Fermentation & Timing: The Heart of Great Sourdough
If sourdough baking has a secret, it lies in fermentation. This invisible transformation is where flour and water become something magical, where wild yeast and bacteria work together to create flavour, texture, and rise. Master fermentation, and you master sourdough.
What Actually Happens During Fermentation
When you mix flour, water, salt, and your sourdough starter, you set in motion one of nature's most fascinating processes. The wild yeast in your starter begins consuming the sugars in the flour, producing carbon dioxide gas and alcohol. Simultaneously, lactic acid bacteria are hard at work, creating the organic acids that give sourdough its characteristic tang.
This isn't just about making dough rise. During fermentation, enzymes break down complex starches into simpler sugars, proteins unfold and reorganise to strengthen gluten structure, and hundreds of flavour compounds develop. A loaf that ferments for twelve hours will taste fundamentally different from one that ferments for four, even if they use identical ingredients.
The challenge, and the art, lies in guiding this process. Fermentation is affected by temperature, hydration, flour type, starter strength, and ambient conditions. There's no single right answer to “how long should I ferment my dough?” Instead, you must learn to read your dough and understand what it's telling you.
Yeast Activity
Wild yeast produces CO2 for rise and alcohol for flavour. Activity increases with warmth, peaking around 26-28°C. Below 4°C, yeast goes dormant.
Bacterial Action
Lactic acid bacteria create acids that strengthen gluten, improve keeping quality, and develop complex flavours. They work even in cold temperatures.
Bulk Fermentation: The First Rise
Bulk fermentation, sometimes called the first rise, is arguably the most critical phase of bread making. This is when your dough develops most of its flavour and structure. Get it right, and everything else becomes easier. Rush it or let it go too long, and you'll struggle to recover.
The name “bulk” refers to the fact that all the dough ferments together before being divided and shaped. During this time, you'll typically perform a series of stretch and folds, which develop gluten structure and redistribute the yeast and bacteria throughout the dough. These folds also help equalise temperature and incorporate air.
A typical bulk fermentation at room temperature (around 21-24°C) lasts between 4-6 hours, though this varies enormously based on your conditions. In a warm Australian summer kitchen, it might take just 3 hours. In a cool winter environment, 8 hours or more. The key is learning to read the signs rather than watching the clock.
Signs Your Bulk Fermentation is Complete
Volume Increase
The dough should increase by 50-75% in volume. Not double—that's too far for most sourdoughs. Use a straight-sided container with markings to track growth accurately.
Domed Surface
The top of the dough should be slightly domed and puffy, with visible bubbles just beneath the surface. If it's flat or starting to collapse, you've gone too far.
Jiggly Texture
When you gently shake the container, properly fermented dough moves as one mass with a slight jiggle, like a soft pillow. It should feel airy but cohesive.
Windowpane Test
A small piece of dough should stretch thin enough to see light through without tearing. This indicates proper gluten development, which fermentation helps achieve.
Pro Tip: The Aliquot Jar
When mixing your dough, set aside a small piece in a tall, narrow jar with straight sides. Mark the starting level with a rubber band. This “aliquot jar” lets you track fermentation progress precisely without disturbing your main dough.
Temperature: Your Most Powerful Tool
If there's one variable that has the greatest impact on fermentation timing, it's temperature. Understanding this relationship gives you enormous control over your baking schedule. Warmer temperatures accelerate fermentation exponentially; cooler temperatures slow it down, but also change the character of the fermentation itself.
At warmer temperatures (26-28°C), yeast activity dominates. You'll get faster rise but less complex flavour development. The bread will be milder, with less tang. At cooler temperatures (4-10°C), bacterial activity continues while yeast slows dramatically. This is why cold retardation produces more flavourful bread—the bacteria have time to create organic acids without the yeast exhausting all the available sugars.
Most home bakers find success with a combination approach: bulk fermentation at room temperature to get the structure right, followed by cold proofing in the refrigerator to develop flavour and make scheduling easier. This flexibility is one of sourdough's great advantages over commercial yeast breads.
| Temperature | Bulk Fermentation | Character |
|---|---|---|
| Cold (4-8°C) | 24-72 hours | Deep, complex, tangy |
| Cool (15-18°C) | 8-12 hours | Balanced, nuanced |
| Room (21-24°C) | 4-6 hours | Mild, wheaty |
| Warm (26-28°C) | 2-4 hours | Quick, mild, less complex |
Final Proofing: The Last Rise
After shaping, your dough enters its final proof. This stage has a different purpose than bulk fermentation. While bulk was about building structure and developing flavour, final proofing is about letting the dough relax and accumulate just enough gas to create oven spring. Shape well, proof carefully, and you'll be rewarded with beautiful, open-crumbed bread.
Most bakers choose between room temperature proofing (1-2 hours) and cold retarding in the refrigerator (8-16 hours, or even longer). Cold retardation has become increasingly popular, and for good reason. Besides the flavour benefits, it makes scheduling easier—you can shape your bread in the evening and bake fresh in the morning. Cold dough is also easier to score, as it holds its shape better under the blade.
The poke test is your friend here. Press a floured finger into the dough about 1cm deep. If the indent springs back quickly, the dough needs more time. If it springs back slowly and incompletely, leaving a slight depression, your dough is ready to bake. If the indent stays completely, you've overproofed—the dough has run out of energy for oven spring.
Room Temperature Proof
- Quick: 1-2 hours typical
- Same-day baking
- Lighter, milder flavour
- Requires closer attention
Cold Retard (Fridge)
- Slow: 8-16+ hours
- Flexible scheduling
- Deeper, more complex flavour
- Easier to score (cold dough)
Common Fermentation Mistakes
Overproofing
The most common mistake. Overproofed dough has exhausted its available sugars and lost structural integrity. Signs include a flat or collapsed appearance, very slack texture, and an overly sour smell. The resulting bread will be dense with poor oven spring and may collapse in the oven.
Fix: Start checking earlier. Use an aliquot jar for precision. In warm weather, consider refrigerating sooner.
Underproofing
Underproofed dough hasn't had enough time to develop flavour or accumulate sufficient gas. The bread will have a tight, gummy crumb, may burst unpredictably in the oven, and taste bland or yeasty. The crust often tears rather than opening cleanly at the score.
Fix: Be patient. If your environment is cool, find a warmer spot or extend fermentation time. Trust the poke test over the clock.
Inconsistent Temperature
Temperature fluctuations make timing unpredictable. A kitchen that's 22°C in the morning might be 26°C by afternoon with the oven on. These swings cause uneven fermentation and make it hard to develop reliable instincts.
Fix: Find a stable spot. Many bakers use their oven with just the light on, a microwave as an enclosed space, or even a cooler with warm water bottles for temperature control.
Sample Baking Schedules
Weekend Morning Bake
Perfect for fresh bread on a Saturday or Sunday morning.
Weeknight Bake
For fresh bread on a weeknight, start the night before.
Ready to Perfect Your Timing?
The right equipment makes consistent results easier. A reliable thermometer and proofing containers will help you master fermentation.
Shop Fermentation Tools