Why does Bread get Moldy?

Michael Anissimov
Michael Anissimov

Bread gets moldy because it provides a good source of food for some types of fungus. The air is usually full of tiny mold spores, and under the right conditions, they can settle on nearly any organic substance and start to digest it. In bread, these enzymes break down the cell walls of the organic material making up the loaf, releasing easily digestible, molecularly simple compounds. This is how bread gets moldy.

Loaf of moldy bread.
Loaf of moldy bread.

Mold, found on old or unrefrigerated bread, comes from fungi, one of the most ubiquitous and successful forms of life on the planet. There are dozens of thousands of species, which can be found practically everywhere. Scientists who study fungi, called mycologists, say that approximately one out of every 20 living species is a form of fungus.

Storing bread in a refrigerator can slow down the growth of mold.
Storing bread in a refrigerator can slow down the growth of mold.

Fungi cannot receive energy directly from the sun because they do not have chlorophyll, and must therefore live off other plants and animals. Some fungi are parasites, actively attacking a host for nutrients. Most, however, are scavengers, turning organic matter into soil. Without fungi, many plants would die, because they require rich soil to thrive.

Most fungi tend to be flexible about their food choices. They feed on a wide variety of organic molecules, and their flexibility is largely responsible for their ubiquity. Fungi produce dozens of digestive enzymes and acids, which they secrete into a material as they grow over it.

Unlike humans, mold digests first, then eats, rather than vice versa. Under the right conditions, there exist forms of fungi that eat practically anything but metal. Special fungi produced through selective breeding are sometimes used as agents to target specific compounds for cleanup.

Fungi reproduce exponentially until all available nutrients are exhausted. Some forms of mold can double their mass every hour. They reproduce by means of spores, tiny vectors which are produced by the fungus en masse. Spores are extremely small and numerous — there are probably millions of fungal spores in any room at one time.

Luckily, these spores can be destroyed by cooking, which is why bread doesn't immediately get infected with mold. Over time, however, airborne spores find their way onto the nutrient-rich surface of bread and start multiplying — even under the cold conditions of a refrigerator. At freezing point, fungi become dormant. If they are exposed to heat again, they can revive and continue to grow.

Mold that is found on old or unrefrigerated bread comes from fungi.
Mold that is found on old or unrefrigerated bread comes from fungi.
Michael Anissimov
Michael Anissimov

Michael is a longtime wiseGEEK contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

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Discussion Comments


I'm doing a science fair project on how to preserve bread, and now that I know how it gets moldy, I can find ways to preserve the bread! Thanks.


Explain how exposure to air makes bread moldy.


I am in fifth grade and this helped me a lot.


Why does mold even exist? How does it reproduce and how can you make it reproduce in three days?


Gluten free bread molds much more slowly for some reason.


When bread goes moldy it is not such a bad thing. Usually it means that that bread has been made fresh and is free of other preservatives and chemicals.

There is a little Middle Eastern bakery close to me that sells amazing bread. But it goes moldy in about three days. You have to eat it fast. Compare that to a store bought loaf in a plastic bag that will sit on your counter for months with no problems. Do you really want to put whatever is keeping that bread fresh in your body?


I'm looking for an identification of a bread mold that looks light brown to lilac in color, circular pattern, and has tiny, raised, conical centers.


I'm doing an eighth grade science project and need help. What amount of mold is unsafe to eat? When does the amount become dangerous?


Mold grows between wallpaper layers.


If bread goes moldy quickly, then break the loaf into two separate bags and freeze 1/2 of it, using the other half first (or 1/3's) This way you'll always have some in the freezer and use what is out before it goes bad. It means having to stay on top of it and defrost it more, but it keeps it from going bad as fast as you say.


Fungi are not plants. They do have a cell wall but it is made of chitin, not cellulose, which is the material that plant cell walls are composed of.


How do you test the type of mold on bread?


thanks for the information. I'm using it for my biology class in ninth grade. need to learn more about mold for our upcoming lab. Thank you a lot.


What in bread makes mold grow in it? Is it carbohydrates?


how long does it take for mold to grow on bread?


this helped me a lot w/ my 5th grade science project


this helped me a lot.


this helps me with my fifth grade project.


this helped me a lot with my fifth grade science project.


thanks wiseGEEK. this helped a lot for my science fair project. you guys are helping me get an A. you people are awesome.


Fungi are not plants.


thanks so much. i used this site for part of my science fair project. you practically did my homework for me! thanks again! Anonymous :P


How do you get mold to go away?


it looks nasty when my bread molds. it looks like someone went to the bathroom on it.


how long does it take bread to get moldy?


this helped me.


this helps a lot.


What amount of bread mold is the safest to consume because my dad ate some moldy bread and is fine?


How can I stop my bread from molding? I can buy a loaf of bread at the local market. After about 2 days mold starts to form and I wind up throwing the entire 3/4 of the loaf away. Then buy another loaf from a different market and the same thing happens. I am tired of wasting my money on 1/4 a loaf of bread.


Mold grows in sunlight the fastest, heat as well, but can still grow in your fridge!


does bread mold faster in the sun or in a dark place?


how do bread molds get energy from food?


What kinds of mold appears on bread?


Why is mold not okay to eat?


how do bread molds get energy from food?


How do people prevent bread from getting moldy, especially with organic bread, and especially in humid conditions?

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