Conditions for Fungal Growth

• Fungi grow well in an environment that has adequate nutrients and plenty of moisture. Food kept too long or that has been left out in humid conditions provides a good substrate for fungal growth. Some fungi are cold tolerant and can even grow on old food in a refrigerator. Some foods with high sugar or salt concentrations will be difficult for most fungi to colonize, but most kinds of bread, fruits and vegetables are ideal. Most food colonizing fungi are molds that produce a white fuzzy growth. In some cases the fungi are yeasts, which form small wet-looking colonies.
  
  

Colonization

• Fungal colonization of food usually begins with a spore or many spores landing on the food. Spores constantly circulate in the air, and it doesn't take long for one to find its way on to any unprotected food. Once a spore lands, if the food is moist or if the humidity is high, it can germinate and begin to send out hyphae. Hyphae are filamentous fungal cells that spread out and absorb nutrients from the substrate.
  
  

Vegetative Growth

• As the fungal hyphae grow, form branches, and continue to develop, they create a tangled mass of cells called a mycelium. This usually is visible as a white fuzzy growth on the food. The hyphae release enzymes into the food, breaking down the food molecules (sugars, starches, proteins, vitamins, etc.) into smaller molecules that are taken up by the fungus and used in its metabolic processes.
  
  

Reproduction

• Soon after the mycelium forms, the fungus begins to produce spores. Spores are evident as a layer or field of tiny specks appearing on the surface of the mycelium. Although the mycelium is white, the spores are often colorful. Mold spores can be brown, grey, black, or just about any shade of green, yellow, pink, or red.
  
  

Do Not Eat!

• Most molds are harmless, but some produce toxins that can cause serious illness if eaten. Do not attempt to scrape or cut mold off of food in an attempt to salvage it. Even though the surface mycelium may be gone, some may remain deep in the food, or the fungus may have secreted invisible toxins into the food.