If you've ever made sourdough bread, you'll know it's a different animal from other bread.
Instead of adding yeast to raise the dough, you'll use sourdough starter, a yeasty, fermented flour-and-water mix. This starter gives sourdough bread its characteristic tang.
At bottom, sourdough starter is simply flour and water that has been left to ferment. The magic ingredient is wild yeast, a little single-celled fungus that is startlingly present among us. It's on vegetation and in soil and water — and also in flour. So, when you let a flour-water mixture sit around for several days, that wild yeast will become active. It feeds on the sugars that are present in flour. When yeast feeds, it releases carbon dioxide that creates air pockets in dough, causing it to rise.
Often someone will give you some starter from their stash. Or you can make your own. The strange thing is that sourdough starter can live for many years, and bits of this living substance can be passed on to others.
There are stories of sourdough starters being passed down for generations — a woman in Newcastle, Wyoming, claimed her sourdough starter dated to 1889 and a woman in Bowling Green, Kentucky, said hers dated to 1948.
Once you've got a starter in your possession, keeping it is something of a commitment, warns the Joy of Cooking. "Generally I feed mine once a day in warm weather," wrote Joy website author Megan Scott.
Kept on a kitchen counter, starter will need frequent feeding. Kept in the refrigerator, not quite so much. The "food" is simply a little flour and water, which gives the live yeast culture something to chew on.
One way to feed your starter is to put some bread dough in with it each time you've taken out starter to make bread.
Here's the problem: With a living being lurking in the back of the fridge, how can you stop baking? If you are feeding the thing, how can you stop using it?
Starters are surprisingly hard to kill. Heat will do the trick, since yeast dies at 140 degrees Fahrenheit, but severe neglect can also cause death.
Failing that, your starter will be sitting there waiting —- nay, calling — for you to bake.