Why Is My Sourdough Flat? Troubleshooting Guide

Why Loaves Bake Flat Instead of Tall

A flat sourdough is a height problem: the dough spreads sideways in the oven instead of springing up. Every cause traces back to one of two failures. Either the dough had no structural tension left to hold a dome (overproofing, weak shaping, or hydration too high for the flour), or it never got the heat shock needed to leaven fast in the first minutes (a cold oven, no steam, or a starter too weak to power oven spring). The quickest diagnostic is the spread ratio: measure the loaf width against its height after baking. A well-risen boule sits around 1.5:1 width to height, while a pancake at 3:1 or flatter confirms lost tension or missing spring. Run your specific starter and timing through the starter troubleshooter to isolate which of the six causes below is dragging your loaf down.

Cause and Fix at a Glance

Overproofing: The Loaf With No Spring Left

Overproofed dough has eaten through its sugars and blown out its gluten. It feels overly soft, jiggly, and wet, often carrying large slack bubbles across the surface, and when it hits the oven it flows outward instead of leaping up because there is no elastic network left to trap gas. This is the most common cause of a flat loaf in a warm kitchen. End bulk fermentation at a 50 to 75% rise rather than waiting for a full double. At a dough temperature of 76 to 78 °F (24 to 26 °C) that point usually arrives in 4 to 6 hours, but a warm 80 °F (27 °C) room can get there in 3 hours, so measure dough temperature and use the rise, not the clock.

The poke test confirms it: flour a fingertip and press 1 cm into the proofed dough. Correctly proofed dough springs back slowly and leaves a slight dimple. If it does not spring back at all and the dent stays, the dough is overproofed and will bake flat. Next time shorten bulk or drop the ambient temperature, and cold-retard the shaped loaf at 38 to 40 °F (3 to 4 °C) overnight to slow the final proof and buy a wider window.

Weak Shaping Leaves No Surface Tension

Surface tension is the drum-tight outer skin that holds a loaf upright while the interior expands. Without it, even perfectly fermented dough relaxes into a disc. Shape on a lightly floured or bare bench: fold the dough into a parcel, then drag the sealed ball toward you in short strokes so the skin grips the counter and tightens. The dough should hold a defined dome and resist spreading for several seconds before it slowly relaxes. If it slumps immediately, the skin is too loose. Rest the shaped loaf seam-side up in a well-floured banneton to hold the form during the final proof.

A clean cut needs a sharp blade, and a confident 6 mm (quarter inch) deep score at a shallow 30 degree angle directs the oven spring upward into an ear instead of letting the loaf burst sideways.

Hydration Too High for the Flour

Water makes crumb open, but past a point the dough loses the strength to stand up. A white bread flour at 12 to 13% protein handles 70 to 75% hydration; push it to 82% without exceptional gluten development and it spreads into a flat, wet mess. If your loaves keep flattening and the dough feels batter-like, drop to 68 to 72% hydration until your shaping and gluten work catch up, then climb back a few percent at a time. Weaker all-purpose flour tops out lower, around 65 to 70%. Set your numbers precisely with the hydration calculator rather than eyeballing, and keep salt at 2% of flour weight, which tightens the gluten and slows fermentation slightly, both of which help a loaf hold height.

No Steam and a Cool Oven Kill Oven Spring

The first 10 to 15 minutes decide the loaf's height. Steam keeps the crust soft and pliable so the dough can keep expanding before the surface sets, and intense heat drives the fast gas expansion of oven spring. A home oven vented dry and running cool sets the crust early and locks the loaf flat. Bake inside a Dutch oven preheated a full 45 minutes to 480 to 500 °F (250 to 260 °C). The trapped moisture from the dough itself steams the loaf with the lid on for the first 20 minutes, then uncover and finish at 450 °F (230 °C) until the crust is deep brown and the internal temperature reads 205 to 210 °F (96 to 99 °C).

Verify the oven with a separate oven thermometer, because many dials read 25 to 50 °F (15 to 30 °C) high or low. A stone or steel preheated the same 45 minutes is the alternative for open baking, paired with steam from a preheated cast-iron tray and a cup of boiling water.

A Weak Starter Cannot Power the Rise

All of the above assumes a starter strong enough to leaven. If yours does not reliably double within 4 to 8 hours of a 1:5:5 feed (10 g starter, 50 g flour, 50 g water) at 78 °F (26 °C), it lacks the yeast population to inflate a loaf and provide oven spring. Rebuild it with one or two daily 1:5:5 feeds for three to five days, hold it at 76 to 82 °F (24 to 28 °C), and feed a portion of whole rye or whole wheat to boost activity. Use it at peak, when it has domed and is covered in bubbles, not after it has collapsed. The float test, dropping a spoon of starter in water, is unreliable; consistent doubling on a predictable schedule and a clean tangy aroma are the real signals of readiness.

Stack the Fixes in Order

Change one variable per bake and track it. Confirm the starter peaks in 4 to 8 hours, end bulk at a measured 50 to 75% rise, build real surface tension with a pre-shape and final shape, keep hydration at 68 to 72% while you learn, and bake in a Dutch oven preheated 45 minutes to 480 to 500 °F (250 to 260 °C) to 205 to 210 °F (96 to 99 °C) internal. Nail those five and the spread ratio tightens toward 1.5:1, turning a flat disc into a domed, well-sprung loaf.