Does processing create bitterness?

Bitterness is a complex sensory experience in coffee, and while it is often associated with dark roasts or over-extraction, the foundation of the bean's flavor is laid during processing. In a healthy, well-processed coffee, the natural sugars and acids are balanced, providing a pleasant sweetness that masks the inherent bitterness of the caffeine and other compounds. When processing goes wrong, that balance is destroyed.

The most common processing-related cause of bitterness is the presence of defects. If coffee cherries are not sorted properly, unripe or damaged cherries can make it into the fermentation tank. These 'defective' beans can introduce harsh, astringent, or even medicinal flavors that are perceived as a sharp, unpleasant bitterness. Similarly, if the fermentation is not managed correctly, the coffee can develop 'off' flavors that are often described as 'rubbery' or 'earthy'—notes that are fundamentally bitter and impossible to roast away.

Another factor is the drying stage. If coffee is dried on the ground rather than on raised beds, it can pick up flavors from the soil or become contaminated with mold. Moldy or fermented beans are a major source of bitterness and astringency. This is why specialty coffee producers invest so much in raised drying beds and rigorous sorting protocols; they are essentially protecting the coffee from the environmental factors that lead to these bitter defects.

It is important to distinguish between 'good' bitterness and 'bad' bitterness. A certain level of bitterness is expected in coffee—it is part of the bean's chemical makeup. However, the bitterness caused by processing defects is harsh, lingering, and unpleasant. It is a sign that the coffee was not handled with the care required to maintain its quality.

For the reader, this means that if you are consistently finding a harsh, unpleasant bitterness in your coffee, it might not be your brewing technique. It could be the coffee itself. Choosing high-quality, specialty-grade coffee is the best way to ensure that the processing was done correctly, minimizing the risk of these bitter, defect-driven flavors.