A starter is a home-grown yeast culture. One which, by virtue of the way it’s made, contains a much higher proportion of acid-producing bacteria than a commercially-acquired yeast culture (one of those little packets). It’s the addition of these bacteria that give home-grown starters their complex flavors, which vary markedly from location to location, since different bacteria live in different climates. Or perhaps I should say that different bacteria live in/on different people that live in different climates. But more on that in a moment.
The popular thinking on home made starters is that they randomly culture whatever yeast and bacteria happen to be in the air and/or in the water where the starter is made, since these types of critters are literally everywhere. Moisten some flour and leave it out on the counter, so the thinking goes, and the wild bugs just move right in. The problem with this line of thinking is that it assumes that the flour that the starter is made from is a pure and uncontaminated medium to begin with…and that’s far from the case. Flour may appear pristine, bright white and uniform, but under the hood there’s no end to the miscellany it contains. Everything from insect parts and eggs to dirt (referred to as “ash”) to traces of rodent hairs and droppings. The more refined the flour, the less of all this stuff you get, but in the end there’s no way to eliminate it all (which is why the FDA imposes “limits” when various contaminants reach unsafe levels).
Of course mixed in among all of these X, Y and Z’s are more than a few micro-flora and fauna. Bacteria, fungi and above all yeast. Why yeast? For the same reason that grapes and plums are covered with yeast (it’s that white film that most people dismiss as refrigerator condensation): because the bugs know where the food is. Yeast cover the outside of sugar and starch-rich food sources hoping to get in. The exteriors of those food sources — the skins of fruit and the bran of wheat berries — do a pretty good job of keeping them out as they grow. But break that exterior, by say, mashing the grapes in a barrel or grinding the wheat, and all bets are off. Of course in contrast to grapes, wheat is kept dry as it’s being processed and that prevents fermentation. Yet plenty of yeast makes its way into the finished product as the wheat berry is crushed, ground and sifted, and from there into the bag, and ultimately into your home-made starter. All of which means that when you’re making a starter from scratch, the yeast that you’re most likely cultivating is the stuff that was on the original wheat berry wherever the crop was grown.
So OK, that’s where the yeast comes from, what about the bacteria? I have the answer, but before you continue, let me make the disclaimer that those of you who gagged on your morning coffee when I mentioned rodent droppings might want to leave the room. For the bacteria in bread starters don’t seem to come from the air either, at least that’s the conclusion that researchers studying San Francisco sourdough have come to. Attempts to culture the bacterium that gives San Francisco sourdough its flavor (called Lactobacillus sanfranciso) from thin air have been across-the-board failures. However scientists have apparently managed to grow thriving cultures of L. sanfranciso from the people who live in the San Francisco area: from saliva, dental scrapings, nasal swabs and various, erm…excreta.
Which means that the bacteria that give sourdoughs the flavor that bread makers so greatly desire does indeed come from the environment, though not directly. What science seems to be telling us is that in order for random bacteria to be viable in a starter bowl, they must first find a staging area where they can multiply. That staging area, it appears, is us. Precisely how those bacteria make their way from point A to point B I’ll leave to your perverse imagination. Enjoy your breakfast.