How to Check How Much Alcohol Is in Your Homebrew

How to Check How Much Alcohol Is in Your Homebrew

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Emma Christensen
May 21, 2015
(Image credit: Melissa Ryan)
(Image credit: Henry Chen)
  • Today's topic: Learn how to check the alcohol in your beer
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There's one thing we haven't talked very much about so far: the alcohol in your beer. Hop aromas and malt flavors are fantastic and all, but let's be honest here — the buzz that we get from a good beer is also part of why we do this!

So where does the alcohol come from? How can we figure out how much is in our homebrew? How can we adjust it if we want to? In today's lesson, I'll answer all these questions and show you what to do.

(Image credit: Melissa Ryan)

Talk Like a Brewer

Fermentable sugar: Simple sugars that are easy for the yeast to eat and turn into alcohol.

Unfermentable (or, nonfermentable) sugar: Sugars with more complex chemical structures that are more difficult for the yeast to eat. In your beer, these sugars add sweetness and body.

Specific Gravity (or, gravity): The measure of your beer's density as compared to water. Sugar increases density, so by measuring the gravity of your beer, you can know how much sugar it contains. By taking one reading at the beginning of fermentation and another at the end, we can calculate how much sugar has been converted into alcohol, and therefore, the alcohol content of the beer.

Original Gravity (or, OG): The measure of the beer's density taken before fermentation begins, when the sugar levels are at their highest.

Final Gravity (or, FG): The measure of the beer's density taken after fermentation is complete, when the sugar levels are at their lowest.

Hitting the gravity: How close you get to the targeted original and final gravity readings of your beer recipe with your homebrew.

Alcohol by volume (or, ABV): The percent alcohol in your beer.

Where Does Alcohol in Beer Come From?

The alcohol in beer is a direct result of the yeast eating sugar. As the yeast consumes the sugar in the wort, it creates alcohol and carbon dioxide — the carbon dioxide floats up and out of the beer while the alcohol stays behind and turns the beer boozy.

So yes, alcohol is essentially yeast pee. And you're welcome to share that trivia fact at your next backyard barbecue.

Why Does Beer Still Taste Sweet?

As fermentation progresses and the yeast munch away on the sugars, the beer wort goes from being very sweet to much less sweet. The reason why finished beer still tastes at least somewhat sweet and malty — and not as dry as pinot grigio, say — is thanks to some unfermentable sugars that get left behind.

During the mash, both fermentable and unfermentable sugars are created. Fermentable sugars have a very simple chemical structure that makes them easy for the yeast to eat and digest. Unfermentable (or nonfermentable) sugars have a more elaborate and complex structure and the yeast have trouble breaking them down. The simple fermentable sugars get consumed, and the complex nonfermentable sugars get left behind. Our taste buds still perceive these complex sugars as sweet, so that's why beer still has some sweetness. (The unfermentable sugars also add some body to beer, which is why some beers taste heavier or more syrupy than other beers.)

How Do We Figure out the Alcohol Content?

To figure out the alcohol content of our homebrew, we need a way to measure the sugars at the beginning of brewing and at the very end. The difference will tell us how much sugar was consumed and therefore how much alcohol is in our beer.

One of the easiest ways to measure the sugars is with a hydrometer. This snazzy tool will tell you the specific gravity of your beer — gravity is a measure of the density of a liquid as compared to water, and sugar increases density. As the yeast consume the sugars, the liquid will become less dense and closer to the density of water.

Original Gravity vs. Final Gravity

The reading taken at the beginning of brewing is called the "Original Gravity" (OG), and the reading taken at the end is called the "Final Gravity" (FG). By plugging these numbers into the following formula, we get the alcohol by volume, or ABV, of our homebrew.

Formula for Calculating Alcohol in Beer

  • Subtract the Original Gravity from the Final Gravity
  • Multiply this number by 131.25
  • The resulting number is your alcohol percent, or ABV%

In shorthand:

(FG - OG) x 131.25 = ABV %

(Image credit: Melissa Ryan)

What to Do: Measuring and Calculating Alcohol Using a Hydrometer

Apart from your chilled wort or finished beer, you will need a measuring cup, the hydrometer, the hydrometer tube, and a thermometer. Be sure to sanitize all the equipment before using it.

