Rolle oats are oat groats that have been rolled into flat flakes under heavy rollers. The oat, like some other cereals, has a hard, inedible outer hull that must be removed before the grain can be eaten. After the hulls have been removed from the bran-covered oat grains, the remainder is called oat groats. Oat groats can be used as cereal, but since the bran layer makes the grains tough to chew and contains an enzyme that can cause the oats to go rancid, oat groats are usually steam-treated to soften them and denature the enzymes. Steel-cut oats are oat groats that have been chopped into smaller pieces and retain bits of the bran layer.