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Alcohol Proof Definition and Examples
What Alcohol
Proof Means and How to Calculate It
by Anne Marie
Helmenstine, Ph.D.
Grain alcohol or
spirits may be labeled using proof rather than percent alcohol.
Here's what proof means and an explanation of why it's used and
how it's determined.
Alcohol Proof Definition
Alcohol proof is twice the volume percentage
of ethyl alcohol (ethanol)
in an alcoholic beverage.
It is a measure of the ethanol (a
specific type of alcohol) content of an alcoholic beverage.
The term originated in the United Kingdom and was defined as 7/4
the alcohol by volume (ABV).
However, the UK now uses ABV as the standard to express alcohol
concentration, rather than the original definition of proof.
In the United States, the modern definition of
alcohol proof is twice the percentage of ABV.
Alcohol Proof Example: An alcoholic
beverage that is 40% ethyl alcohol by
volume is referred to as being '80 proof'.
100-proof whiskey is 50% alcohol by volume.
86-proof whiskey is 43% alcohol by volume.
Pure alcohol or absolute alcohol is
200 proof.
However, because alcohol and water form an azeotropic
mixture, this purity level cannot be obtained using simple
distillation.
Determining ABV
Since ABV is the basis for calculated alcohol proof, it's useful
to know how alcohol by volume is determined.
There are two methods: measuring alcohol by volume and measuring
alcohol by mass.
The mass determination does not depend on temperature, but the
more common percent (%) of total volume is temperature dependent.
The International Organization of Legal Metrology (OIML)
requires volume percent (v/v%)
measurements be performed at 20 °C (68 °F).
Countries belonging to the European Union may measure ABV using
either mass percent or
volume percent.
The United States measures alcohol content in terms of alcohol
percent by volume.
The percentage of alcohol by volume must be labelled, although
most liquors also state proof.
Alcohol content may vary within 0.15% of ABV stated on the
label, for spirits containing no solids and over 100 ml in volume.
Officially, Canada uses
US labeling stating percent alcohol by volume, although the UK proof standard
may still be seen and heard.
Common spirits at 40% ABV are called 70° proof, while 57% ABV is
100 proof.
"Over-proof rum" is rum containing greater than 57%
ABV or exceeding 100° UK proof.
Older Versions of Proof
The UK used to measure alcohol content using proof spirit. The term came from the 16th century when
British sailors were given rations of rum.
In order to demonstrate the rum hadn't been watered down, it was
"proved" by covering it with gunpowder and igniting it.
If the rum didn't burn, it contained too much water and was
"under proof", while if it burned, this meant at least 57.17% ABV was
present.
Rum with this alcohol percentage was defined to be 100° or one
hundred degrees proof.
In 1816, the specific gravity test replaced the gunpowder test.
Until January 1, 1980, the UK measured alcohol content using
proof spirit, which was equivalent to 57.15% ABV and defined to be spirit
with a specific
gravity 12/13 that of water or 923 kg/m3.
Anne
Marie Helmenstine, Ph.D.
Introduction
Ph.D. in
biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge
National Laboratory.
Science
educator with experience teaching chemistry, biology, astronomy, and physics at
the high school, college, and graduate levels.
ThoughtCo
and About Education chemistry expert since 2001.
Widely-published
graphic artist, responsible for printable periodic tables and other
illustrations used in science.
Experience
Anne
Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education
since 2001, and other sciences since 2013. She taught chemistry, biology,
astronomy, and physics at the high school, college, and graduate levels. She
has worked as a research scientist and also abstracting and indexing diverse
scientific literature for the Department of Energy.
In
addition to her work as a science writer, Dr. Helmenstine currently serves as a
scientific consultant, specializing in problems requiring an interdisciplinary
approach. Previously, she worked as a research scientist and college professor.
Education
Dr.
Helmenstine holds a Ph.D. in biomedical sciences from the University of
Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in
chemistry from Hastings College. In her doctoral work, Dr. Helmenstine
developed ultra-sensitive chemical detection and medical diagnostic tests.
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