A Word About Alcohol by Volume (ABV) in Homebrew and
July 26, 2014 by
Alcohol by Volume, or abv as it is often
found on bottles and cans of beer, wine, and spirits.
Beer typically falls between 2 and 12 percent abv, but can
be higher. Wine generally contains about 10 to 17
percent abv. and whiskey, liquor, and vodka are about
40 abv. So, what exactly does the abv number on beer
products mean? More importantly, how do homebrewers
measure the abv in their beer?
Essentially, the amount of alcohol
(ethanol) in a beer or other alcoholic beverage. It
describes the percentage of alcohol found within the total
volume of the drink when measured at 20 degrees Celsius.
Americans measure the level of abv through
"proof", where it usually is twice the amount of alcohol.
So, if the bottle of bourbon is 80 proof, then is contains
40 % abv.
Although there is a simple formula for
determining the level of abv in beer, homebrewers always
measure the just boiled wort with a device known as the
hydrometer. This neat little glass tube contains a
chart inside it showing estimated abv, specific gravity, and
some other info. It has been calibrated to a specific
gravity of 1.000 at 60 degrees F. Anything denser than
that, like sugary water or wort, and the reading is higher.
After boiling, the homebrewer simply drops
the sanitized hydrometer in the wort after it has chilled to
around 60 degrees F. A few measures will be taken.
The most important is the starting (original) gravity.
And, it may read something like 1.040. After the beer
has fermented fully, another check is made using the
hydrometer. This "final gravity" reading is certainly
going to be lower the the first reading (hopefully for the
brewer!) and could read something like 1.005. A quick
calculation using the before and after measures will tell
the brewer the probably abv of the beer.
The formula for performing an estimated
abv check is...
ABV = 1.05/0.79 (Starting Gravity - Final Gravity / Final
Gravity) x 100
A more simple version used by
ABV - 131(Starting Gravity - Final Gravity)
For example, lets say you brew a Belgian
Tripel and take a starting gravity measurement of 1.090,
followed by a final gravity measurement (after fermentation
stops) of 1.010. Subtract the two from each other
(1.090-1.015) and you get 0.075. Multiply that by 131
and you get 9.825 abv.
The hydrometer will also provide an
estimated abv reading when it rests in the wort (before
fermentation begins). This measures is based on the
density of the liquid as a result of the available sugars in
the wort. But, it's not as accurate as taking before
and after fermentation measures. Why? Well, mainly
because most brews never get fully fermented (attenuated).
I.E. not all the sugars were eaten by the yeast.
Sometimes you may find a beer labeled "abw"
or alcohol by weight. When that happens, just multiply
the labeled amount by 1.25. For example, if the abw is
4 %, the abv is 5 %.