The most common reason: your starter isn't active enough

A sourdough starter that looks bubbly on top but hasn't actually doubled in size between feedings won't give your dough the lift you need. The bubbles you see are often just gas trapped at the surface—not a sign of strong fermentation throughout. A truly active starter should roughly double within 4 to 8 hours of feeding, depending on room temperature, and smell pleasantly sour and yeasty, not acetone-sharp or vinegary.

Test your starter before mixing dough by feeding it, waiting the full time, and checking whether it has actually risen. If it's only growing 25 to 50 percent, it needs more frequent feedings or a warmer spot. Feed it once a day for three to five days in a warm location (around 75°F is ideal) before you try making bread again. A weak starter is the reason most home bakers' dough stays flat.

Key Takeaways

  • Your starter must roughly double in size within 4 to 8 hours of feeding before you use it; if it only grows slightly, feed it daily in a warm spot for several days first.
  • Room temperature matters enormously—dough ferments two to three times faster at 75°F than at 65°F, so a cold kitchen can make rise times stretch to 12 hours or longer.
  • Overfermentation (letting dough rise too long) weakens gluten and causes it to collapse rather than spring up in the oven, so watch for a 50 to 75 percent rise, not a doubling.
  • Salt added directly to flour before the starter is mixed in can kill yeast cells and stall fermentation for hours.
  • A dough that feels dense and doesn't pass the poke test (a gentle finger indent springs back slowly or not at all) needs more time, not more starter.

Temperature is slowing your fermentation more than you think

Sourdough ferments at wildly different speeds depending on how warm your kitchen is. At 65°F, bulk fermentation can take 12 to 16 hours. At 75°F, the same dough rises in 4 to 6 hours. Most home kitchens sit somewhere in between, which is why timing information you read online never quite matches what happens in your bowl.

If your dough is rising very slowly, move it to the warmest spot in your house—the top of the refrigerator, an oven with the light on, or a spot near (not touching) a heating vent. Even a 5-degree difference speeds fermentation noticeably. In winter, many bakers use a proofing box, a cooler with a heating pad set to 75°F, or straightforward drape the bowl with a damp towel and place it in a turned-off oven with the door cracked. The goal is consistency: if your dough ferments at the same temperature every time, you'll learn exactly how long it takes.

You may be stopping fermentation too early

The poke test tells you whether your dough is ready to shape, and it's more reliable than the clock. Gently poke the dough with a floured finger about half an inch deep. If the indent springs back when ready, the dough needs more time. If it springs back slowly and leaves a slight crater, it's ready. If it doesn't spring back at all, you've waited too long and the gluten has begun to break down.

Many bakers watch for the dough to double in size, but that's a rough guideline, not a rule. Sourdough is usually ready to shape when it has risen 50 to 75 percent—not doubled. If you wait for a full doubling, you're often overproofing, which means the gluten network has stretched so much that it can't trap gas anymore. The dough spreads flat in the oven instead of rising. Use the poke test, not the timer, to know when to move to the next step.

Salt added at the wrong time kills yeast cells

If you mix salt directly into the flour before adding your starter and water, the salt can draw moisture from yeast cells and slow fermentation for several hours. Salt is necessary—it strengthens gluten and controls fermentation speed—but it needs to go in after the dough has already come together, usually 20 to 30 minutes after mixing the starter and flour.

The standard method is to mix starter, flour, and water first, let the dough rest for 20 to 30 minutes (called autolyse), then add salt and a small amount of water and mix it in thoroughly. This gives the yeast time to wake up before salt is introduced. If you've been adding salt at the beginning, try this order and you'll likely see a noticeable difference in rise time.

Your dough may be too cold or too stiff

Dough that feels dense and heavy, or that was mixed with cold water, ferments much more slowly than dough that's soft and warm. Cold dough can take twice as long to rise. If you're using water straight from the tap, especially in winter, warm it to around 75°F before mixing—this is called the desired dough temperature, and it's one of the easiest ways to speed up fermentation without changing anything else.

A dough that's too stiff (too little water relative to flour) also ferments slowly because yeast cells have less room to move and less moisture to work with. Most sourdough recipes use 75 to 80 percent hydration, meaning if you have 500 grams of flour, you're using 375 to 400 grams of water total. If your dough feels like a stiff ball instead of a soft, slightly sticky mass, add a little more water next time and give it time to fully absorb before judging the texture.

Overproofing in the fridge can flatten your dough

Cold fermentation in the refrigerator is a useful technique—it develops flavor and makes scoring easier—but leaving dough in the fridge for more than 48 hours, or at a temperature below 38°F, can overproof it. The yeast and bacteria slow down dramatically in the cold, but they don't stop. After two days, the dough has often already risen as much as it will, and sitting longer just weakens the gluten.

If you're using the fridge, shape your dough, place it seam-side up in a floured banneton or bowl, cover it, and refrigerate for 8 to 24 hours. Check it before baking: it should feel puffy but still spring back slightly when poked. If it feels completely slack and doesn't spring back at all, it's overproofed and will spread flat in the oven. For longer storage, freeze the shaped dough instead of refrigerating it for days on end.

Your oven isn't hot enough or your scoring is too shallow

Sourdough needs a very hot oven—at least 450°F, ideally 475 to 500°F—to rise quickly in the first few minutes (called oven spring). If your oven runs cool, or if you're not preheating long enough, the dough will bake before it has a chance to expand. Preheat your oven for at least 45 minutes, and consider using an oven thermometer to check the actual temperature, since many home ovens are off by 25 degrees or more.

Shallow scoring also limits rise. A good score should be about a quarter inch deep and at a 30 to 45 degree angle, which allows steam to escape in a controlled way and lets the dough expand upward instead of sideways. If you're barely scratching the surface, the dough can't open properly and it rises less. Use a sharp blade or lame, and score with confidence—a hesitant, shallow cut will give you a flat loaf.

Frequently Asked Questions

How do I know if my starter is strong enough to use?

Feed your starter and wait. A strong starter should roughly double in size within 4 to 8 hours, depending on temperature. It should smell pleasantly sour and yeasty, with visible bubbles throughout, not just on top. If it's only growing 25 percent or less, feed it daily in a warm spot for three to five days before making bread.

What's the difference between underproofing and overproofing?

Underproofed dough springs up dramatically in the oven (called oven spring) and often tears unevenly. Overproofed dough spreads flat and doesn't rise much in the oven. Use the poke test: if the indent springs back slowly and leaves a slight crater, you're in the sweet spot. If it springs back fast, give it more time. If it doesn't spring back, you've waited too long.

Can I speed up sourdough fermentation without changing the recipe?

Yes. Warm your water to 75°F before mixing, move your dough to a warmer spot (aim for 75°F), and make sure your starter is doubling reliably between feedings. These three changes alone can cut fermentation time in half. You can also use slightly more starter (up to 20 percent of the flour weight), though this reduces flavor development.

Why does my dough rise in the bowl but then flatten when I shape it?

You're likely overproofing during bulk fermentation. Shape when the dough has risen 50 to 75 percent, not doubled. After shaping, it should rise again (called final proof) for 2 to 4 hours at room temperature, or 8 to 24 hours in the fridge. If it's already fully risen before you shape, there's nowhere left for it to go.

Does my sourdough need to double to be ready?

No. Most sourdough is ready to shape when it has risen 50 to 75 percent. Waiting for a full doubling often means overproofing, which weakens the gluten and causes the dough to spread flat instead of rising in the oven. Use the poke test instead of watching for a specific size.