Crumb Has Large Tunnels — Causes & Fixes

Large tunnels or long irregular holes in your sourdough crumb? Diagnose the root cause and apply targeted fixes for more even crumb.

Quick Diagnosis

WHAT kind of tunnels do you see?

Long, linear tunnels running along the crumb A few very large isolated holes Many irregular tunnels mixed with normal alveoli Very open top crumb but dense bottom

Causes & Solutions

Insufficient degassing during shaping (trapped gas)

very common

Symptoms:

  • • Long linear tunnels following the seam
  • • Large pocket under the crust on one side

Why does this happen?

During shaping you tense and expel large gas pockets so they don't become isolated tunnels. If gas stays trapped near a weak seam, it expands in the oven and forms tunnels. Controlled degassing preserves overall gas while removing big pockets.[1][2]

🚨 Immediate Fix:

Next bake: when shaping, use a gentle but decisive fold and use a dough scraper to deflate obvious pockets. Create surface tension without folding trapped bubbles into the seam.

📅 Long-term Fix:

Practice consistent pre-shape and final shape routines: coil folds or letter folds to redistribute gas, then bench rest before final tensioning.

🧪 Test:

After shaping, hold dough at eye level and slide your hands—no visible big bulges along the seam.

Overly vigorous bench work or rough handling

common

Symptoms:

  • • Very large isolated holes
  • • Tunnels often near where dough was handled

Why does this happen?

Abrupt handling can shear the gluten network and localize gas into pockets. The damaged gluten cannot evenly distribute stress, allowing one large bubble to grow.[1]

🚨 Immediate Fix:

Be gentler during bench work. Use a light touch when folding; don't slap or heavily degas the dough.

📅 Long-term Fix:

Improve gluten development earlier (longer bulk with folds) so dough withstands handling. Use gentle coil folds rather than forceful pushes.

🧪 Test:

Compare two shaped boules—one handled gently, one roughly—to see the difference after proofing and baking.

Under-fermented gluten (weak structure) with active gas production

common

Symptoms:

  • • Many irregular tunnels among normal crumb
  • • Dough felt slack at shaping

Why does this happen?

If yeast produces gas faster than the gluten network can strengthen (e.g., too warm or insufficient bulk development), bubbles coalesce into tunnels. Strength (gluten alignment) and timing must match gas production rates.[1][2]

🚨 Immediate Fix:

Shorten final proof or cool the proof (move to fridge) to slow gas production and allow gluten to recover.

📅 Long-term Fix:

Build more structure in bulk: more and better-timed stretch-and-folds, longer bulk at cooler temp, or increase autolyse time to hydrate flour enzymes for better gluten formation.[1]

🧪 Test:

Poke test: weakly proved dough will not spring back cleanly and feel slack.

Over-proofed top or under-proofed bottom (uneven proofing)

medium

Symptoms:

  • • Open, airy top crumb but dense, under-expanded bottom
  • • Tunnels concentrated near top

Why does this happen?

Uneven temperature or positioning during proofing (hot spot near top) lets the top overproof while the lower part lags, creating differential gas expansion and tunnels when baked.[2]

🚨 Immediate Fix:

Rotate loaves during proof to even temperature; proof in a banneton proofing basket in a controlled environment like a proofing box.

📅 Long-term Fix:

Standardize proofing environment and monitor dough temp with an instant-read thermometer to aim for consistent dough temperature.

🧪 Test:

Cut loaf vertically—look for banding of large holes near surfaces indicating uneven proof.

Too much fermentation strength combined with under-shaping

medium

Symptoms:

  • • Very sour smell, weak skin on surface
  • • Holey crumb despite long bulk times

Why does this happen?

Strong enzymatic activity and yeast can make very active gas production; if shaping doesn't create sufficient surface tension, gas will collect irregularly and form tunnels.[1]

🚨 Immediate Fix:

Tighten your final shape to build a stronger outer skin; cooler final proof to slow fermentation.

📅 Long-term Fix:

Balance starter quantity, bulk time and temperature to match your flour and schedule; practice shaping to build uniform tension.

🧪 Test:

If smell is very acidic and dough collapses easily, you're past optimal fermentation and need shorter bulk next time.

Large inclusions (fruit, seeds) or uneven dough hydration

rare

Symptoms:

  • • Tunnels forming near add-ins
  • • Patchy crumb with dry spots

Why does this happen?

Inclusions can create voids or interrupt gluten continuity; if not incorporated gently they create weak points where gas collects.[2]

🚨 Immediate Fix:

Re-shape to better incorporate or scatter inclusions; for next time, gently fold inclusions in during late bulk so dough retains strength.

📅 Long-term Fix:

Hydrate add-ins (soak seeds/fruit) and incorporate with light laminations late in bulk.

🧪 Test:

If tunnels align with add-in location, the inclusion is the cause.

🆘 Can I Fix This Loaf?

You already have a baked loaf with tunnels

Solution: Use it: large tunnels don't affect flavor. Slice and toast; large holes are fine for open-crumb recipes like rustic toasts. Use as croutons or bread salad if uneven.

Success chance: excellent for use, cannot reverse crumb

Dough shaped but contains obvious large pockets

Solution: Gently re-open the seam, press out large bubbles with fingertips, reshape with tighter tension and bake immediately.

Success chance: good if caught quickly

Proofed loaf shows big surface bulges

Solution: Gently deflate obvious pockets (use a [dough scraper](https://amzn.to/3LR1f5E)), reshape, then cold-proof briefly in fridge to firm before baking.

Success chance: moderate

Prevention

  • ☐ Develop gluten during bulk with scheduled stretch-and-folds; monitor windowpane occasionally
  • ☐ At shaping, degas deliberately: expel large pockets and build surface tension
  • ☐ Use consistent dough temperature; aim 75-78°F / 24-26°C during bulk where appropriate [1]
  • ☐ Weigh ingredients on a Digital Kitchen Scale and measure salt at 2% of flour weight
  • ☐ Proof in a stable environment — consider a proofing box or fridge for final proof control
  • ☐ When adding inclusions, fold them in late and gently to avoid weak points

Sources

  1. [1]
    The Perfect Loaf – The Perfect Loaf – Link
  2. [2]
    Plötzblog – Plötzblog – Link