A fungus, eating your lunch
What Is the Fluff on Old Bread?
Mould is a fungus growing threads through the bread and lifting spore stalks into the air.
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Step 1 of 5
Spores are already in the air, everywhere.
You cannot keep them off food in a normal kitchen. The question is never whether spores land — it is whether they find what they need to grow.
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Step 2 of 5
Growth needs damp, warm and food together.
Take any one away and nothing happens. Dry crackers keep for months in the same room where bread moulds in days.
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Step 3 of 5
The threads come first and you cannot see them.
The fungus spreads a fine network through the crumb, releasing chemicals that break starch down. By the time a spot appears, the network is wider.
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Step 4 of 5
The fluff is a launch tower.
Those upright stalks lift tiny knobs of spores clear of the surface so the smallest air movement carries them off to new bread.
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Step 5 of 5
Cutting the spot off is not enough.
On soft, damp food the invisible network reaches far past the visible patch. Bread and soft fruit go in the bin; hard cheese can be trimmed.
One of these moulds gave us penicillin: the chemicals it uses to fight bacteria became the first modern antibiotic.
The short version
Mould is a fungus whose invisible threads digest damp food while its visible fluff launches spores toward the next loaf.
Try it yourself
Seal one damp bread slice and one dried-out slice in separate bags. Only the damp one grows anything.
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