What prevents a steam-jacketed kettle from over pressurization?

The correct answer is that a relief valve set at 45 psi plays a critical role in preventing over pressurization in a steam-jacketed kettle. The relief valve is specifically designed to automatically release excess steam pressure once it exceeds a predetermined level, in this case, 45 psi. This function helps ensure that the pressure inside the kettle does not reach a level that could lead to equipment failure or safety hazards, maintaining a safe operating environment.

The presence of a temperature thermostat is relevant for controlling the cooking temperature of the contents in the kettle, but it does not directly address pressure concerns. While a safety valve also protects equipment by preventing over-pressurization, the specific reference to the relief valve set at a specific pressure highlights the direct mechanism designed for this situation. Additionally, a pressure gauge provides valuable information about the current pressure within the system but does not actively prevent pressure buildup.