Chinese deep-frying (炸, zha) in a wok differs from Western deep-frying primarily in temperature management across multiple frying stages. Many Chinese fried preparations require two frying passes at different temperatures — a low first fry to cook through, a high second fry to crisp — called fu zha (复炸, double-fry). This achieves a thin, shatteringly crisp crust over a fully-cooked, juicy interior. It is the technique behind Cantonese crispy pork, whole fried fish, spring rolls, and taro dumplings (wu gok).
Temperature stages: 120-140C (gentle bubbling): First fry — cooking interior without browning exterior. 160-170C (moderate): Single-stage frying for spring rolls, wontons, tofu. 180-200C (high fry): Crisping stage, second pass for double-fried items — only 60-90 seconds. Double-fry method: 1. First fry at 130C: 3-5 minutes. Interior cooked. Exterior pale gold, soft. 2. Rest on rack for 5 minutes. 3. Second fry at 190C: 60-90 seconds. Exterior becomes deep gold, crackling crisp. Wok advantage: The curved sides concentrate oil depth at the base — 1 litre fills a 35cm wok to 6-8cm depth at center.
A wooden chopstick dipped into the oil is a rapid temperature test: vigorous bubbling = 170C+; moderate bubbling = 140-160C; slow bubbling = 120C. Allow double-fried items to rest on a rack (not paper towel) — the rack maintains air circulation under the crust.
Single-temperature frying: Attempting to cook and crisp in one pass — food is either undercooked inside or burnt outside. Overcrowding the oil: Each piece added drops the oil temperature significantly.
Eileen Yin-Fei Lo, Mastering the Art of Chinese Cooking (2009); Ken Hom, Complete Chinese Cookbook (2011)