Grains have been a staple food for much of humanity since the dawn of agriculture, says Harold McGee in the book "On Food and Cooking: The Science and Lore of the Kitchen," but even among the other grains, oats are unusually nutritious. They are high in both soluble and insoluble fiber, which aid digestion and lower cholesterol. They're higher in protein than other grains, and even contain a quantity of healthy unsaturated oils. The majority of the world's oat production goes as animal fodder, according to McGee's book, with rolled oats being the most widely-used version for human food.
Because of their relatively high oil content, oats are more prone to go rancid than other grains. The first step in milling oat kernels is usually to roast them at low temperature, to deactivate the enzyme responsible for that process. This also improves their flavor. These lightly cooked grains are called "groats," and are ready to be milled into other forms. The first stage is usually to break up the grains into a form resembling cracked wheat, known in the market as steel-cut oats after the milling method. This produces larger or smaller pieces of grain for different purposes.
Steel-cut oats cook quicker than whole oat groats, and the Scots use this type of oats for their porridge. However, even steel-cut oats take time to cook, and in 19th century America, a German immigrant hit on the notion of steaming the groats, then pressing the softened grains into quicker-cooking flakes. The original large-flake "old fashioned" rolled oats are made by pressing a whole groat. These oats were more convenient to use, and arrived on the market just as breakfast cereals were becoming a major industry in their own right.
The large flakes made by milling whole groats cooked faster than steel-cut oats, but the definitions of "quick" and "convenient" changed rapidly with the arrival of the 20th century. In the 1920s, oat producers began to mill a smaller, quicker-cooking oat by steaming and pressing steel-cut oats rather than the whole groat. The new format cooked in half the time, and proved to also be a more versatile baking ingredient than the larger flakes, adapting well to use in cookies, breads and muffins.
Minute or Instant Oats
In search of greater convenience for their customers, and improved marketing opportunities for themselves, by the 1960s, milling companies began pressing even smaller pieces of steel-cut oat groats into flakes. These tiny flakes, known as instant or minute oats, can be cooked by pouring boiling water over them and stirring a few times. They are often sold in single-serving pouches with sweeteners and flavorings, needing only a microwave or a kettle to make a hot breakfast for one person.