Measuring Alcohol by Volume in Home Brews

Image above by Kevin from The Beginning at Last

No Theme Thursday: 01.16.25 (First Anniversary Edition)
This is a submission for Kevin’s No Theme Thursday

Beer Styles

Look at that happy and friendly beer muse above. That is Kevin’s picture. Wouldn’t you like a beer? I like beer and I also brew beer at home. My dog Rollo loves it when I spill wort on the kitchen floor. The wort is what you have before fermentation. It is like a grainy sticky sweet soup, and he likes to lick it up. However, my wife does not like it when there’s sticky wort all over her kitchen floor and the stove. Everyone has their own perspective.

Rollo in the kitchen hoping for the wort to boil over or spill.
This is an IPA that I brewed at home, and it came out pretty good. Look how happy my beer garden gnome is.

Beer is one of the oldest alcoholic beverages in the world, dating back over 7,000 years to ancient Mesopotamia. There are more than 100 different styles of beer worldwide, with the main categories being lagers and ales. The beer advocate currently lists 120. Below are a few examples of Lagers and Ales.

Lagers : Pilsner, Märzen (Oktoberfest), Adjunct Lager, Pale Lager, Scwarzbier (a black lager), Bock.

Ales : IPA, Stout, Porter, Wheat Beer, Belgian Beer, Blonde Ale, Saison, Barley Wine, Lambic, Geuze

Brewing Beer at Home

When you brew beer at home you start by boiling the wort. You boil water and you add the malts and the hops for the flavoring and the aroma at specific times. This all depends on the recipe you are following. Warning! The wort easily boils over. Then you cool the wort (I use an ice bath to do this), add the yeast, and you let it ferment, typically for a couple of weeks.

You can add various things for flavoring, such as whiskey infused wood chips if you want your beer to have a taste of whiskey and wood (yes, I have done that). Whiskey and wood are great added flavors in stouts. After the two weeks of fermentation, you add sugar and bottle the beer and let it ferment for a few weeks before you put it in the fridge.

Boiling wort on the kitchen stove. It contains water, malts, hops, and maybe sugar or honey.

A few words about the bottling process. The bottling process below is using siphoning instead of pouring to achieve some filtering and to avoid splashing. Splashing can cause excessive oxidation which can ruin the beer the same way bananas turn brown. This seems to matter for New England style IPAs, but not so much for other beer styles (my observation).

Here I am bottling beer while drinking a renowned IPA called Pliny the Elder, one of the best India Pale Ales in the world.

Measuring the alcohol content in home brews

When you brew beer at home you don’t have the advanced equipment that breweries sometimes do so measuring the alcohol content is a challenge. However, you can do it with an indirect method using a hydrometer. I will explain how to do this. There are instruction booklets, books and online websites that explain how to do this, but I will keep it short and succinct.

During the fermentation process, yeast converts sugars into alcohol (and carbon dioxide). As the sugar is used up, the wort slowly becomes less dense. By measuring the density before and after fermentation (using the hydrometer), you can calculate how much alcohol is in the finished beer. In the beer world this is called measuring the gravity, not to be confused with the fundamental force of attraction between objects with mass. You can buy a hydrometer in a lot of places including Amazon.

This is a measuring cup (left) and a hydrometer (right). Don’t worry about markings on the measure cup. It is the markings on the hydrometer that you use.
Close up of a hydrometer.

The density/gravity of water is used for reference as 1.000. To be exact, it also depends on the temperature, but for now we’ll ignore that. After the initial boil of the wort, and before you add the yeast, there is no alcohol in the wort. This is a good point to measure what is called original gravity (OG).

I should mention that you need to let the wort cool off before doing your measurement. The temperature at this point should be around room temperature, 72 degrees (60 to 75 degrees). Then after fermentation (in your container, carboy, whatever) you measure it again. This is called the final gravity (FG).

Original gravity/density Was 1.072. Final gravity/density was 1.018 (in picture).

I should add that after the fermentation in your container/carboy is done you add a little bit more sugar (called priming sugar), you bottle the beer, and you let it ferment a little bit more, which will add a little bit more alcohol as well as carbon dioxide. You want some carbon dioxide in the beer but not too much. This extra amount of alcohol is not accounted for using the final gravity. However, it is typically around 0.2% and if you wish to include it, you can just add that number.

Using the original gravity (OG) and the final gravity (FG) you can now calculate the ABV, Alcohol by Volume, by using the formula below. For this brew, an IPA (India Pale Ale), I got OG = 1.072 and FG = 1.018. Ideally FG is around 1.010, but for whatever reason I did not get there.

