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Botanical name: Glycine max
Common name: Prepared soybean
Family: Fabaceae, pea family
Part used in Chinese medicine: seeds
Major Chinese medicine actions:
Releases exterior for hot or cold pathogens, relieves irritability,
disperses constrained heat above diaphragm
Glycine max, or soybean, is a legume native to East Asia, growing in lowland thickets. There is evidence that cultivated or wild soybeans have been eaten in China for over 5,000 years, and the legendary emperor Shen Nong (2853 BC) named it one of the five sacred plants, along with rice, wheat, barley and millet. According to archeological dating, sites in Korea show that it was cultivated as a food crop back to 1000-900 BC. During World War II, soybeans became an important food in North America and Europe as a substitute for animal protein. Before that time, the U.S. was an importer of soybeans, but at present grows so much that it exports to Hong Kong, Taiwan, and even mainland China. Soybeans are considered to be the only vegetable that is a complete protein.
The green immature soybean is a popular food in China and Japan (edamame). It is a comes from a variety of soybean sold unshelled, that has a particularly large seed and a hairy pod, called “mao doiu” or “hairy bean”. When sold as the shelled bean, it is called “qing dou” or “green bean”. Black soybeans are considered to be a special health food, and when fermented, are the beans used in Chinese medicine as Dan Dou Chi. Green soybeans are considered the sweetest and best flavored, black soybeans are usually sold dried, and yellow soybeans are best for making soy milk, tofu and tempeh.
Growing and Propagation
Soybeans are relatively easy to grow as long as they have full sun and fertile, well-drained soil. They are a warm weather crop, considered a subtropical plant, and grow best in summers where the temperatures are between 68 to 86 degrees F. Temperatures below 68 degrees F or over 104 degrees F slow plant growth considerably. The plants require at least 120 days to reach maturity and produce full sized beans.
Like most beans, soybeans require nitrogen-fixing bacteria to be present in the soil. When grown on the same land for successive years, it is best to only remove the aerial parts of the plant during harvest and to turn the roots into the ground as they will decay and release nitrogen. When grown in this manner, bean yields will increase each year as the soil improves.
When planting by seed, they should be soaked in warm water for 24 hours before sowing, and best results occur when mixed with an inoculum of the bacterium Bradyrhizobium japonicum. In warm regions seeds can be planted directly outside, but in cool regions they should be planted in a greenhouse in early spring, then planted out in the late spring or early summer when temperatures warm.
Harvesting and Preparation
The beans are left on the plants to dry before harvesting. Humidity and rain can be a problem during this drying process and excessive heat can also cause damage to the beans.
For the herb Dan Dou Chi, the black soybean is prepared with other exterior releasing herb such as Qing Hao (Artemisiae annuae) and Sang Ye (Mori alba) in order to increase its medicinal effectiveness. The added herbs are cooked into a decoction, which is then used to steam the soybeans until very soft. The beans are then mixed with the herb dregs from the decoction, left to ferment for some time, and then dried.