Why Your Sourdough Is Flat: The Complete Troubleshooting Guide

If you have baked sourdough for any length of time, you know the disappointment. You spent hours mixing, folding, shaping, and waiting. You scored the dough with confidence, loaded it into the Dutch oven with hope, and pulled out a pancake. A tasty pancake, probably, because even flat sourdough usually tastes good. But not the tall, proud, ear-bearing loaf you were imagining.

I have baked flat loaves. Lots of them. And every single one taught me something, once I learned how to diagnose the problem. This guide covers every cause of flat sourdough I have encountered, organized from most common to least common. Work through them systematically and I promise you will find your issue.

Cause 1: Over-Fermentation (Most Common)

I covered this in my earlier troubleshooting post and my oven spring guide, but it bears repeating because it accounts for more flat loaves than all other causes combined. Over-fermented dough has exhausted most of its gas-producing potential during bulk fermentation. The yeast has consumed available sugars and produced most of the carbon dioxide it is going to produce. When you put this dough in the oven, there is simply not enough gas production left to create meaningful oven spring.

Over-fermented dough also has weakened gluten. The acids produced by lactic acid bacteria, which strengthen gluten at moderate levels, begin degrading it at high concentrations. The result is a dough that cannot hold its shape and spreads outward instead of rising upward.

How to Diagnose

Over-fermented dough feels excessively slack, sticky, and loose. When you try to shape it, it resists holding tension and slowly spreads out on the counter. It may smell strongly of alcohol or vinegar. During bulk fermentation, if the dough more than doubled and the surface looks flat or concave rather than domed, fermentation went too long.

The Fix

Reduce bulk fermentation time. Aim for a 50-75% volume increase, not a full double. Use a clear, straight-sided container so you can accurately gauge volume change. If your kitchen is warm (above 78°F / 25°C), check your dough hourly because warm environments accelerate fermentation significantly. Understanding temperature's effect on timing is essential.

Cause 2: Weak Starter

A sluggish starter produces a sluggish rise. If your starter does not at least double in volume within eight hours of feeding, it is not ready to leaven bread effectively. You might get some rise during the long bulk fermentation, but the yeast population is simply too low to produce the burst of gas needed for good oven spring.

How to Diagnose

Your starter takes more than eight hours to peak after feeding. It barely doubles (or does not double at all). The dough rises very slowly during bulk fermentation and feels heavy and inert rather than airy and bubbly.

The Fix

Feed your starter twice daily at a 1:1:1 ratio for three to five days before attempting to bake. Use a warm spot (75-80°F / 24-27°C) for the starter between feedings. Only bake when the starter doubles within four to six hours and passes the float test (a spoonful floats in water). If your starter has been stored in the fridge, it needs at least two to three days of daily feeding before it is bake-ready.

Cause 3: Poor Shaping

A dough with no surface tension will spread outward during proofing and baking. This is the most common issue for intermediate bakers who have solved their fermentation timing but still get flat loaves. Shaping is not just about making the dough look nice. It creates a taut outer skin that constrains the dough and forces expansion upward rather than sideways.

How to Diagnose

Your shaped dough immediately starts spreading on the counter during bench rest. It looks more like a thick disk than a rounded dome. When placed in the banneton, it fills the bottom flatly rather than maintaining a proud, rounded profile.

The Fix

Practice building surface tension during shaping. For a boule, use the cupping-and-rotating motion on an unfloured counter to drag the dough into a tight ball. For a batard, try the stitch method. If the dough keeps sticking, use slightly less flour and let friction work in your favor. After shaping, the dough should pass the "finger poke" test: pressing with a floured finger should leave a dent that slowly springs back, indicating both proper fermentation and good tension.

Cause 4: Over-Proofing After Shaping

Even if you nailed bulk fermentation and shaping, an overly long final proof can undo everything. The shaped dough continues fermenting in the banneton, and if it goes too long, you end up with the same problems as over-fermented bulk dough: exhausted yeast, weakened gluten, and a flat result.

The Fix

Either proof at room temperature for one to two hours (checking frequently with the poke test) or do an overnight cold retard in the refrigerator. The cold retard slows fermentation dramatically, giving you a wide window of 8-16 hours where the dough is properly proofed. This built-in margin for error is why I recommend cold retarding for almost everyone.

Cause 5: Scoring Issues

If your scoring is too shallow, the dough cannot expand freely along the score line. Instead, it bursts open at the weakest point (often the bottom or side), releasing gas inefficiently and producing a lopsided, flat result. If you score after the dough has warmed up significantly from the fridge, the surface may have already started proofing and scoring deflates an already fragile structure.

The Fix

Score confidently, at least half an inch deep, at a 30-45 degree angle using a sharp lame or razor blade. Score the dough immediately when it comes out of the fridge, while it is still cold and firm. A cold dough holds its shape better during scoring and does not deflate as easily. Move quickly from scoring to loading into the hot Dutch oven.

Cause 6: Insufficient Steam or Oven Temperature

Without adequate steam, the crust sets too early and physically prevents the bread from rising. If your oven temperature is too low, the initial burst of expansion (oven spring) is weak because the gas inside the dough does not expand forcefully enough to push the crust open.

The Fix

Preheat your Dutch oven for at least 45 minutes at 475°F (245°C) or higher. Keep the lid on for the full 20 minutes of the covered bake. Consider getting an oven thermometer — many home ovens are 25-50°F off from their displayed temperature, and that difference matters. If you are using a steam tray method, make sure you are using enough water and that the steam actually fills the oven before you close the door.

Cause 7: Flour Issues

Low-protein flour (standard all-purpose at 10% protein or less) produces weaker gluten that cannot support a tall rise. Old flour that has been sitting in your pantry for months may have degraded protein quality. Very fresh whole grain flour ferments extremely quickly and can over-ferment before you expect it.

The Fix

Use bread flour with at least 12% protein for artisan sourdough. Check the milling or best-by date on your flour. If you are mixing in whole wheat or rye, keep it under 30% of the total until you understand how it changes your dough's behavior. Fresh whole grain flour is wonderful but ferments fast, so reduce bulk fermentation time accordingly.

One last piece of encouragement: every baker produces flat loaves sometimes. It is part of the process. The difference between a frustrated beginner and a confident intermediate baker is not that the intermediate never gets a flat loaf. It is that when they do, they can look at it, diagnose the issue, and fix it for next time. That diagnostic skill, not perfect technique, is what makes a good sourdough baker. And it comes only from experience — from baking, observing, adjusting, and baking again. So keep baking. The flat loaves are the tuition. The tall, proud loaves are the diploma.