Most people think heating food in a microwave kills 100% bacteria, but new research reveals that over 100 disease-causing bacteria species can live inside it. (Image by arrangement)
The next time you reheat your favourite non-veg pasta or leftover daal-rice in your microwave think again. If you thought the magical radiation box was zapping all the nasty bacteria lurking in your food, you are highly mistaken. A new study has revealed that microwave ovens can be a haven for bacterial growth. Researchers reported in Frontiers in Microbiology that swabs taken from 30 microwave ovens showed over 100 bacteria species thriving inside the microwaves. Micro-bial communities living on coffee/tea machines and dishwashers were a known thing. The latest addition is microwaves.
(Micro) wave
Microwaves work their magic by sending electromagnetic waves through your food, exciting the water molecules inside and creating heat. It’s like a dance party at the molecular level! Ideally, this heat should kill off harmful bacteria by pushing the internal temperature of your food to around 165°F (74°C), which is the safe zone according to food safety experts.
But here’s the catch: your microwave doesn’t heat food evenly. If you’ve ever bitten into a still-cold corner of lasagna after it just came out of the microwave, this uneven heating means some parts of your food may not get hot enough to kill the bacteria hanging out in the cooler spots.
Cold Spots
Microwaves can be a little flaky when it comes to consistency. Dr. Andrea C. Love, a US-based immunologist, biotechnology scientist, public health consultant and microbiologist sums it up perfectly: “Microwaves heat by exciting water molecules, creating a bacteria-slaying heat party. But not all the food gets an invite to this party — some bits stay cool and cozy, leaving bacteria with a free pass.”
Cold Spots
Microwaves can be a little flaky when it comes to consistency. Dr. Andrea C. Love, a US-based immunologist, biotechnology scientist, public health consultant and microbiologist sums it up perfectly: “Microwaves heat by exciting water molecules, creating a bacteria-slaying heat party. But not all the food gets an invite to this party — some bits stay cool and cozy, leaving bacteria with a free pass.”
So, what does that mean for your food? Let’s say you’re reheating some leftover chicken. While one part of the chicken might hit the right temperature, other sections may stay lukewarm. Bacteria like Bacillus cereus and Clostridium botulinum, are no joke. These heat-resistant nasties can survive the microwave’s inconsistent warming, potentially leading to foodborne illness. Dr Love explains, “Giardia lamblia and Cryptosporidium parvum are protozoans that form heat-resistant cysts and can be problematic if food and water are not heated sufficiently. Toxoplasma gondii also poses a risk due to its semi-dormant oocysts that are resistant to heat. Additionally, helminth eggs and larvae, such as those from Taenia species and Trichinella spiralis, can survive heating and lead to parasitic infections like trichinosis and taeniasis, especially in undercooked meat products.”
A 2024 study published in the Journal of Food Protection showed that microwaves can leave some areas of food at unsafe temperatures, allowing bacteria to survive and thrive. Talk about a buzzkill for your dinner plans!
Chill Out
Once the food is cooked, the next crucial step is prompt refrigeration. Leftovers should be refrigerated within two hours of cooking to prevent the growth of any surviving bacteria or spores. In hot weather, where temperatures exceed 90°F (32°C), this time frame reduces to just one hour. This quick action helps to halt bacterial growth and minimizes the risk of foodborne illnesses.
Chill Out
Once the food is cooked, the next crucial step is prompt refrigeration. Leftovers should be refrigerated within two hours of cooking to prevent the growth of any surviving bacteria or spores. In hot weather, where temperatures exceed 90°F (32°C), this time frame reduces to just one hour. This quick action helps to halt bacterial growth and minimizes the risk of foodborne illnesses.
Cooking to this temperature is especially important for dishes that contain poultry, seafood, and ground meats, which are more likely to harbour bacteria like Salmonella, E. coli, or Listeria. Using a food thermometer is the most reliable way to confirm that the food has reached this safe temperature. Insert the thermometer into the thickest part of the food, avoiding bone, to get an accurate reading.
