Why does Bread get Moldy?

Loaf of moldy bread.
Storing bread in a refrigerator can slow down the growth of mold.
Mold that is found on old or unrefrigerated bread comes from fungi.
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  • Written By: Michael Anissimov
  • Edited By: Niki Foster
  • Last Modified Date: 15 November 2015
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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.


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Post 73

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.

Post 69

Explain how exposure to air makes bread moldy.

Post 66

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

Post 63

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

Post 59

Gluten free bread molds much more slowly for some reason.

Post 58

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?

Post 53

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.

Post 52

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?

Post 49

Mold grows between wallpaper layers.

Post 37

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.

Post 36

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.

Post 33

How do you test the type of mold on bread?

Post 32

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.

Post 31

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

Post 28

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

Post 27

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

Post 26

this helped me a lot.

Post 25

this helps me with my fifth grade project.

Post 24

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

Post 23

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

Post 22

Fungi are not plants.

Post 21

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

Post 20

How do you get mold to go away?

Post 18

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

Post 17

how long does it take bread to get moldy?

Post 16

this helped me.

Post 14

this helps a lot.

Post 13

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

Post 12

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.

Post 9

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

Post 8

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

Post 7

how do bread molds get energy from food?

Post 6

What kinds of mold appears on bread?

Post 5

Why is mold not okay to eat?

Post 4

how do bread molds get energy from food?

Post 3

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

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