Ya cai is the ingredient behind the unique fermented tang in many classic Sichuan dishes.
Many classic Sichuan dishes, including dry-fried green beans (gan bian si ji dou) and dan dan mian, feature a distinct underpinning of fermented tang. That trademark flavor comes from the pickled mustard greens known as ya cai. This prized Sichuan foodstuff is made by sun-drying mustard stalks, rubbing them with salt and applying spices and sugar, and allowing the stalks to ferment for months. The most famous brand, Sichuan Yibin Suimi Yacai, comes in small foil packages that you can buy online or in the refrigerated section of well-stocked Chinese markets. (Look for “suimiyacai” as one word on the label, which means the vegetable has been precut into rice grain–size pieces.) Besides its traditional use in Sichuan specialities, ya cai can bring deeply savory umami funk, a touch of warm spice, and a slight sweetness to all sorts of dishes: Sauté a tablespoon with garlic and ginger for your next stir-fry or fried rice; toss a similar amount into a pan of sautéed baby bok choy; or sprinkle a teaspoon over congee, lo mein, or an Asian-inspired grain bowl. (Note: If you add ya cai to a dish, reduce the salt in the recipe by about one-quarter, and then check the seasoning after the pickle is added.)