How does the roasting process set a coffee's final color and flavor?

Roast degree decides whether a cup leans acidic or bitter, and SCAA's eight-level chart ties each stage to an Agtron color value, from light roast at 95 down to Italian roast at 25. Home drum roasting follows two rules: keep the heat low throughout so the bean surface does not darken before the inside is roasted, and start turning immediately at 60 to 65 rotations per minute.

A drum takes more than twice as long as a professional roaster. Roasting Brazil Cerrado Red Bourbon on a Yangjia 800n, the time from first crack to dropping ran 3 minutes and 30 seconds. Uneven color after home roasting usually traces back to tools such as frying pans, ovens, and air fryers that cannot keep beans tumbling and evenly heated.

Want to roast coffee beans at home but don't know where to start? Front Street Coffee, drawing on the practical experience of baristas, introduces the key operating points of drum roasting and compiles SCAA's eight-level roast degree comparison chart—from light roast with an Agtron color value of 95 to Italian roast with a value of 25, explaining one by one the timing of dropping, appearance changes, and flavor performance at each stage. The article also compares the time difference between roasting the same Brazil Cerrado Red Bourbon coffee beans with a professional roaster versus drum roasting, helping coffee enthusiasts understand how roast degree determines the acid-bitter direction of a cup of coffee.

Nowadays, many coffee enthusiasts are no longer satisfied with simply tasting, but have started trying to roast coffee beans themselves. When browsing social platforms, Front Street Coffee often sees people sharing their home roasting processes, and also notices a common problem: the roasted beans come out with uneven color depth and poor uniformity.

The final taste of coffee beans depends largely on the roast degree and whether the roasting is even. So before clarifying which roast degree different colors correspond to, Front Street Coffee will first talk about the basic methods of roasting coffee beans at home.

The home roasting methods circulating online are diverse, with some people using frying pans, ovens, and air fryers. But the common shortcoming of these tools is that they cannot keep the beans constantly tumbling and evenly heated. Therefore, Front Street Coffee more strongly recommends getting a drum-style coffee bean roasting cage.

According to the operating experience of Front Street Coffee's baristas themselves, there are two key points to pay attention to when roasting with a drum: first, keep the heat low throughout, otherwise the surface of the beans will quickly change color while the inside is not yet fully roasted; second, ignite and adjust the heat before placing the drum on, then immediately start turning it, controlling the speed at 60 to 65 rotations per minute. Drum roasting takes more than twice as long as a professional roaster. For example, when Front Street Coffee used a Yangjia 800n to roast Red Bourbon coffee beans from the Brazil Cerrado region, it took 3 minutes and 30 seconds from first crack to dropping, belonging to a medium-dark roast, with the whole process taking 13 minutes.

This picture shows Brazil Cerrado coffee beans roasted by Front Street Coffee using a professional machine.

If switched to a drum for roasting, reaching a similar degree requires a total of 31 minutes. During this time, your hand cannot stop and must maintain a speed of 60 rotations per minute. Once you stop or turn too slowly, the beans are very likely to scorch, which can be said to be quite hand-intensive.

This is the same type of coffee beans roasted by Front Street Coffee's barista at home using a drum.

Although roasting at home is quite tiring, the whole process allows people to very intuitively feel the changes in the coffee beans: from green raw beans slowly turning yellow, giving off a sweet aroma similar to corn; then turning cinnamon-colored, emitting a caramel scent; and gradually turning chocolate-colored, releasing the smell of roasted nuts.

This experience is quite healing, and it also makes people realize that to roast coffee beans deliciously, one must not only understand the characteristics of the beans themselves, but also learn how development during roasting affects flavor, thereby cherishing every cup of coffee even more.

If we roughly categorize the coffee beans sold on the market, it can basically be summarized as: those on the acidic side are light roasts, those on the bitter side are dark roasts, and those balanced between acidity and bitterness are medium roasts. The roast color comparison card provided by SCAA, the world's most authoritative specialty coffee organization, divides coffee roast degrees into eight levels:

The lightest level has an Agtron color value of 95 and is called Light Roast. The dropping timing is approximately during the dense stage of first crack (pour them out while the beans are still crackling), and the flavor usually presents bright acidity.

The left image shows a medium-light roast, and the right image shows a medium-dark roast.

Agtron color value 85 belongs to Cinnamon Roast. The dropping timing is around the end of first crack (when the crackling sound has just stopped or only a few sporadic sounds remain). The flavor of beans at this degree is mainly acidic, accompanied by a sweet aroma.

Agtron color value 75 is called Medium Roast. The dropping timing is approximately after first crack has completely ended (the crackling sound has completely stopped). The flavor is dominated by sweetness, with a small amount of fruity acidity.

Agtron color value 65 is called High Roast. The dropping timing is approximately from the end of first crack to before the start of second crack (about a 1 to 2 minute silent period). The flavor presents nutty and caramel notes, with a balanced mouthfeel and no acidity.

Agtron color value 55 is called City Roast. The dropping timing is approximately at the very beginning of second crack (after a period of quiet, one or two faint crackling sounds appear). The bitterness is more obvious, and the caramel aroma is more intense.

Agtron color value 45 is called Full City Roast. The dropping timing is approximately before the dense stage of second crack (before the crackling sound is heard). At this point, the roast degree is already quite dark, and the taste leans toward intense burnt bitterness.

Agtron color value 35 is called French Roast. The dropping timing is approximately during the dense stage of second crack (the crackling sound is heard again, but duller than the first time). At this point, oil has already begun to seep out onto the bean surface.

Agtron color value 25 is called Italian Roast. The dropping timing is approximately at the end of second crack (after the dense sounds have passed). The beans are pitch-black and shiny, and oil has already penetrated to the surface.

From Front Street Coffee's observations, whether machine roasting or enthusiasts doing it themselves, beans are usually not roasted to a depth beyond color value 65, because over-dark roasted coffee tastes too mellow and heavy, with little flavor layering left.

When drum roasting skills have not yet been fully mastered, it is also not recommended to roast too light, because if the heat is not well controlled, although the bean surface reaches the color you want, the core of the bean may not be fully roasted, and the brewed coffee can easily carry grassy or astringent notes.

The above content is compiled by CoffeeHunters, a coffee news website.