Well That Didn't Take Long!

When I created my first sourdough culture, two years ago, it was a drawn out and somewhat frustrating experience.  I made the mistake of using a very small amount of bleached all purpose flour, with a lot of water, in a bowl.  Days passed without anything happening.  Following advice that I'd found somewhere, I started exchanging half the volume of the mixture every day.  More days passed, and still nothing happened.  Then I came across some new advice:  Add some whole grain flour, make a thicker mixture, and leave it alone until something happens!  That did the trick.  Within a day I started to see activity, which was eventually coaxed into the starter that I've been using since then.

Yesterday I began building the culture that will form the basis of my new starter.  The instructions in Tartine Bread closely align with the method that eventually yielded success two years ago:  the inclusion of whole wheat flour, and a thick mixture.  The book states that something should happen in "2 to 3 days".

Well, here's what I awoke to this morning:

It is alive!  As the yeast begin to multiply, they feed on the protein in the flour in a process called fermentation.  The byproduct of fermentation is carbon dioxide gas, which forms bubbles within the flour/water mixture.  And the expansion of these gas bubbles causes the mixture to expand.  As you can see in the picture above, the mixture has risen approximately a half inch.  Here's the view from the top:

You can see that a few of the larger gas bubbles have risen to the top.  And looking at the side of the jar, you can see one of the reasons that a clear glass jar is the ideal vessel for this process:

Those small bubbles show you what is going on within the body of the paste.

If you look at the label on the side of the jar, you'll note that it has only been a bit over 18 hours since I started the culture.  Why are things so far ahead of schedule?  There are several answers.

First, it's possible that the inside of the jar had some yeast spores already in it.  When yeast find themselves without food, they go into a dormant phase.  All that is necessary to revive them is the addition of food and water.  Providing them with a couple of cups of flour and water would do the trick.  However, this jar had been washed thoroughly with soap and hot water, so that's not likely to be the reason for the aggressive yeast growth.

Second, the culture that I started yesterday contains fresh whole wheat flour.  Few things contain more yeast than whole grain flours, so it's likely that this culture had a good head start in life.

Finally, the culture was build with bread flour.  Bread flour is all purpose flour that contains more protein than normal all purpose flour.  And yeast love protein!

All of those factors, when combined, add up to success.

The question is whether it is a problem if the growth of the culture is due to "contamination" from yeast spores already present in the jar.  The answer is no.  The goal is to develop a healthy culture of yeast that are compatible with the flours being used in your starter.  Whether those yeast arrived with the flour, or were present in the vessel, as long as they love the food that they are being fed you have achieved your goal.  You don't really need to worry about where the yeast came from.

Many people are proud of their "100 year old San Francisco sourdough starter that great grandfather Zeke brought back from California after the gold rush".  There's something to be said for caring for a starter for 100 years, but it would be a mistake to believe that it's the same starter that left San Francisco all those years ago.  Sourdough starters all contain the same species of yeasts and bacteria, but the strains vary from place to place.  And the factors that control the strains in any given starter are temperature, pH of the starter, and the flours used to feed the starter.  In other words the yeast and bacteria present in the starter that came back from California after the gold rush have long ago been replaced by the strains present in the flour that has been fed to the starter in the meantime.  This process doesn't even take years.  A couple of feedings will do it.

In the case of the culture that I'm building, it's likely that the source of the yeast is the whole wheat flour that I started with yesterday.  But even if it was "contamination", I don't have to worry.  Once fermentation gets underway, the natural yeasts present in flour would win the day.

So what's next?

The culture is still very young.  There is obviously some yeast growth taking place.  But there is also some bacterial growth taking place.  A healthy sourdough starter contains a mixture of yeast and bacteria that exist in a balance that is dictated by the pH (level of acidity) of the starter.  Right now the yeast and the bacteria are locked in a battle to decide who will win.  In the end it will be a stalemate.  But more on that in the next post.