Oatmeal is a preparation of oats that have been de-husked,
steamed, and flattened, or a coarse flour of hulled oat grains (groats)
that have either been milled (ground) or steel-cut. Ground oats are also
called white oats. Steel-cut oats are known as coarse oatmeal, Irish
oatmeal, or pinhead oats. Rolled oats were traditionally thick
old-fashioned oats, but can be made thinner or smaller, and may be
categorized as quick oatmeal or instant oatmeal depending on the cooking
time required, which is determined by the size of the oats and the amount
of precooking.
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