The bitter taste of coffee comes from the processing process.

In western countries, people drink a cup of coffee every morning. In order to protect the bitterness of the coffee, they often add some milk powder and sugar. But why is coffee bitter? A seemingly simple question has plagued scientists for decades. At the moment, scientists have scaled down their research and focused on two chemical molecules. At the annual meeting of the American Chemical Society, scientists stated that the two bitter chemical molecules occurred during the processing of coffee, a discovery that could lead to a shift in the coffee processing industry.

When you drink a cup of coffee, you actually drink a mixture of more than 30 chemicals, some of which give off fragrance, some make it taste better, and some have something to do with sour taste. Since the beginning of the 1930s, scientists have had a glimpse of the chemicals in coffee, and the chemicals related to many flavors have been separated by scientists, but no bitter chemical molecules have been found.

To make a discovery, Thomas Hoffman of the University of Science and Technology in Munich, Germany, and his colleagues broke up with the brewed coffee again. They found that coffee flat molecular weight of the smallest part of the chemical molecules, the taste is the most bitter, and this part has become the next object of study. After operating mass spectrometer analysis, Hoffman dissected one of its molecules, chlorogenic acid lactone, which is the differentiation product of chlorogenic acid (found in almost all plants). Hoffman's team then equipped a series of divergent coffees and measured the content of chlorogenic lactone separately.

They found that when roasting coffee beans, it stimulates a chain of spinner hooks, and chlorogenic acid is first differentiated into chlorogenic acid lactone, and if the baking continues, chlorogenic acid will differentiate into another substance, phenyllindane. Although lactone will only produce gentle bitterness in mild and moderate roasted coffee, if coffee beans are roasted for a long time, the secondary differentiation products of lactone will produce strong bitterness.