How Does Mold Grow on Bread?

Written by laura reynolds
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How Does Mold Grow on Bread?
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The World of the Mold Spore

Mold spores are microscopic plants that float on every breeze, inhabit every inch of earth and surround us everywhere we go. Some moulds produce mycotoxins, which are dangerous poisons that can cause serious illness. Some moulds are beneficial, breaking down diseased yard waste and providing building blocks for antibiotics, miracle drugs that have saved millions of lives. Molds helped scientists break the genetic code and today help researchers discover the effects of humanity's "biological clock" and how it works. One of the most familiar forms of this filamentous fungus is the fuzzy green and grey growth that afflicts the foods we keep, particularly breads.

The Birth of a Colony

Once a spore finds a piece of bread in a dark, cool place where air does not circulate well, it sinks its little feet, called "hyphae," into the spaces that make up the surface of bread. Mold spreads rapidly, forming the mycelium or mould colony. Clusters of hypae, called "sporangiophores," grow upward, forming the mature "conidia" that hold the spores and give each mould its distinctive colour. When their cases break open, tiny spores go airborne until they find a hospitable place to land that is cool, damp, dark and has a good food supply and then the process begins anew. The hyphae dig deep into the porous surface of the bread, working through it as well as over its surface.

Looking for a Home

Mold spores are the "seeds" cast off by mature fungi. They are everywhere, but they need the right environment to settle and grow. Aspergillus, Penicillium, Rhizopus and Neurospora crassa are a few of the thousands of mould spores that float around the kitchen looking for places to start colonies. Bread, particularly white bread, is an attractive place to land because it is high in starch, a substance that breaks down into sugars, which is a high-energy food for mould. Bread is also generally kept sealed in a bag, limiting air circulation and is kept in a cool, damp, dark place like a refrigerator or bread box. These are prime conditions for development of mould colonies. If the temperature is too cold, however---like in the freezer---the little spores will not be able to grow and will shrivel up. Mold cannot survive at high temperatures either, making baking a good way of destroying mould. Once the starches in bread begin to "set up," however, it becomes a tempting treat for hungry mould spores. Because moulds do not have chlorophyll like other plants, they are particularly aggressive feeders, and a piece of bread can be covered by thousands of spores overnight and millions in a few days.

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