The concept is appealing but the name seems reductory. Sourdough, despite its fame, is but one type of bread. Seing that you had another book called the bread code I went to check that out but it's marked deprecated by this one. So is this a case of an ill-fitting name that does not do justice to the content, or is the content just limited to sourdough as the end-all of bread making? I'm personally not found of the s…
Otherwise it's a (bad name IMO for a) leavening method. Basically just not using controlled/commercial/instant yeast, but from the environment.
Guarantee original baguettes were made with an environmental yeast starter/levain, probably some bakers continue to.