Now that you mention Tartine, I remember reading about them previously. The books are quite interesting. Regarding sourdough sourness: Sourdough bread doesn't

Now that you mention Tartine, I remember reading about them previously. The books are quite interesting. Regarding sourdough sourness: Sourdough bread doesn't have to be very sour. Certain parameters influence the perceived sourness, and it is definitely possible to bake sourdough bread that is very mild and barely sour. Have a look at the classic Italian lievito madre (mother yeast) or French levain liquide - the former is used for panettone, a special sweet bread commonly eaten around christmas, the latter can be used for croissants. I've baked a few sweet loaves that are only leavened using sourdough (with no added baker's yeast), yet they have essentially no discernable sourness. I agree regarding the guild system.