Adventures in Sourdough

Country White Sourdough

This week I'm somewhat reluctantly beginning a sourdough starter.  Truth be told, I'm a little bit daunted by the whole sourdough thing.  If there's any kind of bread that has a BIG reputation to live up to, it's sourdough.  I've already confessed that I'm an overachiever and a perfectionist which gives me cause for trepidation.  But alas, I promised my labmate a bread of his choosing, and he picked sourdough. *sigh*

But, this got me to wondering, what is it that makes sourdough bread sourdough?  I have been reading through various books on bread (and have consulted some old—quite hilarious—magazine clippings from 1988), and this is what I have been able to gather:

In any type of leavened bread (ie: stuff other than flatbread or matzo), yeast is the agent responsible for making dough rise.  That is because yeast eats sugar (which comes from the breakdown of starch in flour); then it burps up CO2 gas; and this gas gets trapped inside the dough, making it rise.  Commercial yeast, Saccharomyces cerevisiae, is the kind of yeast I typically employ.

But, when it comes to sourdough, there is another important microorganism involved: lactic bacteria.  Like commercial yeast, lactic bacteria eat sugar and burp up CO2.  But, they also produce lactic acid and acetic acid which result in "buttery" and "sour" flavors.  One of the more famous strains of lactic bacteria, Lactobacillus sanfrancisco, is the bug responsible for the distinctive flavor of San Francisco Sourdough.

This brings us to two important points:

1) Lactic bacteria need more time than commercial yeast to produce their respective biometabolites.  This is why 'normal bread' does not have the same flavor as sourdough; it is developed too fast for the other flavors to emerge.  This is also the reasoning behind using a sourdough starter.  Starters provide extra long fermentation times to gradually build up the dough and incorporate more lactic bacteria-derived flavors into the final product.

2) Commercial yeast isn't very tolerant of the acidic conditions produced by lactic bacteria if the two are co-fermented for longer periods of time.  Consequently, a different kind of yeast (one that is more compatible with the acidic conditions), Saccharomyces exiguus, is often used in sourdough starter.  S. exiguus is a wild yeast that grows ubiquitously, but two particularly common places to find it are on grapes and whole grains.  This is why organic, unbleached, whole wheat or rye flours are often used to begin starters.  This is also why the water used in starters is sometimes pre-soaked in raisins before adding it to the flour.  (Note: one of the worst things you can do is try make sourdough starter with bleached white flour!) 

For the time being, I have decided to go with a starter recipe that I found in Peter Reinhart's book, Crust and Crumb.  (A delightful read if I don't say so myself!)  I will post pictures of the starter and outline instructions in a few days.