Figuring the initial sg of a wine that is already fermenting

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Wade E

Jul 3, 2006
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You can thank Luc for this info!

When you buy a bucket of juice and it is already fermenting there is an easy way to obtain the original SG.
It is called the boiling off method.
You take 250 ml must that you want to measure. Take a hydrometer measurement. Boil it down to 120 ml and then fill up with distilled water. Do another hydrometer measurement.
Now start fermcalc:
and go to the alcohol tab and look at the boiling off method.
You will now now the SG of the must and the alcohol that is already in it.
From the amount of alcohol you can derive the amount of sugar that has already been used, and adding that to the sugar that is still in the must you know what the initial SG is.

For keeping records of SG proceedings you can use the already mentioned spreadsheets. I use this one:


Dutch Winemaker
Nov 5, 2006
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Just a small addition for those that not read the original thread that made me write this post.

With the boiling off method the measurements are done with a hydrometer.

Keeping track of the SG is of course easy with a hydrometer. The spreadsheet is intended for refractometer users.