Tian mian jiang (甜面酱, literally sweet flour sauce) is the fermented wheat and bean paste of northern China — used as a condiment, a cooking sauce, and a marinade in Beijing and Shandong cuisine. It is the sauce smeared on the thin pancakes of Peking duck service, the sauce used in zha jiang mian (mixed with huang jiang), and an ingredient in Northern Chinese marinades for grilled meats. It has a deep, fermented, slightly sweet savouriness that is distinct from hoisin sauce (which it superficially resembles) in its greater complexity and milder sweetness.
Using tian mian jiang in Peking duck service: The sauce is typically diluted slightly by warming it with a small amount of sesame oil and a little water or stock — this makes it easier to spread on the delicate pancakes without tearing them. The standard amount for service: approximately 1/2 tsp per Peking duck pancake — it should be present but not dominant. Using tian mian jiang in cooking: In stir-fries (particularly Northern-style pork preparations), tian mian jiang is added to the wok after the protein has been seared — it caramelizes rapidly in the hot oil and needs only 30-60 seconds of frying before additional liquid is added. In marinades: used as a base for duck, pork, and lamb marinades — its fermented notes penetrate the meat during the marination period.
Fuchsia Dunlop, Every Grain of Rice (2012); Fuchsia Dunlop, Invitation to a Banquet (2023)