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A Word About Alcohol by Volume (ABV) in Homebrew and Beer

July 26, 2014 by Rick Morris

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 homebrewers is...

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 %.


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