How Does the Roasting Process Create Sweetness and Smoky Flavor?

The idea that darker roasting always means a stronger sweet aftertaste is incorrect. During the roasting process, sweetness develops through transglycosylation from roughly 160-170°C onward, while caramelization lowers sweetness intensity and adds a slight scorched aroma. From the end of first crack into second crack, caramelization peaks and smoky notes become more prominent in the bean.

Green beans start with no developed sweetness at all, which is part of what a raw coffee bean tastes like before heat is applied. Sweetness climbs through dehydration, first crack, and the gap before second crack, then falls as caramelization takes over. Managing smoke exhaust during roasting helps limit how much smoky character settles into the final cup.

Many people believe that the darker the coffee beans are roasted, the stronger the sweet aftertaste will be, but this is actually a common misconception. During the roasting process, the development of sweetness, the involvement of caramelization, and the production of smoky flavors are all closely related to temperature and time. This article will start from the various roasting stages from green beans to roasted beans, carefully sort out the fluctuations in sweetness intensity, and explain how smoky flavors remain in the coffee beans. It will also share how to reduce the impact of smoky flavors on the taste through smoke exhaust, helping coffee enthusiasts understand the scientific logic behind roasting more comprehensively, and recommend related products from Front Street Coffee.

Roast Level and Sweetness Intensity

"The darker the roast, the stronger the sweet aftertaste" represents "the higher the sweetness intensity" — this is an incorrect concept.

*Green bean stage: sweetness has not yet begun to develop.

*Heating and dehydration stage: in the first half, the temperature is insufficient and sweetness does not develop; in the second half, the temperature just reaches the starting point of pyrolysis at 160–170°C, at which point "transglycosylation" begins, and sweetness starts to develop.

*After dehydration, as the temperature rises into the first crack stage: sweetness continues to increase, but the bean body is not yet evenly fully roasted, so the internal raw, astringent taste and acidity are stronger than the sweetness.

*From the start of first crack to the end of first crack: sweetness continues to increase, and the bean body only approaches full roasting at the end of first crack; the internal raw, astringent taste decreases, acidity is still strong, and sweetness perceptible to the taste begins to emerge.

*From the end of first crack to the beginning of second crack: in addition to "transglycosylation" continuing, "caramelization" also quietly begins ahead of time. "Transglycosylation" is an important step that increases sweetness intensity, while "caramelization" lowers sweetness intensity and instead brings out a slight scorched aroma, adding layers of complexity.

*From the beginning of second crack to the rolling second crack stage: "transglycosylation" enters its final stage, while "caramelization" is at its peak, so sweetness intensity no longer increases and instead becomes weaker and weaker. As scorching continues over time, carbonized bitterness and smoky flavor increase, and some irritating "second crack pungent odor" is also added.

*From rolling second crack to the end of second crack: the sugars produced by "transglycosylation" are fully used by "caramelization" and transformed into caramel with lower sweetness. At this point, because there are no acidity factors, second-crack-end beans usually make people feel "after bitterness comes sweetness." If second-crack-end beans are roasted successfully and brewed successfully, the bitter taste should be suppressed very low, and drinking it will be somewhat similar to high-purity dark chocolate "paste"; the sweetness is very lasting, but its intensity is not high.

Where Does Smoky Flavor Come From?

Where does smoke come from? This has to start with how green beans become roasted beans.

In the process of turning green beans into roasted beans that can be used for brewing, high-temperature roasting must occur to produce "pyrolysis."

Pyrolysis is like the energy in a factory that drives machinery and equipment; it processes and transforms many "raw materials" in green beans into "products."

The energy comes from external "heat," with the addition of thermal energy.

It is like cooking at home: if you accidentally fail to control the heat well, the food burns.

Burnt food is mostly carbohydrates, so during the burning process, moisture is rapidly dehydrated by high heat.

Therefore it cannot maintain the food's original color and turns carbon black.

Carbon black is very close to the composition of charcoal, but that is not the end of its life.

Carbon will continue to burn until it becomes ash.

When burning, it still releases a large amount of smoke.

The essence of coffee beans is also carbohydrates, so the principle applies.

But coffee beans have one more thing to pay attention to, namely the silver skin attached to the outside.

Unlike the coffee bean itself, the silver skin does not have a certain thickness and moisture, so its moisture is very easily dehydrated by high heat.

In addition, at a certain stage, the silver skin separates from the coffee bean itself, and at this time it happens to be in the high-heat stage of continued temperature rise.

(Roasting coffee beans will exceed 200°C.)

In a dry and hot environment, the surface of the coffee beans will smoke, let alone the thin silver skin.

So how does the smoky flavor remain in the coffee beans? And how should the smoky flavor be reduced?

The answer is "smoke exhaust."

If the smoke is exhausted smoothly, then of course the smoky flavor will not attach too much to the coffee beans.

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