Cooking small pieces in a little oil over high heat, tossed quickly in the wok.
Liu works in 2 steps: fry the main ingredient, then add it to a thickened sauce made in a separate pan, or pour sauce over it after frying; another form involves frying until partly cooked and then lightly braising in sauce. A 2018 account uses Yellow River carp as its example: crisp liu, also called fried liu or scorched liu, means scoring, battering and frying the fish before pouring sauce over it; soft liu means cooking the fish in liquid first and then saucing it. Related dishes include Jinan's sweet-and-sour carp and scorched liu meat slices, and Hangzhou's vinegar fish; the available material gives no start date for the method.
What
Liu has 2 steps, with variations: fry the main ingredient, then add it to a thickened sauce in a separate pan; or fry until partly cooked, then lightly braise in sauce. Crisp liu, also called fried liu or scorched liu, involves scoring, battering and frying fish before pouring sauce over it; soft liu cooks the fish in liquid first and then sauces it.1,2,3
When
The available material gives no start date for liu. In the reviewed Qing bai lei chao entry, liu huang cai means scrambled egg; no sauce-liu dish appears, so it cannot date the method. The claim that sweet-and-sour fish was popular in Northern Song Kaifeng appears without a source in a 2018 article, which credits the Jinan version to a chef at the Jizhenyuan restaurant.3,7
Where
Shandong, especially Jinan: liu is a Shandong cooking method, scorched liu meat slices are a Jinan dish, and sweet-and-sour carp is a representative Jinan dish. Hangzhou also has vinegar fish: Qing and Republic-era vinegar-liu fish, now called West Lake vinegar fish, is traditionally considered the same dish as Song Wusao's fish soup. The available material does not establish which place was the start.3,4,5,6
How
Crisp liu: the fish is scored, battered and fried, and a sweet-and-sour sauce is then poured over it. Soft liu: the fish is cooked in liquid first and then sauced.3
Why
One form of liu involves frying until partly cooked and then lightly braising in sauce to soften the outer skin; crisp liu involves frying and then pouring sauce over.2,3
Impact and influence
Sweet-and-sour carp is a representative dish of the Jinan school of Shandong cuisine, and scorched liu meat slices are also a Jinan dish.4,5
The tale goes that Song Wusao ran a fish-soup shop beside West Lake in Southern Song Lin'an and was summoned by Emperor Gaozong (Chinese Wikipedia gives the year as 1179 and traces the account to the Wulin jiushi). The vinegar-liu fish of the Qing and Republic years is traditionally said to be her dish, and the Haibao Jinan article also credits Hangzhou's vinegar fish to Song Wusao. The sources present this connection as a traditional attribution; the entry on her fish soup does not discuss liu as a method.
Told in: Found in Chinese Wikipedia's entry on Song Sao fish soup and in a 2018 Haibao Jinan article. The account concerns a Hangzhou fish dish.
