Back in ye olden tymes, yeast was harvested from the air by fermenting flour and water together in a jar and replenishing it as it got used up. This “sour dough” was carried carefully when moving, protected from extreme heat and cold, and carried a taste all its own. It’s why sourdough bread from San Francisco tastes different from sourdough bread from somewhere else. When you craft your own sourdough starter (also called a mother sponge) you’re harnessing the native yeasty beasties in your habitat to burp and raise your bread. Pretty cool, if you ask me.
First, get a jar with a seal. Breadtopia sells a relatively cheap one, but you can also find self-sealing jars at Goodwill and other quality thrift establishments.
Next, wash it really well in hot, soapy water. Make sure you rinse out all the soap or you’ll kill what you’re trying to cultivate.
Then, plop about a half cup of all-purpose flour into the bottom of the jar. Follow with a cup or so of warm (but not hot) water.
Now, stir it up, seal and set the thing in a warm-ish place in your house. Near the stove is great. On top of it is too hot. The beasts will populate it without you doing anything. They’re opportunists like that. You’ll know it’s working by the bubbling foam on the top of the mixture. That’s the natural, native yeasts moving in and having a housewarming party.
Here’s where it gets tricky. You need to feed the yeast that’s colonizing the mixture EVERY DAY for about a week. If you don’t, the yeasts that are already there will die. You’ll also invite not-so-friendly bacteria and stink up the joint. Set an alarm. Do it when you make coffee in the morning. Whatever. Just make sure you feed it every day for a week or so.
To feed your emerging mother sponge, pour out about half of what’s there and add a half cup of flour and another half cup of water. Stir. Set in the warm place again.
After about a week, it’ll start smelling a lot like the bread you want to bake (or the pancakes, my personal favorite). If it seems a little limp (not a ton of bubbles), ferment for a few days more or put in a warm oven for a few hours to see if the yeast just needs some inspiration–again, not too hot or you’ll kill it. If it’s not bubbly after two weeks, or if it smells more like rotten veggies (or has any mold growing along the edges), discard and try again.
Once your mother sponge is happy and healthy, you can store it in the fridge. Use a half-cup at a time in any sourdough recipe, and try to use some every week or so to keep everything healthy. Just be sure to replenish what you use (or, as I like to call it, feed the beasts).