Rye bread has always been a favorite of mine, as well as the dense brown breads of Northern European tradition. If lightness was not a desirable attribute of these breads, then maybe leaving out the yeast would work just fine. I started my sponge the day before baking, mixing my starter with dark rye flour, warm water, and a little sugar, and mixing in browned onions and crushed caraway seeds. I put that on the counter and walked away.
After only a couple hours it was quite active, putting up the occasional bubble (polenta-style) and acquiring a rather ripe smell. By the next day (about 16 hours of fermentation time) it had developed a thoroughly adolescent personality - impatient, volatile, smelly, and just plain uncomfortable in its body. It was time to graduate it to the mixing bowl.
I folded in the remaining flour (100% rye, as opposed to most rye bread recipes which lighten the loaf with varying amounts of white wheat flour), and let the sticky dough rise and ferment some more.
Eight or so hours later, I gathered the sticky mass and clumped it into a loaf pan, for a final rise of about 90 minutes. Rye flour, unlike wheat flour, does not depend on gluten for its structural integrity and carbon dioxide trapping ability, and so does not require any kneading (read more here), which is fortunate, because rye dough is sticky. It's like kneading bubble gum mixed with Elmer's.
Finally, it went into the oven (350 degrees F) for right around two hours. It's hard to over-bake a bread like this, and you certainly don't want to under-bake it, so shoot for at least two hours, and give it a knock on the bottom to see if it sounds hollow.
A few squares of cold sweet butter and a pinch of crunchy salt would do just about perfectly, but we had the recently canned sauerkraut to debut. Some hot kraut and onions, melted cheese, a few slices of rye, last summer's bread and butter pickles, and a home brew. Prost!