Short definition
Adding sugar to grape must before fermentation to raise the final alcohol level, not to make the wine taste sweet.
In cold years, grapes sometimes do not ripen enough to produce sufficient alcohol through natural sugar alone. Chaptalization adds sugar to the must — the yeast converts it all to alcohol, so the finished wine is not sweet, just stronger. Named after Jean-Antoine Chaptal, Napoleon's agriculture minister. It is a tool for difficult vintages, not a shortcut for lazy farming.