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When you talk about coffee, you most likely touch on a subject of bitterness a lot. Coffee experts are convinced that good coffee should be sweet and well-balanced but definitely not bitter. I’d like to tell you what bitterness is, why it appears in coffee, and if it is always bad.
The bitter taste is intimidating and has unpleasant associations for us. There is an evolutionary background for this fact: most poisonous substances are bitter, so people try to avoid them. Our tongue is able to perceive bitterness 1,000 times better than other tastes. Our receptors distinguish five basic tastes: sweet, salty, sour, bitter, and umami. For some reason, bitter and sour tastes are often defined as negative. However, in coffee, the combination of them all ensures a balanced taste. Can you imagine the coffee taste without bitterness? I cannot.
The bitter taste can also be different. We like bitterness in some food, for example, in grapefruit, dark chocolate, and arugula, but we don’t like it in other products when it makes us wrinkle.
Why is coffee bitter? The intensity of taste is influenced by the concentration of phenolic compounds present in the drink. Chlorogenic acids are among the most common phenols. They account for up to 8% of the dry weight of green arabica beans. Robusta coffee beans contain almost 2 times more caffeine and 2% more chlorogenic acid. That’s why robusta is more bitter. Caffeine is also important in the formation of a bitter taste but to a lesser extent.
Multiple chemical reactions take place in green coffee beans during the roasting process, and the content of organic acids in them changes. The dark-roasted coffee is more bitter because chlorogenic acids are destroyed during the thermal processing and form quinic acid, which is more bitter. In 2007, scientist Thomas Hofmann determined a connection between the amount of phenylindanes in a cup of coffee and the roasting profile. Light- and medium-roasted coffee beans contain more chlorogenic acid lactones that give a drink its pleasant and quality bitterness. In dark-roasted beans, phenylindanes dominate, giving pungent and prolonged bitterness.
The quality and intensity of bitterness in a ready-made drink will also be affected by the way chlorogenic acids are formed in green beans. They depend on a coffee type, where and how the tree grows, and how the beans are processed. To give one more example, if unripe coffee berries are harvested, they will contain more chlorogenic acids. These beans give a drink astringent bitterness.
Also, a lot of factors can affect coffee taste during the brewing process. For example, finely-ground coffee is extracted longer and gives more flavor. The over-extracted beverage results in a bitter taste. At the higher water temperature, the flavoring compounds are extracted more efficiently. To make coffee less bitter, lower the water temperature by a few degrees. So, a recipe with a balanced coffee taste is worked out for each brewing method and coffee bean type.
