How Temperature Really Affects Your Sourdough Fermentation

For years I baked sourdough without giving temperature the respect it deserved. In summer everything behaved beautifully. My dough rose on schedule, fermentation was predictable, and every loaf felt almost effortless. Then autumn arrived, winter followed, and suddenly my results were completely inconsistent. Same recipe, same timings, same technique, yet the dough moved at a totally different pace. Some days it crawled. Other days it seemed to stall entirely. It took me longer than I would like to admit to realise that temperature was quietly sabotaging me.

This seasonal shift is what finally pushed me to build the calculator on this page. I wanted to understand exactly how temperature affects fermentation speed and how much difference a few degrees can make. Once I began tracking dough temperature rather than relying on room temperature alone, everything clicked. My winter doughs, once painfully slow, became predictable again. My summer doughs stopped racing ahead when I did not want them to. Temperature was the invisible ingredient I had been missing.

Why Internal Dough Temperature Matters

Room temperature only tells part of the story. What matters most is the internal temperature of the dough itself. Dough can be cooler than the room if your flour and starter are cold, or warmer if you have used warm water or mixed vigorously. Once I started taking internal readings with an instant-read thermometer, my baking became dramatically more predictable. Suddenly I understood why the dough behaved differently from one bake to the next.

Internal dough temperature shapes the relative speed of yeast and bacteria. Yeast activity increases sharply as dough warms, creating gas and lift. Bacteria respond differently, producing acids that alter flavour and gluten structure. Your dough is most balanced between 24°C and 27°C (75–80°F). Below this, fermentation becomes slower and more forgiving. Above it, fermentation accelerates and can become harder to control.

Optimal Temperature Ranges

Professional bakers and serious hobbyists often target a dough temperature between 24°C and 27°C after mixing. This creates an ideal pace of fermentation, allowing gluten to strengthen and flavour to develop without racing ahead or lagging behind. Too cool and you wait all day. Too warm and the dough sprints toward its peak before it has developed structure.

Cold Dough

Cool dough around 18°C (64°F) ferments slowly, which can be helpful for flavour but unpredictable if you are not expecting it. I’ve made early-winter loaves that spent nearly two extra hours in bulk simply because the temperature dipped a few degrees. The dough eventually reached peak fermentation, but patience and gentle handling were essential.

How Room Temperature Influences Fermentation Over Time

Even if your dough begins at a higher temperature, such as 25°C when mixed with warm water, it will gradually move toward the surrounding room temperature during bulk fermentation. This means that a dough mixed warm but fermented in an 18°C kitchen will slow down as it cools. The early part of the bulk may move quickly, but the overall fermentation will settle into a slower, steadier pace.

Cooler environments lead to dough that is firmer, tighter, and slower to aerate. This does not mean the dough will fail to become fluffy, only that it will take longer for gas to accumulate and gluten to relax. The flavour profile also shifts, with longer cool ferments developing deeper and sometimes more complex acidity. Understanding this temperature drift helps you adjust expectations, timing, and handling throughout the process.

While 24–27°C dough produces fast, open-crumb loaves with dramatic rise, an 18°C dough offers consistency, flavour development, and a wider margin for timing errors. Recognising how dough cools or warms over time allows you to respond to its behaviour rather than relying solely on fixed schedules.

When Should You Take the Dough Temperature?

For the most accurate fermentation prediction, take the dough temperature immediately after mixing, once the flour, water, starter, and salt have fully come together. This reading reflects the true starting point of fermentation and is the number you should enter into the calculator.

You can also take additional readings during bulk fermentation to understand how quickly your dough cools or warms in your kitchen. A dough that starts at 25°C but cools to 20°C within an hour will ferment very differently from one that stays warm. Tracking this occasionally helps you develop intuition, but the calculator should always use the initial post-mix temperature.

Warm Dough

Warm dough at 26°C (79°F) or more can feel almost alive in your hands. It rises quickly, builds bubbles rapidly, and requires closer attention. One summer batch nearly doubled before I had finished my coffee. Using cooler water and fermenting in the lower part of the kitchen brought things back under control.

Measuring Internal Dough Temperature

An instant-read thermometer is one of the simplest tools that make a profound difference. Insert the probe into the centre of the dough right after mixing to determine your starting point. This number tells you how quickly fermentation will proceed. It also helps you adjust water temperature for the next bake: warm water for winter, cool water for summer.

How Temperature Feeds Into the Calculator

Your calculator uses internal dough temperature to estimate fermentation speed, adjusting the reference timing based on hydration, salt percentage, and inoculation. Higher hydration accelerates fermentation. Higher salt slows it down. More starter reduces bulk fermentation time, while less starter lengthens it. These adjustments create a dynamic prediction model far more accurate than any fixed-time recipe.

The Human Side of Fermentation

After years of baking, I’ve learned that dough teaches you as much as you teach it. You develop a feel for when the dough is relaxing, rising, strengthening, or slowing down. Temperature helps decode these signals. A dough at 22°C tells you to settle in for a long, flavourful bulk. A dough at 26°C urges you to stay nearby. A dough that feels cool, slightly resistant, and slow to rise behaves differently from one that feels warm, airy, and eager. These subtleties are what transform sourdough baking from a recipe-driven activity into a craft.

Controlling Dough Temperature

Fortunately, temperature is something you can influence. In winter, you can warm your water, use slightly warmer ingredients, or ferment the dough near a safe warm spot. In summer, you can reduce water temperature, choose a cooler area of the house, or retard part of the bulk in the fridge. Small adjustments make large differences in timing and flavour.

Summary

Temperature is the quiet force behind every successful sourdough loaf. By learning to measure internal dough temperature, adjust for seasonal shifts, and understand the behaviour of your dough, you unlock a new level of consistency and flavour. The more you notice and respond to temperature, the more your baking evolves from guesswork into intuition and skill.

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