Like a lot of foods named after places (the Jerusalem artichoke for example, being neither an artichoke, nor from Jerusalem), the Sichuan pepper isn’t a pepper, nor is it exclusively Sichuanese. It’s more closely related to citrus fruits than peppercorns and a number of varieties of the plant are grown across Asia, from the Himalayas to Japan and Indonesia. It takes its name of course from liberal use in the spicy Sichuanese cuisine of South-western China but crops up as sansho in Japanese cookery, as a ground spice traditionally used with eel; sancho in Korea where the leaves are also eaten as a vegetable; in Nepalese momo dumplings, where this is one of the few spices readily available and in the cooking of some Indonesian peoples who add it to their spicy sambals. A relative grows in the USA that is a popular natural remedy and the Chinese plant can even be successfully grown in the UK.
The Sichuan pepper, or hua jiao (flower pepper), is the dried seed pod named after its flower-like appearance that grows on a wild shrub which thrives in the mountainous terrain of the region. The leaves and berries are also edible, and consumed most outside of China. The spice is used across China as a yang, warming ingredient to dishes, like chillies. In Sichuanese cookery, hua jiao contributes to the ubiquitous ma la or numbing hot flavours when used with the local chillies as a means of combatting the yin effect of the damp climate. It is the numbing effect of the peppercorns however that is their most intriguing quality.
Initially, the Sichuan pepper has a citrusy flavour and mild heat but this is followed by a tingling sensation and numbing of the mouth. Just as capsaicin, the compound in chillies that make them spicy, interacts with the receptors in our mouths that detect heat to create that characteristic burning, a unique compound to the Sichuan pepper family of plants interacts with the receptors in our mouths that detect vibrations. Hydroxy-α-sanshool triggers those touch receptors to give first the tingling sensation, followed by the numbing as the receptor is overstimulated (read a bit more about the science here).
In spite of the name, Sichuan pepper is a really versatile spice that can be incorporated as easily as chillies into Asian cooking, be that a Japanese fish-dish, Korean stew, South-east Asian dipping sauce or a fragrant Himalayan curry. With its unique tongue-tingling properties however, perhaps this is one for the culinary thrill seekers!