Beer drinkers know that the ABV (alcohol by volume) of a beer will determine quite a few things. It’ll tell you how many beers of the same ABV you can have before getting sloshed. It can tell you whether or not you might expect some booziness in the taste of the beer. It can also tell you whether the brewer was following a traditional recipe or shooting for an imperial version of a particular beer style.
How do brewers figure out the alcohol content of a beer, though? That starts with gravity. We’re not talking about the unseen force that caused the apple to bop Newton in the head – we’re talking about something else.
What Is Beer Gravity?
At heart, gravity is a word used to describe the density of a beer, and the amount of sugars present, particularly at the start of the brew.
In the US, ABV is the most common reference format for the alcohol content in a beer. However, in other countries, it’s more common to use gravity readings on the label. That trend is starting to catch on here in the States, too. You’ll find a handful of beer labels out there with a gravity reading on them, sometimes instead of the beer’s ABV. What does that information tell you? Well, if you know a bit about beer science, then it can tell you the ABV range of the beer, as well as a little bit more.
Gravity is measured at least twice during the brewing process, but often multiple times. It’s measured after the boil, prior to pitching yeast to obtain perhaps the most important reading – original gravity, or OG. This is sometimes referred to as starting gravity, or SG. It’s also measured at the end of the fermentation process, which is called final gravity, or FG. The reading will be listed something like 1.052, or 1.080. Brewers check a beer’s gravity throughout the fermentation period, too, in order to determine when fermentation is finished, and the brew is ready for kegging or bottling.
Really, gravity is nothing more than a measure of the amount of dissolved solids in a particular beer. In this case, those solids are sugars. Because yeast eats sugar and produces alcohol, the higher the original gravity of a beer, the more potential alcohol there will be in a beer.
The closer to 1.000, which is the gravity of pure water, the less sugar (and the lower the potential ABV) of the brew in question. The closer to 1.099 (or higher) the more potential alcohol there is in the beer. So, a beer with an original gravity reading of 1.1 would be very, very high in alcohol, whereas one with an original gravity of 1.040 would result in a lower ABV beer.
To figure out the alcohol content of beer, brewers need to subtract the final gravity reading of the beer from the original gravity reading. The resulting number is then multiplied by 131.25 to arrive at the ABV for that brew.
What Else Does Gravity Tell You?
As mentioned, a gravity reading on a beer label can tell you several things about the brew in question. This goes well beyond the alcoholic kick that you’ll enjoy. For instance, a very high original gravity tells you:
- The brewer used a large grain bill in the brewing process. The more grain used, the more costly the beer is to brew.
- The beer may not be true to style according to industry guides. For example, a Russian imperial stout should have a high original gravity. However, a standard kolsch should not. If you come across a kolsch with a high original gravity, you know that the brewer was attempting to do something experimental.
- The beer took a long time to ferment and then to carbonate. Higher-gravity beers take longer for the available sugars to ferment out, often twice or even three times the time it takes a lower gravity beer to be finished. Carbonation also takes longer for high gravity beers (particularly if forced carbonation is not being used).
- The beer is going to have more calories than a lower gravity beer. Whether we’re talking alcohol or potential sugars for fermentation, we’re discussing calories. A beer with a higher gravity will have a greater impact on your waistline than one with a lower gravity.
- In many instances, gravity will tell you about the color of a beer. The BJCP (Beer Judge Certification Program) has extensive guidelines that tie beer color to gravity, although this does not guarantee that any beer with a particular gravity reading will be a specific color.
An Important Note
While a gravity reading on a label can tell you that the beer in the bottle is most likely high-octane stuff, that’s not always a guarantee. It’s really about the difference between the original gravity and the final gravity. It’s about the amount of suspended sugars in the wort converted to alcohol by yeast will. Some sugars cannot be converted, such as lactose, which is used to give milk stouts their sweetness. Adjuncts like oats and even cane sugar will affect everything from final ABV to the body and sweetness of a beer. You’ll need to take information about style, adjuncts used and more into account.
When everything is said and done, gravity is a good yardstick by which to measure beer strength, length of fermentation and even the amount of time and effort that went into producing a beer. However, it is only that – a yardstick. It is not a guarantee.
What have you found with different gravity ratings on beer labels? Have you been surprised by the taste, mouthfeel or texture of a high or low gravity beer?