What is the term for the part of a draft system that automatically stops the flow of beer when the keg empties?

The part of a draft system that automatically stops the flow of beer when the keg empties is known as Foam On Beer (FOB). This device is critical because it helps prevent excessive foam from being released when a keg runs out, which can occur if the tap is left open. When the beer level in the keg drops below a certain point, the FOB detects the absence of liquid and activates a valve to shut off the flow, thereby eliminating waste and maintaining the quality of the beer being served. This functionality is especially important in busy environments, ensuring that servers and bartenders do not have to constantly monitor the kegs and tap system.

The other options relate to different functions within the draft system. A keg coupler is the device used to connect to the keg and allow beer to flow, while a draft tap is the physical tap from which beer is dispensed. The regulator controls the pressure within the system but does not stop the flow based on the keg's contents. Understanding these components is essential for anyone working with draft beer systems, as each has a specific role that contributes to a well-functioning setup.