In August 1989, UK Government-funded research showed that listeria and other potentially fatal bacteria can survive in microwave-cooked food, even where cooking/heating instructions are strictly followed. [1] This was blamed on the inability of microwave ovens to heat evenly, leading to ‘cold spots’, even raw areas, in the food.

According to an article in The American Journal of Epidemiology,[2] microwaving leftover food is not as safe as reheating it in an oven or a frying pan. An outbreak of Salmonella typhimurium in Juneau, Alaska (US), was traced to food taken home in ‘doggie bags.’ While 30 people had taken home doggie bags, only ten became sick. These ten had reheated their food in a microwave oven.

Naturally-contaminated whole raw broiler and roaster chickens were cooked according to manufacturers’ instructions using different brands of microwave oven. Ten of the 174 birds yielded visible listeria bacteria after cooking, most of which came from just two of the seventeen microwave ovens used.

The researchers noted specifically that microwave ovens were unreliable killers of bacteria in food.[3]