Principle of Tofu Coagulation with Gypsum

The principle of using gypsum to coagulate tofu lies in colloidal coagulation. Soymilk is a type of colloid. The protein micelles in it can be evenly dispersed in water because their molecules carry charges of the same polarity. Electrostatic repulsion exists between charges of the same polarity, preventing the micelles from aggregating and thus maintaining a stable dispersed state.

The main component of gypsum is calcium sulfate (CaSO₄). When gypsum is added to hot soymilk, it hydrates and dissolves, ionizing into two types of strong electrolytes: sulfate ions (SO₄²⁻) and calcium ions (Ca²⁺). These strong electrolytes neutralize the charges on the protein micelle molecules, reducing the electrostatic repulsion between the micelles. As a result, the protein micelles aggregate together to form a gel-like substance known as doufunao (tofu pudding/curd).

Therefore, from the perspective of process control for gypsum-coagulated tofu alone, the formation of tofu mainly depends on the speed and concentration of the two electrolytes (calcium ions and sulfate ions) produced by the dissolution and hydration of gypsum in soymilk. In turn, the speed and concentration are primarily influenced by three factors: