ALCOHOL
DOSES
Further
complicating discussions of amounts of alcohol is the difference
between potency measures based upon "percent of alcohol by
volume" and measures based upon "percent of alcohol
by weight." Since alcohol weighs less than water, any discussion
about the proportion of alcohol in a beverage must specify whether
the comparison is "by weight" or "by volume."
A pint of water weights about one pound (16 ounces). A pint of
pure alcohol weighs about 12.8 ounces. If one pint of pure alcohol
is mixed with one pint of water, the result is a beverage that
is 50% alcohol "by volume." If one pound of pure alcohol
is mixed with one pound of pure water, the result is a beverage
that is 50% alcohol "by weight." Since one pound of
water 16 fluid ounces, and one pound of alcohol is about 20 fluid
ounces, the 36 total fluid ounces in a resulting beverage is about
55.5% alcohol "by volume," although it is 50% "by
weight." As an example of the importance of specifying the
system used to measure the percentage of alcohol in a beverage,
Coors Brewing Company promotional materials describe "Zima"
as containing 3.7% alcohol by weight; 4.6% alcohol by volume.
To convert measures by weight into measures by volume (or visa
versa), use a conversion factor of 0.79.
Measures
of Potency; "Proof"
The
strength of an alcoholic beverage is usually expressed as either
the percentage of absolute alcohol by volume, or as "proof."
In the USA, proof is a measure of the amount of absolute alcohol
in distilled spirits, and is calculated as the number of parts
of alcohol in 200 parts of beverage at 60 degrees Fahrenheit (a
beverage that is 50% alcohol is "100 proof;" a beverage
that is 43% alcohol is "86 proof"). Under the American
system, one "proof" is equal to one-half percent of
alcohol by volume.
The
concept of "proof" emerged prior to the 18th century,
when few people had the equipment necessary to make precise measurements
of the percentage of alcohol in a beverage. Exotic formulas, such
as igniting a mixture of equal parts of the beverage and gunpowder,
were used to test the proof of distilled spirits.
A
different system for measuring proof is used in England, In England,
proof is measured by comparing equal volumes of water and the
beverage at 51 degrees Fahrenheit. 100 proof is set at the point
at which the beverage weighs 12/13th as much as water. This means
that a beverage that is said to be 100 proof under the British
system is 114.2 proof under the American system. A beverage that
is 100 proof under the American system is said to be 87.6 proof
under the British system.
Alcohol
Doses
The
dose of alcohol is calculated by multiplying the volume
of an alcoholic beverage by the percentage of alcohol by volume.
For example, twelve ounces of beer that is 4% alcohol by volume
would have a dose of 0.48 ounces of alcohol. Pure alcohol (100%
alcohol) is called "absolute alcohol." Absolute alcohol
is alcohol without any water molecules in it. Alcohol produced
by distillation contains water molecules that are very hard to
remove. The strongest readily available alcoholic beverage, often
called "neutral grain spirits" is about 95% absolute
alcohol (190 proof). It is possible to manufacture absolute alcohol,
also called "scientific alcohol," by synthesis.
The
dose of alcohol in a typical 12 ounce can of beer, is approximately
equal to the dose of alcohol in a 4 to 5 ounce serving of wine,
or in a "shot" of whiskey. This average-sized dose of
alcohol is equal to one-half ounce of absolute alcohol, and is
sometimes called a "drink equivalent."
