Methodology

Q10 is the factor by which fermentation rate multiplies per 10°C. No source states a Q10 for sourdough directly, so it is derived here, and the derivation is ours rather than either source's. Fitting a cardinal-temperature curve to the Tmin/Topt/Tmax values Gänzle et al. publish gives an effective Q10, across the 16-27°C band home bakers actually work in, of 2.4 for L. sanfranciscensis LTH2581, 2.7 for LTH1729 and 2.5 for C. milleri. Weekend Bakery's measured 18-30°C bulk fermentation table independently implies 2.6. The supported range is therefore about 2.4 to 2.7, and 2.4 is retained as the low end, which makes the model extrapolate less aggressively away from the 21°C anchor. The widely repeated rule that fermentation "doubles every 5°C" implies a Q10 of 4 and is rejected: it contradicts the time-temperature table published by the very source that states it.

• Gänzle, Ehmann & Hammes, "Modeling of Growth of Lactobacillus sanfranciscensis and Candida milleri in Response to Process Parameters of Sourdough Fermentation", Applied and Environmental Microbiology 64(7):2616-2623 (1998), Table 2, "Parameter values and correlation coefficients for effect of temperature on growth". https://journals.asm.org/doi/10.1128/aem.64.7.2616-2623.1998 — Reports cardinal growth temperatures for the dominant sourdough organisms: L. sanfranciscensis LTH2581 at Tmin 3.0 ± 0.6°C, Topt 32°C, Tmax 41.0 ± 0.1°C; LTH1729 at Tmin 4.1 ± 0.5°C, Topt 33°C, Tmax 41.0 ± 0.07°C; and Candida milleri LTH H198 at Tmin 8.0 ± 1°C, Topt 27°C, Tmax 35.9 ± 0.3°C. The paper fits its own growth model, not a Q10, so the Q10 figure above is inferred from these cardinal temperatures and is not stated by the authors.
• Weekend Bakery, "The Temperature Equation: Timing Your Fermentation", Bulk fermentation time-versus-temperature table. https://www.weekendbakery.com/posts/the-temperature-equation-timing-your-fermentation/ — Publishes bulk fermentation times falling from 7-9 hours at 18°C to 2-3 hours at 30°C. The same page separately asserts that "fermentation activity roughly doubles for every 5°C increase", a rule its own table does not support.

Midpoint of the conventional 20-22°C room-temperature band, and the anchor all reference timings are quoted at. It is deliberately an ambient kitchen temperature rather than an optimum: Hamelman puts the best dough temperature several degrees higher, at 24-26°C. The anchor only needs to be a temperature a baker can recognise and measure in their own kitchen; the Q10 curve moves the timings away from it.

• American Heritage Dictionary of the English Language, quoted in Wikipedia, "Room temperature", https://en.wikipedia.org/wiki/Room_temperature — Gives the colloquial definition of room temperature as around 20-22°C (68-72°F). The same page quotes the Oxford English Dictionary as "conventionally taken as about 20°C".
• Jeffrey Hamelman, Bread: A Baker's Book of Techniques and Recipes (2004), "Desired Dough Temperature" section. https://app.ckbk.com/section/brea32715b01s005/desired-dough-temperature — States that "the temperature zone that works best, particularly for wheat-based breads, is 75° to 78°F" (about 24-26°C). This is a target dough temperature, and is notably warmer than typical ambient room temperature.

Sits inside the 0-5°C range UK guidance advises and just under the 40°F (4.4°C) ceiling used in US guidance, so it represents a correctly set domestic fridge under both. No timing is derived from it: 4°C is far below the model's 16°C validity floor, and below even the 8.0 ± 1°C minimum growth temperature the Q10 citation reports for Candida milleri, so the equation is never evaluated there. It is recorded because it is the temperature at which cold retard actually happens, and it is what places retard outside the model. Real domestic fridges vary by several degrees between shelves and are frequently warmer than their dial claims, which loosens cold-retard timing further.

• Food Standards Scotland, "Chilling", "Chilled foods and your fridge" section. https://www.foodstandards.gov.scot/consumer-advice/food-safety/food-safety-in-the-kitchen/chilling — Advises to "keep your fridge between 0°C and 5°C - and regularly check the temperature with a thermometer".
• Minnesota Department of Health, "Cold Storage", https://www.health.mn.gov/people/foodsafety/store/coldstore.html — States that "the refrigerator temperature should be 40° Fahrenheit" (4.4°C).

