When mold appears on food or an item, a common reaction is to assume that intense heat will solve the problem. Microwaving the moldy material might seem like a fast and easy method to sanitize it, based on the understanding that heat kills microorganisms. However, using a microwave to eliminate mold is ineffective for making the item safe and creates significant risks of contamination within the appliance itself. The true danger of mold is not always the living organism, but the invisible chemical compounds it produces.
The Effect of Microwave Heat on Fungal Organisms
The energy generated by a microwave oven primarily heats the water molecules within the moldy material, creating thermal energy. This heat can be sufficient to kill the visible, active mold growth (mycelium) and many fungal spores. Mold spores typically begin to die when exposed to temperatures above 140°F (60°C) for a sustained period.
The central issue with using a microwave for sterilization is the highly uneven heating pattern, which creates hot and cold spots throughout the item. This inconsistency means that pockets of mold, especially those deep within porous materials like bread, can easily survive the heating process. While some surface mold may be killed, the microwave cannot guarantee complete eradication.
The Danger of Remaining Mycotoxins
The failure to achieve complete sterilization is secondary to the primary health hazard: the presence of mycotoxins. These are toxic secondary metabolites produced by many common types of mold, such as Aspergillus and Penicillium. Microwaving does not neutralize these poisons because they are highly stable and resistant to heat degradation.
Mycotoxins like aflatoxin B1 and ochratoxin A can withstand temperatures far exceeding those reached in a standard microwave cycle. While a microwave may heat food to a maximum of about 90–98°C, mycotoxins often require prolonged exposure to temperatures above 150°C for even partial reduction. Consuming food containing these heat-stable toxins, even if the mold appears dead, can lead to adverse health effects, including allergic reactions and long-term issues. Microwaving only kills the visible threat while leaving the invisible poison intact.
Spore Dispersal and Internal Contamination
Heating a moldy item in an enclosed space like a microwave creates a substantial contamination risk for the appliance itself. The rapid thermal expansion and moisture changes inside the material can cause the mold structure to break apart. This process aerosolizes the surviving and dead mold spores and mycotoxins, releasing them as a cloud into the microwave cavity.
Once released, these microscopic particles can settle on the interior walls, the turntable, and the ventilation components. This internal contamination means that any subsequent food heated in the appliance risks picking up mold spores or residual toxins. Opening the microwave door immediately after heating releases these aerosolized particles into the surrounding kitchen air, creating an inhalation risk.
Safe Cleaning and Disposal
The safest course of action for any moldy food or porous item is immediate disposal, rather than attempting to salvage it with heat. The item should be sealed in a plastic bag before being placed in the trash to prevent the release of spores into the air. Do not try to scrub mold off food or place it near other uncontaminated items.
If mold has accidentally been heated inside the appliance, a thorough decontamination is necessary. Unplug the microwave to ensure safety before beginning the cleaning process. A mixture of equal parts white vinegar and water should be heated in a microwave-safe bowl until steaming, then left to sit inside the closed appliance for several minutes.
The steam will help loosen any mold residue, and the acetic acid in the vinegar possesses antifungal properties that assist in killing the spores. The interior, including the walls, ceiling, and turntable, must then be carefully wiped down with a clean, damp cloth, ensuring the area is well-ventilated. The turntable should be removed and washed separately in hot, soapy water.