What’s the Difference Between Types of Oatmeal?

What’s the difference between steel-cut, Scottish, Irish, rolled, quick-cooking, old-fashioned, and instant oats?

Some are milled differently, while others are exactly the same but called different names. For every type, the oats first undergo cleaning, hulling, and conditioning, which removes the outer shell (called a hull), leaving the inner kernel or oat groat. The groat is then brushed clean in scouring machines. Next, a kiln heats the groats to about 215 degrees Fahrenheit to deactivate their enzymes, which limits how the oils present in the germ can react with oxygen, making the oats stable for storage. Chelsea Lincoln, a representative from Bob’s Red Mill Natural Foods, says this is important because “oats go rancid very quickly if not stabilized.”

From there, the whole oat groats are processed differently depending on what type of oatmeal they are being made into. Lincoln says that to make steel-cut oats (also known as Irish oats), the groats are chopped up with steel blades. “This allows for a chewier oatmeal,” says Lincoln. For Scottish oats, the groats are ground into a meal, which makes a “porridge-type oat with a nice, creamy texture.” Irish and Scottish oats take about 30 minutes to cook.

Rolled (also known as old-fashioned) oats take less time to cook. The groats are softened by steaming, then run through metal rollers to flatten them. Lincoln says that Bob’s Red Mill regular rolled oats are flattened to 0.024 to 0.032 inches, while quick-cooking oats are rolled even thinner—about 0.017 to 0.022 inches—so they will cook in under five minutes. Instant oats are also rolled thin, but are then “cooked and then dried again,” says Lincoln. Just add hot water and stir.