Why Is My Sourdough Bread Flat? 8 Causes and Proven Fixes
Flat sourdough bread has 8 distinct causes — from an inactive starter to poor shaping technique. This guide diagnoses each one and gives you the exact fix for your next bake.
A flat sourdough loaf is frustrating — especially when you've invested hours into the process and expected something impressive to come out of the oven.
The good news: flat bread is almost always diagnosable, and the fix is usually specific and simple. Flat bread isn't a sign you're bad at baking. It's a sign one step in the process went wrong, and identifying which step gives you exactly what to correct next time.
There are eight distinct causes of flat sourdough. They occur at different stages of the bake, so the key is matching the symptom you see to the stage it came from.
How to Use This Guide
Before diving in, look at your flat loaf and ask yourself:
- Did it spread out sideways and never rise in the oven? → Likely causes 1, 4, or 6
- Did it rise slightly but then fall, or have a dense, gummy crumb? → Likely causes 2 or 3
- Did it rise but only slightly, with little oven spring? → Likely causes 5, 6, or 7
- Is the problem worse in summer or recently started? → Likely cause 8
Cause 1: Your Starter Wasn't Active Enough
What it looks like: The loaf barely rises in the oven. It might spread sideways, have a very dense crumb with few bubbles, and the inside may look doughy or undercooked even after the full bake time.
Why it happens: Sourdough starter is the only leavening agent in your bread. If the starter is weak, sluggish, or past its peak, it simply doesn't produce enough carbon dioxide to lift the dough. This is the most common reason first loaves disappoint.
A starter that looks bubbly and active may still be unreliable if it hasn't consistently doubled in volume at least 2–3 times in a row after feedings. "Having some bubbles" and "being ready to leaven bread" are different things.
The fix:
- Use your starter only when it is at or just past peak — the point where it has maximally risen after a feeding
- Before baking day, give your starter 2–3 consecutive feedings at room temperature to confirm reliable doubling within 4–8 hours
- The texture at use time should feel like a loose, bubbly mousse — airy throughout, not just on the surface
- If your starter is coming out of the fridge, allow 24–48 hours of room-temperature revival feedings before baking
The test: Feed your starter and mark the level. If it reliably doubles within 6 hours at room temperature (22–24°C), it's strong enough to bake with. If it takes longer or doesn't double consistently, it needs more conditioning.
Cause 2: Under-Fermented Dough (Bulk Too Short)
What it looks like: Dense, tight crumb with irregular pockets — sometimes called "fool's crumb" (a few large, random holes surrounded by very dense bread, rather than an even open structure). The crust may be very hard and pale. The dough often bursts at unexpected points during baking rather than at the score. The interior may feel gummy or slightly undercooked.
Why it happens: Under-fermentation is the most common cause of dense sourdough bread. Bulk fermentation needs to run long enough for the yeast to produce sufficient carbon dioxide, the bacteria to build enough acid for flavor and gluten conditioning, and the dough to become extensible enough to hold gas during baking.
When bulk is cut short, the dough doesn't have enough gas structure to rise properly in the oven. No amount of good shaping, cold retard, or oven technique will compensate.
The fix:
- End bulk fermentation only when the dough has increased in volume by 50–75%, feels lighter and jiggly when you shake the bowl, and the surface shows visible bubbles with a slight dome
- Use a clear straight-sided container (or a tall jar) to track volume rise objectively — mark the starting level and watch the dough climb
- Don't use time alone as your guide; the same recipe at 20°C takes 6 hours, at 24°C it takes 3.5 hours
- If your kitchen is below 20°C, consider using slightly warmer water, placing the bowl near a warm appliance, or using a proofing box
Cause 3: Over-Fermented Dough (Bulk Too Long)
What it looks like: The dough is extremely slack and sticky during shaping — almost liquid-like, hard to form into a cohesive shape. It spreads sideways as soon as it's on the work surface. The finished loaf is flat and pale, with a tight, gummy crumb. The flavor may be very sour or sharply acidic.
Why it happens: Over-fermentation degrades the gluten structure. As yeast consumes available sugars and bacteria produce increasing amounts of acid, protease enzymes become more active and begin breaking down the proteins that form gluten. Beyond a certain point, the gluten network that should trap gas and hold the loaf's shape is damaged beyond recovery. No amount of good shaping or baking technique can rescue an over-fermented dough.
This is particularly common in summer when ambient temperatures are high, and in kitchens that run warm.
