Scorching

Scorching is a common roasting defect that occurs when the initial heat applied to the coffee is too high for the beans to handle. When the drum is too hot at the start of the roast, or when the drum speed is too slow, the beans can come into contact with the hot metal surfaces for too long, causing the exterior of the bean to burn. This creates a charred, bitter, and ashy flavor that can easily overwhelm the more delicate notes of the coffee.

This defect is particularly common in drum roasters where the beans are in direct contact with the metal drum. If the drum is not spinning fast enough, or if the charge temperature is too high, the beans will sit against the hot metal, leading to localized burning. This is different from a dark roast, which is an intentional development of the entire bean; scorching is an accidental, uneven application of heat that affects only the surface.

In the cup, scorched coffee is easy to spot. It often has a harsh, acrid bitterness that lingers on the palate, and the aroma may have a distinct smoky or burnt quality. Because the surface is burnt while the interior may still be underdeveloped, the cup can have a confusing mix of raw, grassy notes and harsh, charred flavors.

In practice, preventing scorching is about managing the charge temperature and drum speed. A roaster must ensure that the drum is hot enough to start the roast, but not so hot that it burns the beans upon entry. By adjusting the charge weight and ensuring the drum is spinning at an appropriate speed, a roaster can keep the beans moving and prevent them from lingering against the hot metal. It is a delicate balance, but one that is essential for producing clean, high-quality coffee.