This is the final chapter of my accounts of making desem bread , which is made with just flour, water, salt and nothing else. It's somewhere between regular baking and a science project.
My desem is now about three weeks old, and is quite mature. How do I know it's mature? Because, after it's been fed some fresh flour and water, it turns quite spongy within a few hours. It also dissolves completely in water, leaving no strings of gluten in my hand.
I've moved the desem from the cool but still warmish room where it was growing during its infancy and adolescence, to the colder (about 15°C or 60°F) unheated coom. When it's kept cooler, it grows slower. It could be kept in the refrigerator too. It take a bit of time for the desem to adjust to the cooler temperature, but it does, and it's just more convenient to slow down its growth rate unless you plan to bake with it very frequently.
To keep the desem going, just feed it ever other day or so. Whenever you feed it, give it 1 part unchlorinated water to two 2 parts whole wheat flour - e.g. 1/2 cup water, 1 cup flour. Knead well, wrap in a clean unbleached cloth or a few layers of undyed paper towels, and store in a non-metallic container.
To bake with the desem, just feed it the day before you plan to bake, take 1 1/2 cup of the desem for your baking, and let it ripen at room temperature in a covered bowl. Return the rest to the desem container to continue as the "mother", in the cool storage place.
You can try using the desem as part of a regular yeast-raised bread. It adds a pleasant sour-doughyness to yeasted bread. It can also be mixed up with flour and water to make a stiff dough, rolled out thin, brushed with a bit of water or milk, sprinkled with sesame seeds, and baked to make tasty crackers. And of course it can be used to make desem dosas .
So, here's the recipe for making desem bread with mature desem. This makes two round loaves about 25cm in diameter. It will grow bigger and lighter each time you bake, so don't worry if the first couple of bakings produce smallish loaves. I've repeated some of the instructions from the baking the first loaf  entry. Note though that the amount of desem in the dough is much less (about 1/3rd) and that the times are shorter too - only 4 hours, not 10-12 hours, for the rising period.
Dissolve the desem in the water. Add salt. Mix in the flour to form a slightly stiff dough.
Knead well, for about 20 minutes by hand or 10 minutes with a KitchenAid (or similar machine that can knead, and has a strong motor - this dough is too stiff for most food processors!) until the dough is stretchy, smooth and rather sticky.
Place in a covered bowl and let rise for 4 hours, at cool room temperature (see previous temperature notes  for desem). If you can give it a good punch at around 3 hours. It should rise to about 2x its original size.
Take the dough out of the bowl, taking care not to break the outer smooth surface. Punch it down, cut in half, and round off each half to form two smooth balls.
Place on a baking sheet that's been greased then sprinkled with cornmeal, a bit apart to allow for expansion. Put the whole sheet in a plastic bag that's been moistened with water on the inside, and seal up the bag. Place this whole thing in a warm location - such as inside an oven, at the lowest possible temperature setting if you have an electic oven (around 40°C) or just with the pilot light on if you're using a gas oven. (I've also tried putting it on top of the VCR...just be careful not to drip any water.) Leave it at this warm rising location for 1 1/2 hours, until it's all puffy spongy looking.
Heat up the oven to 230°C (around 450° F). Put the baking sheet (without the plastic bag...) and either cover the whole thing with a large pot or heatproof bowl, or earthenware baking cover that you've soaked in water, or just spray the loaves with water, and spray more into the oven before closing. Bake for about 10 minutes at the high temperature, then lower the heat to around 180° C / 350° F and bake until done, about 50 minutes.