When must a foam-on-beer (FOB) detector be reset?

A foam-on-beer (FOB) detector is designed to prevent excess foam from spilling when a keg is nearing empty. Resetting the FOB detector after changing a keg is crucial because the device needs to recalibrate to recognize the new keg's fill level and ensure proper flow of beer. When a new keg is connected, the FOB detector must be reset to accurately measure the beer level and avoid interruptions in service.

Changing the keg typically involves a brief disruption in the beer flow, which can generate foam in the line. If the FOB detector is not reset, it may inaccurately signal that there is still beer available even when the keg has been switched, causing either foam or beer wastage. Therefore, the reset process is necessary after changing a keg to maintain optimal beer flow and quality.

Other options may relate to circumstances affecting the keg or foaming but do not require the FOB detector to be reset in the same critical way as changing a keg does.