In his early days of baking, Steve created a leavener with a starter inoculated with wild yeast from wine grapes.

BBC: Flour power in San Francisco��s sourdough

And part of that is because of the wild yeast.

NPR: Looking at the World Through Beer Glasses

It's hard to plan a schedule around wild yeast.

WSJ: The Sour and the Glory of Beer

When they add nothing, as lambic-makers do, the untreated wort becomes a refuge for airborne wild microflora, which now have space to grow and food that would otherwise be hogged by beer yeast to eat.

WSJ: The Sour and the Glory of Beer