Today’s post doesn’t pertain solely to beer, but it is an essential step in brewing. When you buy a beer in the store, it generally has the Alcohol By Volume, or ABV listed on the label. This is a measurement system to show what volume of the liquid contained in that bottle or can is pure alcohol. Basically, the higher the ABV, the stronger the alcohol content of the beer. Let’s take a look at what that means for your beer.
What’s with ABV?
Most beers will ring in around the 5-7% ABV range, but there are definite outliers both far above and below that. For example, A session beer is a type of beer that is meant to be consumed in a single session. This means more drinking and less alcohol per drink. So, these session beers will be around 3-5% at most. We mentioned Imperial beers and dubbel/trippel Belgians in a previous post about glasses. Those can be upwards of 8-12% ABV each. There are even some beers, like Dogfish Head’s 120 Minute IPA that clocks in at ~19% ABV! That’s one strong beer!
This may seem nebulous and hard to figure out, but it is actually pretty simple. If you checked out the last post on Brewing Essentials, you know that a tool used in brewing is the Hydrometer. This is used for measuring the gravity of the beer. Before beer is fermented, it’s called Wort (pronounced “wert”). The wort has all the fermentable sugars in it, waiting to be eaten by the yeast. This wort is measured with the hydrometer and a reading is taken. This is called the “Original Gravity,” or OG. In perfect H20 at 60* F, the hydrometer reads 1.000. As the liquid gets denser (more “stuff” in it, like sugars) the reading gets higher.
Skipping ahead a few days/weeks, to when the wort has finished fermenting, and a second reading is taken. This reading is called “Final Gravity,” or FG. This reading will be lower than the first, as the yeast has eating a lot of the sugar in the wort to make alcohol.
Note: Both the original and final readings must be done at 60* F. Hydrometers are calibrated to give precise readings at this temperature. Changing the temperature changes the reading. You can adjust for changes in temperature, but doing them at 60* is the easiest. More on hydrometer readings can be found here.
With the OG and FG readings, you can now determine how much alcohol is in your finished product.
Let’s look at an example. If you were brewing an IPA that had an OG of 1.070 and a final gravity of 1.018, you would subtract the FG from the OG and then multiply the answer by 131.
1.070 – 1.018 = 0.052
0.052 x 131 = 6.812
This means the beer is at 6.812% ABV, or as it is commonly listed, 6.8%
As you can see, it really isn’t that complicated to determine the ABV of a beer. When you brew, it is common to take this measurement a few times, so you know when to pull your beer out of the fermentor and bottle it. The longer it stays in the fermentor (with active yeast), the lower the FG will get, and the higher the ABV will get.