Once prepared formula must be consumed within an hour. Then you better throw it away and start over. Reheating is not a good idea and we also advise against preparing bottles in advance and putting them in the fridge. Freshly prepared formula is best: we do our utmost to ensure the highest possible quality and leaving it standing for more than an hour and/or reheating it is not wise. Improper preparation and storage can pose health risks, especially for the little ones.