Unopened guava paste can be stored at room temperature in a cool, dry place, and it often has a shelf life of a couple of years. Once opened, it should be kept in the refrigerator, where it can last for several weeks to a few months. To keep it longer, you can freeze guava paste, where it will stay good for up to a year. To use, simply defrost in the fridge overnight. It's always best to check for signs of spoilage like mold or a sour smell before using.