Troubleshooting
Sourdough Tunneling and Giant Holes: Causes and Fixes
Big tunnels and irregular caverns near the crust come from trapped gas and uneven shaping — not good open crumb. Here's the fix.
Tunneling — large, irregular holes clustered near the top crust with dense bread below — is caused by trapped gas from loose shaping, underfermentation, or a too-tight skin. It's different from desirable open crumb, which is evenly distributed. Fix it with tighter shaping, fuller fermentation, and gentler degassing.
Tunneling vs. good open crumb
| Tunneling (bad) | Open crumb (good) |
|---|---|
| Huge holes only near the top | Even holes throughout |
| Dense, gummy bottom | Light, consistent texture |
| Sharp-edged caverns | Rounded, glossy walls |
| From trapped gas | From good fermentation |
The four main causes
- Loose shaping. If you don't build enough surface tension, gas pools in pockets instead of distributing. The dough's weak spots blow out near the top.
- Underfermentation. A dough that hasn't bulked enough has uneven gas. It springs unevenly in the oven and tunnels.
- Trapped air from shaping. Folding large air pockets into the dough during shaping creates fixed voids that expand into tunnels.
- Too tight a skin with weak interior. When the crust sets fast but the inside is underdeveloped, gas migrates upward and collects.
How to fix it
- Degas gently and evenly during pre-shape. You want to redistribute gas, not eliminate it — pat, don't punch.
- Shape with consistent tension all the way around so there are no weak spots.
- Let bulk go to 50–75% rise so the crumb structure is mature and even.
- Don't over-flour the bench during shaping — dry patches create seams that become tunnels.
- Score deliberately so the loaf has a designated place to expand.
Frequently asked questions
Why is there one big hole right under the top crust?
Almost always a shaping issue — a large air pocket got sealed under the skin during final shaping. Pat the dough out evenly before the final roll.
Does high hydration cause tunneling?
Indirectly. High hydration doughs are harder to shape, so weak shaping shows up faster. The root cause is still the shaping, not the water.
Is tunneling the same as underbaking?
No, but they often appear together. Underbaked tunnels look gummy; well-baked tunnels are just hollow.
Consistent shaping plus correctly timed fermentation eliminates most tunneling. SourdoughAI's photo crumb analysis can tell you whether your holes mean "shape tighter" or "ferment longer."