Why Is My Sourdough Flat? 7 Common Causes and Fixes

Let me tell you something that might make you feel better: every single sourdough baker on the planet — every one — has pulled a flat loaf out of the oven and stared at it in confusion. I've baked thousands of loaves over twelve years, and I still occasionally produce a frisbee. It happens. The difference between a frustrated beginner and a confident baker is not that the confident baker never fails — it's that they know how to diagnose what went wrong and fix it for next time.

So let's do exactly that. Here are the seven most common causes of flat sourdough, ranked roughly from most likely to least likely, along with the specific fix for each one.

1. Your Starter Wasn't Active Enough

This is the number one cause of flat loaves, especially for newer bakers. If your starter wasn't at peak activity when you mixed your dough, it simply didn't have enough yeast to produce the gas needed to raise your bread.

Signs: Your dough barely rose during bulk fermentation. It felt dense and doughy even after 5+ hours. The finished loaf is dense throughout with few or no air pockets.

2. Over-Fermentation (You Let It Go Too Long)

This one catches intermediate bakers by surprise. If your dough fermented too long during bulk, the yeast exhausts the available sugars, the gluten network weakens from the accumulated acid, and the dough loses its ability to hold gas. The result is a dough that feels slack, sticky, and lifeless — and a loaf that spreads out flat instead of rising up.

Signs: Dough was very bubbly and risen but felt like a wet, sticky mess when you tried to shape it. It spread out immediately on the counter. The finished loaf has a gummy, dense texture despite visible air holes.

3. Under-Fermentation (You Didn't Let It Go Long Enough)

The opposite problem. If you shaped your dough before bulk fermentation was complete, the yeast hadn't yet produced enough gas. The loaf may hold its shape well during proofing (because the gluten is intact) but won't have much rise or oven spring.

Signs: Dough was easy to shape and held its shape perfectly (almost too perfectly). The finished loaf is dense and heavy for its size. The crumb is tight and closed with no large air pockets. The bread may taste bland because the bacteria didn't have time to produce flavor acids either.

4. Weak Shaping (Not Enough Surface Tension)

Shaping is where many home bakers lose their loaves. If you don't create enough surface tension during shaping, the dough has no structural support to rise upward — so it spreads outward instead. Even perfectly fermented dough will produce a flat loaf if the shaping is too gentle.

Signs: The dough spread out during proofing. When you turned it out of the banneton, it immediately flattened. The loaf spread sideways in the oven instead of springing upward.

🔧 The Fix:

• Be more assertive with your shaping. The surface of the dough should feel taut, like a filled water balloon
• Use the bench to create friction — drag the dough toward you on an unfloured surface to tighten the skin
• If the dough is too sticky to shape, let it rest 5 minutes and try again rather than adding flour
• Practice shaping with a piece of dough when the stakes are low — it is a physical skill that improves with repetition

5. Insufficient Steam During Baking

During the first 15–20 minutes of baking, your loaf undergoes "oven spring" — a rapid expansion as the yeast produces a final burst of gas and the water in the dough turns to steam. For this spring to happen, the crust needs to stay soft and flexible. If the crust sets too early (because there's not enough steam), the loaf can't expand and stays flat.

Signs: The loaf has a thick, pale crust. Your score marks barely opened. The loaf feels heavy and dense despite good fermentation and shaping.

6. Wrong Hydration for Your Flour

Not all flour behaves the same at the same hydration level. If you're using a low-protein flour (all-purpose, around 10–11%) at a high hydration (75%+), the gluten network may not be strong enough to support the dough. The result is a wet, slack dough that spreads instead of rises.

Signs: Dough was very wet and sticky throughout the entire process. Shaping was nearly impossible. The loaf spread out immediately on the counter and in the oven.

7. Cold or Under-Preheated Oven

This one is simple but easily overlooked. If your oven wasn't fully preheated — or if your oven's thermostat runs low (many do) — the bread doesn't get the initial blast of heat it needs for oven spring. The yeast is killed before it can produce that final burst of gas, and the crust sets before the loaf has a chance to expand.

Signs: The score marks barely opened. The bottom of the loaf is pale. The loaf is dense but doesn't show signs of over-fermentation or shaping problems.

Diagnostic Flowchart

One More Thing

A flat loaf is not a failed loaf. Slice it thin, toast it, and it makes incredible bruschetta, croutons, or bread crumbs. The flavor of sourdough is in the fermentation, and that's there whether the loaf is tall or flat. So eat it, learn from it, and bake the next one. That's the whole game.

And if you're still working on the fundamentals, start with my step-by-step recipe for your first loaf. It's designed to give you the highest chance of success on your first try.