Flour for Sourdough Baking: How to Choose The Right Type

Flour for sourdough isn't just "whatever's in the cupboard". It's the main ingredient, the main variable, and very often the reason a dough feels glorious one week and like sticky wallpaper paste the next. Because sourdough relies on a long fermentation process driven by wild yeast and bacteria, your choice of flour changes how the dough rises in bulk fermentation, how strong the gluten structure becomes, how much water it can hold, and how the loaf tastes.

This guide is here to make flour feel less like a secret handshake and more like a powerful tool. You don't need to be a miller or buy fancy equipment. You just need to know which flour characteristics matter, what they look like in real dough, and how to pick the right flour for the bake you actually want.

Jump to:

• Wheat First: What Flour Is Actually Made Of
• Protein Content: Structure, Strength and Expectations
• Flour Strength Beyond Protein: Understanding the W Index
• Balance Matters: P/L Ratio Explained for Sourdough Bakers
• Water Absorption: Why Some Flours Drink More Than Others
• Ash Content: Flavour, Fermentation, and Mineral Content
• Falling Number: Enzymes, Not Protein
• Common Flour Types for Sourdough: What to Expect
• Choosing Flour Based on What You Want to Bake
• Reading Flour Labels
• Blending Flours: Your Shortcut to Consistency
• Common Flour Myths in Sourdough Baking
• Quick Reference Table

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If you're a beginner, head to our Best Flour For Sourdough Beginners: Starter Feeding & Bread.

Wheat First: What Flour Is Actually Made Of

Most white flour starts as the same plant: modern wheat. A wheat kernel has three key parts:

• Endosperm: mostly starch plus proteins that can form gluten. This becomes white flour.
• Bran: the outer layers, full of fibre and minerals (higher ash content) and sharp bits that can weaken gluten.
• Germ: the embryo, rich in oils, flavour, and enzymes.

Milling is the art of deciding how much bran and germ to keep, and how finely to grind. White flour is mostly endosperm; whole wheat flour and wholemeal flour include much more bran and germ. That choice changes hydration level, fermentation speed, and handling.

Sourdough is uniquely sensitive because it spends a long time fermenting the flour. With commercial yeast, you might mix, prove and bake within a few hours.

With sourdough, you often have a dough rest, repeated folds, a long rise, and a cold proof. That extra time gives enzymes and acids more opportunity to act on starch granules and proteins, so small flour differences can make a huge difference.

Protein Content: Structure, Strength and Expectations

Protein level in flour is the number most home bakers recognise, and yes, it matters. Protein content tells you roughly how much total protein is present; in wheat flour that includes gluten-forming proteins (mainly glutenin and gliadin). Brands like King Arthur publish typical protein ranges for flour types and explain how that affects performance.

In sourdough, protein content influences:

• Gluten development and dough strength: higher protein content often supports better oven spring and a taller loaf of sourdough bread.
• Extensibility: lower protein flours can feel softer and easier to stretch, but may struggle to hold shape through long fermentation.
• Crumb and texture: high-protein flour can give a toothier bite; lower protein content can suit sourdough sandwich bread and softer bakes.

Typical ranges (useful as a starting point, not a law):

• All-purpose flour / plain flour: often around 10-11.7% protein
• Strong white bread flour: often 12-13%
• Extra strong (including many "Canadian" style flours): 13-14%+

When high protein helps (and when it doesn't)

High-protein flour is great for rustic boules and batards, especially if you're chasing better oven spring. It's not automatically the best flour for sourdough sandwich loaves or enriched doughs if you want tenderness, because very strong flours can bake up chewier unless you adjust fat, sugar and fermentation.

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Flour Strength Beyond Protein: Understanding the W Index

Protein tells you "how much". W index tells you "how it behaves".

The W index (flour strength) comes from the Chopin alveograph test. In simple terms, the test inflates a small sheet of dough into a bubble and measures the energy needed to stretch it before it bursts. That energy is reported as W, and it's especially common on Italian flours.

Why it matters for sourdough

Two flours can share a similar protein level but behave very differently. One will build a strong gluten network and handle long fermentation well; another will feel sticky and fragile, even with "high protein content" on the label. W helps explain that.

Practical W guidance

• W 180-240: often good for everyday breads and shorter fermentation.
• W 240-320: a sweet spot for many artisan loaves and pizza dough.
• W 320+: very strong flours for long fermentation and enriched doughs (sourdough panettone, certain sweet doughs), but they can be thirsty and can feel "tight".

