What is the primary function of a foam on beer (FOB) system?

A foam on beer (FOB) system is primarily designed to stop beer flow when a keg empties. This function is crucial in preventing excessive foam from being generated when the keg runs out. When the beer is about to finish, the FOB system detects the lack of liquid and triggers a mechanism that cuts off the flow. By doing so, it helps maintain the quality of the beer being served, ensuring that customers do not receive a glass filled with foam or air, which would degrade the overall drinking experience.

The other options, while related to beer, do not accurately describe the main function of an FOB system. For instance, increasing carbonation levels pertains to different processes involved in beer production and serving, while enhancing flavor profiles is typically a concern of brewing techniques and ingredient choices. Regulating temperature is also a key aspect of beer storage and dispensing systems but does not relate directly to the function of stopping flow when a keg is empty.