|MadSci Network: Chemistry|
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
Try the links in the MadSci Library for more information on Chemistry.