Rolled oats and steel-cut oats are primarily served at breakfast and are often used for baking. These foods are from the same grain, but the difference is in how they are cut and processed.
Rolled oats are flat flakes that have the oat husks removed. Rolled oats are processed more than steel-cut oats. They are rolled for the flat shape and conditioned with pressure cooking. This results in a grain that is still nutritious, but takes less time to cook. Instant oatmeal is made from rolled oats.
Steel-cut oats are hulled grains that are cut into smaller pieces instead of being rolled flat. They take longer to cook than rolled oats, and have a chewy texture. Steel-cut oats are golden in color and resemble wild-rice grains. Because of the dense nutrients, the serving size of steel-cut oats is only 1/4 cup, whereas a serving of rolled oats is 1/2 cup.
Steel-cut oats and rolled oats are both healthy food choices. While steel-cut oats are slightly lower on the glycemic index -- steel cut is 42 while rolled oats is 50 -- the main difference between the two is processing and cooking time. Steel-cut oats are healthier due to less processing, but can take up to 40 minutes to cook, depending on the serving size. Most rolled oats take under five minutes to cook, but lose nutrients in the process of manufacturing.