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 comprising a peripheral envelope (25) made of plastic to be connected to a heat treatment receptacle (5). It comprises 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.