The Science Behind the Taste and Aroma of Coffee

close up of coffee beans in bowl

Coffee is a beloved beverage enjoyed by people around the world for its rich, complex flavors and aromas. But where do these flavors and aromas come from? In this article, we’ll explore the science behind the flavors and aromas of coffee and how they are created.

Green Coffee Beans

After the coffee fruit is ripe, it is harvested and then processed by dry or wet process to remove the outer pulp and pectin to obtain green coffee beans. The different ways of processing the coffee fruit, including the dry process, the wet process, and the semi-dry or “honey” process gradually developed by modern technology, determine the different flavors of the green coffee beans. 

Green coffee beans are mainly composed of water, carbohydrates, proteins, esters, alkaloids, chlorogenic acid, citric acid, malic acid, quinic acid, phosphoric acid and other natural chemicals. After hot roasting, these chemicals undergo a series of chemical reactions at high temperatures. Different roasting methods allow the percentage of various components in the beans to change, and the different flavors of coffee are then stimulated.

The Bitter Taste of Coffee

There are a few key factors that can contribute to bitterness in coffee.


Caffeine is a bitter xanthine alkaloid compound, which can stimulate gastrointestinal motility and promote defecation. It is also the most widely used psychoactive drug in the world, and it is addictive. Caffeine and its metabolites will accumulate in large quantities in the whole enterohepatic circulation. Excessive caffeine may increase the risk of fatty liver disease, and some studies believe that caffeine is a common inducement of atrial fibrillation.

Maillard Reaction 

Maillard reaction is a complex nonenzymatic browning reaction between reducing sugar and amino acids during food processing that gives food its distinctive flavor. Baked bread, roasted coffee, and grilled steak all owe their tantalizing smells to Maillard reaction. However, in the heat treatment, the Maillard reaction will cause the loss of amino acids, which will reduce the nutritional value of the food and even produce toxic substances.

Brewing Process

Over-extraction of the coffee grounds, where the water is in contact with the grounds for too long, can lead to bitterness. Too hot water may also lead to bitter taste. It is recommended that the brewed coffee should not be left for too long before pouring into personalized coffee cups.

Additionally, the type and quality of the coffee beans can also play a role in bitterness. High-quality, fresh coffee beans tend to have a smoother, less bitter flavor, while lower-quality beans or beans that have been stored for a long time can have a more bitter taste. The roasting process can also affect the bitterness of the coffee, with darker roasts generally having a more bitter flavor than lighter roasts.

The Sour Taste of Coffee

The acidity of coffee comes from natural chemicals such as quinic acid, citric acid, malic acid, phosphoric acid, and new acidic substances produced during the roasting process, such as the decomposition of chlorogenic acid to produce quinic acid and the decomposition of sugars to produce volatile formic acid and acetic acid.

The intensity of the acidity of coffee is related to the degree of roasting of the coffee beans. Before Maillard reaction, the acidity becomes stronger as the roasting degree deepens. After Maillard reaction, the acidic substances formed were decomposed and the sour taste became lighter.

In addition, the intensity of the acidity of coffee is also related to the origin of the coffee beans. Coffee trees from higher altitudes, which grow more slowly, contain higher levels of acidity and sugar in the coffee beans.

The Aroma of Coffee

The aroma of coffee comes from a mixture of volatile organic compounds (VOCs) that are produced during the roasting process. These VOCs are formed from chemical reactions that occur as the raw, green coffee beans are transformed into the dark, flavorful beans that we know and love. The specific VOCs that contribute to the aroma of coffee depend on a variety of factors, including the type of coffee bean, the roasting process, and the brewing method.

In summary, the flavor, bitterness, acidity, and aroma of coffee are all influenced by a variety of factors, including the type and quality of the coffee beans, the brewing method and the roasting process before it reaches our reusable coffee cups. Understanding these factors can help coffee enthusiasts create the perfect cup of coffee, with the right balance of flavors, bitterness, acidity, and aroma.

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