  1. Measure out about a cup of wort (or finished beer).
  2. Fill the hydrometer tube up to about 2 inches from the top.
  3. Insert the hydrometer. The hydrometer will float in the liquid and bob up and down. If necessary, give it a little spin to shake off any bubbles. Wait for the hydrometer to come to a stop.
  4. Look where the liquid intersects the markings on the hydrometer. Most hydrometers have a few different units of measurements printed on them; you are looking for the gravity reading, which will be a number between 1.000 and 1.160 or so.
  5. Record the gravity reading. Most hydrometers are also marked in increments of 0.002. Do your best to determine the precise number. If you're off by a point or two, it's OK. (This is homebrewing after all, not rocket science.)
  6. Adjust the gravity reading for temperature. Hydrometers are calculated to different temperatures, usually 60°F or 68°F. Check the temperature of your beer, then use the instructions that came with your hydrometer for how to adjust the gravity if needed.
  7. Pour the wort or beer back into the container. Since all your equipment has been sanitized, there's very little risk that you'll introduce bacteria here. If you're concerned, you can discard or drink this sample you took for the gravity reading.

The Kitchn's Beer School: Amber Ale

  • Target OG: 1.051
  • Target FG: 1.011
  • Target ABV: 5.2%

Hitting the Original and Final Gravity

Hang out with homebrewers long enough and you'll hear them talk about "hitting the gravity." They're talking about how close they came to the original and final gravities specified in a particular recipe with their homebrew. Hitting your gravity feels a lot like hitting a bull's eye — fist-pumping and hollering included.

But if you don't hit your gravity, and even if you're quite far away from hitting it, don't beat yourself up about it. The gravity readings specified by most homebrew recipes are an ideal-world scenario — meaning, if everything went completely perfectly from brew day to bottling, you would hit those numbers every time.

In reality, we're homebrewers and it's not an ideal world. There are lots of things that affect the gravity reading, from how finely ground your grains were and the quality of your water to how well you were able to hold the temperature of the mash. You'll get better at all of these things — and get closer to hitting the gravity — the more you brew. For now, aim for getting it in the ballpark and don't worry about the home run. Your beer will still be great, and it's still useful to record the gravity readings so you can figure out how much alcohol you have.

You can also drink the beer you used to check the gravity
(Image credit: Melissa Ryan)

4 Easy Ways to Adjust Alcohol in Home Brew

Since the alcohol level in your finished beer is a direct result of how much sugar you started with, and the amount of sugar is a direct result of your mash, start there if you want to tinker with the alcohol level in your finished beer. Here are a few ways to start doing this, from easiest to most difficult:

  • Add extra fermentable sugar: You can boost the alcohol just by adding in some extra fermentable sugar, like malt extract, Belgian candi syrup, or even honey. Be careful — just a little can boost the alcohol by quite a bit! Also, be aware that these sugars will add their own particular flavors to the beer.
  • Adjust the grind of your grain: It's easier to extract the sugars from grains if they're more finely ground. Be careful of grinding them too finely and making flour — you'll end up with a thick, sticky mash that is very difficult to sparge. (However, I wouldn't really suggest grinding the grains less finely to reduce the alcohol level; you can start sacrificing a lot of flavor.)
  • Increase or decrease the amount of base malt: You can easily identify the base malt because it comprises the majority of the grains in your recipe. This malt is where most of your sugars will come from, so by increasing or decreasing it by 4 to 8 ounces, you can reliably increase or decrease the alcohol in your beer without hugely affecting the overall character of the beer.
  • Adjust the mash temperature: A warm mash (154°F to 158°F) will give you a little less alcohol and more of those unfermentable sugars. A mid-range mash (148°F to 153°F) will give you a good balance of fermentable and nonfermentable sugars. A cool mash (143°F to 147°F) will give you more fermentable sugars and therefore a little more alcohol.

Can I Make Non-Alcoholic Beer?

Yes, it's possible to make a non-alcoholic homebrew, but it's rather tricky and not something we're going to cover during this Beer School. If you're interested in this route, I suggest digging into some of the writing that's been done on the topic and the online discussions on forums like Homebrew Talk.

Brew Better Beer: A Companion to Beer School

(Image credit: Emma Christensen)

I love brewing beer so much, I wrote a book about it! Brew Better Beer (May 2015, Ten Speed Press) is a complementary guide to Beer School. Take a look for even more nerdy details about homebrewing, how to brew 5-gallon batches, and plenty of recipes for different beers.

→ Find it: Brew Better Beer by Emma Christensen

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