So asks reader Rainey, who points out very rightly that San Francisco sourdoughs use flour from Kansas and other places, yet they have very distinctive flavor profiles. That’s an excellent question. The reason San Francisco sourdough breads taste the way they do isn’t a result of the yeast so much as it is the lactic acid bacteria that thrive in that area. All starters are tag teams of various yeasts, which consume the simplest sugars in the flour slurry (glucose and fructose), and bacteria which generally consume the more complex sugars (like maltose). The yeast are primarily responsible for the CO2 and alcohol in the dough, and the bacteria — as their name implies — the flavor-giving acid.
The interesting thing about lactic acid bacteria is there are thousands of different kinds in nature. A unique species may live in your water supply, or in your back yard. Assuming those bacteria are capable of thriving in your homemade starter, they just might give your bread a taste that’s completely unique. Speaking for myself, I’ve never managed to culture any critters that deliver anywhere near the tang of L. sanfranciscensis and L. pontis, which are the bacteria that give San Francisco sourdough its unusual taste. These two bugs produce unusually high amounts of acid, and not just lactic acid. Under the right conditions L. pontis will produce large amounts of acetic acid, an acid with a very strong taste that’s most commonly found in vinegar.
But while my starters have never yet delivered the same acid bang for the buck as some San Francisco starters do, they have a nice subtle character that they pass to my breads. Is that character unique? On the microbial level my starter probably is unique to some extent. Flavor-wise I’m not so sure, but then it doesn’t really have to be. Homemade bread in itself is a rarity. Even without the San Francisco tang I get plenty of points for the effort!