Coffee Bean Roasting: The Relationship Between Roast Level and Acidity, Differences Between Light and Dark Roast in Agtron Values

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Introduction

The flavor of coffee comes from various factors, including growing conditions in the origin, coffee varieties, processing methods, and more. Finally, the roaster transforms raw coffee beans into roasted beans, where both the roasting flavors and degree affect the ultimate taste of the coffee.

Roasting can be said to be one of the most important factors affecting coffee flavor. The same bean roasted to different degrees will create different flavor experiences. How does roast degree affect coffee? Does roast degree affect coffee acidity?

How is Roast Degree Categorized?

During the coffee roasting process, coffee beans undergo dehydration, turn yellow, then experience first crack, first crack development, and if roasting continues, second crack, second crack development, and more. When you review different resources, you'll find various expressions for roast degrees. At this point, we introduce the concept of Agtron values.

The Specialty Coffee Association of America (SCAA) uses infrared caramelization measurement technology (Agtron) to measure the color of coffee beans to reflect the degree of roast, dividing colors from light to dark into eight equal parts to create eight standard color blocks for the coffee industry to use as roast recognition.

Agtron value #95: Light Roast
Drop time: First crack development ending

Agtron value #85: Cinnamon Roast
Drop time: Around first crack ending

Agtron value #75: Medium Roast
Drop time: After first crack ending

Agtron value #65: High Roast
Drop time: Quiet period between first and second crack

Agtron value #55: City Roast
Drop time: Second crack beginning

Agtron value #45: Full City Roast
Drop time: Before second crack development

Agtron value #35: French Roast
Drop time: During second crack development

Agtron value #25: Italian Roast
Drop time: When oils begin to emerge on the bean surface

Although this standard still has some flaws, it must be admitted that Agtron values remain a valuable reference method for determining roast degree.

With this Agtron value system, we can examine how different roast degrees affect coffee performance. Will the acidity of coffee differ with different roast degrees?

The Impact of Roast Degree on Coffee Acidity

FrontStreet Coffee measured the Agtron values of several coffee beans with different roast degrees and then conducted cupping sessions separately. FrontStreet Coffee selected Ethiopia washed Gedeb cooperative coffee, Honduras sherry barrel coffee, washed Blue Mountain coffee, and Golden Mandheling coffee.

FrontStreet Coffee used an Agtron value tester to measure the Agtron values of the four coffee beans, with washed Yirgacheffe at 80.8, Honduras sherry barrel coffee beans at 78, Blue Mountain coffee at 65.4, and Golden Mandheling at 61.

Subsequently, FrontStreet Coffee conducted cupping sessions for the four coffee beans. FrontStreet Coffee believes that cupping is an extraction method with the least human interference, best representing the inherent flavor of coffee beans. By slurping and atomizing the coffee liquid, we can better judge various factors of the coffee. Finally, we found that the acidity ranking from high to low was: washed Yirgacheffe > sherry barrel coffee beans > washed Blue Mountain coffee > Golden Mandheling.

Therefore, it's not difficult to understand that the roast degree of coffee affects its acidity to some extent—the deeper the roast, the less acidic the coffee. This is because substances that produce bitterness are gradually generated during the roasting process, such as chlorogenic acid lactone and phenylindanes. As the roast degree deepens, these byproducts increase, especially after entering second crack.

For many customers who dislike acidity, FrontStreet Coffee always recommends darker roasted Mandheling coffee, while for customers who prefer fruity acidity, lighter roasted coffee beans are more often recommended, such as washed Yirgacheffe or Kenya coffees.

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Important Notice :

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