What is used to preserve squashes, jams, and jellies?

Sugar is used as a preservative for jams, jellies, and squash. Along with heat and acid, sugar is used to preserve squashes, jams, and jellies. The sugar helps to thicken the mixture, increase the overall sweetness, and create an environment in which bacteria and mold cannot grow. The heat used during the cooking process helps to sterilize the mixture and break down the fruit or vegetable, while the acid (such as lemon juice) helps to lower the pH, making the environment inhospitable for harmful microorganisms.