If you’re new to sourdough, then the step called bulk fermentation is often where things start to feel a little mysterious. Bulk fermentation begins once you mix your sourdough starter (or levain) into your dough. Now your dough sits and does its thing (while you do your thing). Except… did it do enough? Did it do too much? How can you tell?

In my own classes with beginners, I see this over and over: the dough looks right, but later the loaf is too dense or the crumb too tight. Or the dough got over-slack, too sticky, hard to shape. It often comes down to bulk fermentation: timing it, sensing it, adjusting for your environment. And for busy home bakers (especially when squeezing in sourdough around kids, school runs and daily life) the “just let it ride” advice isn’t always helpful.

So let’s talk about what bulk fermentation is, how to know when it’s done, how temperature plays a big role — and then we’ll answer the most frequently asked questions I see in my social media and from my students. After that, we’ll take a look at the crumb of a few loaves, so we can identify the signs of a good bulk fermentation.

How to Know Bulk Fermentation Is Complete – What to Look For

When you’ve mixed your dough and it’s resting in the bulk fermentation phase, the “right moment” to end that phase and preshape is less a fixed time and more a set of cues. Here are the key signals I look for (and teach beginners to watch for).

Visual & tactile signs

• The dough should look smoother and more cohesive than when you began that rest. Rather than a shaggy, sticky ball of dough, you should begin to see it relax and expand. The gluten is developing (making it feel stretchy and elastic), the surface gently domes and starts to pull away from the edges of the bowl, and there are bubbles visible across the surface.
• If you gently shake or jiggle your bowl, the dough should show a bit of movement (airiness). I love to watch for a jello-jiggle with my artisan dough.
• Touch test: With wet or lightly floured fingers you can feel how the dough stretches and holds. If you pull gently, there should be resistance (indicating good gluten structure) but it should also stretch rather than tear immediately. It should feel smooth and elastic.
• Your dough should be tacky, but not overly sticky. Dough is always kind of sticky, but if you notice that your dough went from manageable to really sticky, that’s a sign you’ve overproofed and need to shape it quickly.
• Note: Rise in volume is helpful but not the whole story. Some doughs won’t double in bulk before they’re ready to shape. Chasing a dough that’s doubled in certain flours or hydrations can lead to over-fermentation. Watch for a light and airy dough, but don’t stress too much over how much it has grown in volume.

How I teach it in my class

When I’m teaching beginners, I say: look for the dough to feel light and airy. Light and airy dough gives light and airy loaves. Heavy, dense dough will produce a heavy and dense loaf. Trust your intuition. If it feels like it needs longer to raise, let it raise longer. If we’re being honest, I like to slightly overproof my loaves because I love the end result that way. As you’re doing stretch and folds or coil folds, try to pay attention to how the feel of the dough changes as bulk fermentation progresses. Is it starting to feel lighter? If so, you’re moving in the right direction.

But my two biggest tips are these:

1. Always just bake the bread. You never really know exactly how it will turn out until you bake it. Never have I ever had a kid say “mom, you kind of over proofed this loaf, you should have shaped it an hour earlier.” They all just devour the bread and are happy for a filled tummy.
2. Watch the dough, not the clock.

How Temperature Impacts Bulk Fermentation

If there’s one factor that throws new sourdough bakers off more than anything else, it’s temperature. You can follow the exact same recipe, use the same starter, and mix the same ingredients — but if your kitchen is a few degrees warmer or cooler than the recipe developer’s kitchen, your dough will behave completely differently.

That’s because temperature acts like your dough’s accelerator or brake pedal. Warm dough ferments quickly; cool dough slows way down. The tricky part is that sourdough recipes rarely account for your actual kitchen environment, so understanding this one variable can make or break your bread.

Warm Environments = Faster Fermentation

When your dough is warm (usually above 76F), the yeast and bacteria inside your starter are extra active. They’re eating through the sugars in your flour and producing gas and acid at a faster rate.

What this means for your dough:

• It’ll rise faster, sometimes much faster than expected.
• Bulk fermentation might finish in four hours instead of seven.
• If left too long, the dough can become over proofed — sticky, slack, and difficult to shape.

If your kitchen tends to run warm, keep a close eye on your dough instead of the clock. A good trick is to check in every hour or so to see how your dough is doing — if your dough already looks puffy, jiggly, and airy, it’s probably close to ready to shape.

