I wanted to make one more Instructable to show how easy it is to transition from a poolish starter to a wild yeast starter. You will see the steps are basically the same as Mark Bittman and Jim Leahy's no-knead bread recipe, except that it takes a week or so to get the starter going until it is ready to use. All the measurements here are in grams as weights are much easier than volume measurements, and a kitchen scale will only cost you $12.

Step 1: Start With Equal Parts Flour and Water....

As with your poolish, start with equal parts flour and water. In this case I used 50 g. of wheat flour and 50 g. of bread flour and 100 g. of filtered water from my refrigerator. I use filtered water to remove the chlorine from tap water that can kill natural yeasts and bacteria. I have also used tap water in the past and it worked fine. Mix the flour and water with a spoon or wash your hands and mix it with your finger because there are wild yeasts on your skin. Loosely cover the container with a paper towel or plastic wrap and wait 2-3 days for bubbles to appear.

Step 2: Wait for Bubbles to Appear

After two days my starter looked like this. I knew it was ready to feed because of the bubbles on top, indicating that fermentation has started. Dump 90% of the mixture, then feed it again with 100 g. of flour and 100 g. of water.

Step 3: Train Your Starter

The next step is to "train" your starter. After the first feeding, wait for bubbles to appear again, which for me took two days. After that feed the starter daily by dumping 90% of the starter and adding 100 g of flour and 100 g of water.

You will know the starter is ready to use for baking when the starter reliably doubles in size. For me this took 3-4 feedings. That said, my first two loaves came out flat as a pancake and the loaf pictured on the cover page is my third attempt.

In the picture here you see the bubbles on the side of the container, and the starter has more than doubled from its original size.

Step 4: Now You Are Ready to Bake

Now you can proceed with your regular bread recipe, subtracting the 100 g of flour and 100 g of water that you already used in your starter. More detailed instructions are documented here.

I like to use a recipe that is roughly 60-70% all purpose flour and 70-75% water.

50 g wheat flour (which is used in the starter)
100 g bread flour (50g from the starter, and an additional 50 g when you mix the ingredients)
350 g all purpose flour
10-11 g salt
350-375 g water

If you subtract the amount of flour and water used in the starter, then you end up with:

50 g bread flour
350 g all purpose flour
10-11 g salt
250-275 g water

Mix all the ingredients and let the mixture rest in what is called the "bulk rise." The bulk rise can take 6-8 hours or longer, depending on the room temperature and the temperature of water you used.

The key to transitioning from bakers yeast to a wild starter is knowing when the bulk rise is complete. I look for the dough to double in size and have lots of bubbles on the side. You can see the bubbles on the side of the food storage container in this picture.

In this case I mixed the dough in the evening with cold water, let the dough sit overnight, and by morning the bulk rise was complete.

I sometimes mix the dough then let it rest in the refrigerator for a few days before the bulk rise. The delayed fermentation allows more time for sour, yeasty flavors to develop.

Step 5: Shape, Bake, and Enjoy!

Once the bulk rise is complete, shape the dough into a ball by folding it under itself and let it rest or "proof" for 2-4 hours. I place the dough seam side up in a wooden proofing basket called a Banneton, but you can also let the ball sit seam side down on a lightly floured cutting board.

I have had the best results when I allow 2-4 hours for proofing. However, if you wake up at 6am, allow a 3 hours proof, then bake for 45 minutes, you do not have fresh bread until 10 am.
I have also tried to accelerate the process by allowing the dough to proof while I'm pre-heating the oven, and trying to accelerate the proof by placing the basket on top of the oven. I get mixed results with this method but at least I get fresh bread with breakfast.

During the last 30-45 minutes of proofing, pre-heat the oven to 450 degrees with the dutch oven inside. Transfer the loaf to the dutch oven, score and bake 30 minutes with the lid on, 15 minutes off.

Step 6: The Baking Life

Now that you have a working starter the trick is keeping it alive within the rhythms of your daily life. I store my starter in the refrigerator and try to feed it once a week, preferably by baking a loaf. Typically I remove the starter from the refrigerator and let it sit 8-24 hours before it has doubled in size and is ready to use.

Some people let the starter lay dormant in the refrigerator for up to a month. If the starter does not look or smell attractive, feed the starter once before using it again.

The times that I used in this instruction are approximate. I have learned that the art of home bread baking, besides the ingredients used, is knowing when the bulk rise and proofing are complete, and adjusting the process to fit within the rhythm of my daily life. The results are not always perfect but at least I get to eat lots of carbs. Enjoy!