To maintain the fresh taste of leftover eggplant and tomato sauce, immediately store it in an airtight container in the fridge. This will preserve its flavor for about 3 to 4 days. For longer storage, freeze the sauce by first allowing it to cool. Then, portion it into freezer bags or containers, where it can be kept for up to 3 months. When ready to use, thaw the sauce overnight in the refrigerator and reheat thoroughly before combining it with your hot pasta.