The fix:
- Learn the bulk endpoint: the 50–75% volume increase rule is your best anchor — don't push past this if you're planning a cold retard
- Track ambient temperature in your kitchen. At 26°C+ (80°F+), bulk can complete in under 3 hours
- Reduce starter percentage in warmer weather: use 5–10% starter (22–45g instead of 90g for this recipe) to slow fermentation
- If your dough regularly over-proofs, try mixing with colder water to lower the Final Dough Temperature
How to tell if your dough is over-fermented: When you try to pre-shape, the dough tears and refuses to hold tension. It sticks excessively to the work surface and has no spring-back when poked.
Cause 4: Insufficient Surface Tension When Shaping
What it looks like: The loaf spreads sideways in the oven instead of rising upward. Oven spring is minimal. The cross-section looks more like a lens or disc than a proper loaf. The scoring may open awkwardly or not at all.
Why it happens: Surface tension is the "skin" you create when shaping. It's what channels the expansion force from oven spring upward through the score, rather than outward in all directions. Without sufficient tension, the dough has no directional structure to guide its rise.
Insufficient surface tension is usually caused by three things: under-shaped dough (not enough folds or tension-building), shaping on too much flour (flour reduces friction — the exact opposite of what you need), or not doing a proper bench rest between pre-shape and final shape.
The fix:
- Shape on an unfloured surface — the dough's stickiness on a bare counter is actually useful; you need friction to build tension
- After pre-shaping, do a full 20-minute bench rest — this relaxes the gluten and makes the final shape dramatically easier
- During final shape, you should feel real resistance and see the surface become taut and smooth. If it's easy, you're not building enough tension
- Drag the shaped round toward you 3–4 times after shaping to create a tight, seamless bottom
Cause 5: Scoring Too Shallow or With a Dull Blade
What it looks like: The bread doesn't open at the score. Instead, it bursts at the sides or bottom — wherever the crust was thinnest and weakest. The loaf may have risen reasonably well but has an asymmetric, ragged appearance rather than a clean ear.
Why it happens: Scoring serves a specific mechanical purpose: it creates a controlled weak point in the crust so that oven spring — the rapid gas expansion in the first 10–15 minutes of baking — can escape upward through a clean opening. If the score is too shallow (less than 5–7mm deep), the crust seals shut in the oven and the expanding gas finds the next weakest point instead. If the blade is dull, it drags and compresses the dough rather than cutting it, effectively sealing the cut.
The fix:
- Score ¼ to ½ inch (6–12mm) deep with a swift, decisive stroke — commit fully to the cut
- Hold the blade at a 30–45° angle to the dough surface (not perpendicular) — this creates the undercut that produces an ear
- Use a fresh, sharp blade — replace lame blades every 3–5 bakes; they go dull faster than you think
- Score the dough straight from the fridge — cold dough is firmer and cuts cleanly; room-temperature dough is sticky and harder to score precisely
- A curved lame naturally provides the correct angle; a straight razor held at the right angle works equally well
Cause 6: No Steam (or Not Enough Steam) in the Oven
What it looks like: The crust sets too quickly and looks hard and thick, with very little oven spring. The loaf may look "closed" — as if it was never properly scored. The crust is pale and cardboard-like rather than deep brown and crisp.
Why it happens: Steam in the first 15–20 minutes of baking is critical. It keeps the outer surface of the dough moist and pliable, delaying crust formation and allowing the dough to expand fully during oven spring. Without steam, the crust hardens almost immediately after going into the oven, trapping the loaf and preventing it from rising. Steam also promotes starch gelatinization on the surface, contributing to the shiny, crisp crust that well-baked sourdough develops.
The fix:
- The most reliable home solution is the Dutch oven method: a preheated cast-iron pot with a lid traps the steam produced by the dough itself during the first 20 minutes of baking. Bake covered for 20 minutes, then uncovered for 20–25 minutes
- Without a Dutch oven: Pour 1 cup of boiling water into a cast-iron pan on the oven's lower rack at the moment you load the bread. Remove the steam source after 20 minutes
- Avoid opening the oven during the first 20 minutes — any opening releases critical steam and heat
Cause 7: Oven and Dutch Oven Not Preheated Long Enough
What it looks like: Modest oven spring, pale crust, bread that rises some but never achieves the dramatic "pop" of a well-baked sourdough. The base of the bread may look under-baked or dense.
Why it happens: Oven spring happens in the first 10–15 minutes of baking when the cold, gas-filled dough hits intense radiant heat. If the Dutch oven isn't fully saturated with heat — which takes 45–60 minutes, not the 15–20 minutes most home ovens claim — the burst of heat required for maximum oven spring simply isn't there.
Most home ovens also run 25–50°F (14–28°C) below their stated temperature, especially at the upper end of their range. An oven that displays "250°C" may only be reaching 220°C internally.
