Rolled Oats

Rolled oats are whole oat groats that have been steamed and pressed flat between rollers. The steaming deactivates the enzymes that would otherwise turn the oat rancid, and the flattening gives each flake a large surface area, so it hydrates quickly without dissolving. In baking that combination does two useful things at once: the flakes absorb and hold moisture, keeping cookies and quick breads soft for longer, and they stay visibly intact, giving the chew and texture that define an oatmeal cookie or a crumble topping. They are not interchangeable with the other oat cuts by volume. Quick oats are rolled thinner and cut smaller, so they pack denser and hydrate faster, producing a softer, more uniform crumb. Steel-cut oats are barely processed at all and will stay hard through a normal bake. Substituting one for another without adjusting liquid is the usual cause of a dry or gluey result.