Let’s Start at the Beginning. What Is Sourdough?
Sourdough is a combination of flour, water, wild yeast, and bacteria that live in symbiotic harmony.
Wild yeast is responsible for leavening (rising) dough by producing carbon dioxide.
The bacteria are responsible for souring the dough by producing lactic and/or acetic acid.
The leavening process starts to happen when the wild yeasts break down the sugars in the flour, predigesting it and using it for energy. The sugars in the flour feed the wild yeasts and allow them to multiply.
While the yeast is multiplying it is producing carbon dioxide as a byproduct. Carbon dioxide is responsible for making the bread rise.
This “leavening” happens when the carbon dioxide gas is trapped under the network of gluten protein that is produced by mixing flour with water.
The beneficial bacteria in sourdough produce the lactic and acetic acids that give sourdough breads their classic sour flavor.
These beneficial acids also neutralize the nutrient-blocking phytic acid that is naturally found in the hull of all grains.
Lactic Acid Also Breaks Down Gluten
Gluten is a kind of protein found in all wheat grains. It forms long protein strands when mixed with water, thus giving bread the structure it needs to trap the gasses of fermentation.
The hard-to-digest gluten protein is predigested by the lactic acid during fermentation. It is then broken down into easier-to-digest proteins and enzymes while retaining the important structure that gives bread its shape.
Flours that are organically grown and have a higher percentage of bran and husk will have more of their own wild yeasts and bacteria attached to the flour. That is why using a whole organic grain like whole wheat or rye is recommended for starting a starter from scratch. Even so, some wild yeast remains in hulled flours, so it is possible to start a starter with just organic white flour.
Wild yeast and bacteria are everywhere. I mean everywhere! It’s on all organic and wild fruit and veggies and is responsible for the beginnings of fermentation. A fallen fruit in the organic orchard will ferment just the same as a fallen fruit in the jungle.
Yeast really likes sugar, so it can be found in higher concentrations on fruits — think wine grapes with their white yeasty skins. Wild yeasts were responsible for the first alcoholic beverages like wine, beer, and mead and have been utilized for leavening bread for countless centuries.