MadSci Network: Microbiology

Re: Bread mold project with rhizopus spores

Date: Thu May 27 10:21:48 1999
Posted By: David Beck, MadSci Admin
Area of science: Microbiology
ID: 927817554.Mi

First, why is the weight decreasing. Quite simply it is decreasing because the 
bread is not in plastic bags. If I take a piece of bread, stick it on the 
counter, and wait - its weight will decrease until the moisture content of the 
bread is equal to that of the moisture content of the environment. If there is 
air currents moving around the bread the moisture content will decrease even 

Second, which will grow best. As you are describing it, it doesn't sound like 
any of them will grow very well. Mold requires moisture in order to grow. That 
is why cereal doesn't grow mold but bread in a bag does. Bread has enough 
moisture to allow the mold to grow. If you make cereal soggy it will grow mold. 
This is a problem when farmers are harvesting things like wheat. They have to 
harvest on days when it is dry so that it doesn't rot in the silos.

Mold grows better in the darker. Why? The sunlight is drying, and it is 
mutagenic. Just like you get a sunburn, the mold can become damaged by the 
sunlight. So dark is better.

Humid - but not wet is better. Mold doesn't like TOO much water. It likes a hard 
surface to grow on, which typically means a dry surface.

How is usually the best way to grow mold. Stick a piece of bread in a large 
ziploc bag (or some other airtight bag). Wet a paper towel and squeeze most of 
the water out. It should be damp but not dripping wet. Stick it in a dark 
warmish place. NOT hot, NOT cold.

Temperature and mold growth. First there are many many different kinds of mold. 
Each mold has an ideal temperature for growth, and I do not know what it is for 
your mold. So I will give you generalities. Most molds don't like it cold. They 
like room tempurature or warmer. Most molds don't like it hot, they like it body 
temperature or less. So for most molds the ideal temperature is in the 20 C - 39 
C range.

Good Luck!
David Beck

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