Sourdough bread
Bread leavened by a maintained culture of wild yeasts and lactic acid bacteria rather than by added commercial yeast.
Also called naturally leavened bread (INTERNATIONAL), levain bread (TRADE)
Sourdough is bread raised by a stable community of wild yeasts and lactic acid bacteria maintained in a flour-and-water culture, rather than by a measured dose of commercial yeast.
The distinction matters for more than flavour. The culture produces carbon dioxide more slowly and less predictably than commercial yeast, so fermentation is judged by the state of the dough rather than by a clock. It also produces organic acids, principally lactic and acetic, which lower the dough’s pH. That acidity changes gluten behaviour, slows staling, and contributes the flavour the bread is named for.
Because the culture is a living population rather than a product, its behaviour shifts with flour, temperature, hydration and feeding schedule. Two bakers following identical instructions with different cultures will not get identical bread, and no instruction can remove that.
What it should be like
- Crumb texture
- Open and irregular, with cell walls that are translucent rather than fluffy
- Crust
- Thick, well coloured and audibly crisp on leaving the oven
- Flavour
- Acidic complexity ranging from mildly lactic to sharply acetic depending on fermentation conditions
- Shelf life
- Keeps notably longer than a comparable commercially yeasted loaf before staling becomes objectionable
Typical hydration
65–85% of flour weight (baker's percentage)
A working range for wheat sourdough rather than a rule. Wholemeal and rye absorb considerably more water; higher hydrations are achievable but demand handling skill rather than producing better bread automatically.
RecordedStanley P. Cauvain, Springer
How to tell it is done
A fully baked wheat loaf reaches an internal temperature in the high nineties Celsius — effectively the boiling point of the dough’s water. Crust colour and a hollow sound are proxies for this rather than independent tests.
The figure follows from the physics of an aqueous system at atmospheric pressure. Internal temperature confirms that starch gelatinisation has completed; it says nothing about crust development.
RecordedJan A. Delcour and R. Carl Hoseney, AACC International
How it keeps
Sourdough stales more slowly than an equivalent commercially yeasted loaf. The acidity produced during fermentation is generally credited with the effect, alongside the lower pH slowing starch retrogradation.
The observation is not in dispute among bakers. The relative contribution of acidity, of enzyme activity during a long fermentation, and of the higher-hydration crumb typical of the style has not been separated here, so this is recorded as inferred rather than established.
Where it comes from
Professional consensus
Agreed by professional bakers and baking-science texts, with an accepted mechanism, though not isolated by controlled experiment.
Naturally leavened bread predates commercial yeast everywhere it is made, so no region owns it. The traditions that are genuinely distinct are the maintained-culture ones — northern and central European rye sours, and the wheat sours of the Mediterranean and later of North America.
More in baking history and culture.
Why sourdough resists timed instructions
A commercial yeast dose is a known quantity of a single organism in a stable state. A sourdough culture is a population whose composition and activity depend on how it has been fed, at what temperature, with what flour, for how long.
The practical consequence is that every useful sourdough instruction is an observation rather than a duration. Dough has roughly doubled; the surface has become domed and bubbled; a poked indentation springs back slowly and incompletely. These describe a state the dough is actually in. 'Four hours’ describes a state it might be in.
Where the sourness comes from, and why more time is not always more sour
Sourness is not one flavour. Lactic acid is comparatively mild and yoghurt-like; acetic acid is sharp and vinegar-like. The balance between them shifts with conditions, and the two respond differently to hydration and temperature — which is why a longer fermentation does not reliably produce a more sour loaf, and can produce a less pleasant one.
What a longer fermentation does reliably produce is more degradation of the gluten network by the flour’s own enzymes and by the culture’s activity. Past a point, this shows as a slack dough that will not hold shape, which is a structural failure rather than a flavour choice.
Related
Part of
Structure comes from a developed gluten network holding fermentation gas, which is the family’s defining characteristic.
Characteristic ingredients
A long acidic fermentation degrades the gluten network over time, so a stronger flour buys tolerance the schedule needs.
Techniques involved
High-hydration doughs cannot be kneaded conventionally, and folding develops them while giving repeated chances to assess fermentation.
The stage where most flavour and most structural change happen, and the one that must be judged by the dough rather than a clock.
Extensibility gained during the rest makes a high-hydration dough considerably easier to shape.
Equipment involved
A slack dough proved unsupported spreads outward rather than upward and arrives at the oven flat.
The single most effective piece of equipment for domestic sourdough, and entirely improvisable — an inverted roasting tin over a tray does most of it.
Things that go wrong
Here the usual cause is a culture that is not yet strong enough rather than dead yeast, which the diagnosis has to allow for.
The product the question is almost always asked about, and the one whose dark crust most reliably misleads about doneness.
The crust is too hard, too thick or not crisp
Lean, high-hydration and entirely dependent on a humid start.
Recorded because the demand data asks about this fault under this product’s name, not because the fault is peculiar to it.
Recorded because the demand data asks about this fault under this product’s name, not because the fault is peculiar to it.
The bread smells or tastes of alcohol, yeast or vinegar
Recorded because the demand data asks about this fault under this product’s name, not because the fault is peculiar to it.
A long fermentation makes under-development and degassing likelier, not less likely — the causes are the same ones.
The bread is crumbly and falls apart
Long fermentation degrades gluten, which is a route to crumbliness a short-ferment loaf does not have.
The dough is too sticky to handle
High hydration and a long ferment together, which is two of the five causes at once.
Compared in
Sourdough starter vs commercial yeast
Compared as products rather than as ingredients, because the difference shows up in timing and handling as much as in flavour.
A subject of the comparison, so it is reachable from the record a reader is more likely to land on first.
Where the distinction is hardest and matters most.
Apply this with a tool
Sourdough is where hydration arithmetic matters most and where the levain is most often left out of it.
A next step from
Learning to read a dough with a predictable leavening removes one large variable before adding a culture that supplies several.
Leavened by
The defining relationship of the product: sourdough is bread raised by a maintained culture rather than by added yeast, which is why its timing is read from the dough rather than from a recipe.
What this product needs done
Gas retention
As for any wheat loaf. Listed so the contrast with the gluten-free case is visible in the graph rather than only in prose.
Structure building
The gluten network that a long fermentation both builds and eventually degrades. Timing it is most of sourdough technique.
Fermentation substrate
A maintained culture needs sugars released from the flour’s own starch, which is why a lean dough with no added sugar ferments perfectly well.
Hydration
THE EXPLORER JUDGED FLOUR AND A STARTER, WITH NO WATER, A PLAUSIBLE SOURDOUGH. A starter carries some water, but a loaf is not made from a jar of starter and dry flour — free water is what turns the two into a dough at all.
Techniques this product depends on
The flavour, the acidity and much of the structure are produced during bulk fermentation. Skipping it does not produce a faster sourdough; it produces different bread.
Covered in
Oven spring — what it is and what causes it
Covered by the guide, which is the resource a reader arrives at with this question.
What freezes well, and what freezing actually does
Where the keeping question is asked most, and where the culture and the loaf behave differently.
Storing bread, and the trade-off you cannot avoid
Where the crust trade-off matters most.
The bread families, and what actually separates them
Culture-raised, and the flavour comes from the hours rather than the ingredients.
History and culture
Sourdough, before and after commercial yeast
The product the record is about.