Sourdough flour & hydration statistics

Higher-protein flour does not absorb more water. Across the 16 cited flours in this dataset, protein content and water absorption correlate at r = -0.54 — mildly negative. Dark Rye Flour (Pumpernickel) (8.0–9.0% protein) takes about 25% more water than Einkorn Flour (15.0–17.0% protein), despite having less of it. Bran and milling extraction drive absorption; protein drives gluten strength.

Every figure here is computed from the same cited flour and recipe data behind our flour pages and hydration chart — nothing is estimated. Free to cite with a link (how).

Protein vs absorption: the myth, measured

The conventional claim is that protein predicts how much water a flour takes. In this dataset it does not: r = -0.54 across 16flours. The relationship only turns positive (r = 0.90) if you include vital wheat gluten — a 75%-protein additive, not a flour anyone bakes with alone. One outlier is enough to manufacture the conventional answer, which is probably how the myth survives.

With 16 flours this is indicative, not definitive — but the direction is the opposite of what most baking content asserts, and the category table below shows the actual driver.

Absorption by flour category

Category	Flours	Avg protein	Absorption	Typical hydration
Rye	3	9.0%	1.070×	87%
Whole wheat	2	13.3%	1.067×	79%
High-extraction	2	14.3%	1.030×	75%
Durum	1	13.3%	1.020×	69%
Refined wheat	4	12.0%	0.992×	68%
Ancient grain	4	14.1%	0.940×	65%

Rye leads absorption at the lowest average protein of any category here; ancient grains sit at the bottom with among the highest. Absorption multiplier is relative to bread flour (1.000×).

Target hydration by bread style

Across 25 documented styles the median target hydration is 72% (range 50–95%). There is no single “correct” sourdough hydration — the style decides it:

hearth — median 78% (55–95%, 13 styles)
pan — median 76% (72–80%, 2 styles)
lean — median 63.5% (58–70%, 6 styles)
enriched — median 55% (50–72%, 4 styles)

Salt is far more consistent than water: median 2.0% of flour weight (range 1.2–2.8%).

Fermentation speed by dough temperature

Time multipliers relative to a 73–77°F baseline — the single biggest variable in a sourdough schedule:

Dough temp	Bulk time	Proof time	Starter activity
36–40°F	10×	10×	dormant
58–62°F	2.5×	2.4×	sluggish
63–67°F	1.5×	1.55×	moderate
68–72°F	1.2×	1.2×	moderate
73–77°F	1×	1×	active
78–82°F	0.75×	0.75×	very-active
83–87°F	0.55×	0.55×	hyperactive
88–95°F	0.42×	0.42×	extreme-mold-risk

A dough at 58–62°F takes roughly 6× longer to bulk than one at 88–95°F. Work it out for your kitchen with the dough-temperature calculator.

Common questions

Does higher-protein flour absorb more water?

Not among real flours. Across the 16 cited flours in this dataset the correlation between protein content and water absorption is -0.54 — mildly NEGATIVE. Dark Rye Flour (Pumpernickel) (8.0–9.0% protein) absorbs about 25% more water than Einkorn Flour (15.0–17.0% protein), despite having less protein. Bran content and milling extraction drive absorption; protein drives gluten strength, which is a different property.

What hydration should sourdough be?

It depends on the bread, not on a single number. Across the 25 bread styles here the median target is 72% (range 50–95%). By style: hearth 78%, pan 76%, lean 63.5%, enriched 55%. Enriched doughs sit lowest because fat and eggs replace water.

How much does temperature change sourdough fermentation time?

Substantially. Relative to a 73–77°F baseline, bulk fermentation takes about 2.5× as long at 58–62°F and only 0.42× as long at 88–95°F — roughly a 6× swing across the range in this dataset.

How to cite these statistics

Free to reuse under CC-BY-4.0 — cite SourdoughHydration with a link to this page. Suggested citation:

SourdoughHydration analysis of 16 cited flours and 25 bread styles (protein–absorption correlation r = -0.54). https://sourdoughhydration.com/statistics

Methodology

Flour protein ranges, absorption multipliers and hydration ranges come from our flour dataset, where every entry carries its own published source (Hamelman, King Arthur, Central Milling and equivalents) — see any flour page for the citation behind that row. Absorption is expressed relative to bread flour at 1.000×. The protein–absorption correlation is computed over the 16 flours only; vital wheat gluten is excluded as a protein additive rather than a flour, the same exclusion this site already applies to flour combinations. Hydration and salt figures are the documented targets for 25 bread styles; temperature multipliers are relative to the 73–77°F band. Figures recompute from the dataset, so this page cannot drift from the rest of the site. Corrections: tell us.

Put the numbers to work: the hydration calculator · flour-by-flour hydration · hydration chart