|MadSci Network: Other
How quickly a bread will mold depends on several things, one being the "water activity" of the bread. An earlier Mad Scientist message gave the following information about bread molding: "Scientists measure "water activity", that is water that is not bound into the product, to help determine "shelf life", or how long a product can remain on the shelf and be edible. Pure water has an activity of 1.0 and 0 is bone dry. Bacteria generally stop growing at a water activity less than .91, but molds grow on drier foods, until the water activity drops below .81. Bread has a water activity of about .95. However, another factor about bread that determines how quickly it spoils is its pH (or acidity). Bread has a pH of about 5.3 - 5.8 which means it is slightly acid. This also helps keep it safe to eat on the shelf." One way to estimate how quickly bread will mold would be to look at its water content. For example the percent of water in several breads is: Navaho fry bread 26%, banana bread 29%, toasted white bread 30%, plain white bread 36%, Oat bran bread 44% and canned Boston brown bread 47%. But this is not the whole story, because other ingredients in the bread may affect the "water activity". Water activity is measured by putting a bread sample in a tight container and measuring the amount of water that vaporizes from the product. If you want to learn more about how food producers determine the water activity of their bread visit the web sites of manufacturers who make the instruments bread makers use to test their product. One place to study this question is at the following URL: http://www.decagon.com/aqualab/questions.html The bottom line is that the dryer the bread the less likely it is to mold. Toasting bread slows subsequent mold growth, as does refrigerating bread. And much commercial bread contains a chemical to slow mold growth. The best policy is to buy only as much bread as you can eat within a few days or store bread in the refrigerator or freezer until needed. Phyllis Phyllis Stumbo, University of Iowa, Iowa City, IA Phyllisfirstname.lastname@example.org
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