Some wines get too dry as they age and need to be sweetened. Avoid the temptation to pour granulated sugar into your carboy of wine. The sugar will not dissolve and without a stabilizer, your wine could begin to ferment again resulting an excess of carbon dioxide in the bottles causing the corks to pop off. Look for the wine stabilizer potassium sorbate at wine making shops or Internet shops.
Bring the sugar and water to a boil over medium high heat in a saucepan, stirring to dissolve the sugar and create a syrup.
Pour 6 oz. of the dry wine into three tasting glasses to start.
Add 1/2 oz. (1 tbsp.) sugar syrup to all of the tasting glasses, keeping track of the sugar syrup added to the wine sample.
Taste the wine in the first glass; add another 1/2 oz. to the other three tasting glasses.
Sip the second glass containing 1 oz. of added syrup. If this does not have the proper sweetness, add 1/2 oz. of syrup to the remaining glasses.
Sample the third glass with 1 1/2 oz. of syrup for sweetness. Pour another 1/2 oz. of syrup into the last of the four tasting glasses, and taste for sweetness.
Determine the proportion of sugar syrup to add to the main carboy of wine: divide the amount of sugar syrup added to your favorite sample by the sample size (6 oz.). For instance, if you preferred the first sample with 1/2 oz. of sugar divide 0.5 by 6 to get: 0.5/6= 0.08.
Multiply the number of oz. in a gallon (128) by the proportion of syrup to add: 128 x 0.08 = 10.24.
Pour this amount of sugar syrup into the carboy of wine.
Mix ½ tsp. of potassium sorbate with 1 oz. of water in a measuring cup and pour this into the carboy, stirring to disperse it throughout the wine.
Use a hydrometer to measure the specific gravity of your wine.
Let the wine sit for one week before measuring the specific gravity again with the hydrometer. Bottle if the two readings match, as this indicates a stable wine.