Proof (alcohol)
From Wikipedia, the free encyclopedia
Alcoholic proof is a measure of how much ethanol is in an alcoholic beverage; proof is twice the percentage of alcohol by volume (ABV, the unit that is commonly used at present).
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[edit] Regulations
[edit] EU
The European Union 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 °F (10.6 °C) and is equivalent to 114.2 proof in the USA. Pure ethanol is 175.25 degrees proof, or more strictly is 75.25 degrees over 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 of alcohol by volume (sometimes abbreviated ABV). The regulations permit but do not require a statement of the degrees of proof as long as it is printed close to the percentage of alcohol by volume.[2]
The degrees of proof 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 US proof) and usually about 4% to 6% (8 to 12 US proof). Depending on the strain of yeast, wines top out at about 14% to 16% (28 to 32 US 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%. [1]
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 madeira. 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 US 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] Origin of proof
The term originated in the 18th century, when payments to British sailors included rations of rum. To ensure that it had not been watered down, the rum was “proved” by dousing gunpowder in it, then testing to see if it would ignite. If the gunpowder did not burn, the rum contained too much water—and was considered to be “underproof.”
A “proven” sample of rum was defined to be 100 degrees proof. This was later found to occur at 57.15% ethanol. This percentage is very close to a 4:7 ratio of alcohol to total amount of liquid. Seventy degrees proof is then equivalent to 40% ABV
[(4÷7) × .7 = 0.4]. And pure, 100% alcohol is 175 degrees proof [(4÷7) × 1.75 = 1.0].
This definition is no longer used in the United Kingdom; the ABV system must be used to state the alcohol content on bottles.
[edit] References
- ^ "Volume 25", Encyclopædia Britannica Eleventh Edition, pp. 694.
- ^ "Chapter 1, Part 5.37", Title 27 Alcohol, Tobacco and Firearms. Bureau of Alcohol, Tobacco and Firearms, Department of the Treasury, pp. 62.
