Bao (爆, literally explosion or burst) is the most extreme of the Chinese wok techniques — cooking so fast, at temperatures so high, that food is barely in contact with heat before it is done. Classic bao preparations include sliced kidney, tender cuts of beef, and squid — proteins that tighten and toughen within seconds of overcooking. The entire cooking process is measured not in minutes but in seconds. Irene Kuo in The Key to Chinese Cooking gives the most precise English-language account of this technique.
Bao produces the most intense wok hei of any Chinese cooking method. The extreme brevity of cooking means aromatic compounds formed are almost entirely surface Maillard products — a concentrated, almost smoky sear on the outside of a near-raw interior.
The three bao variants: 1. You Bao (油爆) — oil-explosion: ingredients are flash-fried in very hot oil (170-200C) for 10-30 seconds, then drained and returned to the wok for final saucing. 2. Cong Bao (葱爆) — scallion-explosion: ingredients stir-fried with large quantities of scallion at maximum heat. 3. Jiang Bao (酱爆) — sauce-explosion: pre-cooked protein rapidly tossed with pre-mixed sauce at maximum heat. The method: Pre-cook or velvet the protein. Have all sauces pre-mixed and at room temperature. Pre-heat wok to maximum — smoking oil. The actual cooking: 15-45 seconds. Remove immediately once surface shows color.
Kidney is the ideal bao protein: scored in a cross-hatch pattern, it curls and flowers as it hits the heat — a visual indicator of correct temperature. A bao dish cannot be held or kept warm. It must go directly from wok to bowl to table.
Underpowered heat: Bao at insufficient temperature produces steamed, grey protein rather than seared, aromatic protein. Over-marination: A protein heavily marinated in soy-cornstarch cannot achieve the surface char needed in bao.
Irene Kuo, The Key to Chinese Cooking (1977); Fuchsia Dunlop, Every Grain of Rice (2012)