Bulk fermentation is the first rise your dough goes through after you mix your ingredients together.
It’s the stage where your starter gets to work, building flavour, creating gas, and developing the strength your dough needs to become bread.
The short answer
Bulk fermentation is the time when your mixed dough rests before shaping.
During this stage:
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the yeast in your starter produces gas, helping your dough rise
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bacteria create flavour
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gluten develops and strengthens
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the dough becomes smoother, lighter, and easier to shape
It is one of the most important stages of sourdough baking.
What actually happens during bulk fermentation?
Once your starter, flour, water, and salt are mixed together, fermentation begins.
Your starter is not just making your dough rise—it is changing the dough.
During bulk fermentation:
Yeast creates gas
The natural yeast in your starter feeds on the flour and produces carbon dioxide.
This gas gets trapped within the gluten structure, creating the air pockets that eventually become your crumb.
Bacteria build flavour
The bacteria in your starter produce acids that create sourdough’s unique flavour.
This is why time matters.
A rushed dough may rise, but it often won’t have the same depth of flavour.
Gluten develops
As the dough rests, the gluten network strengthens.
This helps your dough:
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hold its shape
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trap gas
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rise properly in the oven
Why is it called “bulk” fermentation?
The word “bulk” simply means the dough is fermenting as one large piece before it gets divided and shaped.
This is different from the final proof, which happens after shaping.
How long does bulk fermentation take?
This is where sourdough can feel confusing.
The honest answer is:
It depends.
Bulk fermentation changes depending on:
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room temperature
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dough temperature
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starter strength
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flour used
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amount of starter in your dough
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hydration
A dough in a warm kitchen may finish much faster than the same dough in a cool kitchen.
This is why following the clock alone can sometimes lead to frustration.
What should I look for during bulk fermentation?
Instead of only watching the time, look for changes in your dough.
Signs bulk fermentation is progressing:
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dough becomes smoother
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dough feels lighter and more elastic
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some bubbles appear
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the dough has increased in size
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the surface looks slightly rounded or domed
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the dough has more strength than when first mixed
You are looking for a dough that has developed—not necessarily one that has doubled.
Common beginner mistakes
Ending bulk fermentation too early
If you stop too soon:
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dough may lack strength
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loaf may be dense
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oven spring may be limited
Letting bulk fermentation go too long
If fermentation continues too far:
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dough can become weak
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shaping becomes difficult
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loaf may spread
Following someone else’s timing exactly
This is one of the biggest lessons in sourdough.
A recipe might say:
“Bulk ferment for 4 hours.”
But your kitchen, flour, and starter may need something different.
Learning what your dough looks and feels like is more valuable than following a timer.
How does bulk fermentation fit into the whole process?
The sourdough journey usually looks like this:
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Feed and prepare your starter
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Mix your dough
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Bulk fermentation ← you are here
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Shape your dough
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Final proof
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Bake
Each stage builds on the one before it.
Nikki’s note
Bulk fermentation was one of the biggest lightbulb moments for me.
At first, I thought sourdough was about following a recipe perfectly.
But the more you bake, the more you realise the dough is always giving you clues.
Temperature, timing, flour, and your starter all change how your dough behaves.
The goal isn’t perfect timing.
The goal is learning what ready looks like in your own kitchen.
Related guides
Next steps:
👉 How Long Should Bulk Fermentation Take?
👉 How Do I Know When Bulk Fermentation Is Finished?
👉 What Is Proofing?
👉 Why Is My Dough Sticky?
👉 Overproofed vs Underproofed Dough