Sourdough: Bacteria, Temperature, and Hydration

                              

Sourdough: Bacteria, Temperature, and Hydration

Sourdough is more than just a mixture of flour and water. It is a living ecosystem in which lactic acid bacteria, acetic acid bacteria, and wild yeasts perform a complex dance of fermentation. These microbes, naturally present in flour and the environment, determine not only the speed of fermentation but, more importantly, the flavor, aroma, and texture of the bread.

Interestingly, the composition of this microbiome is strongly influenced by region. In French and Italian sourdoughs, we often find Lactobacillus sanfranciscensis and Candida milleri, which create a mild and layered acidic profile. German starters, on the other hand, are richer in L. brevis and Pediococcus, resulting in a more robust, tangier bread. San Francisco is famous for its fresh, vinegary nuance, while Belgian and Scandinavian starters tend to be versatile and often rye-focused.

Not only the origin of the starter matters—process factors also steer flavor development. Temperature is a powerful regulator: below 20°C more acetic acid is released, making the bread distinctly sour. Around 24–27°C a milder balance emerges, while above 30°C lactic acid bacteria thrive, speeding up fermentation.

Water acts as a second control mechanism. A firm dough with little water (<65% hydration) produces dense, tangy breads, while a very wet dough (>75%) leads to airy loaves with a gentler freshness. The choice of flour—wheat, rye, or whole grain—adds yet another layer of enzymes, minerals, and aromas.

By skillfully playing with these parameters, an almost infinite palette of possibilities unfolds. Whether you dream of a soft French loaf, a bold German rye, or a fruity sourdough à la San Francisco: with flour, water, and microbes, every baker can create their own signature.

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