Microwaves effectively eliminate many germs and bacteria by generating heat. This process disinfects items, significantly reducing microbial populations based on the temperature reached and sustained.
How Microwaves Target Microbes
Microwave ovens emit electromagnetic radiation, causing water molecules within food or objects to vibrate rapidly. This vibration creates friction, generating heat. The elevated temperatures disrupt the cellular structures of microorganisms, including bacteria, viruses, and some spores. Heat denatures proteins and enzymes essential for microbial survival and reproduction, effectively inactivating or killing them. While microwaves produce radiation, the thermal effect (heat) is the primary mechanism for destroying microbes, not direct radiation damage.
Studies show microwaves can destroy microorganisms. For example, exposing Escherichia coli and Staphylococcus aureus cultures to 650 watts of microwave power can kill them within two minutes. A sufficient heat dose will destroy various microorganisms.
Practical Applications for Disinfection
Microwaves offer a practical method for disinfecting certain household items. Kitchen sponges can be effectively sanitized. Saturating a sponge with water and microwaving it on high for one to two minutes can eliminate a significant percentage of bacteria; the USDA found this method killed 99.99999% of bacteria. The moisture in the sponge helps create steam, enhancing the disinfection process.
Wooden cutting boards can also benefit from microwave disinfection. Brief microwaving at a high setting for three to four minutes has been shown to kill bacteria effectively, especially when moist. However, plastic cutting boards do not disinfect well in a microwave oven, as their surface temperatures may not reach sufficient levels to kill bacteria.
Important Safety Considerations
Despite their disinfecting capabilities, microwaves present safety considerations. Uneven heating is a limitation, leaving “cold spots” where harmful bacteria may survive. This unevenness is particularly relevant for irregularly shaped or thick items, making it important to stir or rotate food during heating to promote uniform temperatures.
Heating water or liquids in a microwave can lead to superheating. This occurs when water heats above its boiling point without bubbling. A slight disturbance, such as adding a spoon or instant coffee, can cause the superheated water to erupt violently, leading to severe burns. To prevent this, place a wooden stirring stick in the cup or use a container with a scratched surface to provide sites for bubbles to form.
Certain materials should never be microwaved. Metal objects, including aluminum foil, cutlery, or dishes with metallic trim, can reflect microwaves, causing sparks, arcing, and potentially a fire or damage to the appliance. Sealed containers, such as whole eggs or airtight food containers, can build up pressure and explode. Additionally, some plastics and Styrofoam containers can melt, warp, or leach harmful chemicals into food when heated, unless specifically labeled “microwave safe.”