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Why is Coffee Bitter?

Published: 2026-01-27 Author: FrontStreet Coffee

Last Updated: 2026/01/27, Why is coffee bitter? This question has puzzled scientists for decades. Now, scientists have narrowed their focus to two chemical molecules. At the annual meeting of the American Chemical Society, scientists reported that these two bitter-causing chemical molecules are produced during coffee processing, a discovery that could potentially impact the coffee additive industry.

Why is coffee bitter? For decades, this question has puzzled scientists.

Now, scientists have narrowed their research focus to two chemical molecules. At the annual meeting of the American Chemical Society, scientists reported that these two chemical compounds causing bitterness are produced during coffee processing, a discovery that could revolutionize the coffee industry.

Thomas Hofmann from the Technical University of Munich in Germany and his colleagues separated brewed coffee once again. After analysis using mass spectrometry, Hofmann identified one of the molecules—chlorogenic acid lactone, which is a breakdown product of chlorogenic acid (found in almost all plants). Hofmann's research team then prepared a series of different coffees, measuring the chlorogenic acid lactone content in each. Although in light and medium roast coffees, the lactones only produce a mild bitterness, if coffee beans are roasted for a longer time, the secondary decomposition products of lactones generate an intense bitter taste.

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