Coagulants in Tofu Making
Coagulants are vital in tofu making, inducing curd formation by bonding proteins and fats in soy milk. Calcium-based options like nigari and gypsum, along with acid coagulants, alter texture and flavor, shaping the distinctive qualities of the final tofu product.
Tofu is made from soy milk by coagulating the proteins in the milk and then pressing the resulting curds into blocks. Its subtle flavour and versatile texture have made it a staple ingredient across many cuisines, particularly in vegetarian and vegan diets. In a tofu line, the coagulant is the single ingredient that decides whether the process yields the product the brand promised.
The coagulant is responsible for curdling the soy milk and forming the solid curds that eventually become tofu. It works by causing the proteins in the milk to undergo denaturation, which leads to the unfolding and rearrangement of protein molecules. As the proteins interact and bind together, they begin to cluster and form curds. The choice of coagulant affects the taste, texture and nutritional content of the tofu, contributing minerals such as calcium or magnesium.
Traditional coagulants include nigari (magnesium chloride), a natural mineral-rich substance extracted from seawater containing magnesium chloride and other minerals, commonly used in traditional Japanese tofu-making; it imparts a slightly bitter taste and produces a delicate texture. Gypsum (calcium sulfate), a naturally occurring mineral often used in Chinese-style tofu, creates a firmer texture compared to nigari and has a neutral flavour.
Modern coagulants include calcium sulphate solution, used in liquid form to coagulate soy milk with good curd formation and texture, and glucono delta-lactone (GDL), a slow-acting acid often used in the production of silken or soft tofu, which gradually lowers the pH of the soy milk and causes it to curdle.