A device for monitoring the freezing state of a biopharmaceutical fluid in a container intended to receive a biopharmaceutical fluid that must pass between the liquid state and the frozen state, includes a peripheral envelope (25) made of plastic, to be connected to a heat treatment receptacle (5), a sensor (19) suitable for detecting a control parameter which is a macroscopic parameter of the container, and an analysis system (62) suitable for determining a freezing state of the biopharmaceutical fluid on the basis of the macroscopic parameter of the container.