Sugar is an important part of the winemaking process. Yeast converts sugar to alcohol, and the amount of residual sugar left in the wine after fermentation determines how sweet or dry the finished wine is. Though most sugar is added to wine before or during the fermentation process, additional sugar can be added to the finished wine to sweeten it without increasing its alcohol content. Adding sugar to finished wine gives you more control over the final sweetness of the wine and also can correct weak flavor caused by poor quality wine ingredients.
Choose a sugar type to add to the wine. Different sugars bring different qualities to wine and can subtly affect the flavor and body of the sweetened wine. Common sugars used to sweeten wine include light brown sugar, honey and bar or "superfine" sugar. Bar sugar and honey are easier to mix with finished wine than brown sugar.
Open the wine bottle and pour some or all of it into a carafe or other serving container. This allows the wine to "breathe" and makes adding sugar easier since you have a more open container to add it to and can control the amount of wine you sweeten.
Measure the sugar based on the amount of wine you wish to sweeten. Two level teaspoons of sugar or honey should be added to a full bottle of wine; adjust the amount as needed if you are using less than a full bottle or more than a full bottle. This will add the equivalent of 1 percent residual sugar to the wine.
Add the sugar or honey to the wine slowly, stirring gently with a wooden spoon or similar instrument if needed. You want to make sure that the sugar or honey dissolves and blends with the wine completely, so check to see if any sugar settles to the bottom after you've finished stirring.
Taste the wine to make sure it's sweet enough. Sweet wines typically have a residual sugar content between 1 percent and 4 percent, and adding too much sugar can ruin the flavor of the wine. If the wine isn't sweet enough for your tastes, add additional sugar or honey a teaspoon at a time.
Serve the wine within a few hours of sweetening it for best results. Leftover sweetened wine should be stored in the refrigerator to prevent the sugar from fermenting and building up pressure inside the wine bottle.