San Francisco Sourdough

I saw this advertisment for sourdough bread in our local M&S today.  It got me thinking to when my pen pal from San Francisco visited me two and a half years ago and she brought me a sourdough loaf that she had baked all that way.  It was delicious!

Looked up San Francisco Sourdough and came up with the following about the bread:

The sour flavors come from lactic and acetic acids produced by inevitable environmental bacteria, which are working on the flour's sugars along with the yeast. Different bacteria make different sour flavors; San Francisco is awash in local bacteria species that make its sourdough bread famous.