Balance Matters: P/L Ratio Explained for Sourdough Bakers

The alveograph also gives P and L:

• P = elasticity/tenacity (how much the dough resists stretching)
• L = extensibility (how far it stretches)
• P/L = the balance

Why you should care

Sourdough usually prefers balance, not extremes. Too much P and the dough feels "fighty" at the bench (snaps back, harder to shape, scoring can blow out). Too much L and the dough can feel slack and spread during the final proof.

Typical P/L outcomes (broad but helpful)

• 0.4-0.7: more extensible (often great for pizza flour and very open crumb, but can feel loose).
• 0.6-1.0: a balanced range for many sourdough styles.
• 1.0+: more tenacious (can be great for strong shaping, but needs careful hydration and fermentation).

Water Absorption: Why Some Flours Drink More Than Others

If you've followed a recipe, didn't overferment and still ended up with a sticky dough, you've likely met water absorption capacity of flour.

Water absorption percentage (often on mill specs) describes how much water, as a percent of flour weight, is needed to reach a standard dough consistency in a lab test such as the farinograph (commonly around 500 Brabender Units).

Why "hydration" isn't universal

Different flours absorb different amounts of water because absorption is influenced by protein, ash content, particle size, starch damage, and whole-grain content. That's why the same "75% hydration" can feel manageable with one bag of flour and unmanageable with a new flour.

How to adjust confidently

Hold back a small portion of warm water at mixing, then add it only if the dough feels tight. If it's already slack, don't chase "open crumb" by adding more. Focus on best results for your hands, your room temperature, and your starter.

Ash Content: Flavour, Fermentation, and Mineral Content

Ash content is the mineral content of flour measured in a lab. Higher ash usually means more bran and germ are present, which is why wholemeal flour tends to have higher ash than white flour.

Why it matters in sourdough

Minerals help support fermentation. Higher ash flours often ferment more actively, absorb more water, and bring a deeper, nutty flavour. The trade-off is that bran can weaken gluten structure and create denser loaves if you don't adjust sourdough hydration and handling.

Quick practical take

• Lower ash white flour: easier shaping, often better rise, cleaner flavour.
• Higher ash whole-grain flours: more flavour, thirstier dough, often quicker fermentation and a tighter crumb unless blended.

Falling Number: Enzymes, Not Protein

Falling number is where bakers get confused, because it's not about strength. It's about enzymes.

The Hagberg-Perten falling number test measures alpha-amylase activity, an enzyme that breaks starch into sugars. The test heats a flour-and-water paste and measures the number of seconds a plunger takes to fall through it. Low time means high enzyme activity; high time means low enzyme activity.

How it shows up in sourdough

Because sourdough fermentation is long, enzyme activity has more time to work. Too much alpha-amylase activity (low falling number) can cause starch breakdown that leads to weak structure and a gummy, sticky crumb. Too little activity (very high falling number) can slow fermentation and reduce crust colour because there's less sugar available for the Maillard reaction.

You don't often see it on retail bags

Falling number is more common on flour mill specs than grocery store packaging. But if you buy from mills that publish technical data, it can explain why one batch feels unusually sticky or bakes up with low volume.

Common Flour Types for Sourdough: What to Expect

White and bread flours

Strong white bread flour is a reliable choice for a classic loaf, especially if you're baking in a Dutch oven and using a razor blade for scoring. All-purpose flour can work beautifully too, particularly for softer crumbs and sandwich loaves.

Extra strong and Canadian style flours

Extra strong flour can be great for long fermentation, high hydration dough, and enriched doughs, but it can also create a chewier crumb. Stronger isn't always better; it's about the right flour for your goal.

Wholemeal and whole grain flour

Whole grain flour absorbs more water and can ferment faster. Expect a stickier dough, a more pronounced flavour, and a tighter crumb unless you blend with white flour. A "wholemeal only" loaf can be brilliant, but it's a different bake with different expectations.

Rye flour

Rye has a very different structure (it doesn't build the same gluten network as wheat), and it often has higher enzymatic activity. Rye is fantastic for flavour, for starters, and for adding a small portion to wheat bread dough. It can also turn your hands into glue, so rice flour is helpful for dusting proofing baskets.

Spelt flour and Einkorn

Spelt flour is often more extensible and can over-ferment easily, while einkorn can be delicate and sticky. With both, consider slightly lower hydration than your usual, shorten fermentation, and handle gently.

Choosing Flour Based on What You Want to Bake

This is the actionable heart of flour for sourdough.

Everyday sourdough loaves

Use strong bread flour (or a mix of strong flour plus 10-20% whole wheat flour or rye flour) for consistent structure and flavour. Try My Everyday Sourdough Bread recipe.

