Winemakers measure sugar concentration in "degrees Brix", or just "Brix" (1.0 Brix = 1 g sugar in 100mL water). Being able to test the sugar content of the must or wine at the following stages of winemaking gives us imporatant data that we can use to control our alcohol levels and manage our fermentations:
It is a good idea to test the sugar level at the beginning of fermentation because the amount of sugar in the juice determines the amount of alcohol that will end up in the final wine: for every 1.0 Brix consumed, 0.62% alcohol is created. Sugar testing can be done with a refractometer or a hydrometer. We suggest a starting Brix range of 22-25 Brix for Red wines, and 17-24 Brix for White and Rose wines. If your must is over or under these ranges we recommend correcting it before fermentation starts. Complete information on correcting sugar levels in must can be found in both our Red Winemaking Manual and our White Winemaking Manual.
End of fermentation:
Unless you are trying to make a dessert wine, most wines are fermented to "dryness", meaning there is less than 2 g/L (0.2%) of residual sugar in the wine. A specialized "+5/-5" Brix hydrometer is a good way to tell if you are generally done fermenting the last of your sugars (look for a reading of -1.5 to -2.5 Brix) but it will not give you the most accurate result. If you want the most accurate test for residual sugars in your wine, you will need to run a Clinitest residual sugar test.