The only requirement for your flour is that it is white, not freshly milled, and that it is unbleached and unbromated.
Flours that have been bleached and bromated have less micro-organisms than are needed. Two popular brands that are unbleached and unbromated are Gold Medal (make sure it is labeled unbleached/unbromated) and King Arthur Flour.
Freshly milled flours have a lot of natural oils and bran, so they often go rancid before the yeast can develop. If you want your bread to be healthy, use whole grain flour for the recipe, but not for the starter.
I prefer SAF yeast, an active dry yeast. I've used it for years so I know what to expect from it. It's dependable. But I guess any active dry yeast will do.
I use our well water and have never had a problem. If your water is flouridated or you treat your water to make soft water, then buy some spring water to use for your starter. Why not distilled water? Because distilled water has no minerals...which are helpful for your starter.
Creating your starter Make sure your container is clean. If in doubt, pour some boiling water in it and swish around.
There are two kinds of starters that I've made: domestic and wild. Domestic starters have a little commercial yeast that helps develop the starter faster. This starter smells like alcohol from time to time. Wild starter consists of equal parts flour and water. This starter may take up to a week to develop, and has a sweeter taste. I've made both starters with good success.
One word about wild starters. If you mill your own flour, then your ceiling is probably like mine and covered with millions of yeast spores. In this case, you will find your starter develops much quicker than what most websites say it takes. I have created wild starter in 12 hours, domestic in 8 hours. So don't think these time estimates are concrete.
Okay, here we go. Most folks make this out to be harder than it is:
Whisk together 1 cup flour and 1/4 tsp yeast in a non-metal bowl. Add 1 cup tepid water. Stir until mixed...do not over-stir and develop the gluten. Lumps are fine. (You may halve this recipe.) Just so long as you have equal parts flour and water. For wild starter, mix equal parts flour and water. (You may want to make both a domestic and a wild.)
Here's a very important tip: Always rinse your utensils of any sourdough immediately after using. Sourdough turns into cement if allowed to harden. I am still suspicious every time I see an old log cabin with white chinking...I am just positive it must be sourdough starter! It is especially important to rinse before putting your utensils into the dishwasher...otherwise your glasses and plates will end up with a thin film that will never come off!
Cover your bowl with a piece of wax paper. Set your bowl in a place that is free of drafts, at room temp. You cannot kill a starter by being too cold, but any temps over 100 degrees or so will kill the starter.
Once a week you need to use your starter; otherwise, discard 1 cup of the starter and replace with 1 cup water and 1 cup flour. If you are trying to build up your starter, just add the water and flour and don't worry about discarding any starter.
Dark liquid on top of starter
So what about the dark liquid on top of the starter? Unless it is reddish (bacterial), you may stir it into the starter or pour it off into the sink. Yes, it is grey and sometimes dark grey, but that's okay. I tend to like a "dryish" gloppy starter, not a "wet" watery starter, so I usually pour off the liquid...but I hate that it runs down the side of my crock! It is only a matter of preference...which you will develop the more you use your starter.
Remember: If you have any questions, please leave your question in the comment section (which is automatically emailed to me).
When I first started baking with sourdough, I was very excited about it and immediately started baking a different recipe everyday. It wasn't until a year or two later that I learned that you're supposed to let your starter "regroup" for 4 days or so before using it. Well, I've used it a day later and a week later...same difference. Go ahead as long as your starter looks healthy and is bubbly.
What if your sourdough starter looks thin and syrupy? That means you are not feeding it often enough. Go ahead and add flour and water.
You're all set ~ enjoy your starter!