Sour salt is not salt at all . . . it is citric acid! It is used to add an extra tart flavor to sourdough and rye breads. It may be used in canning to prevent fruit from turning dark. To use to prevent mold from sprouting, use 1/4 tsp Sour Salt per quart of soak or rinse water. In tomato canning, use 1/2 tsp Sour Salt per quart.
When used as an ingredient to flavor foods, it provides a distinctively sour or tart taste to the food dish. It is a common substance used in sausage making or canning to keep the color of fruits from darkening. It is commonly used as a substitute for lemon juice, providing a tart flavor with only a few grains. Since the flavor can overpower some recipes, it is best if used with sugar to arrive at an enjoyable blend between the sweet and sour taste. This type of salt, which may also be referred to as citric salt or citric acid is often used in recipes for Borscht, a cold beet soup, or lemon cheesecake.