Lazy way to catch a sourdough starter
There is a very easy way to obtain a sourdough starter that involves a cup of flour, a cup of water, a glass jar or crock, and a clean dish cloth spread over the top of the jar or crock. The jar or crock must be immaculately clean to prevent cultivating undesirable fungi and bacteria.
On a day when you are baking, mix room temperature water and flour into a slurry. Place it in the container, and cover it with a clean dish cloth. Leave the container on the counter overnight. In the morning look for activity. If you don't see any, add another 1/2 cup each of water and flour. Leave it on the counter another 24 hours. Repeat feeding the following morning, and leave out overnight.
In the morning you should see activity. Remove all but 1/2 cup of the starter, and add a cup each of water and flour. Let it ferment until evening. Add another 1/2 cup each of water and flour, and let sit on the counter for at least two more hours, and then refrigerate (unless you enjoy daily feeding of the starter.)
What will happen over time in the starter is that the local wild yeasts will displace any domestic yeast that was in the original starter - and the domestic yeasts begin to diverge from the original strain with additional generations.
I feed refrigerated starter once a week, removing all but 1/2 cup and adding a slurry made from one cup each of flour and water. When I intend to bake, I take the starter out, and increase the volume by feeding it and leaving it on the counter for a day. I then combine 1 cup of starter with two cups of flour and one cup water and let it ferment overnight on the counter. I then add flour, water, salt, and fat to make up the amount of dough I want, and then let it rise twice on the counter, a process which can be rather slow. Sometimes I start in the morning and let it ferment all day, and then add the additional ingredients and do the first rising overnight.
The important thing with sourdough is to not be in a hurry; traditionally the sponge was started and went overnight before adding additional ingredients, or was started in the morning and the additional ingredients added before going to bed.