Bingfen

The seeds come from Nicandra physalodes, a wild lantern-fruit plant common across southwest China; the dish is generally traced to Pengshan (old name Wuyang) in Sichuan in the late-Ming/early-Qing period, where a woman named Wang Weiyuan is said to have discovered it after the fruit fell into a sachet that set into jelly when washed; Chengdu's street vendors later made it famous, and a similar version is eaten in Yunnan. The Yunnan version stays closer to the original — fewer toppings, sweeter syrup, a piece of raw ginger in the pot.

Lijiang street vendors made it from Nicandra physalodes seeds rubbed in cold mountain water long before Chengdu took the credit. The pectin gels only with calcium — 2 grams of food-grade lime to 1.5 liters. Skip it: cloudy water. Overdo it: tastes like plaster.

Spoon goes in and the jelly cleaves like cold glass — clear, almost weightless, the texture of a soft contact lens. Brown sugar hits first, then ginger warmth, then the crunch of peanuts and the chew of raisins underneath. It's eaten in summer at hutong-side stalls in Lijiang and Chengdu both. If the jelly tastes of anything besides cold water and syrup, it sat too long or had too much lime.

The setting agent is the trick: the polysaccharides in the seed coat (mostly pectin-like polygalacturonans) only gel in the presence of divalent calcium ions, which is why a pinch of food-grade lime water (calcium hydroxide) is mandatory. Skip it and you get cloudy water; add too much and the jelly turns chalky and tastes faintly of plaster. 2 grams to 1.5 liters is the line.