The equation is a constant-Q10 fit inferred over roughly 16-27°C, and it is applied from 16°C to 32°C. The floor is the bottom of the band the Q10 was inferred over, which is the only floor the citation supports. Below it fermentation slows faster than any fixed coefficient describes, because the organisms approach their minimum growth temperatures: Candida milleri, the yeast whose gas raises the dough, stops growing at 8.0 ± 1°C, and at a minimum growth temperature the time to ferment is not long but infinite. Fitting a cardinal-temperature curve to the paper's own values — our inference, not the authors' — makes that concrete: the effective Q10 of such a curve is about 2.7 between 16 and 26°C, about 13 between 12 and 22°C, and about 86 between 10 and 20°C. A single coefficient therefore stops describing reality well above the yeast's minimum, and an earlier version of this model that set the floor at 8.0°C sat exactly on that singularity and returned short, finite times there, which is the opposite of the truth. The cost of the honest floor is worth stating plainly rather than hiding: this site's own cold band midpoint is 16.5°C, only 0.5°C above the floor, so a genuinely cold kitchen sits at the very edge of what this model can describe, and any temperature below 16°C is clamped to 16°C rather than answered. The ceiling is the optimum growth temperature the same table gives for L. sanfranciscensis LTH2581; it is not the warmest optimum in that table, since LTH1729 peaks at 33°C, so 32°C is one degree conservative of the table's warmest figure.

• Gänzle, Ehmann & Hammes, "Modeling of Growth of Lactobacillus sanfranciscensis and Candida milleri in Response to Process Parameters of Sourdough Fermentation", Applied and Environmental Microbiology 64(7):2616-2623 (1998), Table 2, "Parameter values and correlation coefficients for effect of temperature on growth". https://journals.asm.org/doi/10.1128/aem.64.7.2616-2623.1998 — Gives Candida milleri LTH H198 a minimum growth temperature of 8.0 ± 1°C and an optimum of 27°C; L. sanfranciscensis LTH2581 a minimum of 3.0 ± 0.6°C and an optimum of 32°C; and LTH1729 a minimum of 4.1 ± 0.5°C and an optimum of 33°C. A minimum growth temperature is where growth rate reaches zero, so no finite fermentation time exists at or below it. The paper fits a cardinal-temperature model rather than a Q10, and states no validity range for a Q10; the 16°C floor is the bottom of the band over which the Q10 used here was inferred from these values, and that inference is ours.

4-7 hours at 21°C overlaps both King Arthur figures without matching either. Their 4-6 hours is quoted at a warmer 78°F (26°C); their 6-8 hours is quoted at unspecified room temperature. Our range starts at the floor of the first, runs into the second, and stops an hour short of the 8-hour ceiling both pages reach. Feeding ratio moves this far more than temperature does: in the same trial a 1:1:1 feed peaked within 4 hours while 1:4:4 took 12, all at one temperature. This constant therefore carries real uncertainty that the temperature model cannot remove, and a baker watching their starter will beat the clock.

• King Arthur Baking, "Baking trials: Testing different sourdough feeding ratios" (13 March 2025), https://www.kingarthurbaking.com/blog/2025/03/13/sourdough-feeding-ratios — States that "at warm room temperature (about 78°F) a healthy mature sourdough starter fed at 1:1:1 will usually reach its peak after about 4 to 6 hours", and that this "can vary between 4 to 8 hours, depending on the health of your starter and the temperature of your kitchen". In their trials at 78°F, 1:1:1 peaked within 4 hours, 1:2:2 within 8 hours and 1:4:4 within 12 hours.
• King Arthur Baking, "Feeding and Maintaining Your Sourdough Starter", https://www.kingarthurbaking.com/recipes/feeding-and-maintaining-your-sourdough-starter-recipe — Directs bakers to use starter when "it has roughly doubled in volume and become bubbly (about 6 to 8 hours)" at room temperature.

This value is faster than both cited sources and readers should know it. Interpolating Weekend Bakery's table to 21°C gives 5.5-7.25 hours, so our 4-5 hours does not overlap their range at all: it is quicker than anything they predict, not merely at their fast end. The Perfect Loaf's 2-5 hours is stated for a warmer 23-24°C dough, so at 21°C the same source implies slower than 5 hours. Differing inoculation does not explain the gap. Weekend Bakery state their table assumes "a healthy, active starter at around 20% inoculation", which is the proportion this site's calculators use throughout; they also assume 70-78% hydration and a final dough temperature close to ambient, which is what this model assumes too. Matched on every variable the source names, our figure is still materially the faster one, and we do not have an explanation for that which the sources support. The 4-5 hour window is carried over from the site's earlier hand-tuned timing tables; it is retained rather than quietly moved to a number we could not justify either, and it is labelled a deviation from the sources rather than dressed up as agreement with them. Judge the dough, not the clock.

• The Perfect Loaf, "The Ultimate Guide to Bread Dough Bulk Fermentation", https://www.theperfectloaf.com/guides/the-ultimate-guide-to-bread-dough-bulk-fermentation/ — States "I try to keep my dough around 74 to 76°F (23 to 24°C), which is an effective temperature for fermentation and results in bulk fermentation times between 2 and 5 hours."
• Weekend Bakery, "The Temperature Equation: Timing Your Fermentation", Bulk fermentation time-versus-temperature table. https://www.weekendbakery.com/posts/the-temperature-equation-timing-your-fermentation/ — Table gives bulk fermentation of 6-8 hours at 20°C and 5-6.5 hours at 22°C, which interpolates to 5.5-7.25 hours at 21°C. Directly above the table the page states its assumptions: "a healthy, active starter at around 20% inoculation, a standard white or mostly-white dough at 70-78% hydration, and a final dough temperature that's close to the ambient temperature". It separately notes that a 25-30% inoculation speeds fermentation and 8-12% slows it.

