Re: how come bread molds

Dear Chris,

To understand why bread molds, one needs to be aware of what environmental 
conditions are necessary for the growth and reproduction of microorganisms 
(bacteria, yeast, molds) in or on food products. Factors include a source 
of food (i.e. nitrogen, vitamins, minerals), moisture, acidity, 
time-temperature and oxygen (pressence or absence). The ingredients used to 
make bread can be a source of microrganisms,and some of the microorganisms 
can survive the baking process. In addition, microrganisms from the 
environment (i.e. air) may also land on the surface of the bread following 
baking. The critical environmental factor associated with bread that 
selects for the growth of mold rather than bacteria and/or yeast is 
moisture. Molds can reproduce on foods where only a limited amount of water 
is available while bacteria and yeast require higher concentrations of 
water for growth and reproduction. This is why molds are the main cause of 
spoilage of foods such as baked products, cheese, jams and jellies. The 
term used to describe the amount of unbound or free water in a food that is 
available to support biological (i.e. growth and reproduction of 
microorganisms) and chemical recactions is water activity.

Further information on water activity can be found in any introductory food 
science text such as "Food Science" 5th edition, N.N. Potter & J.H. 
Hotchkiss, Chapman & Hall, 1995 ISBN 0-412-06451-0.

Sincerely,

Al Bushway
Professor of Food Science