Chaptalization is the process of adding sugar, or concentrated grape juice, to must to raise the potential ethanol level in the final product. Cane sugar is the most common source of chaptalization, but beet sugar and concentrated grape juice are also used. The sugar is generally added prior or during the fermentation process.
Chaptalization is practiced in regions (or years) where the grapes do not fully ripen by the time they are harvested and the natural sugars in the grapes are not in enough abundance to reach the target alcohol content to produce a balanced wine. Most wine regions have regulations that control the amount of sugar that can be added. Some countries/states that are generally in warmer climates, such as California, Australia and Italy ban the practice of chaptalization, while other countries primarily in cooler regions, such as New Zealand, Alsace, Burgundy and Oregon allow it, but with restrictions. In the US, where chaptalization is allowed, it is limited to adding the amount of sugar that would raise the original density of the must to a maximum of 25 Brix.
The process of Chaptalization is named after the French chemist Jean-Antoine Chaptal, although adding sweetening agents to fermenting grape juice can be traced back to the Roman times.