Coagulants used in food are substances that cause proteins to coagulate or form a solid mass. They are commonly used in the production of cheese and tofu. For example, calcium sulfate is used as a coagulant in tofu production, where it helps soy milk to coagulate and form curds, which are then pressed into blocks. Another example is propylene glycol, which can be used as a coagulant in the production of certain cheeses. These coagulants play a crucial role in the production of these food products, helping to create their characteristic textures and structures.