Why Sourdough Needs Both a Bulk Ferment and a Cold Proof

If you’re new to sourdough baking, you’ve probably heard terms like bulk ferment and cold proof tossed around a lot—and maybe you’re wondering: Why do we do both? Can’t I just let my dough rise and bake it right away? If you’ve ever wondered why we let dough rise on the counter and rest in the fridge, this is for you:

🌀 Bulk ferment = strength + structure
❄️ Cold proof = flavor + flexibility + perfect scoring

Together, they give you the open crumb, rich flavor, and crusty golden loaf we all love.

What Is Bulk Fermentation?

Bulk fermentation (also called the bulk proof) is the first major rise your dough goes through after mixing. It usually takes place at room temperature on your counter. During this phase, the wild yeast and beneficial bacteria in your sourdough starter get to work. The yeast eats the natural sugars in the flour, producing gas that creates rise and airiness in your dough. Meanwhile, the bacteria help develop the dough’s structure and deepen its flavor.

This is also when we build strength in the dough through a series of stretch and folds. Each fold helps align the gluten strands and build tension so the dough can hold its shape later on. You’ll notice the dough becoming smoother, puffier, and more elastic as the bulk ferment progresses.

Why Do We Cold Proof?

After shaping your dough, it goes into the fridge for the cold proof (also known as retardation). This stage is slower, gentler, and just as important. Cold temperatures dramatically slow down fermentation, allowing time for more complex flavors to develop without over-proofing your dough.

There are a few reasons we love the cold proof:

1. Flavor: Longer fermentation leads to more lactic and acetic acid production—this is what gives sourdough its depth of flavor and signature tang.

2. Handling: Cold dough is firmer, which makes it much easier to score. You’ll get those clean, confident cuts that give your loaf a beautiful “ear” and controlled oven spring.

3. Flexibility: Life is busy! Cold proofing lets you control when you bake. You can leave your dough in the fridge overnight or even up to 36 hours depending on your recipe and fridge temp.

The Two-Stage Fermentation Is Key

Both the bulk ferment and cold proof play essential roles. The bulk ferment builds strength, rise, and structure. The cold proof develops flavor, improves texture, and makes baking more convenient.

Skipping one or the other will affect your results. So if you want a loaf with an open crumb, chewy crust, rich flavor, and beautiful rise—trust the process. You can't rush sourdough.

Want more sourdough tips? Browse our blog or follow us on Instagram @summitsourdoughyeg for step-by-step videos and recipes.