What are the defect flavors in coffee? How to identify and distinguish negative flavors in coffee tasting?

When learning coffee tasting, everyone tends to focus on describing positive flavors. For instance, when describing a cup of coffee, people can effortlessly say "jasmine, lemon, strawberry, caramel, chocolate," but when encountering unpleasant flavors, they can only say "bitter, miscellaneous flavors, unripe taste."

In fact, to master coffee flavor appreciation, one must not only understand how to taste coffee's positive flavors but also learn to recognize coffee's negative flavors. FrontStreet Coffee believes that when evaluating a coffee's flavor profile, we typically approach it from three aspects: its volatile aroma, taste, and mouthfeel.

Astringency

Actually, astringency refers to the taste of unripe fruits (think starfruit, green papaya) or grass. This flavor doesn't typically cause disgust, but can create some discomfort in the mouth and throat, though this depends on the intensity of the astringency. This taste often appears in coffee with many immature beans, lightly roasted coffee beans, and coffee brewed without the tail end of the extraction.

Over-Fermented Flavor

The taste of over-fermentation might be unfamiliar to many, but if I mention the taste of rotten apples, you should have some impression. Fermented flavor isn't necessarily a negative flavor—for example, wine-like aromas or jackfruit flavors. However, sometimes the difference between jackfruit and rotten apple flavors is incredibly fine. The taste of over-fermentation is similar to that of rotting fruit, fermented black beans, or miso soup. This flavor usually appears in coffee beans that have undergone heavy fermentation processing.

Miscellaneous Flavors

Miscellaneous flavors encompass a wide range of tastes—essentially, any slightly unpleasant bitterness encountered in coffee can be categorized under miscellaneous flavors. However, each mention of "miscellaneous flavors" might not refer to the same specific flavor, so it's necessary to clearly identify which specific taste you're referring to. For example:

Earthy Flavor

This doesn't mean you should taste soil—rather, it refers to the aroma emitted from earth after rainfall.

Woody Flavor

This refers to the aroma emitted from compressed wood boards or wood chips. This flavor generally appears due to over-extraction. This should be distinguished from the aromas of cedar or pine, as some Southeast Asian coffee beans carry coniferous (resinous) aromas, which are considered positive flavors. The difference is like that between plywood and agarwood.

Smoky Flavor

This sensation is like the choking smoke emitted from burning wood. This is usually caused by improper roasting.

Rubber Flavor

This refers to tastes emitted by sulfide compounds, specifically the pungent smell emitted by tires. This flavor easily appears in Robusta coffee beans.

Medicinal Flavor

This actually refers to the bitterness of plant alkaloids, concretely represented by white pills. In coffee, many people mistake this flavor for burnt bitterness.

Charcoal Flavor

This refers to the burnt bitter taste exhibited when food is overcooked and carbonized. This usually appears in dark roast coffees or over-extracted coffee.

Musty Flavor

This taste is like the smell emitted from clothes during rainy seasons. This flavor rarely appears in coffee. When it does appear in coffee, it might be due to the presence of moldy beans or black beans in the coffee, or because the roasted beans have been stored for more than half a year.