In What Conditions Does Mold Grow on Bread?

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In What Conditions Does Mold Grow on Bread?
Bread mould is different than the mould grown on cheese and can be quite dangerous. (Craig Veltri/Photodisc/Getty Images)

The greenish, white or brown patches of fuzz found on your old hot dog buns or ends of bread loaves are common fungi. Penicillium or Rhizopus grow on yeasted or unyeasted breads and can be harmful to humans if ingested, even though they are related to edible mushrooms. Despite the seemingly unconquerable growth, knowledge of ideal conditions can help combat the fungus that destroys your sandwich.

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Molds digest their food outside of their bodies and can only process certain types of foods. Bread moulds grow on all types of bread, depending on the conditions and the strain of fungus.


Molds are made mostly of water. Wet conditions reduce dehydration and make it easier for the moulds to digest the bread. Place your bread in a dry area to reduce mould growth.


The enzymes within the mould cells work best at warmer temperatures, generally around 26.7 degrees Celsius. Too much heat, however, will decrease the efficiency of the enzymatic digestion.


While light is needed for moulds to pass through different growth stages, too much light can dehydrate the cells. Bread moulds grow best in dark conditions, because it keeps them moisturised.


Bread moulds need very little oxygen to function, but they do need it. Vacuum packing your bread is sometimes the only way to prevent mould growth due to insufficient oxygen.


Molds need specific concentrations of salt to digest bread. Each mould needs a different concentration. Too much salt can kill the mould, but it is rare a person keeps bread with a high enough salt concentration to prevent mould growth.

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