Fresh mozzarella must be used within a few days. To store it, immerse any leftover cheese in brine (a strong saltwater mixture). To make a brine, add 1 tablespoon (15g) of salt to a pint (500 mL) of water or milk, add the cheese, cover, and store it in the refrigerator. Salted mozzarella will keep for about one week; unsalted will keep for just a few days. Semisoft “pizza cheese” has a longer shelf life; check the “Use-By” date that is generally printed on the packet.