Of all the steps in sourdough baking, bulk fermentation is arguably the most critical—and the most misunderstood. It’s the period of time after you mix your dough and before you shape it. During this time, the wild yeast and bacteria in your starter are multiplying, fermenting the sugars in the flour, and filling the dough with gas.

Why You Can’t Trust the Clock

Many recipes will say “bulk ferment for 4 hours,” but the clock is the least reliable indicator of dough readiness. Fermentation speed depends entirely on dough temperature, room temperature, starter strength, and hydration. A dough that takes 4 hours at 26°C (79°F) might take 8 hours at 20°C (68°F).

Signs Your Dough is Ready

Instead of watching the clock, watch your dough. Here are the true signs that your bulk fermentation is complete:

1. Volume Increase

Your dough should have increased in volume by about 30% to 50%. Using a straight-sided, clear container (like a cambro or glass bowl) makes it much easier to track this volume increase than using a sloped bowl.

2. The Jiggle Test

Give your bowl a gentle shake. If the dough is fully fermented, it will wiggle and jiggle like a bowl of jelly. It should feel light, airy, and aerated, not dense and heavy.

3. Bubbles and Webbing

Look at the sides and bottom of your clear container. You should see a network of small and large bubbles trapped against the glass. If you gently pull the dough away from the side of the bowl, you should see a web-like structure of gluten strands.

4. Domed Edges

A well-fermented dough will show strength. Instead of sitting completely flat against the sides of the bowl, the edges of the dough will pull away slightly and form a subtle dome shape.

Mastering the bulk fermentation is the true turning point in any sourdough baker’s journey. Once you learn to read the dough rather than the recipe, you’ll find your bread is lighter, more open, and far more consistent.

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Shop the Tools for Sourdough Baking

Sourdough baking is a labor of love, but having the right tools makes all the difference. To master fermentation, you need control and observation:

• Bread Proofer: The ultimate tool for taking the guesswork out of fermentation times. Buy my recommended bread proofer here.
• Glass Jar: Perfect for monitoring your starter’s fermentation before you even begin the dough. Get the Kilner Round clip jar I use here.
• Kitchen Scale: Accurate flour and water ratios directly dictate how your dough ferments. Get our recommend kitchen scales.
• Dough Scraper: Essential for checking the tension and removing your perfectly fermented dough from its container. Get your dough scraper today.

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