关键词: 豆腐, 点卤, 胶体, 聚沉, 凝固

Abstract: Tofu, a quintessential Chinese invention, embodies both a fundamental element of Chinese culinary tradition and a profound representation of philosophical simplicity on the Chinese dining table. From the smooth and tender tofu pudding found on streets and lanes to the delicate soft tofu served at the home dining table, and then to the firm old tofu suitable for frying, stir-frying, stewing, and deep-frying, these various forms of tofu delicacies all originate from the same magical transformation. This paper examines the physical and chemical mechanisms underlying the remarkable transformation from soybeans to tofu, using firm tofu, soft tofu, and douhua (tofu pudding) as analytical entry points. Soybean milk constitutes a protein colloidal system, whose stability is maintained by electrostatic repulsion between charged colloidal particles and the protective hydration membrane surrounding them. The bittern curdling process, traditionally known as “brining”, is fundamentally an electrolyte-induced colloidal coagulation reaction. By precisely modulating the type and concentration of coagulants, we can systematically engineer a diverse spectrum of textural properties, ranging from the delicate consistency of douhua to the resilient firmness of laodoufu. This study elucidates the scientific principles embedded in traditional tofu production, revealing the intricate interplay between physical chemistry and everyday culinary practice, and also demonstrating our understanding and appreciation of cultural heritage.

Key words: Tofu, Bittern curdling, Colloidal system, Coagulation, Coagulants