The hydrometer is an indispensible aid to those who wish to be scientific about wine and beer making.
Even if you are not interested in the finer details, it is a great tool for diagnosing problems with stuck ferments and judging whether your wine and beer has consumed all the available suger.
The principle behind a hydrometer is quite simple. A suger solution is denser than plain water, thus when you put a weighted hollow object in a suger solution, it will sink less than it would in plain water. Thus you can measure the <strong>density</strong> of the water.
Alchohol on the other hand is lighter than water and so a fermented out solution, will have a density less than plain water.
A hydrometer may come with a few different scales, but the relevent one to home brewing will run from below a 1000 to maybe 1200.
Simple use of a hydrometer
At its simplest you can use the hydrometer at the start of wine making to check that the reading which is called the <strong>specific gravity</strong> or <strong>SG</strong> is in the range 1070-1090. It is in this range that there is enough suger to make a dry wine 9.2% to 12% alchohol by volume. Add more suger than this, and you may find the ferment struggles to start, less and the keeping qualities of the wine may be less.
At the end of fermantation you need to check that the suger really has fermented out, and the ferment is not simply <strong>stuck</strong>. The hydrometer reading should be taken and checked that it has fallen below the 1000 mark.
The above usage is really very easy, and will avoid you making the basic mistakes, that lead to problem ferments or burst bottles.
Advanced use of a hydrometer
Apologies for the use of imperial scales, but we brew wine in gallons, so it makes life easier.
The primary advanced use of a hydrometer is if you want to <strong>feed</strong> your wine suger, as it ferments, if you are trying to brew a high alcohol wine, it is bettter to <strong>feed</strong> the wine suger in stages.
In this case what matters it the total drop in SG throughout the process, each time you add suger you take before and after readings, enabling you to add up each drop in SG from the previous stage. This total is then divided by 7.36 to give alcohol by volume.
|Specific gravity (SG)||Potential %vol alcohol|
|1040||5.1||1 lb 1 oz|
|1045||5.8||1 lb 3 oz|
|1050||6.5||1 lb 5 oz|
|1055||7.2||1 lb 7 oz|
|1060||7.8||1 lb 9 oz|
|1065||8.6||1 lb 14 oz|
|1070||9.2||2 lb 1 oz|
|1075||9.9||2 lb 4 oz|
|1080||10.6||2 lb 6 oz|
|1085||11.3||2 lb 9oz|
|1090||12.0||2 lb 12 oz|
|1095||12.7||2 lb 15 oz|
|1100||13.4||3 lb 2 oz|
|1105||14.1||3 lb 5 oz|
|1110||14.9||3 lb 8 oz|
|1115||15.6||3 lb 11 oz|
|1120||16.3||3 lb 14 oz|
|1125||17.0||4 lb 1 oz|
|1130||17.7||4 lb 4 oz|
4 lb 7oz
When wine making, boiling ingredients to extract flavour is a common process and you may want to get a reading before the <strong>must </strong>has returned to room temperature.