A hydrometer isn’t essential for home brewing – but is an inexpensive tool you’ll want to invest in if you want to be able to work out the alcohol content of your mead.
A hydrometer is used to calculate the specific gravity of a liquid. It is a sealed glass tube with a weight at the bottom and a graduated scale along the neck. The hydrometer reads specific gravity of a liquid in comparison with water. If you place the hydrometer in plain water it would read a density of 1.00. Home-brewing hydrometers such as the one shown above are pre-calibrated for use in brewing beers, wines and ciders. You calculate the alcohol content of your finished mead by taking two measurements – one when starting the mead, and the second when bottling it.
Take a sample of your mead before you add the yeast. Float the hydrometer in the sample and make a note of the number. Read the number at the bottom of the curved line of liquid (the meniscus). This is your starting specific gravity (SG). For most wines and meads this will be somewhere between 1.060 and 1.120.
When the mead is ready for bottling, take another sample to check the final SG. It will be much lower than the first reading, as alcohol has a much lower density than a water-sugar mixture. The lower the reading, the dryer the mead:
- Dry Mead: 0.099 to 1.006
- Medium Mead: 1.006 to 1.015
- Sweet Mead: 1.012 to 1.020
- Dessert Mead: 1.02 +
There are several handy online calculators, but calculating the strength of your mead is fairly simple. Subtract the final SG reading from the beginning SG reading, and divide by 0.00736 to get the percentage of alcohol by volume (ABV), e.g. if starting SG is 1.109 and final SG is 1.018 then the final ABV is 12.36%.