Gatorade does not easily go bad after opening, but it is important to store it in the refrigerator to prevent bacteria from growing and to maintain its best taste and freshness. Even when stored properly, Gatorade will start to lose its electrolytes and taste flat after several days to a week if left out at room temperature.
The recommendation to refrigerate opened Gatorade bottles is due to the presence of yeast, which can thrive in a sugar and salt rich environment, potentially leading to the growth of bacteria that could make you ill if consuming them. Additionally, leaving Gatorade opened at room temperature for an extended period can cause the electrolytes to become flat, making the drink bland and unenjoyable.
Therefore, it is generally recommended to store Gatorade in the refrigerator after opening to avoid these issues. If you forget to refrigerate a opened bottle, it is still possible to save it by pouring out the contents and drinking it quickly while the yeast is still active, but drinking it slowly may help reduce the risk of bacterial growth.