Coffee Bean Roast Levels Dark Roast Coffee Beans Characteristics and Features

Characteristics of Dark Roast Coffee Beans

Coffee beans undergo various changes during different roasting stages. As green coffee beans absorb heat, their color transitions from green to yellow, and the moisture content begins to decrease. Heat converts the internal moisture in coffee beans to steam, creating carbon dioxide inside the beans. When the internal pressure reaches 25 bar (pressure units), the first crack occurs - a distinctive popping sound during the roasting process.

Flavor Development: Longer Roasting Time Reduces Acidity and Enhances Bitterness

After dehydration, coffee beans begin to release heat and turn brown, shedding a layer of silver skin. Roasted coffee beans increase in volume by 1.5-2 times, while losing at least 11% of their original weight.

Continued roasting causes continuous production of carbon dioxide, leading to the second crack.

Dark Roast Stage

As the coffee beans darken further, they enter the medium-dark roast stage. At this point, weight loss reaches approximately 22% of the original. After the second crack, coffee beans develop surface oil due to pyrolysis reactions and begin to carbonize, requiring careful attention to prevent burning.

With longer roasting times, acidity gradually decreases while bitterness increases, and many aromatic compounds begin to volatilize.

During the final roasting stage, nearly 800 flavor compounds develop, and the coffee's flavor characteristics, acidity, sweetness, and body reach maturity. However, roasting can sometimes bring out undesirable flavors in coffee. In the final stages, aromatic compounds are destroyed and replaced by bitterness, while acidity disappears and body diminishes.

Appropriate roasting can highlight the natural acidity of coffee beans. The heat from roasting destroys over 40 types of chlorogenic acids in coffee beans, breaking them down into quinic acid and caffeic acid. Both of these compounds have astringent properties that may affect the mouthfeel.

About FrontStreet Coffee

In short, FrontStreet Coffee is a coffee research facility dedicated to sharing coffee knowledge with everyone. We share our expertise without reservation to help more people fall in love with coffee. Each month, we offer three low-discount coffee events because FrontStreet Coffee wants to provide more friends with the best coffee at the lowest possible prices. This has been our mission for the past six years!

For professional coffee knowledge exchange and more coffee bean information, please follow Coffee Workshop (WeChat public account: cafe_style).

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