The recipe for bread is flour, water, and salt. Everything else we add is for flavor, dough conditioning, or convenience. Flour naturally contains yeast spores, but they are slow acting so we buy fast acting yeast. We add sugar to feed the yeast, and maybe more sugar to make the bread sweet. Oil makes the bread seem moister. Try 1/4 cup oil with your cake recipe and see how you love it. Don't add more than 1/4 cup or it will soften to death. Shortening, lard, grease, or other fats will give different textures. Milk will feed the lactobacillus (yogurt), giving the bread a sour taste because lactobacillus produces acid. Lactobacillus is rather slow acting, days instead of hours, and that is why sourdough is such a time consuming hobby.
Wine grapes also carry their own yeast spores. Some experimenters have used grapes to leaven their bread. I can only imagine what that would be like.