ABV = (OG – FG) x 131.25 = 0.054 x 131.25 = 7.1%

So that would be 7.3% with the bottle fermentation. That is a good enough measurement, but if you want precision, there is a more exact formula.

ABV = (76.08 x (OG – FG) / (1.775 – OG)) * (FG/0.794) = which in my case yields ABV = 7.23% which would yield 7.43% with the bottling. I can add the recipe predicted ABV = 7.5%. There are even more exact formulas that account for the temperatures at the points of measurement of original gravity and the final gravity. But that would be really nerdy.

To see the Super Facts click here

Author: thomasstigwikman

My name is Thomas Wikman. I am a software/robotics engineer with a background in physics. I am currently retired. I took early retirement. I am a dog lover, and especially a Leonberger lover, a home brewer, craft beer enthusiast, I’m learning French, and I am an avid reader. I live in Dallas, Texas, but I am originally from Sweden. I am married to Claudia, and we have three children. I have two blogs. The first feature the crazy adventures of our Leonberger Le Bronco von der Löwenhöhle as well as information on Leonbergers. The second blog, superfactful, feature information and facts I think are very interesting. With this blog I would like to create a list of facts that are accepted as true among the experts of the field and yet disputed amongst the public or highly surprising. These facts are special and in lieu of a better word I call them super-facts.

45 thoughts on “Measuring Alcohol by Volume in Home Brews”

  3. How cool Thomas, I have never tried to self-brew beer. The finished product looks great and is making me thirsty, I can well understand and indeed see (look at those eyes) Rollo’s desperation to get in on the action. I enjoyed reading about the processes involved, mist of which was either new to me or I’d forgotten from the many brewery tours I’ve taken over the years.

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    1. Thank you so much Leighton. Sometimes it comes out good, like my last IPA, but sometimes it is not great. I’ve had a New England style IPA oxidize fairly quickly (must have splashed it during bottling), and my latest Hefeweizen / wheat beer had the problem with half the bottles being flat. It has been suggested to me that the cap on some of my bottle are leaking. Professional breweries don’t worry about these things.

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    1. Yes I remember that. It was very interesting to learn about the beer they brewed. I forgot the name of it at the moment. There are many interesting beer brewing traditions around the world. It is too bad so many people think of beers as bud light.

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  6. This brings back many good memories. It’s been several years since I’ve brewed a batch of beer. I need to clear some days on my calendar and brew a batch again. I sent two of my beers to the state fair in New Mexico and they both won silver medals. One was a porter and the other was a smoked ale with chipotle peppers added for flavoring.

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  9. A few notes.

    First, this is fascinating, as I know nothing about home brewing. I have considered trying it, but have not yet!

    Second, that whiskey and wood beer sounds excellent!

    Finally, Rollo is beautiful!

    Thank you, Thomas. I truly enjoyed this!

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  10. That’s much more complicated than I expected, Thomas, and it involves math! Oh no. Hehehe. But what a fun hobby, especially if it comes out well. I’ve made (undrinkable) wine before, and I do ferment a decent kombucha, which requires no special skills. Cheers!

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  11. I both read and watch a lot of historical fiction, and I am always amazed by the amount of ale consumed. I had no idea of what was involved in the home brewing process having only ever seen the elaborate processes in retail brewery outlets, so this was of great interest. Thank you for this play by play. I really enjoyed it.

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    1. Thank you so much for your kind words Violet. Ales were often safer to drink than water back in the day because you boiled the wort. There were so many kinds of Ales with so many different flavors. Then came the Lager, which is a great invention but the pale mass produced lagers became so popular that the Ales with all their variety of flavors and types are being forgotten a bit.

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  14. Where I work, we have a client that makes yeast that’s used in home-brewing (professional breweries use it too). I never got into home-brewing myself though. Kind of in the same way I never had the urge to bake my own bread, I never had the urge to brew my own beer. The people who are into it are really into it, though! Kind of like how the people who bake bread are really into baking bread. Maybe it’s a yeast thing. 😉

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    1. A Yeasty thought. You are right it is kind of like baking bread but slower. The yeast is quite important and type of yeast you use can result in a lot of different flavors. It is not just the hops. Some yeast result in a lot of esters, which in general you don’t want unless you get the right yeast for that. You get banana flavored esters when you brew with wheat and the right yeast (in wheat ales like Hefeweizen and Witbier) and you fruity and tart flavors with wild yeast when brewing Lambics, Geuze, and other Belgian fruity style beers.

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