1.5-3 hours sits inside the 1-4 hour room-temperature range this source gives, and its 3-hour ceiling matches the longest room-temperature proof the author reports using. The 1.5-hour floor is our own conservatism, not the source's: the source puts its floor at 1 hour and explicitly at room temperature, and reports 1 hour as its author's own shortest room-temperature proof. The separate warm case, 80°F/27°C, is where the source gives 1-2 hours. Raising the floor to 1.5 hours narrows the window for planning; a baker whose dough is ready sooner should trust the dough.

• The Sourdough Journey, "FAQ - Final Proofing", https://thesourdoughjourney.com/faq-final-proofing/ — States that "at room temperature, this process can take anywhere from 1 to 4 hours"; that if dough is "very warm, for example 80F/27C ... may only take 1-2 hours to final proof"; and that the author's own shortest room-temperature final proof is one hour and longest is about three hours.

The 30-minute floor is supported: it clears King Arthur's 20-minute minimum and sits at the top of The Perfect Loaf's conservative 15-30 minute starting point. The 90-minute ceiling is not. King Arthur stop at 60 minutes, and The Perfect Loaf's everyday advice is 15, 30, 45 or 60 minutes, so our ceiling runs half an hour past both. The Perfect Loaf do go longer, but as a recommendation rather than a warning: they suggest "2 hours or more" for doughs with a high percentage of aged whole wheat, and say that autolysing overnight is "just fine" with some doughs, reporting good results. Their caution that too far is hard to reverse is attached to overnight or many-hour rests and names no threshold, so no source fixes a ceiling here at all. 90 minutes is a site choice, made to leave room for whole-grain blends, and it is above the cited range rather than a subset of it. Held fixed across temperature because autolyse is enzymatic rather than microbial, and because neither source varies its recommendation by kitchen temperature.

• King Arthur Baking, "Using the autolyse method", https://www.kingarthurbaking.com/blog/2017/09/29/autolyse-sourdough — Defines an autolyse as "the gentle mixing of the flour and water in a bread recipe, followed by a 20 to 60 minute rest period", and attributes the technique to Prof. Raymond Calvel, who developed it in 1974.
• The Perfect Loaf, "The Ultimate Guide to Autolyse Bread Dough", https://www.theperfectloaf.com/guides/how-to-autolyse/ — States a preference to "start conservatively at 15-30 minutes", to stick to "15, 30, 45, or 60 minutes" for most recipes, a 1-hour autolyse for mostly-white flour loaves, and that "with high percentages of aged whole wheat flour, I might increase to 2 hours or more". On autolysing "overnight (or for many hours)" it answers "with some doughs it's just fine. I've done this with recipes that have a large percentage of aged whole wheat and have seen great results", while noting that "once you go too far with an autolyse, it's hard to reverse the slackening of the dough". It names no specific duration as the point of no return.

No source was found that puts a duration on mixing all ingredients in one go. Recipes describe the end state instead, for example King Arthur's "kneading to form a smooth dough". 10-15 minutes is carried over from the site's previous timing tables as a practical estimate and is flagged unsourced rather than given a citation that would not support it. Mixing is a mechanical task, so it does not vary with kitchen temperature.

No adequate source found. Treat this value as a working estimate.

No source was found supporting this range. The nearest figure located was King Arthur's Rustic Sourdough recipe, which specifies a 15-minute bench rest; that supports a bench rest existing but not the 20-45 minute combined shaping-plus-rest window used here, so it is deliberately not cited in support. Carried over from the site's previous timing tables and flagged unsourced. A human task, so independent of kitchen temperature.

No adequate source found. Treat this value as a working estimate.

Brackets the 40-45 minutes on a stone and 50 minutes in a Dutch oven that King Arthur give for a standard boule at 450°F. The 55-minute upper bound extends a little past the source to allow for larger loaves and is not itself stated by it. Governed by oven temperature, not kitchen temperature: the previous tables varied this across temperature bands, which was incorrect.

• King Arthur Baking, "Artisan Sourdough Bread made with a stiff starter", https://www.kingarthurbaking.com/recipes/artisan-sourdough-bread-made-with-a-stiff-starter-recipe — At 450°F, directs bakers to "bake the bread for 30 minutes. Remove the lid and continue to bake for 20 minutes" in a Dutch oven, a total of 50 minutes; and on a baking sheet or stone to bake "until it's a deep golden brown, approximately 40 to 45 minutes".