If you’ve ever baked sourdough and wondered why one loaf turns out tall and airy while another comes out denser and heavier, the answer often comes down to one key detail: flour protein content.

In this guide, I'm breaking down the difference between all-purpose flour, bread flour, whole wheat flour, and rye flour, and how protein affects gluten development, dough strength, and your final loaf.

Flour Quality Matters More Than Most People Realize

Before we even get into protein levels, here’s something every sourdough baker eventually learns: your flour matters just as much as your technique. Two flours can both be labeled “bread flour,” and still perform completely differently in real-life baking.

If you’ve ever grabbed a cheap bag of flour at the grocery store and felt like your dough was suddenly weaker, stickier, or harder to handle — you’re not imagining things. Many lower-cost flours are produced for maximum shelf stability and mass consistency, and they can be more heavily processed and standardized. That convenience is great for everyday baking, but it doesn’t always translate into the strongest performance for artisan-style sourdough.

Higher-quality bread flours are often milled for better baking performance and consistency. The difference you may notice is dough that develops gluten more easily, holds its shape better, and rises more reliably — even when you’re using the exact same recipe.

📌 Important note: Price isn’t the only indicator of quality, and not all inexpensive flour is “bad.” But if your sourdough results feel unpredictable, upgrading your flour is one of the simplest changes that can make a big difference.

Why Flour Protein Matters in Sourdough Baking

In wheat flour, protein matters because it affects how much gluten your dough can build.  When flour is mixed with water, two proteins in wheat (gliadin and glutenin) hydrate and connect, forming a stretchy network known as gluten. Gluten is what helps sourdough dough:

• hold its shape
• stretch without tearing
• trap fermentation gases
• rise higher in the oven
• In simple terms:

✅ More protein = more gluten potential = stronger dough + better rise

All-Purpose Flour for Sourdough: The "Middle of the Road" Option

All-purpose flour is the most common flour in home kitchens because it’s designed to work for everything from cookies to muffins to quick breads.

Typical all-purpose flour protein level:

Most all-purpose flour falls around 9–12% protein, depending on the brand and where it’s milled.

What all-purpose flour does in sourdough:

All-purpose flour can absolutely make beautiful sourdough bread, but you may notice:

• a softer dough feel
• a loaf that spreads more
• slightly less height than bread flour
• a more tender crumb

✅ Best for: everyday sourdough, softer loaves, experimenting, beginners

Bread Flour: Higher Protein for Stronger Dough + Better Rise

Bread flour is higher in protein than all-purpose flour, which is why it’s a go-to for sourdough boules, batards, sandwich loaves, and bagels.

Typical bread flour protein level:

Bread flour is often around 11–14% protein (and sometimes higher depending on brand).

King Arthur Baking lists their bread flour at 12.7% protein, which is a great example of a high-protein flour used for bread structure and strength.

What bread flour does in sourdough:

Bread flour usually gives you:

• stronger gluten development

• better oven spring

• more height and structure

• a chewier texture

• improved dough handling during shaping

✅ Best for: sourdough loaves you want tall, strong, and structured, feeding your starter

Whole Wheat Flour: More Flavor + Nutrition, But Often Denser

Whole wheat flour is made from the entire wheat berry, meaning it contains the bran, germ, and endosperm.  Even though whole wheat flour can have a higher total protein number, whole wheat loaves often turn out more dense than white flour loaves.  Whole wheat contains all parts of the grain, and the bran can cut gluten structure, leading to denser bread. 

Why whole wheat sourdough can be heavier:

Whole wheat contains bran, which can interfere with gluten development:

• bran has sharp edges that can cut gluten strands

• it also changes how water is absorbed

• the dough often needs more hydration and time to relax

Scientific research also supports that wheat bran negatively affects dough structure and can reduce loaf volume.

✅ Best for: added nutrition, flavor
📌 Pro tip: Try 10–30% whole wheat blended with bread flour for a great balance.

Rye Flour: Ferments Like a Dream, But Doesn’t Build Strong Gluten

Rye flour is a sourdough baker’s secret weapon for flavor and fermentation strength — but it behaves very differently from wheat flour.

Why rye makes denser sourdough loaves:

Rye contains proteins, but it doesn’t create the same strong gluten structure as wheat. Instead, rye dough relies more on natural gums and fibers (often described as a “sticky” or “paste-like” dough).

That’s why rye loaves are typically:

• shorter

• denser

• darker

• deeply flavorful

• more moist

✅ Best for: boosting sourdough activity, deeper flavor
📌 Try: 5–20% rye added into your flour blend

Quick Flour Protein Comparison 

Here’s a simple way to remember it:

• Bread flour (higher protein) → stronger dough, better rise, chewier texture

• All-purpose flour (medium protein) → softer dough, good everyday baking

• Whole wheat flour → more nutrients + flavor, often denser due to bran

• Rye flour → powerful flavor and fermentation, but less structure and dense