Types of Coffee Defect Beans and Their Formation Causes - How to Select Defective Coffee Beans and Differences Between Good and Bad Beans

Have you ever wondered why coffee beans go bad? What are the defects in raw coffee beans? Why do these defects occur? Today, FrontStreet Coffee will guide you through the types of defective beans and the reasons behind their formation!

Coffee processing typically begins on the same day as harvesting to prevent unnecessary fermentation that could alter the chemical properties of the coffee beans. Additionally, coffee seeds are usually graded and sorted according to size, color, and shape to reduce the presence of defects and ensure uniform roasting (Batista and Chalfoun, 2014, Franca et al., 2005b, Illy and Viani, 2005). The main metabolic categories present in raw coffee beans have been identified as amino acids, carbohydrates, organic acids, fatty acids, chlorogenic acids (CGA), and volatile organic compounds (Farah, 2012). Several metabolites accumulated in raw beans contribute to flavor and aroma after roasting. The main categories of defective coffee beans fall into three major groups: physical deformities (such as peaberries, withered seeds, and shells), seed damage (due to processing or insect damage), or beans with color abnormalities (such as entirely black, partially black, or bleached seeds).

The Five Major Defective Beans That Most Affect Coffee Taste and Aroma

Over-fermented Beans

Have a pungent astringent taste, sour odor, and bitterness.

Black Beans

Include black beans and partially black beans with earthy and astringent aftertaste. These occur due to fungal attack and produce very defective flavors in the cup. In coffee grading, full black beans serve as the basis for scoring all other defects.

Insect-Damaged Beans

Have a burnt odor and rotten, fermented taste.

Moldy Beans

Have a musty odor and putrid bitterness. Usually a storage damage issue.

Floating Beans

Previously called floaters. Coffee beans that don't have the density to float in water.

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