Chaptalization is the addition or concentration of sugars in grape juice. Grapes reaching full maturity can be a concern in some cooler climates. Mature flavors will quite often develop, but the corresponding sugar concentration may not. This can lead to low alcohol wines. Winemakers are allowed to add sugar to correct this problem (adding sugar to juice is illegal in California however). Common sucrose is typically used to correct low sugar juices. Other fermentable sugar products like glucose, fructose, and high fructose corn syrup are also possible. The winemaker should consider something that balances both glucose and fructose concentrations in the juice though, as these two sugars are basically present in equal quantities naturally. Adding excessive amounts of fructose should be avoided, as juices that are high in fructose can potentially cause problematic fermentations.

Some finished wines may also benefit from a very slight addition of sweetness to offset overly acidic flavors. When sweetening finished wines, syrups are more commonly used as they dissolve much easier into the wine. Syrups also tend to contain more fructose, which is sensed as being much sweeter and therefore less of it is required in the finished wine. A bench trial should be performed to find the desired level of sweetness when adding sugar to a finished wine. The winemaker must make sure that the sugar added fully dissolves into the juice or wine.