Sourdough Hydration and Dough Temperature: The Complete Guide

Two numbers decide whether your sourdough schedule works: hydration (how much water against flour) and dough temperature (how fast the culture will run). Both are simple once you see the math - and both have a classic trap involving the starter. The calculators handle the arithmetic: the hydration calculator, the starter feeding calculator, the dough temperature calculator and the flour protein blender.

Hydration: total water over total flour

Baker's percentage sets flour at 100% and expresses everything else against it. Hydration is therefore:

The trap is the word total. A starter fed at 100% hydration is exactly half flour and half water. If your recipe says "500 g flour, 350 g water, 100 g starter", the real totals are 550 g flour and 400 g water - a 72.7% dough, not the 70% the numbers suggest. At 200 g of starter the drift is worth 5 hydration points, which is the difference between dough you can shape and dough that owns your counter. The hydration calculator splits the starter automatically and can also solve in reverse: give it a target and it returns the exact water to add.

What hydration actually does

Flour quality bounds what you can use: higher protein absorbs more water, fresh flour absorbs less than tired flour, and rye absorbs plenty but sets into a different structure entirely. Numbers start the recipe; dough feel finishes it.

Dough temperature: the throttle of fermentation

Fermentation speed is driven by temperature. The classic bakery formula targets a desired dough temperature (DDT) by adjusting only the water, since it is the one ingredient you can practically heat or chill:

Each factor contributes roughly a quarter of the final dough temperature. For a 24°C DDT with flour at 20°C in a 21°C room, the water lands at 55°C - warm but far from hot. The friction factor stands in for mixer heat: 0 for no-knead, 1-3 for stand mixers. The dough temperature calculator runs the formula in C or F and shows what the water temperature should be for your numbers.

How temperature reshapes bulk fermentation

In the practical sourdough range, fermentation activity roughly doubles every 5°C. That means the same dough that bulk-ferments in 4 hours at 25°C needs about 8 hours at 20°C and 16 hours at 15°C. Sourdough authors such as The Sourdough Journey publish empirical bulk curves that match this pattern well. The practical consequences:

• Read recipes as temperature-tagged. "4-hour bulk" means 4 hours at whatever temperature the author used - usually 24-26°C.
• Warm kitchens need shorter bulk or colder water. The DDT formula is the steering wheel.
• Cold retard is a schedule tool, not a fermentation stop. Activity slows drastically but does not stop.

These are planning heuristics: watch volume growth (typically 50-75% for a side-by-side bulk) and the jiggle of the dough, not the clock.

Protein: the strength budget

Protein percentage predicts gluten potential. Blending is simple weight math: to hit 11.5% from a 12% bread flour and a 10% all-purpose, three quarters of the blend is bread flour. The protein blender does the split for any two flours, and reads protein straight off nutrition labels (grams per 100 g).

Common mistakes

• Ignoring the starter's flour and water - the most common hydration error, worth several percentage points.
• Feeding on autopilot at 1:1:1 when the bake schedule needs a 1:4:4 or 1:5:5. Ratios are timing tools.
• Mixing by temperature without measuring the flour. Flour straight from a cold pantry drags the dough down more than people expect.
• Trusting the clock over the dough. Every number in this guide is a starting point for observation.

Frequently asked questions