Heated:

When Alexander Roman first experimented with sourdough, he hung a plum, presumably covered with yeast, above his starter. He has used grapes to jumpstart batches at home and has even heard of bakers adding cabbage leaves to their ferments. Now, as head baker of High Street Hospitality in Philadelphia, he doesn’t use any tricks to propagate yeast. “It’s everywhere. In a bakery, no matter what, flour and water turns into starter.”