Making a Sourdough Starter (Levain) from Scratch

Ingredients:
organic rye flour or organic whole wheat flour, bread flour, bottled water, A 4-cup glass canning jar OR 4-cup glass measuring cup, large heavy plastic spoon OR clean wooden spoon, plastic wrap

Instructions:
In an immaculately clean bowl, combine a scant cup/4.2 ounces/120 grams organic rye flour and ½ cup/4.2 ounces/120 grams bottled water. With a clean hand or spoon, stir until the flour is moistened and a stiff dough is formed. If there are still loose flour particles after 2 minutes, add more water by the droplet. Scrape the starter into the 4-cup container. You will have about 1 cup/8.5 ounces/240 grams. Cover it tightly with plastic wrap (it's fine to use the ring that screws onto the canning jar to keep the plastic wrap in place) and place it in a cool area (65°F) for 48 hours. (If you don't have a cool area, let it sit for only 24 hours [until Day 2] and feed it the same way as described for Day 3.)
There will be no visible change in the color or texture of the starter.
The consistency of the starter will now resemble a thick pancake batter and there may be a few bubbles in the surface. With a clean spoon, remove and throw out about half of the starter (about ½ cup/4.5 ounces/120 grams).
Stir in: a scant ½ cup/about 2 ounces/60 grams bread flour and ¼ liquid cup/about 2 ounces/60 grams bottled water.
You will again have 8.5 ounces/240 grams of starter, but it will have expanded in volume from just under 8 fluid ounces to about 10 fluid ounces. Cover again tightly with plastic wrap and leave at room temperature (70° to 75°F) for 24 hours. (After 12 hours, the starter may have increased by one and a half, to 14 fluid ounces, and have lots of bubbles. Don't be concerned if it then deflates and falls.)
The starter may give off a faint citrus aroma. With a clean spoon, again scoop and throw out about half of the starter (about ½ cup/4.25 ounces/120 grams).
Stir in: a scant ½ cup/about 2 ounces/60 grams bread flour and ¼ liquid cup/about 2 ounces/60 grams bottled water.
You will again have 8.5 ounces/240 grams of starter, about 10 fluid ounces in volume. Cover it with plastic wrap, but not tightly, as gases should now be forming that need to escape. Leave it at room temperature (70° to 75°F) for 24 hours.
If the starter is active, it will have increased in volume to at least 3 cups, or even 4 cups. It will dome and then start to recede. (If it is not yet at this point, continue throwing out half the starter and feeding it with the scant ½ cup/about 2 ounces/60 grams bread flour and ¼ liquid cup/about 2 ounces/60 grams bottled water every 24 hours until it reaches this state of activity.)
With a clean spoon, again remove and throw out about half of the starter (about ½ cup/4.25 ounces/120 grams).
Stir in: a scant ½ cup/about 2 ounces/60 grams bread flour and ¼ liquid cup/about 2 ounces/60 grams bottled water.
You will now have about 1 cup/8.5 ounces/240 grams of active starter. (You may feel the impulse to give it a name. Give in to it: I named mine Billo.) Cover it with plastic wrap and let it sit at warm room temperature (75 to 80°F) for about 4 hours or until it has almost doubled. You can now "expand" it (feed with flour and water) for baking bread or refrigerate it overnight and start expanding it the next day. If you don't plan to use it for several days, feed it again to double it, let it sit for 1 hour, and then refrigerate it.
This starter will mature over the next couple of weeks, gaining in strength and flavor. For the first 2 weeks, store at least 1 cup (8.5/240 grams) of it and feed it at least three times a week. After two weeks of regular feeding (equal weights flour and water or, by volume, 1 ½ times flour to water, to at least double it; when the jar gets half-full, pour off half), at least three times a week, the culture is mature and bread made from it will be more mellow and complex. You can now switch to once-a-week feeding if you only make bread once a week.
Once your starter is mature, all you need to store is enough for 1 or 2 loaves plus enough to start the next batch (about a full ¾ cup/7 ounces/200 grams). If you plan to bake in larger quantities, simply increase the amount you store by throwing out less of it before each feeding.