Fermentation is the process of yeast converting sugars into alcohol. In winemaking, the yeast reacts with the natural fructose (fruit sugar) to produce alcohol. The percentage of alcohol by volume in the finished wine depends on the sugar content of the grape, the strain of yeast and other factors, including fermentation temperature. Stopping fermentation may be desirable if the winemaker wants to add additional sugar, such as for some varieties of fruit wine, or to control the alcohol content to avoid creating an overpowering wine.
Determine the volume of must (fermenting wine). For example, a standard glass carboy (water-cooler bottle) holds five gallons.
Crush one Campden tablet for each gallon of must.
Pour the crushed Campden tablets into the must using a funnel. A piece of paper folded in half can improvise as a trough for guiding the powder into a bottle if a funnel is unavailable.
Allow the must to sit for 10 days while the Campden tablets halt the fermentation process.
Add 1/4 teaspoon of potassium sorbate per gallon of wine before bottling and corking as a preservative. This reacts with the sulfites from the campden tablets to prevent re-fermentation after bottling the wine, which could lead to bursting corks and exploding bottles if the fermentation gases (carbon dioxide) create too much pressure. Add 1/2 teaspoon of potassium sorbate per gallon if the wine will be fortified with additional sugars before bottling, such as when making fruit wines.
Campden tablets release sulfur dioxide into the fermenting wine. The yeast dies from the sulfites.