Soybean

The soybean is a bushy annual legume about 0.5 to 1.5 metres tall, covered in fine hairs and bearing small white or purple flowers. The pods are fuzzy, hold two to four seeds each and are borne in clusters. The round to oval seeds are usually yellow but may be green, brown or black. They contain about 35 to 40 per cent protein and roughly 18 to 20 per cent oil, an unusual combination among legumes. Edamame are immature soybeans harvested while the pods are still green.

Soybeans were domesticated in East Asia, probably in China, several thousand years ago, from the wild species Glycine soja. Cultivation spread to Korea, Japan and Southeast Asia, and the crop reached Europe and the Americas in the eighteenth century. It expanded rapidly in the United States in the twentieth century, and today the United States, Brazil and Argentina are the world's largest producers, followed by China, India and Paraguay. Most of the global harvest is crushed for oil and meal, with much of the meal used as livestock feed.

Soybeans were among the five sacred grains of ancient China, and by the Zhou dynasty were farmed widely. Fermentation techniques were developed to make beans digestible and flavourful, producing soy sauce, miso, natto and tempeh. Tofu is traditionally attributed to China around two thousand years ago, and spread with Buddhism to Japan and Korea.

Soy came to Europe in the 1700s as a curiosity and was introduced to North America in the same period. The twentieth century saw the rise of industrial soy crushing for margarine, oil and animal feed, and plant breeders developed varieties adapted to many climates. Soy-based foods now range from traditional tofu to soy milk, protein isolates and meat alternatives, and the crop is also discussed in debates over land use and deforestation in South America.

Whole soybeans are boiled for soups and stews, roasted as soy nuts, sprouted, and eaten as edamame. They are pressed into soy milk and curdled into tofu, fermented to make tempeh, natto, miso, doenjang and soy sauce, and ground into flour. Textured soy protein appears in many meat alternatives. Soybean oil is among the most widely used cooking oils, and lecithin from soy is used as an emulsifier in chocolate and baking.

Soybeans are among the few plant foods that supply all essential amino acids, and they are rich in fibre, iron, magnesium, potassium, folate and vitamin K. They contain isoflavones, plant compounds that act as weak phytoestrogens, and the research on these is mixed and still evolving. Traditional soy foods eaten as part of a varied diet are associated with a healthy dietary pattern in many studies. Fermented forms can be easier to digest. Processing and sodium content differ greatly between products.