What is facing in coffee roasting?

Facing is a roasting defect in which beans develop a burnt or darkened patch on one flat side - the 'face' - from prolonged contact with the hot drum wall. Unlike scorching, which typically shows up early in the roast when the drum is hottest, facing can develop throughout the roast if drum rotation speed isn't keeping beans adequately mixed and tumbling.

The mechanism: if beans aren't moving freely in the drum - because rotation is too fast or too slow to achieve proper agitation, or because the batch size is too small relative to the drum volume - individual beans can press against the drum surface and sit there long enough to burn on that contact face. The result is a bean that's charred on one side while the interior remains relatively underdeveloped.

In the cup, facing produces a combination of bitter, smoky, burnt notes alongside an underdeveloped flatness - similar to scorching, but typically softer because only one face of the bean is affected. The fix is usually mechanical: adjusting drum speed, checking that batch size is within the machine's optimal range, or reviewing heat application in the early stages of the roast where contact burns are most likely to initiate.