To ensure that leftovers cool down rapidly and evenly, divide large quantities of food into smaller, shallow containers. This method allows the food to cool more quickly, reducing the time it spends in the “danger zone” between 40°F (4°C) and 140°F (60°C), where bacteria can multiply rapidly.
Storing leftovers correctly is crucial for maintaining their safety and quality. Use airtight containers to store leftovers, as they help to minimize potential cross-contamination and preserve the food's freshness.
Labelling containers with the date of storage can also be helpful. This practice makes it easier to track how long the food has been stored and ensures that you use it within a safe time frame. Most leftovers are best consumed within 3-4 days.
Some viruses, like Norovirus and Hepatitis A, as well as fungi, can also withstand a less-than-thorough microwave zap. A 2024 study in Food Microbiology revealed that up to 25% of Norovirus particles can survive if your food doesn’t reach the right temperature. Dr Love explains, “Bacillus cereus produces spores that are highly resistant to heat and can cause two types of food poisoning: vomiting (emetic) and diarrheal. Found ubiquitously in soil, B. cereus can contaminate a variety of foods. Clostridium botulinum also produces spores and is responsible for botulism, caused by a toxin that can be inactivated with heat, although the spores themselves may survive if they contaminate food.’’ Additionally, Clostridium perfringens, another spore-forming bacterium, is a common cause of food poisoning in the US, responsible for 10-15% of cases, leading to acute gastroenteritis with symptoms like diarrhea, nausea, and abdominal cramps.
Microwave Myths
There are some wild myths floating around about microwaves. One popular misconception is that microwaves ‘zap’ bacteria instantly. The truth is microwaves heat food, but they don’t sterilize it. If the heat doesn’t reach the right level, bacteria can still be alive and kicking. Another myth? That microwaves kill everything. While they do a great job at killing off some microbes, they’re not invincible. Bacteria like *Bacillus cereus*, viruses, and fungi can all survive if they aren’t heated properly.
The Bottom Line
Microwave Myths
There are some wild myths floating around about microwaves. One popular misconception is that microwaves ‘zap’ bacteria instantly. The truth is microwaves heat food, but they don’t sterilize it. If the heat doesn’t reach the right level, bacteria can still be alive and kicking. Another myth? That microwaves kill everything. While they do a great job at killing off some microbes, they’re not invincible. Bacteria like *Bacillus cereus*, viruses, and fungi can all survive if they aren’t heated properly.
The Bottom Line
Microwaves are fantastic for convenience, but they aren’t a foolproof bacteria buster. Uneven heating can leave bacteria — and other microbes — alive and well in your food. Wendy Fernandes, a homemaker from Mumbai says, “If something smells off, I throw it out. It’s always better to be safe than sorry.” So, the next time you pop something into the microwave, remember: it’s not just about heating your food; it’s about heating it right.
Micro Management
Let’s be honest—no one’s giving up their microwave anytime soon. Below tricks can work in your favour:
Stir and Rotate: Microwaves come with a turntable. Make sure you stir your food halfway through the cooking process to help distribute the heat evenly.
Cover It Up: Use a microwave-safe cover or plastic wrap to help trap steam, which in turn helps your food heat uniformly.
Use a Thermometer: If you want to be extra sure your food is safe, grab a food thermometer.
Let It Sit: After the timer dings, don’t dig in right away. Let it sit for
2 mins. This allows the heat to even out across your dish.
Store Smart: Store leftovers in airtight containers and refrigerate them promptly.
Cover It Up: Use a microwave-safe cover or plastic wrap to help trap steam, which in turn helps your food heat uniformly.
Use a Thermometer: If you want to be extra sure your food is safe, grab a food thermometer.
Let It Sit: After the timer dings, don’t dig in right away. Let it sit for
2 mins. This allows the heat to even out across your dish.
Store Smart: Store leftovers in airtight containers and refrigerate them promptly.
( Source : Deccan Chronicle )
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