When I started brewing I made a beer using malt extract a little bit of crystal malt and some East Kent Goldings hops. I had found a process online and followed it, I brewed the beer, waited for it to ferment and then bottled it. It tasted like beer and wasn’t too bad for a first attempt, I had one question left unanswered though and that was how strong was my beer. I had looked at the guide I found online and couldn’t see where the % ABV (alcohol by volume) was written.
So How Do You Work Out How Strong Your Home Brew Is?
Calculating the percentage of alcohol in a beer is simple so don’t worry, the only thing you need is a hydrometer. Using a hydrometer is a simple. It is basically a measuring device that measures the density of a liquid. When you measure the density of plain tap water you pop your hydrometer in it and it sinks to a certain depth. The scale on the stem of the hydrometer indicates the density. The density of water is 1.000
Unfermented beer (wort) on the other hand is full of simple sugars and carbohydrates, these things will alter the density of the liquid meaning when you drop your hydrometer in the wort it won’t sink as much. The added density will mean the hydrometer sits higher up in the liquid giving us a different reading say 1.050.
When the beer ferments the sugars will be consumed by the yeast, this process removes the sugar turning it to alcohol as well as carbon dioxide and this reduces the density back down. Once fermentation is complete another reading is needed from the hydrometer, you will find it will not be 1.000, this is because there are some unfermentable carbohydrates in the beer. A more usual reading will be 1.012 for instance. It is with this information we can calculate the alcoholic content of the beer.
Calculating Alcohol By Volume or the Strength of Your Beer
Using the readings above as an example you have the following information:
Hydrometer reading before fermentation: 1.050
Hydrometer reading after fermentation: 1.012
To calculate the ABV we simply subtract the lower gravity figure from the original gravity figure like so:
1.050 – 1.012 = 0.038
Multiplying the result by 131.25 will give us a good approximate alcohol content:
0.038 x 131.25 = 4.99%
So the strength of the beer is approx. 4.99% ABV.