Depending on where you live, there are two main systems for measuring the alcohol content of beverages. In the US, the alcohol content is measured in alcohol proof which is twice the percentage of alcohol by volume (ABV), used in Europe. Therefore, 150-proof Rum has 75% ABV. Simple math, right? Right… until you start hanging out with Brits, whose proof system equals to roughly 1.75 times of the alcohol by volume.
A look back in the history of measuring alcoholMany different ways of measuring alcohol content evolved throughout the history and gunpowder used to play an important role in that. See, in the 16th century England, gunpowder was used for measuring the alcohol content of spirits.
Back in the day, spirits were taxed at different rates, depending on how much alcohol they had. A pellet of gunpowder was soaked in the liquid and could the pellet still be ignited afterwards, the spirit would be rated as above proof and thus taxed at a higher rate. Gunpowder would not burn in Rum (spirit of choice back then) with less than 57.17% of alcohol by volume.
Rum with this percentage of alcohol was defined as 100 degrees proof—this is not to be confused with what 100 degrees proof means today.
The gunpowder test was officially replaced by a specific-gravity test in 1816.
Traditional equipment for measuring alcohol contentNowadays, some experts still like to use fairly traditional manual methods of measuring alcohol content, which is usually done with two similar-looking but very different glass contraptions: alcoholmeter and hydrometer.
While travelling through the Cognac region, our good friend Thibault Mauxion from Louis Royer was kind enough to demonstrate the measuring of alcohol content with the aforementioned traditional method.
The amount of alcohol in a pure base spirit (distilled spirit) is measured with the alcoholmeter. As soon as any sugar or other soluble substances are added to the spirit, the readings will be off. This is where its cousin, the hydrometer, comes into play.
First, the liquid is poured into a tall container, often a graduated cylinder, and then the alcoholmeter/hydrometer is gently lowered into the liquid until it floats freely.
Alcoholmeter is used to determine the volume of alcohol or proof. It is calibrated to the density of pure ethanol and is only to be used on pure, distilled spirits.
Hydrometer, on the other hand, is calibrated to the density of water and is used during the pre-fermentation and post-fermentation phase. Hydrometers are used to determine the potential alcohol content.
Tips, tricks, and things to look out for in the processAlcohol readings also vary depending on the temperature of the spirit. The temperature that the instrument is calibrated to is usually listed on its side (20°C in most cases). Should the spirit still be warm when measuring its content, it will be “lighter” than at standard temperature, thus the meter will sink lower, making you think that it has more alcohol than it actually does.
Adding more sugar will also make the liquid thicker, thus the meter will be harder to sink. When fermentation occurs, the sugar is converted into alcohol, the liquid becomes thinner, and the meter sinks deeper. If using a hydrometer, a reading is taken before and after fermentation and the approximate alcohol content is determined by subtracting the post-fermentation reading from the pre-fermentation reading.
Modern alcohol-measuring methodsToday, many distilleries threw away their analogue devices and replaced them with state of the art digital alcohol meters, which are quicker and easier to use.
Operation of devices is easy, results are displayed in seconds and there’s no need to temperature-correct them. While they might be handy, we’re still asking ourselves where’s the fun in that?