The best flours for sourdough - and when to pick which

Choice of flour shapes everything: rise speed, crumb openness, crust colour, flavour profile. The lazy default ('use whatever bread flour the supermarket has') gets you 70% there; understanding flours gets you the last 30%.

70% T550 + 20% T1050 + 10% whole rye, 75% hydration. The T550 gives reliable structure, the T1050 adds flavour and accelerates fermentation, the rye wakes the starter and adds the country-loaf tang. Bake this mix three times before changing anything; it's a forgiving baseline that teaches you the rest.

The single most useful flour number isn't the Type - it's the protein percentage, printed on every bag's nutrition panel. Protein builds the gluten network that traps fermentation gas, so more protein means more structure, better oven spring, and a more open crumb that survives a long ferment. Rough bands: all-purpose / T550 sits around 9-12% protein, bread flour / French T65 / UK strong white around 12-14%, whole wheat 13-14% (but the bran cuts the dough so it bakes denser), and rye is low-gluten and can't carry a loaf on its own. There's a ceiling, though: very high-protein flour that's under-hydrated turns gummy and tough, which is why strong flours want more water. For most sourdough you want 12-13% - enough structure, still forgiving.

Type numbers measure ash (the mineral and bran content left after milling), not protein - which is why an American or British baker can't read them at a glance. The handy rule: the German type is the French number times ten (French T55 = German Type 550). Here's the map for the flours above:

These are two different questions that the same search hides. For feeding a starter, you don't need bread-flour-grade protein at all - a starter isn't building a gluten network, it's a microbe farm, and it's only a small fraction of the final dough's flour. A plain all-purpose / T550 (or our 70/20/10 mix) is perfect; unbleached or organic is a touch better because it carries more wild yeast and minerals than bleached, inert white. A spoon of whole rye or whole wheat in the feed is the classic activity boost. For baking the loaf, reach for the higher-protein T65 / strong white for structure and oven spring. So you can happily feed with cheap all-purpose and still bake a specialty whole-grain loaf - the flour in the jar and the flour in the dough don't have to match.

Can I use all-purpose instead of bread flour for the loaf? Yes - expect a slightly slacker dough, so drop hydration by roughly 50ml per loaf, and accept a touch less oven spring. A splash of vital wheat gluten closes the gap if you want it.

Is bleached flour OK? For baking, fine. For a starter, prefer unbleached or organic - the bleaching leaves the flour more inert, so a wild-yeast culture establishes faster on unbleached. Do I actually need bread flour? No. A 2:1 all-purpose-to-bread blend, or even straight all-purpose with adjusted hydration, bakes excellent sourdough. Can rye or whole wheat be my only flour? Not ideally - rye has almost no gluten and 100% whole wheat is dense; both shine as 10-30% of a mix with a stronger white base.

Here's the whole thing on one page. Tap it to download, or pin it for your next bake.