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.