Sourdough bread works kinda like yogurt

I was recently explaining Nadia's mom's yogurt process to a friend, and somehow we got to talking about sourdough bread and how that process works. Neither one of us knew. Neither did anyone I've asked in the days since. Seems silly with most everyone I talk to living in SF, so I looked it up. Here it is, for your general edification -- how sourdough bread is made.

From Exploratorium.edu:

"Out of yeast? Don’t worry, it’s not hard to find. The feisty critters that make bread rise actually live all around us. In fact, the use of yeast in bread-making probably got its start accidentally, when 'wild' yeast caused doughs meant for unleavened flatbreads to ferment.

To this day, many bakers still use 'wild' yeast to make bread, especially in San Francisco, a city famous for its sourdough. To make sourdough, bakers use a 'starter,' a piece of dough in which yeast is continually reproducing with the help of regular doses of flour from the baker. The yeast that gets the starter 'started' usually comes from the air in the kitchen or bakery where the bread is made, but some starter recipes also use store-bought yeast.

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


Also, from KitchenProject.com:

"During the gold rush days in California, some of the Boudin family who were well known master bakers from France came to the San Francisco area. They found out that the sourdough culture there was very unique and they became very famous for their bread with this special flavor. The miners flocked to this bakery every morning for this special tasting bread. Since 1849 they have been using the same sourdough culture, which they call a 'mother dough' and the same recipe, flour, water, a pinch of salt and some of the this 'mother dough.' So important is their 'mother dough' it was heroically saved by Louise Boudin during the Great San Francisco Earthquake of 1906."