Using the old stew to make new stew does the opposite of lengthening it ' s life . It shortens it even more from what it already has . The more times you heat and cool it , the more times it passes through the danger zone . 42 F 130 F , which is the temperature range that bacteria thrives in , bacteria that makes food unsafe to eat . In particular , the more time it is spent cooling , the more bacteria growth you will find . In restaurants you ' re not permitted to reheat something more than once cook it once , cool it down , then heat it once again to serve , leftovers must be thrown out , but these precautions are largely to prevent those who are immunocompromised from becoming ill . That said , I would just eat the soup as is and then make a new soup later . If you make a new soup with the old soup you ' ll just have more bad soup that you didn ' t finish .