Sid Greaves asked about sourdough characteristics.
Books have been written on the subject of sourdough. So I will not do the
topic injustice by trying to explain it all with one post. Thus I refer
you to someone who knows better than I.
I don't know if you can find a better website than
<http://www.nyx.net/~dgreenw/sourdoughfaqs.html> to learn about
Sourdough. They have a ton of info and links on that site, including the
answer to your question.
And I have never seen a better book (for sourdough) than Ed Wood's,
Sourdough from Antiquities. Ed has a site where you can by his starters
and order other goodies. <http://www.sourdo.com/> I have not tried his
starters, but I have heard good things about them. He explains the
differences between the different starters he has. I have been pretty
lucky with sourdough. I made a starter with plain Flour and water (maybe a
little sugar, I don't remember). Now I just feed it equal amounts of flour
and water i.e. one-cup flour and one-cup water each time I use it or 2 Cups
each, whatever. Hope this helps.
Fellow Bread Fiend,
Pedro