To store leftover keto albondigas soup, allow the soup to cool down to room temperature before transferring it to an airtight container. The soup can be stored in the refrigerator for up to 4 days. If you want to keep it for a longer period, you can freeze the soup for up to 3 months. When you're ready to reheat the soup, simply thaw it in the refrigerator overnight and reheat it on the stove over medium heat until it's heated through.