Proof (alcohol)

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Alcoholic proof is a measure of how much ethanol is in an alcoholic beverage, and is approximately twice the percentage of alcohol by volume (ABV, the unit that is commonly used at present).

1 Regulations
2 Levels of alcohol during liquor production
3 Origins
4 External links

[edit] Regulations

[edit] EU

The European Union, including Britain, follows the recommendation of the International Organization of Legal Metrology (OIML) which states percentage of alcohol by volume (ABV) at 20 °C.

[edit] British proof spirits

Britain originally specified alcohol content in terms of proof spirit, originally defined as the most dilute spirit which would sustain combustion of gunpowder. In this system, spirit of 100 degrees proof contains 57.1% alcohol by volume or 49.28% alcohol by weight at 51 deg F (10.6 deg C) and is equivalent to 114.2 proof in the USA. Pure ethanol is 175 degrees proof. [1]

From the 1740s until 1816 Customs and Excise and London brewers and distillers used Clarke's hydrometer to measure proof. From 1816 the Sikes hydrometer was used to measure degrees proof. Officially the Customs and Excise Act of 1952 defined "spirits of proof strength" (or proof spirits):

"Spirits shall be deemed to be at proof if the volume of the ethyl alcohol contained therein made up to the volume of the spirits with distilled water has a weight equal to that of twelve-thirteenths of a volume of distilled water equal to the volume of the spirits, the volume of each liquid being computed as at fifty-one degrees Fahrenheit."

Britain now uses the EU ABV standard.

[edit] United States

In the United States of America too, alcohol content is stated as ABV. US Federal regulation (CFR 27 5.37 Alcohol Content) requires that liquor labels state the percentage alcohol by volume (sometimes abbreviated ABV). The regulations permit but do not require a statement of the proof as long as it is printed close to the percentage alcohol by volume. [2]

The proof number is twice the percentage of the alcohol content measured by volume at a temperature of 60 °F (15.5 °C). Therefore "80 proof" is 40% alcohol by volume, and pure alcohol is "200 proof". US proof differs significantly from British proof.

[edit] Levels of alcohol during liquor production

Alcohol is produced by yeast during the process of fermentation. The amount of alcohol in the finished liquid depends on how much sugar there was at the beginning for the yeast to convert into alcohol. In beer, the alcohol is generally 3% to 12% (6 to 24 proof) and usually about 4% to 6% (8 to 12 proof). Depending on the strain of yeast, wines top out at about 14% to 16% (28 to 32 proof), because that is the point in the fermentation process where the alcohol concentration denatures the yeast. Since the 1990s, a few alcohol-tolerant 'superyeast' strains have become commercially available, which can ferment up to 20%. [3]

Fortified wines, such as sweet and dry vermouths become fortified by adding alcohol. These added alcohols are typically distilled wines such as brandy, port, sherry, marsala, and madiera. This second source of alcohol is added before the wines are finished fermenting, as the added alcohol kills the yeast in fermenting wine, leaving an abundance of sugar.

Stronger liquors are distilled after fermentation is complete to increase their alcohol content. This way, the alcohol content can be raised up to a maximum of 95.6% (191 proof), the concentration of the water/alcohol azeotrope. When 100% ethanol (absolute alcohol) is required for scientific, commercial, or industrial purposes, other methods must be used. 100% ethanol is hygroscopic, and if it is left open, it will absorb water out of the air, reducing the concentration.

[edit] Origins

The term originated in the 18th century, when payments to British sailors included rations of brandy. To ensure that the brandy had not been watered down and was of good quality, it was "proved" by dousing gunpowder in the liquor, and testing to see if it would ignite. If it did not, the solution contained too much water—and the alcohol content was considered low or "underproof".

A "proven" solution was defined as 100 degrees proof. This was later found to occur at 57.15% ethanol; if this is rounded to 57.00%, it can be expressed as a ratio of total liquid to alcohol of 7:4; i.e. 70 degrees proof is very close to 40% alcohol by volume, and pure alcohol is about 175 degrees proof. This definition still holds in Britain but is no longer used; the ABV system must be used to mark bottles.