What is the primary function of a keg's coupler?

The primary function of a keg's coupler is to admit gas into the keg. This mechanism is essential for enabling the flow of beer from the keg to the tap. The coupler establishes a seal with the keg and facilitates the introduction of carbon dioxide or nitrogen gas, which creates the pressure needed to push the beer out through the faucet. Without this gas input, the beer would not properly dispense, as it relies on the pressure difference created by the gas to flow smoothly.

While dispensing beer may seem like a primary function, it is actually a result of the coupler's ability to introduce gas and create pressure. Measuring pressure and keeping the beer cold are important but secondary functions that do not capture the primary role of the coupler itself. Understanding this mechanism highlights the importance of gas lines and pressure management in draft beer systems, ensuring efficient and optimal beer service.