Levain: Where do the aromas come from? What are the health benefits?

Have you ever wondered how come no bread leavened with wild yeast ever tastes the same from one bakery to the next, even when made from the same formula? Ever wondered whether or not there are any health benefits to eating bread made with levain as opposed to bread leavened with commercial yeasts? And if so, what those benefits could be? Well, wonder no longer. Robert Low, a Professor of Molecular Physiology and Biophysics at the University of Vermont and a lifelong baker and levain aficionado himself as well as a good friend of Gérard's (which is how I happened to meet him), has been reading the scientific literature on the subject for some time now and he has kindly agreed to share with his conclusions with us. Please click here to see his paper (a work which will be updated as needed when new material comes to light). Interestingly I was just reading here this morning in the French version of Wikipedia that, even though commercial yeast can be a source of vitamins and other nutrients, it isn't a good idea to leaven whole grain breads with it as, contrary to levain, during the fermentation process, it doesn't destroy the phytic acid present in the grain. This acid prevents the body from assimilating calcium and other nutrients. The article asserts that, in the long run, consumption of yeast-based whole grain breads can contribute to calcium deficiencies. So I checked Wikipedia under "phytic acid" and here is what I found. It dovetails with what Professor Low is saying in his paper. There is so much to learn about nutrition. What an interesting science! In my next life I want to be a baker AND a nutritionist.