Roller Milling

The wheat kernel has three functional parts: the starchy endosperm, the oil-bearing germ, and the fibrous bran layers that enclose them. Roller milling exists to recover the endosperm as cleanly as possible, because bran and germ change a flour’s colour, keeping quality, and baking behaviour.

It works by exploiting a difference in mechanical behaviour. Correctly conditioned bran is tough and leathery and resists shattering; the endosperm inside is friable and breaks away readily. Fluted break rolls therefore open the kernel and scrape the endosperm off the bran without pulverising the bran itself. The bran stays in large pieces that a sieve can remove, and the process repeats: break, sift, reduce, sift again.

A flour mill is a separation plant with several saleable streams. Flour is the intended product; bran and germ are genuine co-products with established food and feed markets, not residues to dispose of. How much of the grain is recovered as flour — the extraction rate — is a commercial and technical decision, and it moves the composition of every stream at once.

Flour

The reduced endosperm. The primary product, specified by protein, particle size, and ash.

Bran

The separated outer layers, carrying most of the kernel’s fibre. A co-product, widely used in feed and as a food ingredient.

Germ

The embryo, separated because its oil shortens a flour’s keeping quality. Recovered as its own stream.

Milling cannot add quality the grain did not have: protein content and soundness arrive with the wheat. What milling decides is how cleanly the fractions are separated and what ends up in each. Poor separation leaves bran specks in flour and endosperm on bran — the first is a flour quality fault, the second is yield walking out of the mill in the wrong stream.

• Endosperm retained on bran — recoverable yield lost to the co-product stream
• Bran fragments carried into flour, raising ash and darkening colour
• Starch damage from over-reduction, which changes water absorption
• Dust and spillage across transfers

Milling is energy-intensive and dust-generating. Its residual streams are almost entirely used rather than discarded: bran and mill feed go to animal feed, and germ into food and oil. Dust extraction is both an air-quality measure and a safety one.