Sourdough Bulk Fermentation: A Beginner's Guide to the First Rise

Bulk fermentation is where sourdough either succeeds or falls apart. Here is exactly what it is, how to time it, and how to know when it is done. No guesswork required.

If you have ever pulled a sourdough loaf out of the oven and wondered why it came out dense, gummy, or flat, bulk fermentation is almost always the answer.

It is the most important step in sourdough bread baking. It is also the most misunderstood. Most beginner recipes tell you to let your dough rise for a certain number of hours. The problem is that time alone is not the right measure. Your dough does not know what time it is. It knows temperature.

This post breaks it all down simply. What bulk fermentation actually is, why temperature matters more than time, how to track your rise, and how to know when your bulk ferment is done. There is also a free reference chart at the end to keep on your counter.

What is bulk fermentation?

Bulk fermentation, also called the first rise, first proof, or bulk rise, is the period between when you add your starter to the dough and when you shape it.

During this stage, the wild yeast in your starter eats the sugars in the flour and produces carbon dioxide gas. That gas gets trapped in the gluten network you built during mixing. The dough rises, develops flavour, and builds the structure that will carry it through shaping, cold proofing, and the oven.

This is also when lactic acid bacteria are producing the organic acids that give sourdough its signature tang and improved digestibility. The bulk ferment is not just a waiting game. A lot is happening in that bowl.

Why temperature matters more than time

Here is the thing most beginner sourdough recipes get wrong. They give you a time range like "bulk ferment for 4 to 6 hours" without telling you that this number is only accurate at a very specific dough temperature.

Yeast is sensitive to heat. Warm dough ferments fast. Cool dough ferments slowly. A dough sitting at 80F in a warm summer kitchen could be ready in 5 hours. That same dough in a 68F Canadian kitchen in February might need 14 hours.

If you follow the time and ignore the temperature, you will undershoot in winter and overshoot in summer. Every single time.

The fix is simple. Use a probe thermometer. Take your dough temperature right after mixing. That number tells you what ballpark you are in and how long your bulk is likely to take. Then track your rise percentage and read the dough. Not the clock.

This is especially relevant if you are baking with our Better Bread Flour. Our 100% stone-milled flour is alive in a way that industrially processed flour is not. The naturally occurring enzymes are active and intact, which means fermentation is genuine. It responds to temperature just as it should.

How to measure your dough temperature

You need a probe or instant-read thermometer. Insert it into the centre of the dough right after mixing, before your first stretch and fold. That reading is your starting dough temperature and your anchor for the whole bulk window.

A few things that affect dough temperature:

• Water temperature is the easiest lever. Warmer water raises dough temp, cooler water lowers it.
• Cold flour straight from a cool pantry will bring dough temp down.
• The room temperature matters but dough temperature is what you are actually working with.
• Friction from mixing adds a small amount of heat.

The sweet spot for most sourdough recipes, including our basic sourdough, is a dough temperature between 72F and 76F. That gives you a reliable 7 to 10 hour bulk window that fits into a normal day.

How to track your bulk rise percentage

Percentage rise is the most reliable way to know when bulk fermentation is done. More reliable than time, more reliable than visual guessing.

Here is how to do it. After mixing, transfer your dough to a straight-sided container. A large mason jar or a clear dough bucket works perfectly. Mark the top of the dough with a rubber band or a piece of tape. That is your starting point.

As bulk fermentation progresses, you watch the dough rise against that mark. If the dough started at 1000g of volume and it is now at 1650g of volume, that is a 65% rise. Simple math.

Most sourdough recipes are calibrated for a 50 to 75% rise. Not double. Not triple. The exact target depends on your dough temperature. Cooler doughs need a higher rise percentage. Warmer doughs need a lower one. The reference chart below shows the targets for every temperature range.

How to know when bulk fermentation is done

You are looking for all of these signs together, not just one of them.

• The dough has reached your target rise percentage for its temperature
• The surface is slightly domed. Not flat, not collapsing
• You can see bubbles on the sides and top of the dough
• The dough jiggles as a single mass when you shake the container
• A wet finger poke springs back slowly. Not snapping back immediately, not leaving a permanent dent
• The dough feels lighter and more airy than when you started

If your dough passes all of these checks, it is ready to shape. If it is only hitting one or two, give it more time and check again in 30 minutes.

What happens if you get it wrong

Underproofed dough has not fermented long enough. The yeast has not produced enough gas, the gluten is still tight, and the loaf will not have enough oven spring. The crumb will be dense and chewy, sometimes with a gummy layer near the base.

Overproofed dough has gone too far. The gluten structure has started to break down from the acids in the dough. It will feel slack and sticky. It will spread during shaping and not hold its form. In the oven it bakes flat with a dense, sometimes gummy crumb.

The good news is that both problems are fixable. Every bake tells you something. If you got a dense crumb, extend your bulk slightly next time. If it spread and baked flat, shorten it. Small adjustments add up fast.

Our Better Bread Flour and Dehydrated Sourdough Starter are a reliable combination for this process. Consistent flour means consistent fermentation, which makes it much easier to dial in your timing bake over bake.

Your bulk fermentation reference chart

We built a full bulk fermentation temperature and rise chart using our Better Bread Flour as the base. It shows the approximate bulk fermentation time and target rise percentage for every dough temperature from 65F to 80F.

The chart is embedded below. You can also download it as a printable PDF to keep on your counter.

A few things to note when using this chart. These times are based on 100% Better Bread Flour at 70 to 75% hydration with 20% starter. If you are using a higher hydration dough or a very strong starter, fermentation may move faster. These are guidelines. Always finish with the dough, not the number.

A note on cold proof

After bulk fermentation and shaping, most sourdough recipes call for a cold proof. This is an overnight rest in the fridge before baking. It is not a second bulk ferment. It is a slow, final proof that develops flavour and makes scoring and oven spring more reliable.

Here is something worth knowing if you are baking with our Better Bread Flour. Because our flour is stone-milled and nothing is stripped out, the enzymes are fully intact. Once the dough cools to fridge temperature, the yeast goes nearly dormant. But the enzymes in a whole grain flour like ours keep working slowly. That ongoing enzyme activity affects the texture and flavour of the finished loaf in a way you do not get from a processed flour where much of that has been removed.

I personally do a 12 hour cold proof. That is my sweet spot with our flour. It gives me great flavour development without pushing the dough too far. You can go to 16 hours but I would not push past that. Watch your dough the first few times you try it. It should hold its shape in the banneton and look slightly puffed. If it looks overly jiggly or has spread, it went too long.

The cold proof is one of the reasons sourdough fits so well into a real life routine. Mix and bulk on day one. Shape and refrigerate before bed. Bake first thing in the morning.

Real flour. Real fermentation. Real food, the way it was always meant to be made.