Microwave cooking can be dangerous
October 6, 2008
OMAHA, Neb. – Zapping frozen meals in the microwave may be fast and easy, but it also can make you sick if it’s not done properly.
That message has been slow to catch on, despite a spate of illnesses last year from improperly microwaved frozen foods. On Sunday, the government issued a new warning urging consumers to thoroughly cook frozen chicken dinners after 32 people in 12 states were sickened with salmonella poisoning.
“Given how people use microwaves, it’s great for reheating, but maybe not so good for cooking,” said Doug Powell, scientific director of the International Food Safety Network based at Kansas State University.
The problem is that microwaves heat unevenly, and can leave cold spots in the food that harbor dangerous bacteria, such as E. coli, salmonella or listeria. So microwaving anything that includes raw meat, whether it’s frozen or thawed, can cause problems.
“I think most food-safety experts probably would have said it’s not a good idea to microwave anything that’s from a raw state,” said Michael Davidson, a University of Tennessee food microbiologist.
Many people wrongly assume all frozen meals are precooked and only need to be warmed. It’s a misconception fostered in part by foods prepared to appear cooked, such as chicken that has been breaded or prebrowned.
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“I haven’t worried about the safety of frozen food. Maybe I should,” Kathy Tewhill said while perusing the frozen-food aisle of a Hy-Vee grocery store.
In reality, even some meals designed to be microwaved can be unsafe if they are not heated thoroughly enough, or are cooked using directions meant for a microwave with different voltage.
The government doesn’t track microwave-related foodborne illnesses, but every year, more than 325,000 people are hospitalized for food-related illnesses. Last fall, hundreds became ill when Banquet pot pies made by ConAgra Foods were linked to a salmonella outbreak and frozen pizzas made by General Mills were tied to an E. coli outbreak. Both products were recalled.
Since then, food companies have revamped the cooking instructions on their frozen foods to ensure they are sufficient for killing off any dangerous bacteria, says Leslie Sarasin, head of the American Frozen Food Institute trade group.
ConAgra and Nestle Prepared Foods, two of the largest frozen-foods producers, have rolled out revised instructions on many of their brands which include Stouffer’s, Lean Cuisine, Banquet and Healthy Choice.
But preparing frozen foods safely may require a change in consumers’ microwave habits, too. In the latest outbreak, some of the meals were microwaved even though the products weren’t intended to be.
Microwaves produce short radio waves that penetrate food about 1 inch and excite water, fat and sugar molecules to produce heat. Food safety experts say that method poses more risk than a stove or oven because it heats food unevenly.
To be safe, they suggest getting a food thermometer and using it to check the temperature of microwaved food in several places, especially if the product includes raw ingredients.
“If you were going to make one of these things for a kid, you’d definitely want to be checking the temperatures on the things or using your (conventional) oven,” Davidson said.
But spotting a raw ingredient isn’t always easy because the only clue most companies offer is the two words “COOK THOROUGHLY” on the front of the package.
Consumers also need to become better acquainted with the technical specifications of their microwaves. The unit’s wattage – how powerful it is – influences how well it heats food, and cooking instructions are written for specific wattages.
But microwaves lose power over time, and some smaller microwaves may not produce enough power to safely cook some products. Banquet pot pies, for example, now include a warning that the product shouldn’t be cooked in microwaves with less than 1,100 watts output.
Kathy Barges, another Hy-Vee shopper, says she tries to follow the directions on her Lean Cuisine meals exactly but hadn’t noticed the package’s warning to adjust cooking time if she doesn’t have an 1,100-watt microwave.
“I’m not sure what mine is,” Barges said. “It’s an expensive microwave, so I assume it’s got the most wattage on it.”
And if most people don’t know the wattage of their home microwaves, forget the ones they might use to nuke their lunch at work. “Who’s got a thermometer in their desk drawer?” Davidson said.
College student Jordan Sullivan said he regularly eats frozen pizza and pizza rolls but never has given much thought to the safety of it.
“I just toss them in and wait till they look good,” Sullivan said of the rolls, which do include raw ingredients.
While following directions helps, experts say the bottom line is that cooking raw food is still a job best left to stovetops, grills and ovens.
The uneven nature of microwave cooking can make it a dangerous way to prepare frozen raw foods. When not all of the food is heated to a safe temperature, pockets of bacteria can survive and sicken people.
U.S. Department of Agriculture food safety experts and major food companies offer several tips for preventing that.
KNOW YOUR MICROWAVE: Microwave cooking instructions are calibrated to cook food to a safe temperature based on particular wattages, or power. Food takes longer to cook safely in a microwave with lower wattage than one with higher wattage.
But checking your user manual for wattage ratings may not be enough. A microwave’s actual output can differ from whatever figure the manufacturer states, and it can deteriorate over time.
To test your microwave, place several ice cubes in water and stir to make sure the water is ice cold and then remove any remaining ice and discard. Then measure 1 cup of ice water and set it in the microwave. Heat on high for 4 minutes, but watch to see when the water boils. If the water boils in less than 2 minutes, the oven has at least 1,000 watts.
If water boils in 21Ú2 minutes, the microwave produces about 800 watts. If water boils in 3 minutes or longer, it is a low-wattage oven producing about 700 watts or less.
CHECK THE TEMPERATURE: Food safety experts recommend that consumers use an instant-read food thermometer to check the final temperature of microwaved food. Be sure to check in several places to ensure there are no cold spots.
If the cooking instructions call for letting the food sit for a bit after cooking, wait until after this period before taking the temperature. This time is part of the cooking process and allows the heat to spread evenly through the food.
Foods that contain raw chicken must be heated to 165 F, according to federal guidelines.
USDA Food Safety and Inspection Service: http://www.fsis.usda.gov
Grocery Manufacturers’ Association: http://www.gmabrands.com
American Frozen Foods Institute: http://www.affi.com
Additional information is available online at the following sites: