Calculating alcohol content in your homebrew beer

The method most employed by homebrewers involves the use of a hydrometer.

The process is very simple:

1. Using a hydrometer, measure the initial density of the must before starting fermentation: $\delta_i$
2. Then, after the fermentation has finished, take a second density reading: $\delta_f$
3. Now subtract both readings and multiply by a given factor:
   \[ (\delta_i - \delta_f)* f= ABV \]  

The value obtained is the ABV (alcohol by volume) often expressed as a percentage.

This is simple to calculate, but not many homebrewers know where this formula comes from.

In a later post, I will explain how to derive this equation.