You may have grown mold on a piece of bread as a childhood science project. As an adult, if you’ve left bread around your house long enough, you’ve probably seen it grow there, as well. If you’ve wondered what makes bread so tasty to mold spores, you may be relieved to know that just like people, bread molds simply like to eat when they’re hungry.
A Bread Mold's Banquet
The molds that eat bread eat all parts of it, from carbohydrates to dairy products that may have been used in a specific bread’s recipe. Molds are scientifically classified as fungi, and can eat just about anything organic or man-made. Also, it’s possible for more than one type of mold to be present and feeding on something at any given time -- including on bread. Many store-bought breads include preservatives that prolong bread’s shelf life, including mold inhibiting chemicals such as calcium propionate. That’s why homemade breads mold more quickly -- most home bakers don’t use chemical preservatives in their recipes.
Most molds like moisture and warmth, so keeping your bread in a plastic container on your counter during the summer will attract mold spores more quickly than keeping it in the refrigerator. However, some molds will also grow in the comparatively cold fridge temperatures as well. Eating bread quickly, before it has a chance to attract mold, is the safest bet against mold growth.
If you’ve got moldy bread, what you see on the bread’s surface is only part of the mold organisms that now inhabit it. Like plants, or even like the hair on your head, mold has roots that extend deep down inside whatever it’s growing on. Bread is relatively porous, as compared to things like hard cheeses, and the roots of mold are generally too small to see with the naked eye. For these reasons, the USDA Food Safety and Inspection Service says that it’s not safe to eat any bread on which you see mold growing, even if you cut the moldy part off. Since there’s no way to know if the mold has infiltrated the entire loaf without lab testing, your best bet for food safety is to throw all moldy bread away.
High sugar breads, such as quickbreads or breads with a lot of fruit in them, may attract mold more quickly than non-sugary breads, like Italian bread or a standard sandwich loaf. Sugar is hygroscopic, which means that it attracts moisture -- so a sugary bread sitting on your counter is essentially a welcome mat for mold. You can deter mold growth by keeping uneaten bread in your refrigerator -- but if you keep it there for a very long time, mold will eventually grow.