If Chicago has deep dish pizza and Boston has cream pie, San Francisco has sourdough bread. And just like the pizza and pie, San Francisco sourdough just isn’t the same outside its hometown.

But that’s because only San Francisco is home to a certain bacterium that bears its name– Lactobacillus sanfranciscensis.

Of course bread uses another microbe– the yeast that turns sugar into the air bubbles that lighten the loaf. For sourdough, though, local bacteria then add their secret ingredient. They eat up the yeast’s waste and turn it into acid, making the bread San Francisco sour.

The bacteria also make the dough inhospitable for other microbes, keeping all that doughy goodness for the yeast and itself. The yeast and bacteria make such great partners because the yeast can’t eat the sugar maltose, which the bacteria absolutely need.

San Franciscans have been noshing on this local concoction since at least the Gold Rush. Boudin Bakery first baked buns in 1849. Some bakeries even claim to have a “starter”– the bit of dough that contains yeast and bacteria– that’s over a century old. They pinch off a piece of starter for every new loaf, and care for the dough with regular feedings of flour and water.

If you’ve got a favorite brand, chances are it’s because of the unique mix of yeast and bacteria from that bakery. Other towns’ sourdough will taste a little bit different because their bacteria aren’t the San Francisco kind.

Want to whip up a loaf unique to your backyard? The Exploratorium has a recipe to make your own starter that will pick up local yeast and bacteria. Or if you prefer that authentic San Francisco flavor, buy the original.

For more on Lactobacillus sanfranciscensis, check out the Berkeley Science Review.

Amber Dance is the Quest Intern and a science communication student at UC Santa Cruz.

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SF's Hometown Bacteria 6 March,2008Amber Dance


Amber Dance

Amber Dance is an intern for QUEST. She earned her Ph.D in Biology at UC San Diego, and before that studied the subject at Brown University. Amber grew up in State College, Pennsylvania. She was always interested in science, pestering her mother with dozens of "why" questions. While at UCSD, she discovered there are people who make their careers writing about scientific discoveries. Determined to join their ranks, she interned at the Los Angeles Times and is currently a science communication student at UC Santa Cruz. She delights in showing up after all the difficult experiments are finished, and being the one to share the discoveries with regular people. As the winter QUEST intern, Amber is taking the opportunity to learn all about broadcast. After this year, she hopes to finally have enough education and start working.

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