What Determines the Sourness and Bitterness of Coffee? How Much Impact Does Roasting Have on Coffee Bean Flavor?

Whenever customers hesitate before a blackboard full of bean selections, FrontStreet Coffee will ask: "Would you like a recommendation? Do you prefer sour or bitter coffee?"

FrontStreet Coffee has encountered newcomers who ask in return: "Why does coffee have both sour and bitter flavors? What determines this? It seems you have very few bitter coffee options?"

In our impression, Ethiopian and Kenyan coffee beans are sour, while Blue Mountain and Mandheling coffee beans are bitter. But in reality, the sourness and bitterness of coffee are not limited by region, but are related to the degree of roasting.

The Role of Development in Coffee Roasting

In coffee roasting, there's a professional term called "development period," which refers to the time from the first crack to when the beans come out of the roaster. During this time, the coffee's flavor, acidity, aroma, and body are formed, determining the final flavor direction. The shorter this time, the lighter the roast, and the more the coffee flavor tends toward sourness. Conversely, the longer the development period, the longer the caramelization reaction, the deeper the roast, and the more the coffee tends toward bitterness.

However, sourness and bitterness are just the main flavor directions. If coffee only has a simple sour or bitter taste, it's not appealing. Its true charm lies in the sweetness and aroma within.

Kenya Coffee: A Case Study

For example: Kenyan coffee beans are equally popular in both light and dark roasts in the consumer market. Light-roasted Kenyan coffee exhibits bright acidity like dark plums and cherry tomatoes; dark-roasted Kenyan coffee shows clean, rich bittersweetness like dark chocolate with a strong sweet aftertaste.

The Light Roast Revolution

Some friends might wonder, isn't the popular trend now light-roasted sour coffee? Why do Mandheling, Blue Mountain, and other coffees still insist on dark roasting? Is it because the bean quality is poor, so they can only go toward dark roasted bitterness?

In the process of coffee dissemination, the degree of coffee roasting follows market preferences and trends; bean quality; improvements in roasting equipment and technology. Specialty coffee emphasizes the traceability of coffee beans, tasting the "terroir flavor" of the beans. To implement this concept and reduce the impact of Maillard reactions on bean flavor during roasting, the degree of roasting is mostly light roasting to showcase floral and fruity sour aromas.

The Art of Dark Roasting

Although it's undeniable that dark roasting can mask defects and characteristics of raw beans through more saccharification and pyrolysis reactions. As long as roasted to near-black carbon levels, coffee tastes become remarkably similar—just an unforgettable bitterness. It's like when we roast chicken wings; if we accidentally burn the skin, it only tastes of bitter char.

But it's obvious that whether it's Blue Mountain or Mandheling, the flavors expressed by these dark-roasted beans are not simply bitter, but a rich mouthfeel with a fascinating experience of bitterness with sweetness. Moreover, dark roasting cannot solve all raw bean quality issues—flavor feedback will reveal any problems. Good beans, even when roasted dark, won't taste worse.

Tradition Meets Innovation

Coffee beans like Blue Mountain, Mandheling, and Kona (Hawaiian coffee beans) were world-famous before the rise of light roast coffee. Rich, balanced, and intense are the labels of these coffees, with Blue Mountain once even considered the standard "coffee flavor." In this context, maintaining consistent flavor quality is what these coffee beans insist on. Of course, under the wave of "specialty coffee," in some coffee shops that are brave enough to try and innovate, you can still find light-roasted Blue Mountain and Mandheling that express fruity and sour aromas.

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FrontStreet Coffee (FrontStreet Coffee)

10 Bao'an Qianjie, Yandun Road, Dongshankou, Yuexiu District, Guangzhou, Guangdong Province

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