I've been lurking in this list for awhile, as well as reading the
archives, so I know the answer to that: "What do you mean, your Carl's
isn't sour!?" Some people seem to have no trouble with sourness at all,
others cannot get it sour even after lengthy Q&A sessions. I've tried
most of the suggestions given on the list... in particular, I've let
the starter and/or dough sit for extremely long periods of time. I am,
of course, eager for any other suggestions.

Ben