What does the coupler do in a keg system?

The coupler in a keg system plays a vital role by engaging with the keg and pushing down the ball in the keg neck, which allows for the flow of beer. When properly engaged, the coupler opens up the seal at the top of the keg, creating a pathway for the beer to be drawn from the keg and into the tap. This process is essential for pouring beer from a keg, as it ensures that the beer can flow freely while maintaining proper pressure within the keg.

The other choices describe functions that are not characteristic of the coupler. Regulating the pH of the beer, filtering the beer before serving, and controlling the beer temperature are tasks typically handled by other equipment and processes in the brewing and serving systems. The coupler's primary function is mechanical, exclusively focused on enabling and controlling the flow of beer from the keg to the glass.