Disclosure: Crock & Loaf is reader-supported. When you buy through links on our site, we may earn an affiliate commission at no cost to you.

Answer first

Cause 1: Underfermentation (the actual answer 8 times out of 10)

If your crumb is tight, gummy near the base, or has a band of dense dough below an open top, the dough did not ferment long enough. Yeast produces carbon dioxide as it metabolizes sugars; that gas creates the open structure of the crumb. Less time fermenting equals less gas equals denser crumb.

This sounds obvious. It's worth being specific because most home bakers think they fermented their dough plenty when they actually stopped 2 to 4 hours too early.

What "fully fermented" actually looks like at the end of bulk:

The single most common mistake is following a recipe's clock instead of the dough's actual state. "Bulk for 4 hours" assumes 75°F. At 68°F, that same dough needs 8 to 10 hours. At 80°F, 3 hours. The clock is a guide, not the answer.

Cause 2: Your starter wasn't at peak

You can do everything else right and still get a dense loaf if your starter wasn't at peak activity when you used it. Peak means:

If you used your starter when it was already starting to fall (a concave or wrinkled surface, fewer bubbles, weak smell), the yeast population was past its productive phase. You used a tired culture. The dough never had enough yeast to do the job.

A starter that smells of solvent is a particularly clear sign it is past peak and underfed, covered in sourdough starter smells like acetone. If your starter consistently does not reach peak, that's a separate problem. We cover it in why is my sourdough starter not rising.

Bulk fermentation time by temperature (including 68°F kitchens)

Dough fermentation is roughly thermodynamic: fermentation rate doubles for every 10°F (5.5°C) increase in temperature within the normal range. Treat that as a working heuristic rather than a measurement, since we could not find a published figure behind it. See what the microbiology of fermentation temperature actually says for the numbers that are established. The practical effects:

Dough temperatureBulk fermentation time (approx.)
78°F (26°C)3.5 to 4 hours
74°F (23°C)5 to 6 hours
70°F (21°C)7 to 9 hours
68°F (20°C)8 to 10 hours
65°F (18°C)10 to 14 hours

"Dough temperature" is not the same as room temperature. A bowl of dough on a cold counter can be 5 to 8°F below ambient. A dough that started at room temperature and sat on a granite counter for four hours can drop 10°F over that time.

The fix is mechanical: measure the dough. An instant-read thermometer stuck into the dough itself for 2 seconds tells you what's actually happening. Knowing the actual dough temperature is the single piece of information most beginners are missing.

The shortcut that works: if your kitchen is cold, put the dough in the oven with just the oven light on. The light raises the interior temperature to roughly 78–82°F, ideal for bulk fermentation. Most home ovens are well-insulated enough to be effective proofers when you do this.

Cause 4: You're not weighing the ingredients

If you measure flour by volume (cups), your hydration is wrong. A cup of flour can weigh anywhere from 110 grams to 160 grams depending on how it was scooped and settled. A dough that was supposed to be 75% hydration might actually be 60% (dense and dry) or 90% (slack and unmanageable). Both of those produce poor crumb structure.

If you do not own a scale yet, get one. The OXO 11-pound scale is the default recommendation; we go into detail in best sourdough starter kit. Around $50, accurate to 1 gram, lasts forever. There is no version of "getting good at sourdough" that does not involve weighing your ingredients.

Cause 5: Overproofed, not underproofed (the less common version)

Occasionally dense crumb is the opposite problem: the dough overproofed. The yeast exhausted its food supply before baking, then the gluten structure collapsed under its own weight. The bake produces a flat, dense loaf with a wrinkled or sunken surface.

Telltale signs you overproofed rather than underproofed:

This is less common than underproofing but worth knowing about. The fix is the opposite of cause 1: less time, or cooler temperature, or a less active starter.

If the loaf came out flat and wide rather than dense and tight, overproofing is only one of four possible causes and the crumb tells you which. We separate them in why does my sourdough spread out flat instead of rising up.

How to systematically improve

If your last three loaves have all been dense, do not change the recipe. Change one variable per bake and observe:

  1. Bake 1: Measure dough temperature throughout bulk fermentation. Write it down. Bulk until the visual signs above are present, ignoring the clock.
  2. Bake 2: Same recipe, but use the starter at exactly peak (not 30 minutes after).
  3. Bake 3: If still dense, increase bulk by 25 percent past what felt "right" in bakes 1 and 2.

Most people get to good crumb within three bakes of doing this. The information you're collecting (actual dough temperature, actual starter behavior, actual fermentation time) is what makes the next bake better, not the recipe.

FAQ

Why is my sourdough bread so dense and gummy?

There are two different causes and the test is when you cut it. If you cut the loaf warm, gumminess is expected: starch is still setting, and the crumb is not finished until the loaf has cooled fully, which takes at least 2 hours and closer to 4 for a large loaf. If the crumb is still gummy once fully cooled, the two real causes are underfermentation and underbaking. Check the bake first, because it is the faster thing to rule out: the internal temperature should reach 205 to 210°F. If the bake was correct, the dough was underfermented.

How do I get a more open crumb in sourdough?

Open crumb requires three things in combination: a strong active starter at peak, hydration matched to your flour, and full bulk fermentation. Hydration is not one number. Bread flour at 12 to 13 percent protein handles 75 to 80 percent hydration. All-purpose at 10 to 11.5 percent does not, and pushing it there is a common cause of a slack dough that spreads instead of rising. Start at 68 to 72 percent with all-purpose.

Should sourdough double in size during bulk fermentation?

No, and bakers disagree about the number because it depends on temperature. Tartine works to a much smaller rise at warm dough temperatures, closer to 30 percent, while cooler doughs are taken further. For most home bread doughs at 70 to 74°F, target 50 to 75 percent. Judge the signs rather than the percentage: visible doming, a jelly-like jiggle when you shake the bowl, and clear gas bubbles at the edge where the dough meets the bowl. A full double at room temperature usually means you have gone past the point where the gluten can still hold the gas.

How long should bulk fermentation take at 68°F?

Roughly 8 to 10 hours at a dough temperature of 68°F, assuming a healthy starter at around 20 percent of the flour weight. That is about double the 4 hours most recipes assume, because those recipes are written for a 75°F kitchen. Measure the dough itself rather than the room: dough sitting on a cold counter often runs 5 to 8°F below ambient.

Can underproofed sourdough be saved?

Yes, if caught early. If the dough is shaped but visibly underproofed before baking, return it to a warm spot for another hour or two. Once baked, you cannot fix density, but a dense loaf still tastes good and toasts well.