Lots and lots of preferment and starter questions these days as industrious home bakers gear up to make Christmas panettone, stollen and other festive breads. One question keeps recurring and it is: what’s the best way to encourage the unique wild yeasts in my kitchen to grow into a starter? The answer, unfortunately, is that there really is no practical way to culture the wild yeasts that occur in your home.
There’s a pervasive myth out there — and I don’t know where it started or who started it — that homemade starters are local yeast capture devices. Which is to say, that home starters grow because wild yeasts in the kitchen invade the flour slurry and start growing there. In actual fact, home-grow starters grow because the yeast that’s already in the flour when you buy it starts to multiply and thrive.
Wheat berries, you see, get covered with yeasts of different kinds as they grow in the field. The little beasties wait on the berry surfaces in hopes of being first to the starch buffet when the seed germinates and cracks open. If you’ve ever noticed the thin white film of yeast that covers grapes or plums when you buy them, it’s pretty much the same phenomenon. That yeast isn’t — and really can’t be — completely removed when the wheat berries are ground into flour. Which means that every bag of flour arrives at the grocery store with some yeast already in it. It’s this yeast that we cultivate when we make a starter.
Which is not to say that some local microbes won’t invade your starter either at the beginning of the process or over time, however they’ll tend to get out-competed by the more numerous yeasts that are already in the flour. Still if you keep your starter going for months or years you’ll increase the odds that it will start taking on some local character, even though you’ll be constantly re-inoculating it with yeast from Kansas or North Dakota or Idaho whenever you feed it.
Sorry to burst the bubble of any starter romantics out there!