How sourdough bread is made
Sourdough is raised by a living jar of wild yeast and bacteria that bakers feed like a pet.
- stations
- 6
- things upstream
- 28
- raw sources
- 11
- steps from the ground
- 9
The short version
A starter of flour and water is fed until a stable culture of wild yeast and lactic bacteria takes hold. A portion of that starter is mixed into fresh flour, water and salt, and the dough rises slowly while the bacteria make lactic acid, which gives sourdough its tang. The dough is shaped and baked with steam.
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Grow the starter
Flour and water are mixed and kept warm for a week or two. Natural enzymes break flour starch into sugars, which wild yeast and bacteria eat.
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Feed it fresh flour
Bakers add flour and water to the starter every day to keep the culture active. In a bakery the starter is fed several hours before it goes into dough. When it turns bubbly and floats in water, it is ready.
fed 4 to 12 hours before use
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Mix the final dough
A portion of the active starter is mixed with fresh flour, water and salt. The starter usually weighs 13 to 25 percent of the flour.
starter at 13 to 25% of flour weight
Goes in -
Rise slowly
Yeast produces carbon dioxide and a little ethanol while the bacteria make lactic and acetic acid. The acids give the sour taste, and they also slow staling. Warmer, wetter starters make more lactic acid and cooler, drier ones more acetic.
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Shape the loaves
The risen dough is divided and shaped into loaves, then given a final rise.
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Bake with steam
Heat makes steam inside the dough, which inflates it further, and the surface browns into a crust.
Worth repeating
- One of the oldest sourdough breads known dates to 3700 BC and was found in Switzerland.
- Sourdough was the main way to leaven bread for most of history. Baker's yeast has only been around for under 150 years.
- Some modern bakeries use starters made from isolated microbes grown in fermentors, then packaged as baker's products.
Back to the ground
Follow every input upstream and sourdough bread starts as these 11 raw sources.
Everything it is made of See it on the map
Open the whole family tree
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Sources
Cite this page: "How sourdough bread is made." Assembly Line, 2026-11-03. https://assemblyline.org/make/sourdough