The same sourdough recipe will give you wildly different bread depending on what flour you put in it. A 75% hydration loaf made with bread flour is a soft, manageable dough. The same 75% with 50% whole wheat is a sticky mess. With 50% rye it's something close to a paste. With 50% spelt it's a dough that breaks down before you can shape it.
This isn't a defect of the recipe. It's that flour types differ from each other in three key ways that bakers need to adjust for: water absorption, gluten strength, and fermentation speed. Understand those three variables and you can swap any flour into any sourdough recipe with confidence.
Different flours hold different amounts of water. Whole grain flours absorb more because the bran (the outer layer of the grain) is essentially a sponge. Refined white flours absorb less because most of the bran has been removed.
This means a recipe at 75% hydration with bread flour will feel completely different at 75% hydration with whole wheat — the whole wheat version will look almost dry. Either you increase the water to compensate, or you accept a stiffer dough.
Gluten is the protein network that traps gas during fermentation and gives bread its structure. Different flours produce different gluten:
Stronger gluten = more structure, more rise, more open crumb. Weaker gluten = denser bread, flatter shape, less spring.
Whole grain flours ferment faster than refined ones. The bran contains enzymes and food for the bacteria and yeast that white flour doesn't have. The same dough at the same temperature will be ready 30 minutes to an hour earlier with significant whole grain content.
This catches a lot of people out. They follow a recipe written for bread flour, swap in 30% whole wheat, and wonder why the dough is overfermented when bulk ends.
If you're swapping all-purpose flour for bread flour (or vice versa), the adjustment is mostly about water:
Gluten is also weaker in all-purpose. Don't expect the same dramatic open crumb you get with bread flour — the structure can't hold huge bubbles. You'll get a softer, less chewy bread that's still excellent, just different.
Fermentation speed is similar between the two; no major timing change needed.
A reasonable substitution rule: if your recipe calls for bread flour and you only have all-purpose, drop the hydration by about 3–4% and accept a slightly tighter crumb.
Whole wheat is the most common and most useful flour to add to a white-flour sourdough. Even 10–20% whole wheat dramatically improves flavor, fermentation activity, and crust color.
The adjustments depend on how much you add:
This is the easy zone. Most bakers replace some of the white flour with whole wheat in this range without changing anything else and it works fine. If you want to be precise:
Now the dough behaves noticeably differently. The bran is starting to interfere with gluten development. You'll need:
This is "whole wheat sourdough" territory. Big changes from a white-flour recipe:
A different beast entirely. You need:
The bread will be dense, hearty, deeply flavored, and excellent. It just won't have artisan open crumb.
Rye is a different category. It contains pentosans — sticky carbohydrates — that absorb water and make rye doughs feel slack and gluey. Rye also has very little of the gluten-forming proteins that wheat has.
A rye dough that "looks slack" isn't necessarily underproofed or over-hydrated. It's just rye.
This is the hidden weapon of sourdough. Adding even a small amount of rye to a wheat-based loaf:
Adjustments at this level: add 1–2% more water, reduce bulk by 15 minutes, otherwise treat it as a normal wheat dough.
Now the dough starts feeling different. Stickier, less elastic, but still recognizably wheat-like. Adjustments:
You're now in true rye-bread territory. Wheat techniques mostly stop applying:
A 100% rye sourdough is a great loaf to know how to make, but it's a different recipe to a wheat sourdough, not a substitution. Find a dedicated rye recipe rather than trying to convert a wheat one.
Spelt is genetically related to wheat and has gluten-forming proteins, but the gluten is much more delicate. Spelt doughs that get over-mixed or over-fermented break down dramatically.
Easy substitution, similar to whole wheat in terms of effect. Add a touch more water (1–2%), reduce bulk slightly. Spelt brings a distinctive sweet, nutty flavor that pairs well with bread flour or white flour.
Bigger adjustments needed:
Quite challenging. Most successful 100% spelt loaves use:
Spelt produces incredibly flavorful bread but the technique is different enough that I'd recommend a dedicated 100% spelt recipe if you want to go all-in.
These ancient grains are increasingly available and each has its own quirks:
Einkorn has very weak gluten and behaves almost like a cake batter at high hydration. Most einkorn sourdough recipes use 60–70% hydration max and bake in loaf pans. Don't expect sourdough boules. Do expect amazing flavor.
Kamut (khorasan) has stronger gluten than spelt but similar fragility. Treat similar to spelt — slightly lower hydration than wheat, shorter bulk, gentle handling. It's expensive but produces a dough with a beautiful golden color and rich, buttery flavor.
Emmer is between einkorn and modern wheat in gluten strength. Treat similar to spelt at most percentages. It tends to produce a denser crumb but exceptional flavor.
A general principle: ancient grains all want gentler handling, lower hydration than equivalent whole wheat amounts, and shorter fermentation times. Their gluten is more fragile than modern wheat. Don't try to push them like you would a strong bread flour.
Once you've decided what flour you want to swap in, the math is straightforward in baker's percentage. Flour is always 100% — split however you want between flour types.
Original recipe at 100% bread flour:
Modified to 70% bread flour, 30% whole wheat:
Bulk fermentation: aim for about 30 minutes shorter than the original recipe.
The calculator handles the percentage math instantly when you enter mixed flours. The hydration adjustment is something you set based on what flour you're working with.
A summary table for quick reference, assuming you start with a recipe at 75% hydration and bread flour:
| Substitution | Hydration adjustment | Bulk time adjustment | Other notes |
|---|---|---|---|
| 20% whole wheat | +1–2% | -15–20 min | Easy, almost no change |
| 50% whole wheat | +3–5% | -30–45 min | Long autolyse helps |
| 100% whole wheat | +5–8% | -60–90 min | Use whole-wheat-fed starter |
| 10% rye | +1% | -15 min | Speeds fermentation, deepens flavor |
| 30% rye | +2–3% | -30 min | Sticky; wet hands when handling |
| 30% spelt | +1–2% | -20 min | Gentle handling, watch over-proof |
| 50% spelt | -1 to +1% | -30 min | Lower hydration than equivalent whole wheat |
| 100% einkorn | -10% (use ~65% hydration) | -45 min | Loaf pan, gentle mix |
These are starting points. Every flour brand is slightly different, so adjust based on what you observe over a few bakes.
When you're swapping a flour you haven't used before, treat the first bake as a calibration. Take notes. Take a photo of the dough at the end of bulk. Cut into the loaf and look at the crumb. Then adjust one variable for the next bake — usually hydration first, then timing.
After two or three bakes, you'll have your version of the recipe dialed in. Sourdough rewards repetition. Flour swaps are no different.
Ready to adjust your recipe?
🧮 Open the Calculator