Nothing makes a bowl of piping hot steel cut oatmeal less appetizing than a thin film of bluish-green foam bubbling up to the surface. While some jokingly blame the color change on oats of Irish origin, a study conducted in 2009 reveals that the real cause has nothing to do with what country the oats come from. It actually has a thoroughly scientific explanation and reveals that the phenomenon, while unsightly, is not harmful to consume.
Oat eaters around the world occasionally report noticing the presence of green foam on the top of the pot when cooking steel cut oats on top of their stoves. The foam appears during cooking after the water has reached its boiling point. Cookers react with an understandable measure of alarm and a general desire not to consume the oats.
Researchers at the USDA-ARS Wheat Quality Laboratory on the campus of North Dakota State University conducted a study in 2009 which found that the foam can be green, blue and even green-blue-brownish in color. However, they identified the cause and determined that the phenomenon is not harmful and that consuming the oats will not result in poisoning, delirium or death. By extracting the color with methanol and high-pressure chromatography, researchers found that steel cut oats can turn brown-green or even blue-green in color when they are cooked in alkaline conditions. Alkaline conditions are achieved when the water used to cook the oats has a pH balance of 9 to 12.
Phenolic Acid Presence
Researchers also found that the presence of phenolic acid or avenanthramide in the steel cut oats could cause the unnerving color change during cooking. When 50 mm or more of NaHCO(3) is present in the water in which the steel cut oats are cooking, the water will turn alkaline. As carbon dioxide burns off during cooking, negative, OH(-), ion remains which leads directly to the odd-colored oats. Phenolic acid is sometimes added to oats when baking soda is present at the manufacturing plant during processing.
As an aside, researchers found that as little as 10 parts per million (ppm) of iron or Fe(2) in water can also cause oat products to turn gray-green during cooking. Since as much as 50 ppm of iron may be found in freshly pumped well water, people who cook steel cut oats with well water may be more likely to experience the phenomenon of green foam while cooking them. However, the phenomenon can be averted by allowing fresh well water to sit under normal atmospheric conditions for a few hours before cooking.
References and ResourcesOnibasu: Steel Cut Oats and Green Foam
NCBI: The Green Oat Story
Princeton: FeII and FeIII