Kelp and Mung Bean Sweet Soup

Mung beans (绿豆) have been central to Chinese summer food medicine since the Tang dynasty — Sun Simiao's Qianjin Yaofang (千金要方) describes their cooling, detoxifying properties. The specific Cantonese tong sui tradition of cooking mung beans until they fully burst open into a thick paste (起沙) is a technique refined in Guangdong and Hong Kong kitchens. Adding dried kelp — an ingredient more common in Fujian and Lingnan coastal cooking — is a distinctively Guangdong adaptation, contributing iodine-rich mineral depth and a savoury counterpoint to the sweet beans.

The soup is comfortingly thick but not heavy, with a creamy, gently grainy texture from the burst mung beans; the kelp provides mild marine umami that keeps the sweetness in check, and the tangerine peel contributes a distant citrus fragrance.

Mung bean skins are rich in flavone glycosides (vitexin, isovitexin) with documented antioxidant activity. Their high potassium-to-sodium ratio promotes renal sodium-potassium exchange, supporting the traditional claim of cooling and diuretic benefit. The starch within the beans gelatinizes fully on long simmering; skimming the floating hulls produces a smooth, creamy paste (起沙) rather than a granular texture. Kelp (Saccharina japonica) contributes iodine, alginic acid, and fucoidan — the latter with clinical evidence for cholesterol-lowering effects.