And here's another way:Harvesting wild yeast is relatively easy, but it doesn't perform half as well as commercial yeast. The only way I've found that you can get anywhere close to a good strain is if you keep a starter going for ages and ages. It takes about a month after putting the jar out for the thing to ferment to where it's mostly yeast and you've got to watch it really closely because lactic acid bacteria can build up if you let it go for too long.
That being said, if you gather a few different strains from different areas, combining them can produce a pretty solid yeast for making bread with.
You need to warn people before links like that. I'm going to have to go wash my eyes out.And here's another way: