Rolled Oats

Oats are cleaned and sized first, because a dehuller works best on grain of uniform dimension. Impact dehullers then throw the oats against a ring so the loose hull splits away from the groat, and aspiration separates the light hulls from the dense groats. The groats are kilned, and then either flaked whole or cut into pieces with steel blades and flaked as smaller flakes — which is the difference between thick old-fashioned oats and the thinner, faster-cooking grades. Steam softens the groat immediately before the rollers so it flattens rather than shatters.

Groat

The oat kernel with the hull removed. Still carries its own bran and germ.

Steel-cut oats

Kilned groats cut into pieces rather than flaked. The same material at an earlier stop on the same line.

Flake thickness

The roller gap, which sets cooking time. Thicker flakes hold their texture; thinner flakes cook faster and break down more.

Flakes are specified by thickness and size distribution, by how few are broken, by colour, and by moisture. Buyers also look at the completeness of the kilning, since under-kilned oats will develop rancidity in the pack, and at beta-glucan content, the soluble fibre for which oats carry health claims in several jurisdictions. Most of this is set upstream: a mill needs plump, uniform, sound groats to make even flakes, which is why oat lots are bought on groat recovery and plumpness in the first place.

• Food — porridge and oatmeal, the dominant use
• Food — muesli, granola, flapjacks, and baked goods
• Food — ground into oat flour, and used as the base of oat drinks
• Feed — broken flakes, fines, and off-specification material

Properly kilned flakes are stable for a long shelf life, which is precisely the point of kilning them. They are hygroscopic, and they are fragile — flakes break into fines under handling, and fines are both a quality complaint and an unwanted dust load. Packaging protects against moisture, insects, and physical damage, and stock rotation matters because the oil, though its enzyme has been stopped, remains slowly susceptible to oxidation over the life of the pack.