Brine, known as salt brine, is made from seawater or salt lake water salt, residual in the salt pond mother liquor, the main ingredients are magnesium chloride, calcium sulfate, calcium chloride and sodium chloride, etc., the taste is bitter, toxic. After evaporation and cooling precipitation of magnesium chloride crystals, known as brine block. It is the coagulant commonly used in the north of China tofu making, which can make the protein in the soybean milk coagulate into gel and analyze the water out. Salt brine as coagulant made of tofu, hardness, elasticity and toughness, known as old tofu, or northern tofu, hard tofu. Proverb cloud: brine point tofu, one thing to another. Salt brine as a coagulant when making tofu, the concentration is generally 18-22 ° Be′, the amount of raw soybean weight of about 2% to 3.5%. In addition to brine, tofu in the south, usually with gypsum point. Currently also commonly used a point called gluconolactone tofu, pad out of the tofu called lactone tofu.