Sourdough isn't a modern trend dressed up in old-fashioned branding — it's close to the original way bread was made for most of human history.
An old, practical solution
Before commercial yeast was isolated and packaged in the 19th century, bakers had no other way to leaven bread than to rely on wild yeast and bacteria naturally present in flour and the air. Leaving a mixture of flour and water out long enough would eventually capture those organisms and start fermenting on its own — and bakers learned to keep a portion of that fermented dough going to leaven the next batch, rather than starting from scratch each time.
A tradition carried across cultures
Naturally leavened breads using this same basic principle show up across many culinary traditions around the world, each with its own regional flours, hydration levels, and baking methods, long before anyone called it "sourdough."
Why it nearly disappeared
When commercial yeast became widely available, it offered something sourdough couldn't: speed and consistency. A baker no longer needed to maintain a living culture or plan a day or more ahead — a packet of yeast could leaven bread in a couple of hours. Naturally leavened baking became far less common in everyday kitchens and commercial bakeries as a result.
Why it's back
In recent years, more bakers and home cooks have returned to slow fermentation for the flavor, texture, and process itself. It's slower and less convenient than the alternative, which is exactly why it fell out of favor in the first place — and exactly why some of us think it's worth doing anyway.