I seldom cross-post, but I posted this on the bread blog today and thought it might be of interest to my Lilting House readers too:

Jane and I are exploring the science behind the sourdough loaves we’re baking. Found this fun site: The Science of Cooking. An excerpt from the sourdough page:

In addition to flour, water, and yeast, your starter also contains
bacteria. When these bacteria feed on the sugars in flour, they produce
acidic by-products. This is what gives sourdoughits sour taste.

Actually, all doughs contain at least some bacteria. So why aren’t
all breads sour? In doughs made with bakers’ yeast (the kind you buy in
the store), the yeast outnumber the bacteria. Since both compete for
the same sugars, the yeast win out, and the bacteria don’t have a
chance to produce their acidic by-products. In sourdough, yeast and
bacteria are more closely balanced, so the bacteria have a chance to
add their flavors to the bread.

Sourdoughs and other raised breads also differ from one another
because of the eating habits of the yeasts that make them rise. The
predominant yeast in sourdough, Saccharomyces exiguus, cannot
metabolize maltose, one of the sugars present in flour. Baker’s yeast,
on the other hand, has no trouble feeding on this sugar. Since the
bacteria that give sourdough its taste need maltose to live, they do
much better in the company of sourdough’s yeast because they don’t have
to compete for this sugar.

Other links:

Wikipedia on sourdough

How Stuff Works on sourdough

The history & microbiology of sourdough

That Science of Cooking site has a lot of other neat stuff. The candy page is especially interesting. We might just have to do a unit study on candy one of these days…chemistry AND physics! (And with sourdough we’ve got biology too.)