How flour is made

A wheat kernel is cracked open between rollers and sifted again and again until only its white heart is left.

stations: 7
things upstream: 24
raw sources: 9
steps from the ground: 8

The short version

Wheat is cleaned, dampened and run through a series of roller mills. Each pass cracks the kernel a little more, and sifters pull off the bran and germ while the starchy center is ground finer and finer. The white endosperm powder is blended to a target protein level, sometimes bleached or matured, and bagged.

Scour out stones and chaff

Incoming grain passes over screens, through air streams and past magnets that pull out stones, straw, seeds of other plants and stray metal. Every kernel that reaches the rollers has to be clean, because grit would wear the rolls and show up in the bread.

Goes in
Wheat
Dampen the kernels

The wheat rests in bins after a measured dose of water. Moisture toughens the bran so it peels off in big flakes instead of shattering into specks, and it softens the starchy middle so it grinds cleanly.

Goes in
Water
Crack it between rollers

Pairs of corrugated steel rolls turning at different speeds split each kernel open and scrape the endosperm off the bran. This is the first of several passes. Roller mills replaced stone grist mills in the 19th century.
Sift the fractions

A plansifter, a vibrating box of stacked sieves that get finer toward the bottom, sorts the broken stock. Flour falls through, while bran and coarse pieces ride over the end and go to the next pair of rolls.
Reduce the white granules

Smooth rolls grind the endosperm granules to powder, and each pass is sifted again. A mill may repeat the grind and sift cycle many times, and each cycle yields a stream of flour with slightly different protein and ash content.
Blend to specification

Streams from different parts of the mill are blended to hit a protein target, because higher protein gives stronger, chewier dough and lower protein gives a softer, more tender crumb. A small dose of ascorbic acid is often added as a maturing agent that strengthens gluten.

Goes in
Vitamin C tablet
Bag it or blow it into silos

Finished flour is checked for moisture and protein, then packed in sacks or pumped by air into bulk trucks for industrial bakeries.

End of the lineFlour Next it goes into bread, instant noodles, tortilla and 14 more.

Worth repeating

Archaeologists have found evidence that people were making cereal flour over 32,000 years ago.
England's 1086 Domesday survey counted 5,624 water-powered flour mills, about one for every 300 inhabitants.
The first rolls in a flour mill are fluted and set to open each kernel as gently as possible, so the bran stays in big flakes.