In the art and practice of coffee roasting, we deal with a number of factors that affect the outcome of the process. Some, such as the mechanical design of the machine or the airflow capacity of the roaster, cannot be controlled by the roaster operator. However, other factors can be directly controlled, including the time/temperature roasting profile, the cleaning procedures used, and the facilities and conditions around the roasting machine. Generally, there is a greater likelihood for roasting defects to occur when any of these factors are not adequately managed.
Roasting defects fall into three main categories:
Roasting inconsistencies, the most common type and the easiest to prevent
Roasting deficiencies caused by ignorance of processing or market requirements.
Roasting errors that actually damage the bean, like tipping, scorching, baking or bean cracks.
Picture 1 shows a roasted, dry-processed Brazil bean with minor scorch and char marks on outside layers. Picture 3 shows the massive scorching that occurs when the same bean type is exposed to excessive heat in the first stage of roasting. This type of defect leads to burnt and acrid flavor profiles.
Picture 1 – Minor Scorching
Picture 2 – Medium Scorching
Picture 3 – Uneven Development
Tipping is a roast error where the bean appears burned on one spot, indicating that the beans experienced too much heat around a specific area.
Too Much Heat
This puffed up coffee bean was under a lot of heat stress and most likely the roast was happening too fast.