Here’s a jar of flour and
water, also known as my sourdough starter. It’s pale, bubbly, and sour-smelling.
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| Photo by blog author. |
My sourdough starter, like every sourdough starter, contains a
unique combination of yeasts—which make sourdough bread rise—and lactic acid bacteria—which
make sourdough bread sour. The external environment, the temperature, and the
type of flour used influence which specific types of yeast and lactic acid
bacteria are present in a sourdough starter. Each sourdough microbiome produces
a distinctively flavored sourdough bread. The bread made with my starter tastes
different than the bread made with any other starter, but the process for
making all sourdough starters is basically the same.
Inside of a sourdough
starter both yeasts and lactic acid bacteria break down carbohydrates in the
flour for fuel. (To learn more about this process see my last post.)
Do yeasts and lactic acid
bacteria compete with each other for resources in the starter or do they work
together?
Well, they do a little
bit of both.
Yeast and lactic acid
bacteria do compete with each other for resources like carbohydrates, and
nitrogen, used to make proteins. But, despite
occasional skirmishes, yeast and lactic acid bacteria work together to
successfully survive in the sourdough starter.
We know that yeast and
lactic acid bacteria both break down carbohydrates in flour. What I did not
mention yet is that there are different types for carbohydrates in flour, like
maltose, glucose, fructose, and sucrose. Yeast can digest some of these
carbohydrates and lactic acid bacteria can digest others. Yeast and lactic acid
bacteria collaborate to consume all these carbohydrates. Here’s an example of
how the common sourdough yeast species Saccharomyces
exigus and lactic acid bacteria cooperate.
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| Image by blog author |
While the yeasts are
digesting carbohydrates, they also release amino acids lactic acid bacteria
need to survive.
But what do all these
microbial interactions mean for us, the ones eating the sourdough?
While breaking down
carbohydrates for their own fuel, yeasts and lactic acid bacteria make these
carbohydrates easier for us to digest. Because of this, eating sourdough bread
does not cause abrupt spikes and drops in blood sugar levels like eating bread
made with packaged yeast does.
Sourdough yeasts also
help us absorb minerals more easily. Here’s how:
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| Image by blog author. |
In addition to being
healthy, well-made sourdough tastes great! Yeasts and lactic acid bacteria in
the sourdough starter produce lots of tasty compounds, like buttery diacetyls,
and sour organic acids. Just think—most of the flavor and microbial complexities
in sourdough bread originated in a jar of flour and water.
