Sourdough with Big Holes Only at the Top: What's Happening

Short answer: big holes only at the top of a sourdough loaf usually mean shaping pushed all the gas to the surface, then proof concentrated activity there. Build even tension and let bulk go further.

What this crumb looks like

Slice the loaf and you see:

• 2–3 large holes (1 inch+) in the top third
• Tight, dense crumb in the bottom two-thirds
• A clear horizontal line where the bread changes character

This is sometimes called a "tunnel" or "headspace" defect.

Why it happens

Two things together cause it:

1. Loose shaping — gas wasn't evenly distributed
2. Under-bulked dough — bottom half didn't ferment as much
3. (Sometimes) Over-proof in the basket — top expanded faster than bottom recovered

The result: top of loaf has gas, bottom doesn't.

The 3 main causes

1. Build more shaping tension

A loosely-shaped loaf lets gas redistribute upward during proof. By the time you bake, all the gas is at the top.

Build tension:

• Pre-shape into a tight round
• Rest 30 min
• Final shape: drag across the bench to tighten the surface
• Place seam-down (not seam-up) in the basket

The dough should feel firm and smooth on top.

2. Catch the proof window

Over-proofed dough flattens out and large bubbles coalesce at the top. The bottom doesn't have the gas pressure to expand upward.

Bake at 50–60% rise (visible), not 100%.

3. Even bulk

If you stop bulk early but proof long, the proof has to do all the gas work. This unevenly inflates the top.

For even crumb:

• Bulk to 60% rise (most of the gas is built)
• Cold retard 12 hours
• Bake straight from fridge

The cold retard equalizes gas distribution throughout the loaf.

Why the bottom stays dense

When dough sits in a basket, the bottom is compressed by the weight of the dough above. This compression:

• Slows gas expansion
• Prevents bubbles from forming
• Leaves the bottom denser than the top

A tighter shape and shorter proof minimize this effect.

Lamination as a fix

A lamination during bulk evenly distributes gas pockets:

• After the second fold, instead of folding, stretch the dough into a thin rectangle on the bench
• Fold it back like a letter
• Return to the bowl

This redistributes gas evenly, preventing top-heavy crumb.

A test bake

Recipe:

• 500g bread flour
• 350g water (70%)
• 100g starter
• 10g salt

Method:

• Mix
• Bulk 4h at 75°F, 3 folds + 1 lamination at fold 2
• Pre-shape, rest 30 min
• Final shape (tight)
• Cold retard 12 hours
• Bake at 475°F, Dutch oven, 20 covered + 22 uncovered

This bake produces an even crumb without top-tunnel issues.

When tunnels are okay

For some breads, a slight tunnel near the top is normal:

• Open-crumb tartine-style boules often show one or two larger holes at the top
• Ciabatta is supposed to have irregular holes throughout

But a hard line dividing dense bottom from open top is a defect, not a feature.

A diagnostic question

Ask: did the dough have visible gas activity at the bottom of the basket during proof?

If yes: bulk was sufficient. If no: bulk was too short. The bottom didn't have enough fermentation to build crumb structure.

Pre-shape and final shape build the structure; bulk fills it with gas. If bulk is short, no amount of shaping recovers the bottom.

The role of basket shape

A round basket with a curved bottom helps gas distribute evenly. A flat-bottomed basket can encourage flat-bottomed loaves.

If you're using a flat-bottomed basket and seeing dense bottoms, switch to a round or oval banneton.

Cold retard equalizes

Cold retard is a great equalizer. Yeast continues slowly throughout the dough, and gas distributes evenly because the cold inhibits violent expansion.

For top-heavy crumb fixes, cold retard 12+ hours.

A consistent fix

If your loaves consistently show big holes at the top:

• Bulk to 60% rise (use a clear container)
• Lamination at fold 2 of bulk
• Tight final shape
• Cold retard 12 hours
• Bake straight from fridge

This combination eliminates top-tunnels in most cases.

A note on flour

Whole wheat and rye doughs are more prone to top-tunneling because they ferment faster on top (where gas concentrates) and slower on the bottom. For high-whole-grain breads, drop bulk by 60 min and shorten proof.