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Alcohol Strength: Volume, Weight, Proof

There are many questions that have long preoccupied humankind. What’s the meaning of life? What is love? Is there anybody out there? Why do cats purr? How strong is actually this drink?

Let’s stick to the latter, for now at least, since it might be of higher interest for our whiskey still matters. As it happens with such universal questions, there is no clear-cut answer. People use a couple of different ways of describing alcohol strength, some relying on straightforward science, some on old practices.

  • Alcohol by Volume (ABV)

This is the standard measure of how much alcohol (ethanol) is contained in a given volume of an alcoholic beverage, expressed as a volume percent. That is, how many milliliters of pure ethanol in 100 milliliters of liquid, at 68 °F (20 °C).

Temperature is relevant because it influences alcohol density: alcohol is “lighter” when warm and “heavier” when cold.

  • Alcohol by Weight (ABW)

ABW measures the alcohol content in a beverage, expressed as a percentage of total mass. It’s not as popular worldwide, but some states use it to regulate and tax alcoholic beverages, and you’re likely to find it on domestic beer brands. ABW is calculated by using the AVB, with the following formula:

AVB * 0.78924 = ABW * density of beverage at 68 °F (in g/ml)

  • Proof

Now, the plot increases in density. Measuring alcohol strength by “proof” has its origins in the UK, back in the day when people wore funny hats and used gunpowder to test if liquor did indeed contain a “correct” measure of alcohol. With no safety regulations to stop them, they poured some liquor over a little gunpowder and set it on fire. If the alcohol content was adequate, it would burn with a nice, steady blue flame and eventually ignite the gunpowder –thus granting the liquor with “100 proof”.

The formula evolved, as declared by the British Parliament in 1816: “a quantity of 100 proof liquor would have the same weight as 12/13ths of the same volume of pure water at 51° F.” So: 100 proof (UK) = 57.06 %ABV 

Meanwhile, the Brits have generally given up the gunpowder procedure (yet not other far more puzzling ones, but let’s not go there), and generally using alcohol proof as a measure, and in 1980 adopted the standard AVB.

In the US, the relationship between proof and AVB is simple:

Proof (US) = 2 * %AVB

Now breathe, put that gunpowder down and stay tuned, we’ll soon get to the ‘how to’ of measuring the alcohol content of your home made liquors.

Posted by Jason Stone on

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