Mold is a type of fungus that appears on food as fuzzy spots of green, white, or black growth. Finding mold on groceries or leftovers is common, and the instinct to salvage the food by cooking the visible mold away is understandable. Many assume that if high heat kills bacteria, it should also eliminate mold, making the food safe to consume. While cooking affects the mold organism, this assumption does not hold up when considering overall food safety. The issue is understanding the difference between the living organism and the toxic chemicals it leaves behind.
Heat and the Mold Organism
Cooking temperatures are generally effective at destroying the mold organism itself. Most common food molds are inactivated when exposed to temperatures exceeding 140°F (60°C). Sustained heat, such as boiling at 212°F (100°C) or baking at 350°F (175°C), typically kills the fungal structures, including the hyphae and spores.
The mold’s microscopic threads, which form the visible fuzzy patches, are composed of proteins that denature and become non-viable under high heat. This thermal inactivation prevents the organism from continuing to grow or reproduce. A few species of mold can produce heat-resistant spores, which may require prolonged exposure to higher temperatures to be neutralized. Even when the mold organism is killed by cooking, food safety is not resolved, as the heat only addresses the living fungus.
The Hidden Danger Mycotoxin Persistence
The primary reason cooking moldy food is considered unsafe is the persistence of toxic chemical byproducts known as mycotoxins. These toxins are stable chemical compounds produced by certain molds, such as Aspergillus and Penicillium, during their growth. Mycotoxins, including types like Aflatoxin, Ochratoxin A, and Deoxynivalenol, are highly resistant to thermal degradation.
Standard home cooking methods, like boiling, frying, or baking, often do not reach the temperatures necessary to break down these chemicals. A study found that mycotoxins remained almost 100% intact after 45 minutes of boiling. While some mycotoxins decompose at very high temperatures, such as those above 302°F (150°C) achieved in industrial processes, a significant portion still remains.
The presence of mycotoxins in cooked food poses a health risk even after the mold is dead. Ingestion can lead to acute symptoms like digestive upset and allergic reactions. Prolonged exposure to low levels of certain mycotoxins carries serious long-term health implications. Since the toxins have already permeated the food, killing the mold does not eliminate the underlying chemical contamination.
Safe Handling and Disposal of Moldy Food
Since mycotoxins are heat-stable, the safest response to finding mold on food is to discard it immediately. The appropriate disposal method depends on the food’s texture and moisture content. For soft, porous foods like bread, soft fruits, cooked leftovers, and yogurt, the entire item must be thrown out because mold roots penetrate deeply beneath the surface.
In contrast, hard, low-moisture foods, such as carrots, bell peppers, and hard cheeses, may sometimes be salvaged. If the mold is only on the surface, the United States Department of Agriculture (USDA) suggests cutting away at least one inch around and below the mold spot.
When discarding any moldy item, wrap it in plastic or place it in a small paper bag before putting it in a covered trash can. This prevents the release and spread of spores into the air. It is also prudent to clean the area where the moldy food was stored, such as the refrigerator shelf, and check nearby items for potential cross-contamination.