Now this has been a fun one... I started cultivating a wild starter about three weeks ago, right when we got home from Oregon. This is actually my second attempt at making bread with it and I'm relatively happy with the result -- the crust is beautiful, the crumb a little bit too tight, and it's only just a little bit sour. The addiction center of my brain is fickle and usually gives up when something gets difficult but I'm hoping I stick with this long enough to make a truly face-twistingly sour loaf of bread.
So then, a wild starter is different from a regular starter in that it contains ... surprise, wild yeast. This is as opposed to commercial baker's yeast (also brewer's yeast) in other types of bread. It is apparently widely misconceived that wild yeast comes right out of the air -- I say apparently because I didn't even know that wild yeast was a thing, let alone a thing to be misconceived, until a few weeks ago. The yeast actually lives right there on the flour (particularly rye flour, particularly organic rye flour) and given some time to grow and ferment with regular feedings (i.e., adding more flour) it will turn itself into a little self-sustaining ball of bread-rising power. The really cool implication is that this bread is literally made from flour, salt, and water only (although the complete truth is that the starter began life in half a cup of pineapple juice to stave of leuconostoc bacteria that can sometimes, and on my first attempt did, delay the starter a few days)
All credit to Bread Baker's Apprentice by the way for this information. So another interesting thing is that it's actually bacteria and not the wild yeast that makes the bread sour. San Francisco sourdough is so distinctive because it contains a type of bacteria that lives only in that hallowed city (Lactobacillus sanfranciscensis believe it or not). The reason the wild yeast is important is that it can live in the acidic environment that the bacterias thrive in, and live long enough for the bacteria to grow.
Extra bonus Multigrain Extraordinaire. Incredibly delicious multi-grain loaf with millet, brown rice, wheat bran, and rolled oats. Instead of a pre-ferment, this bread starts with a "soaker" where you let the grains soak in water overnight, which actually made it one of the easier breads I've made so far, though it doesn't give me quite the same zen feeling of fermenting, kneading, and rising regular bread. Reinhart alleges that this bread makes the best toast ever, and he is correct in doing so.
It was a little bit too sweet for anything but breakfast -- Some of the people on The Fresh Loaf recommended cutting the sugar in half which I will definitely try on my next batch. And there will be a next batch.