What is the point of measuring the Specific Gravity? The goal is to determine and correct the amount of alcohol you will have in the finished wine.
- Measure the acidity of your juice.
- Measure the S.G. with the hydrometer.
- Check the corresponding column in the table according to the acidity to find out the alcohol percentage and amount of sugar. If you don’t know the acidity you can use the middle column. (6 to 10 g/l acid) It is not such a big difference to the others.
- In case you want more alcohol; look up the amount of sugar that you need for this percentage and compare it to the amount of sugar available in the juice.
- Determine the amount of sugar per liter you need to increase the S.G. to the desired value and add it.
A simple example.
You want to make 10 liter wine of approximately 11 %.
Let’s say that the acidity of your juice is 5.
The hydrometer measurement is 1050.
In the table (see below) you can see that there is 110 gram sugar in 1 liter and the result would be an alcohol % of 6,1.
In the table you can see that you need 201 gram of sugar per liter for 11,2 % alcohol.
So you need to add 201-110 = 91 gram per liter.
Put 10×91=910 gram of sugar in the fermenter and fill it to 10 liter.
Note: Do not fill the fermenter to 10 liter and then add the sugar. This is not completely correct because the sugar also has volume and you will end up with more than 10 liter.
Some things about the table that you don’t really need to know but may be interesting:
I copied it from a book that I have, and another wine maker that I know also has used it for years.
Since you can make wine from a lot of different fruits the table is a compromise. I guess you could make a similar table for every fruit there is, but probably they would also be different every year.
Because acids influence the S.G., the table is divided in three parts.
The table is based on the following formula’s:
Juice with acidity lower than 6:
sugar (g/l) = 2,6 x (SG-1000) – 20
Juice with acidity between 6 and 10:
sugar (g/l) = 2,6 x (SG-1000) – 25
Juice with acidity higher than 10:
sugar (g/l) = 2,6 x (SG-1000) – 30