As If the World Needs Another Tutorial on Sourdough Starter ...
I've found that combining flour* and unchlorinated water is all one needs to make sourdough starter.
There is no need for pineapple juice, vinegar, grape skins, cabbage leaves, potato water, milk, yogurt, cumin, etc. No need to try to manipulate the pH. The pH will take care of itself. Cover and let it sit at room temperature, stirring once per day. Within the first few days it will go through a phase where there are surface bubbles and it smells like cheese, but this too will pass. If you want a little more assurance that the yeast will take off, add a pinch of salt. See the Kline & Sugihara patent below.
* I recommend unbleached all-purpose or bread flour for starter because millers add (usually) malted barley flour to adjust the falling number and this helps out the amylase which is needed to break down the components of flour.
Many thanks to proth for enlightening me on the falling number. Thanks also to phaz, whom I haven't seen post here in a while, for emphasizing that just flour and water was how they did it in the olden days and they made wonderful bread.