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General Food Safety
Should infant formula be reheated?
No. Infant formula is a good growth environment for bacteria. It contains all the necessary nutrients and is in fact superior to most laboratory nutrient broths. The infant formula is powdered and contains sugars and grains (e.g. sucrose, corn syrup solids, soy) plus other ingredients. These food ingredients are known to contain Bacillus and Clostridia spores. Heating the formula after hydrating and then partially feeding activities the spores and also contaminates the formula with bacteria from the infant through backslop. Clostridium perfringens is the fastest growing genus encountered normally. It can double in numbers every 10 minutes under ideal temperature conditions. Each reheat cycle allows greater numbers of bacteria to grow, requiring a higher kill-ratio each heat treatment. Each reheat cycle selects for heat resistant strains. After multiple heat treatments, significant heat resistance will be found. Recommendation for consumers. Try not to reuse formula. If you must save it, refrigerate it quickly to stop growth of Clostridia. When you reheat it, bring it to a boil again, or heat 5-10 F higher than you did the first time, to defeat heat resistance. Formula, which is promptly (within one hour) refrigerated and then re-boiled will be safe. Remember that the infectious dose for an infant is much less for an adult.