This Sourdough Bread recipe calls for you to "fold the dough" a couple of times during the bulk fermentation (first rise), and I thought it might be helpful to some people if I explained what that means. (If you are a seasoned dough-folder, you can skip this section.) The folding helps to encourage those long gluten strands, and create those lovely sourdough bubbles. Many, if not most, bread recipes call for you to punch down the dough after rising. Punching down the dough does a number of things. Most importantly, it removes some of the gas bubbles from the dough and redistributes the yeast cells, sugars, and moisture so that they can ferment and rise again during the proofing stage. Folding yields similar results: it too expels the carbon dioxide produced during fermentation, strengthens the dough by stretching the gluten strands, and redistributes cells, sugars, moisture and heat spots in the dough to even out the rising. Punching dough down will result in a fine crumb, which is desirable when making sandwich breads or pastries. Folding, on the other hand, will give you a loftier rise and a looser crumb - resulting in all those lovely little air pockets in our sourdough and artisan breads that we love so much.