Open-crumb artisan boules

Choose higher protein content flour with good gluten quality. If you have W data, a mid-to-higher W can help. Keep hydration realistic. It's better to bake a confident 72% loaf than wrestle an 85% swamp and call it "rustic". I often go for extra-strong flour when I make my 80% Hydration Sourdough Bread.

Sandwich loaves

A slightly lower protein level, or a blend of strong flour and all-purpose flour, can give a softer crumb. If you want extra tenderness, a little olive oil, milk or butter helps. Readers love my Sourdough Sandwich Bread and Sourdough Milk Bread.

Focaccia and flatbreads

These love high hydration and lots of olive oil. Strong flour helps with structure, but blending with all-purpose flour can create a softer bite. Tray baking also makes high hydration dough easier to manage. Explore my sourdough focaccia recipes to get inspired!

Wholegrain-heavy loaves

Blend. Whole grains bring flavour and fermentation energy, but they also need more water and a careful eye on timing, which I further discuss in my Rye Sourdough Bread and Wholemeal Sourdough Bread recipes.

Reading Flour Labels

On UK bags you'll usually see "strong" or "plain", sometimes a protein percentage, and sometimes origin notes.

If you buy from mills that publish specs (Shipton Mill is a good example), you may also see ash and other technical data that helps you predict behaviour.

If you don't have numbers, use clues:

• A very pale white flour with lower protein tends to feel less thirsty.
• Wholemeal flour and whole grain flour are thirstier and can ferment faster.
• A new flour that suddenly gives sticky crumb might point to enzyme activity differences, not "bad shaping".

Blending Flours: Your Shortcut to Consistency

Blending is often better than constantly switching to a totally new flour.

Why blending works

It lets you keep structure while adding flavour, and it smooths out variability between different bags. It's also the best way to introduce new flour without tanking your bake.

Practical blends

• 80% strong white bread flour + 20% wholemeal flour for flavour and reliable dough strength.
• 90% bread flour + 10% rye flour for a more active fermentation process and deeper flavour without compromising texture.
• Or try my absolute favourite - French Sourdough Pain De Campagne - which blends strong flour, whole wheat flour and rye.

When you blend, assume you may need a little extra water and slightly shorter bulk fermentation if you increase whole grains.

Common Flour Myths in Sourdough Baking

"Higher protein is always better"

High-protein flour can help, but it can also make bread chewier and thirstier. Protein level is one factor, not the whole story.

"Strong flour equals open crumb"

Open crumb comes from proper bulk fermentation, shaping, and sourdough hydration, not just a bag that says "strong".

"Wholemeal just needs more water"

Wholemeal often needs more water, yes, but it also ferments differently and needs gentler handling.

"One flour works for everything"

You can do a lot with one bag of flour, but choosing flour types intentionally makes baking easier and more repeatable. Flour for sourdough is about matching the flour to the bake, then adjusting water and fermentation with confidence.

Quick Reference Table

Flour type	Typical protein level	Water absorption	Fermentation behaviour	Gluten strength & handling	Best used for
All-purpose / Plain flour	10–11.7%	Medium	Moderate, steady	Softer gluten, easier to stretch but less strength	Everyday loaves, sandwich bread, softer crumbs
Strong white bread flour	12–13%	Medium–high	Stable during long bulk fermentation	Strong, elastic gluten, holds shape well	Artisan loaves, boules, batards, most sourdough baking
Extra-strong / Canadian flour	13–14%+	High	Slower but very resilient	Very strong, can feel tight or “fighty”	Long fermentation, enriched doughs, panettone-style bakes
Wholemeal / Whole wheat flour	12–14% (effective strength lower)	High	Faster fermentation due to minerals	Gluten weakened by bran, denser crumb	Flavourful loaves, blends with white flour
Rye flour	Low gluten quality	Very high	Very active enzymatically	No true gluten network, sticky dough	Rye loaves, starters, flavour additions (5–30%)
Spelt flour	11–13%	Medium	Ferments quickly	Extensible but fragile gluten	Blended loaves, softer rustic breads
Einkorn flour	~13% (weak gluten)	Low–medium	Fast fermentation	Very delicate gluten, sticky handling	Flatbreads, blended loaves, gentle fermentation
Whole-grain blends	Varies	High	Fast, active	Needs careful hydration & handling	Nutrient-dense sourdough, flavour-forward breads
Rice flour (for dusting)	No gluten	N/A	N/A	Non-stick, doesn’t absorb moisture	Banneton dusting, preventing sticking