You followed the recipe. You were patient. You did every fold. And then you pulled a flat, brick-dense loaf out of the oven and wondered what went wrong.
The disappointing thing about sourdough is that the failure often looks the same regardless of the cause. A loaf that didn't rise could mean three very different problems at three very different stages of the process. This audit walks through each one so you can identify exactly where your process broke down — and fix it before the next bake.
Your starter is the engine of the entire process. If it isn't active and healthy, no amount of technique will produce a risen loaf. This is the most common cause of flat bread, especially for bakers who don't bake frequently and keep their starter refrigerated.
How to diagnose it: Do the float test. Drop a small spoonful of starter into a glass of water just before you plan to mix your dough. If it floats, the starter has enough gas production to leaven bread. If it sinks, it isn't ready.
Other signs of a weak starter: no visible bubbles after feeding, no predictable rise and fall cycle, flat or unresponsive after 8+ hours at room temperature.
Feed your starter twice daily for 2–3 days at room temperature before baking. Use it at peak activity — when it has doubled, is domed, and passes the float test. Never use a starter pulled straight from the refrigerator without this warmup phase.
Wild yeast is extremely sensitive to temperature. It thrives between 75–82°F (24–28°C). Below 65°F (18°C), fermentation slows significantly. In a cool kitchen, a bulk fermentation that should take 5 hours might take 10 or 12 — and if you go by the clock instead of the dough, you'll end up underfermented.
How to diagnose it: Your dough didn't increase by 50–75% during bulk fermentation. It looks the same as when you started. It feels dense and doesn't jiggle when the container is shaken.
Common scenario: A 68°F kitchen in winter, following a recipe written for a 75°F summer kitchen. The timing is completely different.
Stop following time alone — follow the dough. Use a probe thermometer to know your ambient temperature. For a warmer proofing environment, place your covered container in the oven with just the light on (typically 75–80°F), or near a warm appliance. In summer, do the opposite: move fermentation to a cooler spot to slow things down and avoid over-fermentation.
Counterintuitively, a flat loaf can also mean the dough fermented for too long. Over-fermented dough has used up all its food supply and exhausted its gas production. The gluten structure breaks down, becoming slack and unable to hold any structure. The loaf spreads rather than rising.
How to diagnose it: The dough is extremely slack and sticky — almost liquid-like — and doesn't hold its shape during shaping. When you cut the baked loaf, the crumb is dense with tiny, uniform bubbles (not open and irregular).
Common scenario: Left the dough to bulk ferment overnight in a warm kitchen, or used a very active starter at a higher percentage than the recipe intended.
Learn the visual cues for the end of bulk fermentation: 50–75% volume increase, a domed (not flat) top, visible bubbles on the sides and surface, and a jelly-like jiggle. If you need to slow things down, move the dough to the refrigerator before it over-ferments. Cold retard can buy you several hours of flexibility.
The Diagnostic Checklist
Next time you get a flat loaf, run through this before your next bake:
- Did the starter pass the float test before mixing?
- What was the actual room temperature during bulk fermentation?
- Did the dough visibly increase in volume during bulk?
- Was the dough domed or flat at the end of bulk?
- Was the shaped dough firm or very slack?
- Did the loaf spring up in the oven at all, or stay flat throughout?
The answers to these questions will point clearly to one of the three culprits above. Sourdough has a reputation for being mysterious, but most failures have a straightforward explanation once you know where to look.
Every flat loaf is a lesson. Keep notes in your bake log, note the temperature, the starter activity, the bulk timing — and the next loaf will be better for it.