Potassium Sorbate is a yeast inhibitor used to prevent further fermentation in wines with residual sugar. It doesn't kill yeast, but prevents them from dividing to produce new yeast cells. It also does not inhibit the growth of malo-lactic bacteria and malo-lactic fermentation occurring after the addition of sorbates will produce an undesirable distinct off-odor of geranium leaves. This problem can be forestalled if you maintain at least 50 ppm of free sulfur dioxide after sorbates are added to the wine.

Best practice is to add the sorbate to the mixture of sugar and water used to sweeten the wine, because the sorbate dissolves better in a warm liquid. There is never any reason to add potassium sorbate to a dry wine. Normal usage is 1 to 1-1/4 grams per gallon of wine (equivalent to 1/2 to 3/8 teaspoon per gallon). This is the equivalent of 200 to 250 ppm.

Potassium sorbate should be stored where it is dry and out of direct sunlight. Even with proper care shelf life is normally only six to eight months.