The fix:
- Preheat your oven and Dutch oven for at least 45 minutes — 60 minutes is better
- Set the oven to its maximum temperature (250°C / 480°F or higher if your oven allows)
- Invest in an oven thermometer (€5–10) — put it on the rack where you'll bake and check what temperature you're actually reaching vs. what the display shows. This single piece of information often explains years of disappointing results
- If your oven runs hot or cold, adjust your set temperature accordingly
Cause 8: Temperature Problems — Too Hot or Too Cold
What it looks like: Inconsistent results across bakes using the same recipe. The bread works in one season but not another, or seems unpredictable from week to week.
Why it happens: Every step in sourdough baking is governed by temperature. Fermentation speed roughly doubles with every 10°C increase in temperature. A recipe written for a 22°C kitchen will over-ferment in a 28°C summer kitchen, and under-ferment in a 16°C winter kitchen. This is why following recipe timings without measuring ambient temperature is unreliable.
Common seasonal problems:
- Summer (hot kitchen, 26°C+): Dough over-ferments during bulk, resulting in flat, slack loaves
- Winter (cold kitchen, under 18°C): Dough under-ferments despite following the schedule, resulting in dense loaves
The fix:
- Measure your kitchen temperature before every bake with a simple thermometer. This one habit transforms your troubleshooting ability
- In summer: Reduce starter amount (5–10%), use cold water to lower dough temperature, shorten bulk fermentation, and monitor the dough's volume rather than the clock
- In winter: Increase starter amount (20–25%), use warmer water, extend bulk time, or use a warm place like an oven with just the light on to maintain dough temperature
- Calculate water temperature to target a Final Dough Temperature (FDT) of 24–26°C: Water temp = (FDT × 3) − (flour temp + room temp + starter temp)
Quick Diagnosis Reference
| What you see | Most likely cause |
|---|---|
| Loaf spreads flat, almost no rise | Inactive starter or over-fermented dough |
| Dense crumb, gummy inside | Under-fermented bulk, or cut too early |
| Hard crust, barely any oven spring | No steam, or oven not hot enough |
| Burst at the side instead of the score | Shallow score, dull blade, or insufficient tension |
| Works in spring, fails in summer | Temperature — over-fermentation in heat |
| Every loaf is unpredictable | Not measuring temperature |
One Change at a Time
When troubleshooting, resist the temptation to change everything at once. Change one variable per bake, note what happens, and adjust from there. Sourdough baking is a system of interdependent variables — temperature affects fermentation, fermentation affects shaping, shaping affects oven spring — and the fastest way to understand it is methodical observation, not random experimentation.
Keep a simple baking log: date, kitchen temperature, bulk start and end time, bulk rise percentage, shaping notes, bake time. After three or four bakes you'll see patterns that tell you exactly what needs adjusting.
Frequently Asked Questions
My bread looks fine on the outside but the crumb is completely dense. What went wrong? Dense crumb with a reasonable crust is almost always under-fermentation. The crust can develop correctly even when the interior hasn't had enough time to build proper gas structure. Extend bulk fermentation next time — aim for the 50–75% volume increase and the bubbly, light-feeling dough rather than relying on time.
The bread was great last week and terrible this week using the same recipe. Why? Ambient temperature is the most likely explanation. If your kitchen is even 3–4°C warmer this week, bulk fermentation completes significantly faster. Start measuring kitchen temperature and tracking it in your baking notes.
Can I save an over-fermented dough? Partially. You can't undo over-fermentation, but you can still bake it and get edible bread — just don't expect good oven spring or open crumb. Shape it gently, don't attempt a long cold retard (that would continue fermenting), and bake immediately at high heat. Treat it as a learning bake and adjust your process for next time.
Does the type of flour affect oven spring? Yes, significantly. Bread flour (12–14% protein) builds stronger gluten and achieves better oven spring than all-purpose flour (9–11% protein). Austrian W700 at 10.5–11.5% protein is a reliable middle ground for sourdough. Whole grain flours ferment faster (bran accelerates fermentation) and produce denser crumb than white flour, which can look like under-rise but is actually a flour characteristic.
I got a good rise but the bread deflated when I took it out of the Dutch oven. What happened? Deflating after removing the lid usually means the structure wasn't fully set yet — the bread needs more time uncovered at lower heat to complete the crumb structure. Extend phase 2 (uncovered) by 5–10 minutes. Also ensure the internal temperature reaches 96–99°C before removing from the oven.
Is it possible to score too deep? Very rare in home baking — most beginners score too shallow, not too deep. Scoring deep enough to open properly is the goal. A cut that goes more than 2cm deep into a well-fermented, properly shaped loaf is unusual. Focus on confident, decisive strokes at the correct angle rather than worrying about depth.