First:
Sourdoughhome - An Exploration of Sourdough
Second:
Yeasties in the air aren't important. I have started a starter in middle February, with a HEPA filter on the house.
The basic method I have had success with is this:
25g of rye flour, 25g of water. Make a paste, stick it in a container and let it sit for 24 hours.
50g of flour, 50g of water and your rye paste from above. Mix and let it sit for 24 hours.
Take 50g of above (discard the rest), 50g of water and 50g of flour mix and let sit for 24 hours.
You should see some activity in the above at this point. If you don't, then don't despair, just repeat again at the 24 hour mark. If you have seen activity at this point repeat at the 24 hour mark. Simple.
If you saw activity on the last one start the process at the 12 hour mark. It doesn't need to be a lot of activity. Once you start the 12 hour feedings you will need to keep them up and the starter should get stronger over time. It is ready when it can double itself in about 6-9 hours.
Once it is ready you can make bread with it, but before you do you should make more than the standard feed. For example doing a 1:1:1 feed of 50g each of water, flour and stater you might consider taking 120g of the starter and match it 1:1:1 so that you end with about 360g so you have enough for bread AND to continue your starter.
You should go through a really foul smelling phase 4-8 days in. It will be bad. That is the bad things in the stew dying. It will mellow and smell right at some point.
If the thing gets black spots in it then you should pitch and start again, that is mold and you don't want that.
