Determining your ABV

Posted by Barley Beaver on

A hydrometer is an instrument that helps you determine the ABV in your homebrew or wine. How does it do this? Sugar is denser than alcohol, so the reading before pitching your yeast (OG or original gravity) and the reading difference of your fermented wort/mash (*FG or final gravity) is used to calculate the ABV. As the yeast turns the sugar into alcohol, the reading on your hydrometer will show a lower number as the hydrometer will sink deeper into your liquid. The hydrometer sinks because once your wort is fermented, the alcohol is not as dense as the sugar, so the hydrometer does not float as high. The temperature of your wort can also factor into this reading. Most hydrometers are set to a standard of 60F, so read and follow the instructions that came with your hydrometer. 

Another measuring device many homebrewers use are refractometers (most have automatic temperature control). A brewing refractometer is an optical device that uses only a drop or two of liquid to give you a reading. If you use this instrument after fermentation has started, the alcohol will skew the reading. If you use a refractometer for before and after readings, you should use a refractometer calculator (many of which may be found online) to obtain an approximate ABV reading. Many refractometers need to be calibrated before each use to get the correct readings.

When buying a hydrometer, you should make sure that it is NOT a Proof & Tralle if you plan to use it for your homebrew. A Proof & Tralle hydrometer/alcoholmeter measures spirits in distilled liquors, not the sugar/alcohol content in beer and wines.

Which of these two instruments is right for you? Once again, I have scanned over many forums and read the comments, and it seems to be a matter of personal preference. Many homebrewers use the refractometer for the OG reading since the liquid is hot and only need a few drops are needed. They then use the hydrometer for the FG reading as the fermented liquid is at room or lager temperature.

Next week, I will look at some of the calculations used to determine your ABV once your OG and FG readings.

*Just a reminder - when you are taking your FG readings, you should do so a few days apart to ensure that fermentation has fnished. The FG reading should be the same for two readings in a row. 

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