Proof (alcohol)
From Wikipedia, the free encyclopedia
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).
Contents |
[edit] Origins
This system dates to the 18th century, and perhaps earlier, when spirits were graded with gunpowder: A solution of water and alcohol "proved" itself when it could be poured on a Pinch of gunpowder and the wet powder could still be ignited. If it didn't ignite, the solution had too much water in it and the proof was considered low or "underproof".
A "proven" solution was defined as 100 degrees proof (100°). This has since been found to occur at 57.15% ethanol. This is still used as the British definition, although only the ABV system is used on bottles and sales. A simpler ratio to remember is 7:4, i.e. 70° proof is approximately 40% alcohol by volume. Thus pure alcohol is approximately 175 degrees proof (175°).
A hydrometer was traditionally used to measure the precise proof of a spirit, a practice which has gone through many formal changes.
[edit] Regulations
[edit] EU
The European Union member nations have broadly adopted the recommendation of the International Organization of Legal Metrology (OIML) which measures percentage of alcohol by volume at 20 °C.
[edit] British proof spirits
In Britain, this replaced the Sikes hydrometer system (based on proof spirit) which was used since 1816, although 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."
Previously, Clarke's hydrometer had been used since the 1740s when Customs and Excise and London brewers and distillers began to use Clarke's hydrometer.
[edit] United States
In the definition current in the United States, 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 (most of the other 60% is water), and pure alcohol would be "200 proof". If a 150-proof beverage is mixed half-and-half with water, the product is 75 proof. US proof numbers are properly cited as, for instance, "86 proof," not "86 degrees proof." The use of the word "degrees" in this context is incorrect.
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 right next to the percentage alcohol by volume. [1]
[edit] Alcohol during production
Alcohol is produced by yeast during the process of fermentation. The other product of fermentation is carbon dioxide, which is the gas that can make beer bottles explode or blow their tops off. 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%. [2]
Very few microorganisms can live in alcoholic solutions. The main three are yeast, Brettanomyces, and Acetobacter. In what is essentially disinfection, yeast keeps multiplying as long as there is sugar to "eat", gradually increasing the alcoholic content of the solution and killing off all other microorganisms, and eventually themselves. There are "fortified" wines with a higher alcohol concentration than that because stronger alcohol has been mixed with them. As this is usually done before fermentation is complete, these products contain a much higher quantity of sugar and therefore are typically quite sweet.
Stronger liquors are distilled after fermentation is complete to separate the alcoholic liquid from the remains of the grain, fruit, or whatever it was made from. The idea of distillation is that a mixture of liquids is heated, the one with the lowest boiling point will evaporate (or "boil off") first, and then the one with the next lowest boiling point, and so on. The catch is that water and alcohol form a mixture (called an azeotrope) that has a lower boiling point than either one of them, so what distills off first is that mixture that is 95% alcohol and 5% water. Thus a distilled liquor cannot be stronger than 95% (190 proof); there are other techniques for separating liquids that can produce 100% ethanol (or "absolute alcohol"), but they are used only for scientific or industrial purposes. 100% ethanol does not stay 100% for very long, because it is hygroscopic and absorbs water out of the atmosphere.
Everclear, a neutral grain spirit is sold at 190 U.S. proof in parts of the U.S. where it is legal. For comparison, absinthe (one of the highest-alcohol commercial liquors available) usually tops out at around 70% ABV and ranges from about 120 to 130 U.S. proof. Austrian Stroh 80 rum is an exception with a ABV of 80% (proof U.S. 160).
