Sourdough Flour Types Compared: Which to Use When

Why Flour Choice Drives Everything

Flour is 100% of the flour weight in every baker's percentage, which is a reminder that it is the foundation the whole loaf stands on. Three properties matter most: protein content (which sets gluten potential), ash content (which reflects how much bran and mineral the flour carries), and grain type (which brings flavor, enzyme activity, and its own gluten quality). Change any one and you change the hydration the dough wants, how it handles, and how it bakes. Below is a working reference for the flours a sourdough baker meets most, followed by the mechanics behind the numbers.

Flour Comparison Table

Treat the hydration column as a starting point, not a rule. Because whole grains and rye drink far more water than white flours, switching even 20% of your flour changes the dough feel immediately. When you swap flours mid-recipe, recalculate the water against the new blend with a hydration calculator so you land on the same dough consistency instead of guessing.

Bread Flour vs All-Purpose

Bread flour at 12-14% protein builds the strongest gluten network, which is what gives tall loaves with dramatic oven spring and a defined ear. It absorbs water readily, comfortably handles 75%+ hydration, and forgives minor technique errors because there is simply more gluten to work with. King Arthur (12.7%) and Central Milling are common reference brands.

All-purpose at 10-12% protein produces a softer, more tender crumb but less structure. Loaves spread a little more and the ear is subtler. It works for sourdough, especially sandwich bread, but wants more careful gluten development and slightly lower hydration around 65-70%. Blending all-purpose with bread flour is a practical way to dial crumb tenderness up or down without changing anything else.

Whole Wheat and Whole Grain

Whole wheat carries the entire kernel, including bran and germ, which adds nutty flavor, darker color, and more nutrition. But the sharp bran particles physically slice through gluten strands, so a 100% whole wheat loaf is denser and needs 80-90% hydration to stay open, since the bran soaks up so much water. Most bakers run 10-30% whole wheat blended with bread flour for flavor without a brick.

Whole grains also ferment faster. The germ and bran feed the starter enzymes and yeast, so a whole wheat dough can move noticeably quicker than a white one at the same temperature. Watch the rise rather than the clock, and shave time off bulk if you push the whole grain percentage up. Fresh-milled flour amplifies all of this: more enzyme activity, more vigorous fermentation, and more complex flavor than store-bought, which has often sat for months.

Ash Content and Extraction Rate

Ash content measures the mineral left after a flour sample is burned, and it is a direct proxy for how much bran and outer kernel the flour contains, in other words its extraction rate. White flour runs low, around 0.4-0.5% ash; higher-extraction and whole grain flours run 0.6% up past 1.5%. The European type numbers work the same way: German Type 550 or French T65 are moderate-extraction bread flours, while T80 and T110 carry more bran and mineral. Higher ash means more flavor, more enzyme activity, faster fermentation, and a slightly weaker, thirstier dough. It is the number behind why two 12% protein flours can behave completely differently.

Malted vs Unmalted Flour

Many bread flours, including most U.S. supermarket brands, are malted, meaning a small amount of malted barley flour is added to supply amylase enzymes. Amylase breaks starch into sugars the yeast can eat, which supports steady fermentation and good browning. Unmalted or unmalted-and-unbromated flours (common in European and some artisan mills) leave you to rely on the flour's own enzymes and the long sourdough fermentation, which already generates plenty of enzyme activity. For sourdough this rarely matters much, but if a dough is browning poorly or fermenting sluggishly, malted flour or a pinch of diastatic malt (about 0.5% on flour weight) can help.

Rye, Spelt, Einkorn, and Other Specialty Flours

Rye brings an earthy, slightly sweet flavor and ferments aggressively thanks to high enzyme activity, but its gluten is very weak and its pentosan gums make dough sticky. Use 10-20% rye in a wheat base for complexity without losing structure; for true rye breads, pan baking and higher hydration (often 80-100%+) accommodate the weak network. Dark rye carries more flavor and bran than light rye.

Spelt has plenty of protein (12-15%) but a fragile, extensible gluten that tears if overworked, so handle it gently, keep hydration around 60-70%, and expect a flatter loaf. Einkorn, the oldest cultivated wheat, has a very different gluten structure that barely builds strength; it makes slack, dense, deeply flavored doughs best kept below 60% hydration and often below 50% of the total flour. Spelt and einkorn both reward short mixes and careful shaping.

Among the rest, 00 flour is finely milled at moderate protein and shines in pizza and focaccia where extensibility beats strength. Semolina and durum give a golden, chewy crumb at 10-20% of the flour. Kamut (khorasan wheat) bakes rich and buttery and has become a favorite among artisan bakers. The pattern across all specialty flours is the same: the further you get from strong hard wheat, the weaker the gluten, the lower the hydration you can handle, and the gentler your technique needs to be.

Protein, Structure, and Choosing Your Flour

The through-line is simple: more and stronger protein means a tighter gluten network, which holds more gas, which gives a taller loaf with an open crumb and a bold ear. Weaker protein, or protein disrupted by bran (whole wheat) or gums (rye), gives a denser, flatter, more tender result. Match the flour to the goal. Want maximum oven spring and an open crumb? Reach for 12-14% bread flour at 75-80% hydration. Want a soft sandwich loaf? Lean on all-purpose or a bread-AP blend at lower hydration. Want flavor and nutrition? Blend in 10-30% whole grain and accept a tighter crumb. Once you understand what protein, ash, and grain type each contribute, flour stops being a mystery and becomes the first lever you pull on any recipe.