A hydrometer is essential in determining both the alcohol content of your finished beer, and when to bottle. Always make sure you have a spray bottle on hand when taking samples from your fermenter. After drawing beer ( wort ) from the fermenter, spray the tap with water or sanitizing solution to clean the tap outlet. If you don't take this step bacteria may form in the residue and go on to contaminate your beer when bottling or kegging.

To take a hydrometer reading, fill your tube from the tap to about 2cm from the top. Gently put your hydrometer in, drop and twist to dislodge any bubbles. Blow away any froth to get a clear reading of Specific Gravity ( S. G. ) at the liquid level.

To ascertain the alcohol content of your beer you need a reading when you first fill your fermenter. This will be about 1038 S.G. or more depending on the style of beer you are making. You then take a reading at bottling time, this will be about 1010 S.G.. Subtract 1010 from 1038, leaving 28. Multiply 28 by 0.14 which gives you an alcohol content of 3.92%. There are small variations depending on beer temperatures but it will be close enough.

Second reading

When you are ready to bottle your beer the hydrometer reading should be around 1010 for normal beers or you may get eruptions when opening your bottle or worse still, explosions. It is O.K. to bottle at higher readings than this if you are making higher gravity beers. Just make sure fermentation has finished by getting two readings the same on two consecutive days. You should always check final gravity before bottling.