How do you test alcohol content?

Answered by Tom Adger

Testing the alcohol content of a beverage is an important step for brewers, as it helps them determine the strength and quality of their product. There are several methods available to measure alcohol content, with the most common ones being the use of a hydrometer or a refractometer.

1. Hydrometer:
A hydrometer is a simple and inexpensive instrument that brewers have been using for centuries to measure the specific gravity of a liquid. To test alcohol content using a hydrometer, you will need two specific gravity readings: one before fermentation and one after fermentation.

– Before fermentation: Take a sample of the beer wort (unfermented beer) and fill a hydrometer tube or cylinder. Immerse the hydrometer into the liquid, making sure it is floating freely. Take the reading from where the liquid surface intersects the scale on the hydrometer. This reading will give you the original gravity (OG) of the beer.

– After fermentation: Once fermentation is complete, take another sample of the beer and repeat the same process. This reading will give you the final gravity (FG) of the beer.

To calculate the alcohol by volume (ABV) percentage, you can use the following formula:

ABV = (OG – FG) × 131.25

The result will give you the approximate ABV percentage of your beer. However, it’s important to note that this method assumes that all the sugar in the wort has been converted into alcohol, which may not be the case in certain situations.

2. Refractometer:
A refractometer is another handy tool that can be used to measure the alcohol content of a beverage. Unlike a hydrometer, a refractometer measures the refractive index of a liquid, which can be correlated to the alcohol concentration.

To use a refractometer, simply place a few drops of the liquid on the refractometer’s prism and close the cover. Look through the eyepiece and read the scale where the boundary between light and dark areas meets. This reading is called the Brix value, which represents the concentration of dissolved substances in the liquid.

However, when it comes to measuring alcohol content, there is a caveat with refractometers. As the fermentation process produces alcohol, the refractive index of the liquid changes due to the presence of alcohol. This can lead to inaccurate readings if not properly compensated. Brewers can use online calculators or specific formulas to adjust the refractometer readings for alcohol content.

Both hydrometers and refractometers are useful tools for brewers to test the alcohol content of their beverages. The hydrometer method is more traditional and straightforward, while the refractometer method requires additional calculations to account for the presence of alcohol. Whichever method you choose, it’s important to follow the instructions carefully and ensure accurate measurements to achieve the desired alcohol content in your brew.