Also known as northern tofu, old tofu or brine tofu, it is a common variety of tofu. The main raw materials of Beidoufu are soybeans and black beans, and its production process includes processing beans into soybean milk, and then adding bittern or brine as coagulant. The main component of bittern is magnesium chloride, which will make soybean milk quickly coagulate into blocks and form a hard texture during pressing and dehydration. The water content of Beidoufu is relatively low, generally between 80% and 85%, so it has higher hardness, stronger toughness and relatively rough taste. Nevertheless, Beidoufu has high nutritional value and is rich in protein and calcium. Because of its high hardness and toughness, Beidoufu is suitable for frying, frying, stewing and other cooking methods, which can show its unique tough taste and rich nutritional value.