This simple tool is essential for wine makers and beer makers. It measures the so called “Specific gravity”. To put it another way; it measures the weight of a liquid compared to water.
This number by itself does not mean anything for a wine or beer maker but with tables or formula’s you can say something about the amount of sugar in the liquid.
However a big ATTENTION here. Sugar is very heavy and it is of great influence on the specific gravity. Usually other influences can be more or less discarded. But keep in mind what you are doing. You are NOT measuring sugar contents, you are measuring “weight”.
I found that out when I was measuring a juice that I bought from a supermarket. On the box it mentioned that there should be 110 gram sugar per liter in it. When I measured it the hydrometer reading was around 1037 which means, according to the table that I use, only around 80 gram sugar per liter!
I did not understand what was happening because I did not believe that the manufacturer could be wrong by this much.
Luckily I also have a refractometer (which measures sugar in a completely different way) so I also measured the juice with it. The refractometer said that the package was correct with its 110 gm/l.
Then I noticed something on the package. The keyword was carbonated! There was CO2 dissolved in the juice. Since CO2 is much lighter, the specific gravity of the juice was much lower than expected.
So be aware that other factors (like alcohol) can influence the SG.
Another point that is worth mentioning is that there can be more scales on the hydrometer. It can also have a scale for potential alcohol and / or sugar contents. Do not use these! The hydrometer can be used for beer making and wine making and you can imagine that these liquids have a different amount of sugar in them at the same SG.
So use the value for SG and use a table or a software program to determine the sugar and alcohol amounts.
Now that we have that out of the way; let’s measure something!
It is very simple. Just put some of the juice in the measuring cylinder and put in the hydrometer.
Read the value as shown in the drawing.
Check in the table what the amount of sugar is and how much alcohol will be produced. In case you want more alcohol you can use the table to find out how much sugar to add.
- As always: Work cleanly.
- The meter should not be stuck to the wall of the cylinder
- Make sure that there are no air bubbles stuck to the hydrometer.
- In case you are making wine from fruit; make sure there is no pulp in the cylinder