Does The Microwave Kill Bacteria?

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Does the microwave kill bacteria? What do we actually know about microwaves? How do they work? And are they the ultimate answer to food safety?

Microwave ovens are great time-savers and can help you in a bind. These days microwave ovens can cook, grill, defrost and reheat any foods. These features can really help when grills or convection ovens take time to reheat or cook foods. Microwaves can be very effective in the reheating process if used correctly.

Here’s the deal, microwaves don’t actually kill bacteria.

The microwaves instead, create heat that is able to kill bacteria in foods. But microwaved foods can be cooked unevenly because of irregular shapes or differences in thickness. Think about a solid frozen meal compared to reheating a soup or other liquids. Liquids heat up much faster than solid foods.

Even turntable-equipped microwave ovens can cook unevenly and leave cold spots where harmful bacteria can survive.

How do microwaves cook food?

1. Inside the microwave oven there is a magnetron that creates radio wave energy.
2. These waves blast the foods in the compartment through what is called a wave guide.
3. The microwaves bounce back and forth off the reflective metal interior, until they reach the food sitting on the inside of the food compartment. The food absorbs these waves generating heating.
4. The heat, then cooks the food.

Does a microwave kill bacteria?

Microwaves can not penetrate more than 2 cm’s (1-inch) into food. So microwaving becomes dependant on the size, shape and nature (liquids/solids) of the food you are reheating.

By default does the microwave kill bacteria?

No. Not in the way you would expect it to.

Surprisingly, most people think that a microwave cooks from the inside out. This is simply not the case.

A microwave actually cooks from the outside in. Meaning that the surface cooks before the core of the food does.

This results in cold spots where bacteria can survive the heating process. This is most evident when attempting to use the defrost function of the microwave oven. The surface can become cooked, while the inside core remains frozen.

However, the heating process, like any other oven, can easily kill bacteria if used correctly. This means fully frosting foods and cooking these for the correct amount of time.

Can the microwave kill bacteria from a dirty compartment?

If we look at how the microwave works, then NO.

The walls of the microwave oven do not get heated to the point that can kill bacteria. This means that you need to keep your microwave clean. Any food spillages, especially blood spillage from meats should be cleaned and disinfected immediately. Essentially following the clean-as-you-go procedure.

Studies have shown that both E.coli and Salmonella can survive inside the microwave. This study claimed that microwaves can actually be microbial hotspots.

Not only is the inside of the microwave risky, but also pose a risk in public/general areas. Especially in offices and retail stores, the handle for the microwave ovens have been shown to be cleaned less frequently than expected. Creating a high chance of cross-contamination.

How do you lower the risk of using the microwave oven?

Ok, so realistically, there is very little chance of food splatters falling into the food you are reheating. Especially dirty microwaves, more than likely have dried food particles, making it very difficult for bacteria to survive.

Remember bacteria need an ideal ambient temperature, nutrient source and moisture to grow and survive. The microwave oven does tend to dry out the food splatters.

So there can be very little risk if:

1. Foods and placed on a plate off the glass surface.
2. These foods are covered before reheating, cooking etc.
3. Liquids are placed in shallow containers.
4. Foods should be fully defrosted before attempting to reheat.

But really there is no excuse for not cleaning out any food splatters in the compartment and wiping off the handles and buttons with a detergent and sanitiser. The microwave should be treated like any other high-risk equipment. Meaning clean-as-you-go should follow suite.

And if you have discovered that food has hardened from continual splashing, you could try placing a cup of cold water into your microwave and turning it on high for around three minutes to create a steam, which should mean the food particles are easy to wipe off. This method avoids using abrasive cleaners that may scratch and harm the microwave surface.

Cleaning in a commercial kitchen should always follow the chemical supplier’s recommendations for cleaning and sanitising. The standard chemicals include the use of the a multi-purpose cleaner and surface sanitiser.