Knowing the ABV (Alcohol by volume) of your homebrew is pretty useful. It is not necessary for you to enjoy your drink but it can be a helpful insight into what you just brewed. Simple changes can have huge effects and it is very easy to see this in your ABV. We provide the approximate ABV on each of the sheets we provide with our 1 Gallon Homebrew kits, which should be accurate if you follow the instructions but even then there can be small variations.
The first thing you will need is a hydrometer, which we sell in our store. A Hydrometer measures the specific gravity of a liquid, which is to say it measure how heavy it is by volume (density) compared to water. This is done by placing a hydrometer in a cylinder of the liquid you wish to measure, then taking a reading from the stem.
To figure out ABV you will need two readings. One before fermentation and one after. These are known respectively as Original Gravity (OG) and Final Gravity (FG). You will find that OG will give a larger number than FG, this is because much of the sugar in your beer has been turned into alcohol. So a higher sugar content gives a larger OG, more sugar for the yeast to convert and thus a higher alcoholic content.
Now you are required to do some maths, I apologise for no warnings earlier but the sum is pretty simple and I will break down how you can do it in parts.
ABV = (Original gravity – Final Gravity) X 131.25
1.050 – 1.010 = 0.040
0.040 X 131.25 = 5.25% ABV
(1.050 – 1.010) X 131.25 = 5.25% ABV
As Suggested in other articles we recommend that you keep all this down in a log book, this is a helpful way to keep track of your brews and to understand what you have done different.