Rolled oats are traditionally oat groats that have been de-husked, steamed and then rolled into flat flakes under heavy rollers before being stabilized by being lightly toasted. The oat, like the other cereals, has a hard, inedible outer husk that must be removed before the grain can be eaten. After the outer husk (or chaff) has been removed from the still bran-covered oat grains, the remainder is called oat groats. Oat groats are a whole grain that can be used as a breakfast cereal; various forms of oatmeal and rolled oats, and pinhead oats are cooked to make porridge. Steel-cut oats (pinhead oatmeal) are oat groats that have been chopped into smaller pieces before any steaming and thus retain bits of the bran layer. Since the bran layer, though nutritious, makes the grains tough to chew and contains an enzyme that can cause the oats to go rancid, raw oat groats are often further steam-treated to soften them for a quicker cooking time (modern "quick oats") and to denature the enzymes for a longer shelf life.