Cool Environments = Slower Fermentation

Cooler dough (below 72F ) ferments more slowly because the yeast and bacteria are less active. This can be a good thing for flavor development — slower fermentation gives your bread more complex, tangy notes — but it also means you’ll need to be patient.

What this means for your dough:

• Bulk fermentation can take 8-10 hours (or longer).
• The dough may feel tighter and show fewer bubbles for much of the process.
• If it’s too cold, fermentation can almost stall completely.

If your kitchen is cool, you can help things along by:

• Finding a warm spot (on top of the fridge, inside the oven with the light on, or near a sunny window).
• Use warm water when mixing.
• Increase the amount of starter in your recipe.
• Extending bulk fermentation until your dough shows the right signs of readiness.
• Do an overnight bulk ferment … then your dough is working while you’re sleeping.

Why It Matters So Much

Temperature affects more than just timing — it also changes how your bread tastes and feels.

• Warm fermentation produces milder, sweeter bread with a softer crumb.
• Cool fermentation leans more toward complex, tangy flavor and chewier texture.

Frequently Asked Questions (FAQs) About Bulk Fermentation

Here are some of the questions I hear most all the time from my students in my classes and on my social media pages — with answers based on what I’ve learned and what I teach.

How long should bulk fermentation last?

There’s no one-size-fits-all answer for this. Temperature, hydration, starter strength and the type of flour you’re using all play a role in how long bulk fermentation will be.

Can I over-ferment in bulk?

Yes — definitely. Over-fermentation can weaken the gluten network, making the dough slack and sticky, harder to shape, and the final loaf may collapse or have a poor crumb.

What if my dough isn’t doubling in size?

Volume rise is a visual cue for bulk fermentation, but it’s not the only one — and sometimes it can be misleading. For example, a high-hydration or whole-grain dough might not double in volume, yet may be ready. Conversely, chasing a “double size” target can lead to overdoing it.

When I’m baking at home, if my dough is really warm (78-80F) then I shape it when it’s almost half way to doubled in size. I know it’s going to continue to raise after it’s shaped while the dough cools in the fridge. However, if my dough is cold (only 70F), I’m going to let it come really close to double in size because it’s not going to take long for it to cool down to fridge temperatures.

I’m also looking for other signs that my dough is ready to shape – like feeling light and airy, having a domed top, scattered air bubbles and tacky, but not super sticky.

Do I need to do stretch & folds during bulk?

Yes! Your stretch and folds help to strengthen the gluten in your dough, equalizes the temperature of your dough and gives you a chance to check on how your dough is progressing. I like to do 3 sets of stretch and folds every 30 minutes in the beginning and then do a couple folds every hour or two through the rest of bulk fermentation.

Should I cover the dough during bulk fermentation?

Yes! Covering your dough helps to prevent the surface from forming a dry skin. Cover with a lid, plastic wrap, a damp cloth, whatever keeps the dough surface from drying out.

What about cold bulk fermentation – can I do that?

Yes — cold bulk is a technique where the dough is fermented at cooler temps (in the fridge) to slow activity and develop flavor. It’s a great way to be able to make sourdough fit into your busy schedule. The fridge helps to pause the fermentation process and gives you flexibility in when you’re ready to bake your bread.

Why is my dough so sticky?

Possible causes: over-hydration (too much water for your flour); under-mixed; not enough gluten development; dough is over fermented and starting to breakdown.

How does hydration affect bulk fermentation?

Higher hydration tends to ferment more quickly (more free water allows yeast/bacteria to move more freely) but handling becomes trickier (stickier dough). Lower hydration ferments more slowly but is easier to shape.

What temperature should my dough be during bulk fermentation?

As a guideline: dough in the 74-78F is a good target for many home sourdoughs. Warmer than 80F speeds things up; cooler than 70F really slows things down.

What if my kitchen is very warm?

Then bulk will proceed faster — keep a closer eye on it, maybe reduce total bulk time, maybe aim for somewhat less volume rise if you’ll shape and proof in the fridge later (so you don’t over-ferment before shaping). You can also mix your dough with ice cold water to slow down fermentation a little bit.

What if my kitchen is really cold?

Then bulk will be much slower. Try to use warm water when mixing and keep your dough in a cozy corner of your kitchen. Find a warm spot, like on top of the fridge, in the microwave or on a heating pad to help keep bulk fermentation moving. If you can’t warm up your dough, be prepared for a really long (12-18 hour) bulk fermentation.

After bulk fermentation what the next step?

