The Strength (not alcohol) of Beer Explained

Steiger beer labelIn most countries, the strength of a beer refers the percentage of alcohol by volume or ABV. In Slovakia, and other parts of central Europe, the beer’s strength is thought to be the amount of fermentable material used to make the beer. If you look at a bottle of beer in Slovakia you’ll often see a large number with a percent sign after it (usually between 10 and 12%). Many of the beers even incorporate the number in their names (Steiger 10% Classic, Topvar 12% Premium).  This often leads to people thinking that the beers are 12% alcohol but in reality they are probably 3-5% ABV.  The number simply means that 12% of the ingredients’ density is made up of fermentable materials.

Let’s make some beer. Take some water, add a starch source (I recommend a malted barley), throw in hops for some bitterness, and then the magic ingredient, yeast! The amount of fermentable sucrose in the starch source plus the variety of yeast used to ferment that sucrose, determines the alcohol content. Yeast, as creepy as it sounds, is alive.  It’s a type of fungus that eats sugar then craps out alcohol and farts out carbon dioxide. If only humans could pull that off.  Basically, the more sucrose the yeast ferments, the more alcohol the beer will have.

Beer fermenting in vatWe determine how much sucrose is fermented by measuring the beers’ density, or its “gravity”. There are three stages of gravity during the fermentation process: the gravity before fermenting (the original gravity or OG), the gravity that it currently sits at (the specific gravity or SG), and the gravity that it is when it stops losing density (final gravity or FG). By measuring the difference between the OG and the FG, the brewer is able to determine the amount of alcohol in the beer. In the brewing industry, the scale used to measure the gravity is usually the “Plato scale”. Using math and a giant brain, you can take the numbers you get from the Plato scale and convert them to a percentage of alcohol.

In Slovakia, they take the original gravity and display it as a percentage of density. If it’s a 12% beer, then 12% of its density was fermentable. Sometimes, instead of a percentage you will see a degree. This simply refers to what it’s measured at on the Plato scale, 12° is equal to 12%.

So what’s better, having the ABV or the density of fermentable material? Well both is good, which Slovakia usually displays, but you should know that the ABV isn’t 100% accurate. In fact, on the back of a Slovak bottle it will often read, “Obsah alkoholu min.” followed by the ABV. This means the “minimum alcohol content”. The correlation between the density and the percentage of alcohol isn’t linear. Since, methanol is less dense than water but sucrose is more dense, determining what exactly caused the change in density cannot be done with 100% accuracy. So the ABV of a beer is an estimation, however with modern brewing practices and Drunk on bar stool.an understanding of the biochemistry of yeast, it’s pretty accurate. If you are a brewer, degrees Plato might have a lot more use to you than the ABV, but most of us just want to know how drunk we are going to get after having 3 or 4. The ABV, along with a number of other factors (body weight, how much you’ve eaten, what you’ve eaten, etc.), will give you a pretty good idea. Alternatively, use the “fall off the bar stool” method. The stronger the beer, the harder you fall.


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