The Honest Assessment
All-purpose flour is the flour people already have. It's what's in the pantry when you decide to make sourdough at 10 p.m. on a Sunday, which means it's also the flour more people start with than any other. This makes it worth documenting properly, despite the fact that it's not the best choice for sourdough bread.
The gap between all-purpose and bread flour comes down entirely to protein. All-purpose flour typically runs 10–12% protein. Bread flour runs 12–14%. That 2–3 percentage point difference sounds small, and in cookies or pancakes it doesn't matter at all. In sourdough, where you're asking the gluten network to hold fermentation gas for 12–16 hours while the dough develops, rises, is shaped, proofed, and baked — it matters quite a bit.
The practical result: sourdough made with all-purpose flour will have a tighter crumb, less dramatic oven spring, and less tolerance for high hydration. A 78% hydration dough that behaves beautifully with bread flour will be unworkably slack with all-purpose. The gluten simply isn't strong enough to hold the structure together through long fermentation at high hydration.
When It Works
All-purpose flour can produce genuinely good sourdough under specific conditions. The adjustments are: lower hydration, a slightly firmer dough, and respect for what the flour actually is.
The sweet spot for AP sourdough is 68–72% hydration. At these levels the dough is manageable, the gluten can do its job, and the crumb will still have visible openness. Don't try to push into 78–80% territory — that's bread flour's domain. Work within the flour's actual protein content and you'll get a satisfying loaf.
All-purpose also tends to produce a milder-flavored loaf — the lack of strong gluten means the dough doesn't hold as much character through fermentation. This is not necessarily a problem. A clean, mild, well-baked country loaf with decent crumb is a fine result for a flour you already owned.
AP vs Bread Flour: The Real Comparison
| Property | All-Purpose | Bread Flour |
|---|---|---|
| Protein content | 10–12% | 12–14% |
| Max practical hydration | 70–73% | 78–85% |
| Oven spring | Moderate | Strong |
| Crumb openness | Tighter | More open possible |
| Forgiveness of long fermentation | Lower | Higher |
| Availability | Everywhere | Most grocery stores |
| Price | Cheaper | Slightly more |
Unbleached vs Bleached: This Actually Matters
All-purpose flour is sold both bleached and unbleached. For sourdough, always buy unbleached. The difference is meaningful in two ways.
First, bleached flour has slightly weaker gluten. The bleaching process (typically benzoyl peroxide or chlorine gas) oxidizes some of the proteins and softens the gluten structure. In all-purpose flour where the gluten is already less robust than bread flour, further weakening is a problem you don't need.
Second, unbleached flour retains more natural wild yeast spores on the grain surface. This is subtle, but it contributes to a more active, more characterful fermentation — particularly for your starter feedings.
Bleached all-purpose is common in the US (Gold Medal's standard bag is bleached). Unbleached is easy to find in the same store. King Arthur and Bob's Red Mill both sell unbleached AP. Read the label — it'll say "unbleached" if it is.
AP Flours Worth Using
| Brand | Type | Protein | Notes |
|---|---|---|---|
| King Arthur All-Purpose | Unbleached, unbromated | 11.7% | The highest-protein AP flour you'll find at a regular grocery store. Closer to bread flour behavior than most. This is the AP to use if you're using AP. |
| Bob's Red Mill Organic AP | Unbleached, organic | ~11% | Good organic option. Solid for sourdough at 68–72% hydration. |
| Gold Medal Unbleached AP | Unbleached (their standard is bleached — read label) | ~10.5% | Make sure you buy the unbleached version. Gold Medal Blue = bleached. Gold Medal Unbleached = fine for AP sourdough. |
| Pillsbury Unbleached AP | Unbleached | ~10–11% | Widely available. Fine at lower hydrations. Don't push it past 72%. |
Making the Most of AP Flour
If all-purpose is what you're working with, here are the specific adjustments that make the biggest difference:
Lower hydration. Start at 68–70%. This keeps the dough workable and gives the weaker gluten network a reasonable job to do. The crumb will be tighter than high-hydration bread flour loaves, but it will be bread, not a puddle.
Shorter bulk fermentation. Weaker gluten degrades more quickly under accumulated fermentation acid. If bread flour can go 5–6 hours at 75°F, AP flour is done in 4–4.5 hours. Check it earlier and use the poke test — the window between properly fermented and overproofed is narrower.
Cold proof, always. A cold final proof firms up the weaker gluten network and gives you a cleaner score. With bread flour, same-day proofing is viable. With AP flour, refrigerating the shaped dough overnight produces meaningfully better results.
King Arthur AP if you can get it. At 11.7%, it's significantly stronger than Gold Medal or Pillsbury AP. If you're going to use all-purpose flour, this one behaves the most like bread flour.