Mold

Molds are microscopic fungi that grow on food and send root threads below the visible spot. Some trigger allergic reactions, and certain kinds produce mycotoxins that can make people sick.

  • Food safety
  • Germs & illness

Molds are microscopic fungi that grow on plant and animal matter. The fuzzy, colored patch you see is only part of the organism: thread-like roots can reach deep into the food, while the surface carries spores that travel by air, water or insects to start new colonies. Molds handle salt and sugar better than many microbes and need less available water. Kansas State University places their lower limit at about 0.61 water activity, compared with roughly 0.90 for most spoilage bacteria. Most molds prefer warmth, yet many still grow at refrigerator temperatures.

Some molds cause allergic reactions or breathing problems, and certain species make mycotoxins. FDA highlights aflatoxins from Aspergillus molds in peanuts, corn and tree nuts; deoxynivalenol in wheat, oats and other grains; and ochratoxin A in grains, coffee and grapes. These toxins usually form while crops grow or sit in storage, and FDA and USDA monitor crops such as peanuts and field corn for aflatoxin. For bread, mold is also the leading cause of spoilage, and research traces it mainly to Penicillium and Aspergillus picked up after baking.

Key facts

Cut-away margin for hard cheese and firm produce
At least 1 inch around and below the mold
Lowest water activity for mold growth
About 0.61 aw
World crops affected by mycotoxins
About 25% (FAO estimate cited by USDA)
Main bread spoilage molds
Penicillium and Aspergillus

In a bakery or commercial kitchen

  • Keep cooling, slicing and wrapping areas clean, since bread is mostly contaminated with mold after it leaves the oven
  • Keep products covered during handling, because mold spores spread through air, water and insects
  • Ask grain and nut suppliers how they manage mycotoxins; FDA sets action levels for aflatoxin and an advisory level for DON
  • Discard moldy baked goods instead of trimming them, since porous bread lets mold spread beneath the surface
  • Replace musty cloths, sponges and mops, and clean refrigerators regularly to remove mold

For home and cottage bakers

  • Throw out moldy bread, baked goods, soft cheese, jams and jellies rather than scraping off the spot
  • Save hard cheese or firm produce by cutting at least 1 inch around and below the mold
  • Avoid sniffing moldy food, which can cause breathing trouble, and discard it where kids and pets can't reach
  • Cover foods, refrigerate leftovers within 2 hours and use them within 3 to 4 days

Related entries

Sources

Written by VanillaGoods in our own words from these sources. Last reviewed October 17, 2026.

  1. Molds on Food: Are They Dangerous?, USDA Food Safety and Inspection Service
  2. Mycotoxins, U.S. Food and Drug Administration
  3. Water Activity of Foods (Food Safety Fact Sheet MF3674), K-State Research and Extension, Kansas State University
  4. Quality and mold control of enriched white bread by combined radio frequency and hot air treatment (Journal of Food Engineering, 2011), Washington State University (author-hosted research article)