Why Does My Sourdough Crack on the Bottom?
A sourdough loaf should expand through the score made across its surface. But sometimes the score barely opens while a deep crack appears along the bottom or side of the bread.
This is not a random defect. The dough is producing steam and expanding in the oven, but the pressure cannot escape through the intended opening. It finds a weaker place instead—often the seam underneath the loaf.
A bottom crack usually points to a problem with proofing, scoring, shaping, steam, or oven temperature. Understanding when the crust formed and where the dough was weakest will help you identify the real cause.
The Dough Was Underproofed
Underproofing is one of the most common reasons sourdough cracks underneath.
Dough that has not fermented long enough still contains a great deal of unused rising power. Once it enters the hot oven, fermentation speeds up briefly and the gases inside expand rapidly.
If the surface cannot stretch enough, the pressure pushes through the bottom seam and tears the loaf open.
Underproofed dough often feels dense, tight, and unusually elastic before baking. When pressed gently, the indentation disappears almost immediately. The shaped loaf may also look compact rather than light and slightly puffy.
After baking, you may notice more clues:
- A very rounded or sharply domed loaf;
- Dense crumb near the bottom;
- A few large tunnels surrounded by tight crumb;
- A score that opened very little;
- A thick, torn crack underneath or along one side.
The solution is to extend bulk fermentation or the final proof. Do not judge readiness by time alone. Look for increased volume, visible bubbles, a lighter texture, rounded edges, and a gentle wobble when the dough is moved.
The Score Was Too Small or Too Shallow
The score is not only decorative. It creates a controlled weak point that allows the loaf to expand during baking.
If the cut is too short, too shallow, or made with a dull blade, the surface may seal before the loaf finishes expanding. The pressure then moves downward and opens the bottom seam.
For a simple round or oval loaf, one confident main score is usually more effective than several tiny cuts. The blade should move smoothly through the dough without dragging or tearing the surface.
A cold loaf is generally easier to score. If the dough feels soft and sticky, keep it refrigerated until the oven is completely ready.
The ideal depth depends on the dough and the angle of the blade, but a main expansion score is commonly about 1–1.5 centimetres deep. Very shallow decorative cuts cannot replace a proper expansion score.
Bake immediately after scoring. If the loaf sits for too long, the cut can begin to close.
The Surface Dried Out During Proofing
A dry skin makes it difficult for the dough to expand evenly.
This can happen when the proofing basket is left uncovered in the refrigerator or when the dough is exposed to moving air. The surface becomes firm while the interior continues fermenting.
In the oven, the dry outer layer resists expansion. The pressure searches for a softer area, and the moist seam underneath may split first.
Cover the proofing basket well before refrigeration. A reusable plastic cover, large food-safe bag, or covered container will prevent excessive moisture loss.
The surface should feel dry enough to release from the basket, but it should not feel leathery, cracked, or stiff.
The Bottom Seam Was Not Sealed Properly
During shaping, the bottom of the loaf becomes a seam where the edges of the dough meet. If this seam remains loose, it can open in the oven.
After shaping, check the underside of the loaf. Gently pinch any open areas closed before placing the dough seam-side up in the proofing basket.
However, do not add a large amount of dry flour to the seam while shaping. Flour between the layers prevents them from sticking together.
Use only enough flour to keep the outer surface manageable. Try to keep the inner edges of the seam relatively clean so they can seal properly.
If the loaf repeatedly cracks along exactly the same line underneath, the shaping seam is likely contributing to the problem.
The Baking Surface Was Not Hot Enough
Strong heat from below helps the base of the loaf set quickly and supports upward expansion.
If the baking stone, steel, Dutch oven, or tray is not thoroughly preheated, the bottom stays soft for too long. The loaf may begin expanding sideways or push through the weak seam before the base develops enough structure.
Preheat the oven and baking vessel for at least 40–60 minutes, especially when using a heavy Dutch oven or thick baking stone.
Do not rely only on the oven’s preheat signal. That signal usually means the surrounding air has reached the selected temperature; the heavy baking surface may still need more time.
For many sourdough loaves, an initial baking temperature of approximately 230–250°C (445–480°F) provides strong oven spring. The exact temperature will depend on your oven, flour, loaf size, and baking method.
There Was Not Enough Steam
Steam keeps the crust flexible during the first stage of baking. This gives the loaf time to expand before the surface becomes firm.
Without enough steam, the upper crust can set too early. The expanding dough then breaks through a weaker area near the bottom.
A preheated Dutch oven naturally traps moisture released by the dough. If you bake on an open stone or tray, you need another safe method of producing steam.
The oven should contain plenty of steam during approximately the first 15–20 minutes. After the loaf has expanded and the crust has begun to set, release the steam so the bread can brown and become crisp.
Be careful when adding water to a hot oven. Avoid pouring water directly onto the oven floor or glass door, as thermal shock can cause damage.
The Top of the Loaf Set Too Quickly
Even with steam, the surface can harden too early if the loaf is positioned too close to the upper heating element or strong convection dries the crust.
If the top browns quickly while the bottom remains pale, move the baking surface to a lower rack.
You may also need to reduce or temporarily disable the fan during the steaming stage. Strong air circulation removes moisture and can cause the crust to form before expansion is complete.
In a Dutch oven, keep the lid on during the first part of baking. Removing it too early releases the trapped steam and exposes the loaf to dry heat.
The Dough Stuck to the Proofing Basket
If part of the dough sticks to the basket, turning it out can stretch or tear its surface. A damaged area may become the weakest point during baking.
Rice flour is especially useful for dusting proofing baskets because it absorbs less moisture than wheat flour. A mixture of rice flour and bread flour also works well.
Turn the loaf out gently rather than pulling it from the basket. If it sticks, loosen the edges carefully before attempting to release it.
A small tear may not look serious before baking, but rapid oven expansion can enlarge it dramatically.
How to Prevent Bottom Cracks
The best correction depends on the appearance of both the dough and the finished loaf.
Before the next bake:
- Allow the dough to ferment until it looks lighter and properly aerated.
- Keep the shaped loaf covered during proofing.
- Seal the bottom seam without trapping flour inside it.
- Preheat the baking surface thoroughly.
- Make one clear expansion score with a sharp blade.
- Provide enough steam during the first stage of baking.
- Bake immediately after scoring.
- Check whether the upper crust is setting too quickly.
Change one or two things at a time. If you change the starter amount, fermentation time, scoring, steam, and baking temperature all at once, it will be difficult to discover which adjustment solved the problem.
Is Bread with a Bottom Crack Still Good?
A crack underneath does not make the bread unsafe or inedible. If the loaf is fully baked, it can still taste excellent.
The defect mainly affects shape, crumb structure, and appearance. A severely underproofed loaf may have dense or gummy areas, but a small crack can occur even when the rest of the bread is well fermented.
Let the loaf cool completely before cutting it. The crumb continues setting as the bread cools, and slicing it too early can make a properly baked loaf appear wetter than it really is.
Final Thoughts
When sourdough cracks on the bottom, the loaf is showing you that it could not expand through the intended score.
Underproofing is the first thing to check, especially when the bread is very domed and the crumb contains large tunnels beside dense areas. If fermentation looks correct, examine the depth of the score, the shaping seam, surface moisture, steam, and the heat coming from below.
The goal is to keep the outer crust flexible long enough for the loaf to expand upward through a well-placed score. Once fermentation and oven conditions are balanced, the bottom should remain intact and the score will become the natural opening for oven spring.
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31.07.2026
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