Stages in the coffee roasting process

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There are several key stages in the coffee roasting process and the duration of each stage is known as the roast profile for that stage. Roasters monitor their roast profiles very carefully to ensure that different roasts have stages that vary in time and temperature very slightly.

Stage 1: drying

Between 7 and 11 percent of the weight of a raw coffee bean is water, evenly distributed throughout the bean structure. Coffee beans cannot turn brown if they contain water; in fact, browning occurs when anything is cooked.

After the coffee beans are poured into the roaster, it will take a certain amount of time for the coffee beans to absorb enough heat for the water to evaporate, so the drying process requires a relatively large amount of heat and time. The coffee beans will not change much in color or smell because in the first few minutes of this stage.

Stage 2: Yellowing

Once the water has evaporated from the beans, the first browning reaction begins. At this stage, the beans are still very dense and have a basmati rice (Indian rice) and slightly bready flavor. The beans then begin to expand and the parchment is removed. The parchment is separated from the beans by the airflow into the roasting drum and is then safely collected to prevent burning.

The first two stages are crucial: if the coffee is not dried properly, it will not roast evenly in the following stages and may roast well on the outside while the inside remains undercooked. Such beans will not be good, as the flavor will be a combination of the bitterness of the outside combined with the sourness and grassiness of the unripe inside. Slowing down the roasting process will not solve the problem, as different parts of the bean are affected at different rates .

Stage 3: first crack

As the browning reaction of the coffee beans begins to accelerate, gas (mainly CO2) and steam are formed inside the beans. As the pressure begins to build, the beans will burst, making a popping sound and almost doubling in size. From this stage, the characteristic coffee flavor will begin to emerge and the roaster can stop the roasting process at any time from this point.

The roaster must be able to observe the point at which the rate of temperature rise of the beans begins to slow down despite the constant heat input. Failure to provide adequate heat to the beans will delay the roasting process, resulting in over-roasting of the beans, resulting in a loss of quality.

Stage 4: Roast development

After the first crack, the surface of the coffee bean will be smoother but still not perfect. This stage will determine the color and roasting level of the coffee bean. At this point, the roaster will choose the balance between sourness and bitterness of the coffee bean, because sourness will decrease very quickly while bitterness will increase as the roasting process continues.

Stage 5: Second crack

At this stage, the coffee beans will pop a second time, but with a quieter sound. At this point, the oils will start to spread to the surface of the coffee beans, most of the acidity will have disappeared, and a completely new flavor will be formed, often considered the “normal” roast flavor.

This flavor is independent of the coffee variety used as it is the result of burning the coffee thus losing the original natural flavor of the coffee bean.

Continuing the roasting process after the second crack can cause the coffee beans to catch fire, which is extremely dangerous especially with large commercial roasters.

There are two terms used in the coffee roasting industry: “French Roast” or “Italian Roast”. Both terms refer to a very dark roasting method, which often results in a bitter and full-bodied flavor, but most of the other characteristics of the coffee are lost. While this roasting method may be preferred by many, it does not allow for the discovery of the unique flavors of high-quality coffees from different regions of the world.

Translated from: The World Atlas of coffee