Don’t worry, understanding hydrometer readings has been confusing people for years. Here is a simple explanation on how to check the alcohol content of your beer.
First you need to understand what you are measuring.
During the brewing process yeast is added to malt and some other fermentable ingredients, maybe dextrose, and during fermentation the yeast organisms eat the malts and sugars and produce alcohol.
The density of the sugar in the water is lower than the density of alcohol so you use a hydrometer to measure the specific gravity of the solution before and after fermentation.
The volume of the alcohol in the solution can be calculated as follows.
Specific Gravity at the start of fermentation, minus the specific gravity at the end of fermentation, divided by 7.36.
So let’s go through this step by step.
1/ Mix all your ingredients in your fermenter and take a specific gravity reading. The reading will vary depending on how many ingredient you have added so don’t worry too much just record the reading.
2/ Add your yeast and let your beer ferment as normal.
3/ When fermentation is finished take a final specific gravity and record the reading.
4/ Now the calculation is simple. Opening specific gravity minus finished/final specific gravity divided by 7.36 is the alcohol content
So let us look at an example.
If I made a full flavoured beer like Guinness the opening specific gravity would be something like 1074 and the finished or final specific gravity would be something like 1025.
1074 – 1025 = 49 Now divided this number by 7.36
49 / 7.36 = 6.65 % alcohol.
It’s that simple.