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Why does Bread get Moldy?

Michael Anissimov
Updated May 21, 2024
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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.

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.

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.

All The Science is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Michael Anissimov
By Michael Anissimov
Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology, astronomy, chemistry, and futurism to his articles. An avid blogger, Michael is deeply passionate about stem cell research, regenerative medicine, and life extension therapies. His professional experience includes work with the Methuselah Foundation, Singularity Institute for Artificial Intelligence, and Lifeboat Foundation, further showcasing his commitment to scientific advancement.
Discussion Comments
By anon986192 — On Jan 23, 2015

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.

By anon932092 — On Feb 11, 2014

Explain how exposure to air makes bread moldy.

By anon926347 — On Jan 18, 2014

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

By anon335574 — On May 21, 2013

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

By anon311028 — On Dec 28, 2012

Gluten free bread molds much more slowly for some reason.

By jonrss — On Dec 01, 2012

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?

By vrorrer — On Oct 23, 2012

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.

By anon295147 — On Oct 04, 2012

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?

By anon254541 — On Mar 13, 2012

Mold grows between wallpaper layers.

By anon125874 — On Nov 10, 2010

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.

By anon121918 — On Oct 25, 2010

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.

By anon113253 — On Sep 23, 2010

How do you test the type of mold on bread?

By anon111179 — On Sep 15, 2010

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.

By anon85958 — On May 23, 2010

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

By anon79684 — On Apr 23, 2010

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

By anon78941 — On Apr 20, 2010

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

By anon78861 — On Apr 20, 2010

this helped me a lot.

By anon78668 — On Apr 19, 2010

this helps me with my fifth grade project.

By anon74813 — On Apr 04, 2010

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

By anon73604 — On Mar 28, 2010

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

By anon63967 — On Feb 04, 2010

Fungi are not plants.

By anon59821 — On Jan 10, 2010

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

By anon55379 — On Dec 07, 2009

How do you get mold to go away?

By anon52267 — On Nov 12, 2009

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

By anon52133 — On Nov 11, 2009

how long does it take bread to get moldy?

By anon50959 — On Nov 02, 2009

this helped me.

By anon49977 — On Oct 24, 2009

this helps a lot.

By anon45080 — On Sep 13, 2009

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

By anon42380 — On Aug 20, 2009

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.

By anon27190 — On Feb 25, 2009

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

By anon26987 — On Feb 22, 2009

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

By juwanins — On Feb 19, 2009

how do bread molds get energy from food?

By anon25142 — On Jan 24, 2009

What kinds of mold appears on bread?

By anon17794 — On Sep 07, 2008

Why is mold not okay to eat?

By anon15765 — On Jul 21, 2008

how do bread molds get energy from food?

By anon2130 — On Jun 29, 2007

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

Michael Anissimov
Michael Anissimov
Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology...
Learn more
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