First off, no matter the formula type, once a sterilized bottle comes in contact with your baby’s mouth, you should never reuse the formula that’s left over in that bottle. Always throw out any unfinished formula directly from the bottle you were using. Still, all types of formula can be stored for a little while after they’ve been prepared, but only if you follow the parameters laid out below.   Powder If you’ve mixed the powdered formula and it’s in a container you didn’t use for the feeding—here are the musts: Feed your baby within 1 hour without reheating the formula. Discard any leftover mixture. Reusing leftover formula isn’t recommended due to a risk of bacterial contamination.   Concentrate and Ready-to-feed If you’ve poured formula into a sterilized bottle and it hasn’t touched your baby’s lips—here are the musts: Ensure it’s the appropriate amount to feed your baby. Feed your baby within 1 hour without reheating the formula. Discard any remaining formula.   Open packages If you’ve opened a Tetra of concentrate or ready-to-feed formula and don’t wish to use it all right away—here are the musts: Cover the package with plastic wrap. Put it in the fridge immediately after opening. Store it in the fridge for no more than 24 hours.   In addition, following the label instructions is important for the health of your baby. For safety reasons, it is not recommended that formula be reheated if it’s been warmed or left out at room temperature, as there’s an increase risk of bacterial contamination.