Once you determine bulk is done, you’ll want to preshape, bench rest, final shape, cold ferment, and bake.

Understanding the Crumb: Overproofed vs. Underproofed vs. Well-Proofed Loaves

Once you’ve shaped and baked your bread, your crumb tells the story of what happened during bulk fermentation. It’s like reading the dough’s diary — every air pocket, tear, and dense spot has a reason.

Let’s break down what to look for so you can connect the dots between how your dough behaved during bulk fermentation and what you see inside your finished loaf.

The photos above show three loaves of bread. All were mixed at the same time and baked at the same time, for the same amount of time. But, I manipulated the speed of fermentation by changing the dough temperature while they were proofing, so one over proofed, one under proofed and one was well proofed. Can you spot the difference? If so, you’re a pro all ready. If not, keep reading and we’ll talk through reading the crumb.

Under Proofed Loaf — The Dough Needed More Time

If you slice into your loaf and see a tight, dense crumb with small, uneven holes, especially near the bottom, it usually means your dough was underproofed.

What you’ll notice:

• The loaf might burst open dramatically at the score line or even crack along the sides — that’s trapped gas expanding quickly in the oven because the dough wasn’t stretchy or airy enough yet.
• The crumb often looks patchy — a few big random holes surrounded by dense, gummy areas.
• The loaf may feel dense and heavy and the crumb isn’t very soft. It might also have a bit of a gummy/wet texture.
• The crust may be thick and tough rather than thin and crisp.
• The loaf bakes up more pale. Under proofed loaves often bake up pale because the dough hasn’t fermented long enough for enzymes to break down starches into simple sugars — the ones responsible for caramelization and that golden crust. The tight, dense dough also traps moisture, which cools the surface and prevents full browning (and also sometimes causes a gummy texture on the inside).

What happened:
Your dough didn’t ferment long enough for the yeast and bacteria to create enough gas or acidity. The gluten didn’t have time to relax and expand properly, so you ended up with an aggressive, uneven oven spring.

How to fix it next time:

• Give your dough a little more time in bulk. Watch for those tell-tale signs: more bubbles, smoother surface, slight jiggle when you shake the bowl.
• Check your dough temperature — if it’s cooler than 74F, it may simply need more time.

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Over Proofed Loaf — The Dough Went Too Far

An over proofed loaf can look deceptively beautiful before baking — big, puffy, full of air — but then collapse in the oven or bake up flat.

What you’ll notice:

• A flatter loaf with minimal oven spring – possibly resembling a UFO.
• The crumb feels fragile and web-like — big irregular holes at the top, compressed dense areas at the bottom.
• The crust might be pale and dull because sugars were already consumed during fermentation. (You’ll notice this more with really over proofed loaves, not slightly over proofed loaves.)

What happened:
Your dough fermented too long — either your kitchen was warm, or the dough sat out beyond its peak. The gluten network weakened, meaning it couldn’t trap gas anymore. When it hit the oven, it deflated and spread instead of rising.

How to fix it next time:

• Shorten your bulk fermentation slightly, especially in warm weather.
• Use your eyes and hands instead of the clock — if the dough looks super jiggly and sticky, or feels loose and hard to shape, it’s likely gone too far.
• Try a slightly cooler bulk temp (or refrigerate partway through).

Well-Proofed Loaf — Just Right

This is what you’re aiming for! A well-proofed loaf will have a light, open crumb — not too tight, not too wild — with even distribution of air pockets throughout.

What you’ll notice:

• A balanced, consistent crumb with small to medium holes all over.
• The crust opens beautifully along your score line, showing confident oven spring.
• The loaf feels light for its size and the texture is tender but strong — you can slice it without it tearing or crumbling.

What happened:
Your dough reached that sweet spot: strong gluten network, good gas retention, and perfect balance of yeast activity and acidity. The bulk fermentation ended at its peak — before the gluten began to weaken.

How to repeat it:

• Note your dough temperature, room conditions, and how long it took to reach that state.
• Keep track of the look and feel: smooth, bubbly, airy, and still holding shape.
• Take a quick photo or video of your dough before shaping — this makes a great teaching moment for future bakes.

A Simple Way to Remember

Underproofed: tight crumb, explosive oven spring.
Overproofed: flat loaf, weak crumb.
Well-proofed: balanced rise, open and even texture.

Your crumb is your best teacher — and once you’ve connected how it looks inside with how the dough felt before baking, you’ll start trusting your instincts instead of the clock.