I’ve been using the Bread in 5 no knead method with Bioreal yeast. Since the dough is kept in the refrigerator for up to a week does it eventually turn to sourdough?
Part of the fermentation in sourdough comes, not from the yeasts, per se, but from bacteria. Dough made with baker’s yeast (or even with no yeast at all) can turn sour simply because of bacteria present in the flour. I think, if there is an appreciable quantity of yeast in the dough, though, that by the time the dough turns sour, the yeast will have eaten most of the available sugars and starches, so you wouldn’t be able to turn it into anything like a good loaf of bread.
If you start a pre-fermentation dough, or “biga,” a day in advance, using part of the water and flour from your recipe and just a pinch of yeast, you can get some bacterial development going which lends good flavor and superior texture to your bread. (Carol Field’s book, The Italian Baker, goes into the process of prefermentation with great clarity. I think it was this book that popularized the use of bigas among home bakers in America.)
I have experimented with adding a couple of tablespoons of (liquid) buttermilk—the kind with live culture—to yeasted dough. When I did that, I used a very small quantity of yeast (1/4 tsp) so that the fermentation would take a long time. This gave the bacteria in the buttermilk (acidophilus, I think) time to get active. The resulting bread did have a sourdough kind of flavor, and the long fermenting process gave it a good texture and blistered crust.