Why is my sourdough loaf flat and spread out?
A flat sourdough has lost the surface tension that holds it up until the crust sets. Five things decide that — flour strength, bulk fermentation, shaping, final prove and how it was baked — and the loaf tells you which failed.
- Difficulty
- intermediate
- Time
- 15 min
- Read
- 5 min
Short answer
The commonest cause by a long way is a slack shaping that left no tension in the skin. Second is over-fermentation. Shape on a bare worktop with a scraper, drag the dough to tighten the surface until it resists, and prove it in a banneton so it cannot spread sideways.
Do this first
A sourdough loaf is a bag of gas held up by a stretched skin until the crust sets. Everything that goes into producing a tall loaf is really about that skin: strong flour to make it, bulk fermentation stopped before the gluten degrades, shaping to tension it, a prove that stops before it relaxes, and a covered pot so it stays flexible long enough to spring. Fail any one and the dough spreads sideways instead of upwards. The drawing follows a tight loaf and a slack one side by side from shaping to bake.
What you'll need
- Strong white bread flour
- A dough scraper
- A banneton or a bowl lined with a floured tea towel
- A lidded casserole (optional)
Step by step
- Look at how the score opened.A clean lifted ear means the dough had tension and oven spring — the loaf may still be flat for another reason. A ragged score that tore sideways, or a score that barely opened at all, points straight at slack shaping or over-proving.
- Check the flour.Plain flour cannot make a tall sourdough. You want strong white bread flour, ideally 12.5 per cent protein or higher. High proportions of rye, spelt or wholemeal all reduce the achievable height — a 100 per cent rye loaf is flat by nature and that is not a fault.
- Judge the bulk fermentation by rise, not by hours.Roughly a 50–75 per cent increase in volume with a domed, jiggly, bubbled surface. Taken much further, the gluten breaks down and no amount of shaping will hold the dough up. In a warm kitchen this happens hours earlier than the recipe says.
- Shape for tension, and be firmer than feels right.Pre-shape, rest twenty to thirty minutes, then final shape. Use a bare unfloured patch of worktop so the dough grips, and drag the round towards you with the scraper and your hand so the skin tightens. It should end up taut and resist a light push. A dough that has been folded loosely and dropped in a basket has no tension at all.
- Prove it in something that supports it.A banneton, or a bowl lined with a well-floured tea towel. Free-standing on a tray, a wet dough simply relaxes outwards during a long prove.
- Do not over-prove the final rise.The poke test: flour a fingertip, press 1cm into the dough. It should spring back slowly and leave a slight dent. Springing back instantly means under-proved; staying fully dented and sighing means over-proved and it will spread. A cold overnight prove in the fridge is far easier to judge.
- Bake covered and hot.A preheated lidded casserole traps the loaf's own steam, keeping the crust soft for the first fifteen minutes so it can expand. On an open tray the crust sets early and the loaf spreads instead of springing. See `bake-bread-in-a-casserole`.
Tips
- Reducing hydration by five points is a legitimate and underrated fix. A 68 per cent loaf that stands tall beats a 78 per cent one that spreads.
- Cold-proving overnight in the fridge makes the dough firmer to handle and score, and it makes the timing far more forgiving.
- A loaf baked in a tin cannot spread. If tall free-standing loaves keep failing, bake it as a tin loaf while you work on shaping — the bread is just as good.
- Rice flour in the banneton sticks far less than wheat flour, so the dough releases cleanly instead of deflating as you shake it out.
Common mistakes
- Blaming the starter for a shaping problem — A starter that doubles reliably is doing its job. If the crumb has holes and the loaf still spread, the gas was made and then not held — that is shaping or fermentation length, not the culture.
- Flouring the worktop for the final shape — Flour is a lubricant. The dough needs to grip the surface so that dragging it tightens the skin. Use a bare, clean patch and a scraper.
If it doesn't work
Spread flat, crumb open but even, score tore sideways
Cause: No shaping tension. The skin was never tightened. — Fix: Pre-shape, rest, then final shape firmly on a bare worktop until the surface is taut.
Spread flat, crumb full of large irregular holes, strong sour smell, sticky dough
Cause: Over-fermented. The gluten has degraded and cannot hold gas. — Fix: End bulk fermentation earlier — go by the volume increase and the surface, not the clock.
Flat with a dense, tight crumb
Cause: Under-fermented, or a weak starter that never produced enough gas. — Fix: Check the starter doubles reliably within four to six hours of feeding before using it. See `sourdough-starter-not-rising`.
Rose well in the basket, spread the moment it was tipped out
Cause: Over-proved final rise, or a very high hydration handled roughly at the transfer. — Fix: Prove cold in the fridge and bake straight from cold; tip it onto parchment and lower it in rather than handling it.
Flat only when baked on a tray, fine in a pot
Cause: No steam. The crust set before oven spring finished. — Fix: Bake covered for the first two-thirds, then uncovered to colour.
Questions people ask
How do I know when bulk fermentation is done?
Volume increase of roughly 50–75 per cent, a domed rather than flat surface, visible bubbles at the edges of the container, and a wobble when you shake it. Use a straight-sided container and a rubber band at the starting level — it is far more reliable than any time given in a recipe, because temperature changes everything.
Is a flat sourdough still worth eating?
Entirely. It will taste the same and slice fine, just in shorter pieces. Over-fermented dough is the one exception — it can be gummy and unpleasantly sour, and is better used as flatbread or pizza base than as a loaf.