Ash Content in Flour: What It Means for Sourdough Baking

Ash measures the mineral content left behind when flour undergoes high-temperature burning. It’s a reliable indicator of how much of the whole grain—especially the bran and germ, remains in the flour. The higher the ash content, the more nutritious (and flavoursome) the flour is.

Understanding Ash in Flour

Milling grains concentrates most of the minerals in the outer layers, bran and germ. These include calcium, magnesium, iron, zinc, and potassium. Firstly, during testing, flour is incinerated, and the residue left behind is called “ash.” It’s expressed as a percentage of the flour’s total weight.

White flour has low ash content (usually below 0.55%), since it contains mostly endosperm.
Wholegrain or high-extraction flour has a higher ash content (0.9% or more), indicating more bran and germ remain.

This value doesn’t mean the flour has ashes in it, it simply shows its natural mineral richness.

Why Ash Content Matters in Sourdough

Undoubtedly, flours with higher ash levels offer more nutrients for both the baker and the microbes in your sourdough starter. These minerals support strong fermentation and bring out deeper, earthy flavours in your bread.

At The Sourdough School, we favour using botanical blend flours with naturally higher ash content. These blends support better microbial activity and add nutritional complexity to each bake.

Ash Content and Health

Mineral-rich flours contribute to a broader nutritional profile in bread. Breads made from high-ash flours typically provide more magnesium, zinc, and iron. Furthermore when combined with long fermentation, as taught in our BALM framework which enhances the bioavailability of nutrients.

For those looking to increase fibre and nutrient intake through bread, the Proven Bread subscription offers a convenient option. Each loaf includes botanical blend flours, 6g of fibre per slice, and comes with a 12-week lesson plan to help you eat bread in a way that supports your gut and metabolic health.

Learn and Bake with Confidence

Understanding flour’s ash content helps bakers choose the right ingredients for flavour, nutrition, and fermentation strength. Also if you’re curious about how flour quality impacts your sourdough, explore our online memberships, starter kits, and equipment designed for home bakers.

All reasonable care is taken when writing about health aspects of bread, but the information it contains is not intended to take the place of treatment by a qualified medical practitioner. You must seek professional advice if you are in any doubt about any medical condition. Any application of the ideas and information contained on this website is at the reader's sole discretion and risk.