Sourdough guide updated

Made a few changes that should make the experience easier (complete with warnings about the mess!).

Additionally, I added a few paragraphs explaining the logic of using commercial yeast in your starter.  This is often frowned upon by purists who insist that if you aren't using wild yeast, its not sourdough starter.  This is what I added to the guide to clarify the method to my madness..

Yeast isn't very sensitive to the pH level of the growth medium, or acids in general, besides acetic acid.  Acetic acid is produced to some degree by lactic acid bacteria (lactobacilli).  In an ideal culture, both yeast and lactobacilli are present and thriving.  It is the latter that produces the sour in sourdough, and it is already present in the flour.  Once you add water, both yeast and lactobacilli will  start to break down the carbohydrates and feed.  As the acetic acid builds up, the commercial yeast will die off, while in parallel being replaced by wild yeast that is more tolerant of the acidic environment.

This, of course begs the question as to why to use commercial yeast at all?  After all, it will eventually become extinct in the culture.  Unfortunately it's not as simple as that, and that's why excluding commercial yeast at first makes a starter based purely on wild yeast so hit-and-miss.  As the commercial yeast eats the simple sugar you added, it produces alcohol.  This alcohol will inhibit the growth of  leuconostoc bacteria which often gain an early foothold in traditional starters.  They produce antibiotic proteins which in turn inhibit the growth of wild yeast and lactobacilli.  Make sense?  In other words, using commercial yeast can be thought of an as insurance policy against the development of the antibiotic proteins that will ruin your starter.  And as I said earlier, eventually the culture will be too acidic for the commercial yeast to survive, and it will be supplanted by wild yeast that can flourish in that environment.  Once your starter is established, all traces of the commercial yeast will die off after a few feedings, and you will have a "proper" culture.

So there you have it, purists :)  Full guide here.