Cantonese Red Bean Soup

Red bean soup as a Cantonese tong sui (糖水) has no single documented inventor or date. It belongs to the broad Lingnan sweet-soup tradition of Guangdong and Hong Kong, where tong sui — a catch-all for sweet soups simmered from beans, grains, fruits, or starches — is eaten as an everyday dessert and a household remedy. Red bean soup sits at the front of the tong sui repertoire, alongside mung bean soup and black sesame soup, and is a fixture of the dedicated tong sui shops (糖水铺) of Guangzhou and Hong Kong. The canonical Cantonese form pairs the beans with aged tangerine peel (陈皮), prized from Xinhui in Guangdong, which lifts the sweetness with citrus fragrance.

A bowl of deep red-brown, thick enough to coat the spoon. The beans have largely broken down into a soft, faintly sandy purée — the grainy 'sand' texture the dish is named for — with a few whole beans left for body. It is sweet but clean, never cloying, and through the sweetness runs a thread of dried-tangerine-peel fragrance, citrusy and slightly bitter at the edge. Served hot in winter, sometimes chilled in summer.

Getting the beans to 'sand' (起沙) is the whole point. Red beans (红豆, the round adzuki that cooks down readily) are used rather than the elongated chi xiao dou (赤小豆), which stays firm and is meant for soups. The beans are soaked 6–8 hours so they cook through faster and break apart evenly. They are brought up with enough water in one go — no topping up midway, which would interrupt the breakdown — and held at a steady simmer for one to two hours until the skins split and the starchy interiors disintegrate into a purée. Crucially, sugar goes in late, only after the beans have collapsed: added early, dissolved sugar draws water out of the beans and toughens the skins, so they never soften and 'sand' properly. Rock sugar or slab sugar is preferred over white sugar, which is said to thin the texture and lose the silky cling. The aged tangerine peel is soaked and its bitter white pith scraped away, then simmered with the beans; its volatile oil, rich in limonene, carries a citrus aroma that perfumes the soup and cuts the sweetness, while a trace of its natural bitterness keeps the dessert from cloying.