Buckwheat, Fagopyrum esculentum, is a plant in the Polygonum family, a relative of rhubarb and sorrel. It’s a native of central Asia, was domesticated in China or India relatively recently, around 1,000 years ago, and was brought to northern Europe during the Middle Ages. It tolerates poor growing conditions and matures in a little over two months, so has long been valued in cold regions with short growing seasons.
Buckwheat kernels are triangular, a sixth to a third of an inch/4–9 mm across, with a dark hull (pericarp). The inner seed is a mass of starchy endosperm surrounding a small embryo and contained in a light green-yellow seed coat. Intact seeds with the hull removed are called groats. Buckwheat is about 80% starch and 14% protein, mostly salt-soluble globulins. It contains about double the oil of most cereals, and this limits the shelf life of groats and flour. The hulled groats are about 0.7% phenolic compounds, some of which give the grain its characteristic astringency. The distinctive aroma of cooked buckwheat has nutty, smoky, green, and slightly fishy notes (due respectively to pyrazines, salicylaldehyde, aldehydes, and pyridines).