Potassium Sorbate 2 oz
Potassium Sorbate dissolves completely in wine to prevent yeast from fermenting. This is a very common 'stabilizer' or 'preservative' for wines, meads, ciders, and especially after fermentation on a product that has been back sweetened and then bottled. This product will not stop an active fermentation. Add at bottling just before whatever you are using to back sweeten your finished product.
As a common preservative, ensure that any store bought apple juice you are using for cider DOES NOT contain potassium sorbate in the ingredients list, as you will have a hard time fermenting it.
Use at a rate of 1/2 teaspoon per gallon.