Sourdough starter is a living culture of wild yeast and lactic acid bacteria.

The longer version

A sourdough culture is a stable community rather than a single organism. Wild yeast living on flour and in the air ferment sugars and produce carbon dioxide, while lactic acid bacteria generate acids that give the bread its sour note and help protect the community from invaders. The two groups tolerate each other because each uses different parts of the flour.

A starter is maintained by discarding part of it and adding fresh flour and water, which dilutes accumulated acid and feeds the remaining microbes. Temperature and feeding rhythm shift the balance between the two populations, so the same jar can produce a milder or a tangier loaf depending on how it is kept.

Where this entry sits

Everyday ingredients turn out to be full of quiet chemistry and long history. This collection gathers short, plain explanations of how bread rises, why onions sting, where common spices originate, and how coffee, tea, and chocolate reached the modern kitchen. The full list sits on the Food and Drink page, where every entry is listed in order.