How do insect-damaged beans affect coffee grade?

The coffee berry borer is one of the most significant threats to coffee production worldwide. This tiny beetle bores into the coffee cherry to lay its eggs, and the larvae feed on the developing bean. The result is a physical defect that is easily spotted by a trained grader: small, dark holes or tunnels in the green bean. Because these beans are physically compromised, they are classified as a secondary defect in the SCA grading system.

Beyond the physical damage, the real issue with insect-damaged beans is the flavor. The holes created by the insects provide an entry point for bacteria and fungi, which can lead to fermentation or mold growth within the bean. When these beans are roasted, they often produce 'off' notes—ranging from a mild earthiness to a harsh, fermented, or medicinal taste. Even a small percentage of these beans in a batch can negatively impact the overall cup quality.

Grading for insect damage is a meticulous process. During the cupping and sorting phase, graders look for these tell-tale holes. If a sample contains too many insect-damaged beans, the lot is downgraded. This is why integrated pest management (IPM) is so important on coffee farms. Farmers use a variety of techniques, including traps, biological controls, and careful harvesting, to minimize the impact of these pests.

In practice, the presence of insect-damaged beans is a direct reflection of the challenges faced by coffee farmers. It is a reminder that coffee is a crop that must be protected from the elements and pests. For the roaster, identifying these defects is crucial for maintaining the quality of their product. By working with producers who prioritize farm health and careful sorting, roasters can ensure that the coffee they serve is clean, vibrant, and free from the negative flavors associated with insect damage.