01 — Foundation
Why Temperature Controls Everything
Of all the variables in sourdough baking, temperature has the most dramatic effect on fermentation speed. A dough that takes 10 hours to bulk ferment in a 68°F kitchen can be ready in under 4 hours at 80°F. Miss that window in either direction, and you’re looking at underproofed or overproofed bread.
The wild yeast and lactic acid bacteria in your starter are living organisms — they thrive in warmth and slow dramatically in cold. Understanding this relationship lets you stop guessing and start baking with precision. It’s the single biggest unlock for consistent results at home.
The Golden Rule
Always go by dough behavior, not the clock. Time charts are guides, not guarantees — your flour, starter activity, and ambient humidity all affect fermentation speed. The chart below assumes a moderately active starter (peak in 4–6 hours) and 75% hydration white dough.
02 — The Chart
Sourdough Proofing Time Chart by Temperature
This is the reference chart you’ll want to bookmark. It covers the full range from cold retard to warm summer kitchens, with both bulk fermentation and final proof windows at each temperature range.
| Temperature |
Bulk Fermentation |
Final Proof |
Fermentation Speed |
Notes |
| 38–40°F / 3–4°C |
Not recommended |
8–16 hours |
|
Fridge only — cold retard for final proof |
| 55–60°F / 13–16°C |
16–24 hours |
6–10 hours |
|
Cool pantry / garage in winter. Great flavor development. |
| 63–66°F / 17–19°C |
10–14 hours |
4–7 hours |
|
UK / European kitchen in winter. Reliable overnight bulk. |
| 68–70°F / 20–21°C |
7–10 hours |
3–5 hours |
|
Most comfortable indoor temperature. Easy to manage. |
| 72–75°F / 22–24°C |
5–7 hours |
2–3.5 hours |
|
Ideal range. Predictable, forgiving, excellent results. |
| 76–80°F / 24–27°C |
4–6 hours |
1.5–2.5 hours |
|
Watch dough closely. Easy to over-ferment in summer. |
| 81–85°F / 27–30°C |
3–4.5 hours |
1–2 hours |
|
High risk of overproofing. Use cold water, refrigerate promptly. |
How to Use This Chart
Measure your kitchen temperature with a thermometer (not your thermostat — actual air temp near your dough). Find your range in the chart, then use the bulk fermentation window as your starting estimate. Check dough behavior at the early end of the window: look for 50–75% volume increase, jiggly and domed surface, and bubbles around the edges.
03 — Bulk vs. Final Proof
Bulk Fermentation vs. Final Proof: What’s the Difference?
These are two distinct fermentation stages with different goals, different timings, and different signs of completion. Confusing them is one of the most common reasons bakers end up with dense or flat loaves.
Stage 01
Bulk Fermentation
The first and longest fermentation stage. It begins the moment you mix your starter into your dough and ends when you shape. During bulk, yeast produces CO₂ that inflates the dough, while bacteria produce acids that build flavor.
The goal is for the dough to increase 50–75% in volume, develop structure through stretch-and-fold sets, and become airy, jiggly, and slightly domed at the surface.
At 74°F: 5–7 hours · At 68°F: 7–10 hours
Stage 02
Final Proof
The second fermentation after shaping, typically in a banneton or loaf pan. The dough rebuilds tension after shaping and continues to ferment at a gentler pace. A successful final proof gives good oven spring and an open crumb.
The goal is a dough that passes the poke test — springs back slowly when pressed with a floured finger, not immediately (underproofed) or not at all (overproofed).
Room temp: 2–4 hours · Cold retard: 8–16 hours
The Poke Test: Your Best Friend
The poke test works during final proof: lightly flour your finger and press about ½ inch into the shaped dough. If it springs back immediately — it needs more time. If it springs back slowly and almost fully — it’s ready to bake. If it doesn’t spring back at all — it’s overproofed.
“Fermentation is a feeling, not a formula. Learn to read your dough, and the clock becomes just a reference.”
04 — Slowing Things Down
How to Slow Fermentation When Life Gets in the Way
One of the great advantages of sourdough over commercial yeast is how controllable the timing is. Cold slows fermentation dramatically — you can essentially pause and resume your bake to fit your schedule.
01
Cold Bulk Fermentation (Overnight Bulk)
After 2–3 hours of room temperature bulk and your stretch-and-fold sets, cover the dough tightly and place it in the fridge (38–40°F). It will continue fermenting slowly overnight. In the morning, remove it, check for the 50–75% rise, shape, and bake directly from cold or after a 30-minute warm-up.
02
Cold Final Proof (Cold Retard) — Recommended
The most popular method for home bakers. Shape your dough after room-temp bulk, place it in a banneton, cover with a plastic bag, and refrigerate overnight (8–16 hours). Cold retard firms up the dough for easier scoring, builds a thicker crust, and develops more complex sour flavor. Bake directly from the fridge.
03
Use Cold Water During Mixing
On warm days, use cold or even ice water when mixing to lower your dough temperature. This buys you 30–60 minutes of extra working time before fermentation accelerates.
04
Reduce Your Starter Percentage
Using 15–20% starter gives faster fermentation; dropping to 8–10% slows it down considerably. This is a useful lever when you want longer overnight fermentation at room temperature without refrigeration.
Never Guess Your Timing Again
The Sourdough Archive Course walks you through reading dough at every stage — bulk, shaping, and final proof.
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05 — The Fridge
How the Refrigerator Changes Your Sourdough
Cold Retard Reference
Refrigerator Proofing at 38–40°F (3–4°C)
At fridge temperature, yeast activity slows to a crawl. Bacteria remain slightly more active, continuing to produce acidity and flavor compounds. This imbalance is what makes cold-proofed loaves taste more complex and develop a thicker crust.
8–16hOptimal Window
24–36hMax Cold Retard
0minWarm-up Needed
There’s a persistent belief that you need to warm your dough up before baking after a cold retard. You don’t. Baking cold dough is firmer and easier to score cleanly, and the thermal contrast creates better oven spring.
❄ Can You Over-Retard in the Fridge?
Yes. Beyond 24–36 hours, continued bacterial activity can lead to over-acidification and a weakened gluten structure. For most home bakers, 8–16 hours is the sweet spot.
06 — Hot Kitchen Adjustments
Warm Kitchen? Here’s How to Adjust
Summer baking is a different game. When your kitchen climbs above 78–80°F, fermentation moves fast — sometimes dangerously fast.
⚠ Hot Kitchen Warning
Above 82°F (28°C), fermentation can outpace your ability to shape and score. Your bulk fermentation window shrinks to 3–4 hours and the final proof to 1–1.5 hours.
| Problem |
Cause |
Fix |
| Bulk finishes too fast |
Kitchen above 78°F |
Use cold water to mix, reduce starter to 8–10%, move dough to coolest room |
| Dough feels slack and wet |
High temp + high humidity |
Reduce hydration 3–5%, use fridge for final proof |
| Overproofed before you can bake |
Fermentation too fast |
Reduce bulk time, shape earlier, cold retard immediately |
| Loaf spreads flat |
Over-fermentation weakens gluten |
Earlier shaping, cold retard, check starter isn’t over-ripe |
| Very sour flavor |
Warm temp amplifies acid production |
Shorten bulk, use cold retard instead of room-temp final proof |
Measuring Dough Temperature
A cheap instant-read thermometer is one of the most useful tools in your kitchen. Stick it into the center of your dough after mixing — your dough temperature tells you exactly how fast fermentation will proceed.