoholic fermentation. Other terms for liquor include: spirit drink, distilled beverage or hard ...
*
Cask strength Cask strength (also known as barrel proof/barrel strength) is a term used by whiskey (often spelled "whisky" outside of Ireland and the United States) and rum producers to describe a whiskey or rum that has not been substantially diluted after its ...
*
Volume percent In chemistry and fluid mechanics, the volume fraction φ''i'' is defined as the volume of a constituent ''V'i'' divided by the volume of all constituents of the mixture ''V'' prior to mixing: :\phi_i = \frac Being dimensionless quantity, dim ...


References

{{DEFAULTSORT:Alcoholic Proof Alcohol measurement Customary units of measurement in the United States