Coffee Roasting

From the coffee cherry to the roasted coffee bean

It is not the type of coffee that determines the later aroma of the coffee, but the method of preparation and roasting. The individual coffee roasting phases lead via the drying process and the associated coloring of the coffee cherry to the first and second crack until the roasted coffee bean is cooled. You can find out what happens to the coffee beans during roasting, and what roasting methods are available.

Roasting coffee: The individual roasting phases

Researchers have so far been able to identify more than 800 aroma substances in a roasted coffee bean. Therefore, coffee is one of the most aromatic natural products. Hence, we roast coffee beans to release these aromas. The roasting process consists of dry heating of the seeds without fat and water. However, some special measures are required to allow the flavor to develop fully.

green coffee beans

Green coffee beans

Phase 1: Drying of the coffee beans

Green coffee contains up to 11 percent of water distributed throughout the bean—this water we have to evaporate before roasting. Therefore, in the first phase of the roasting process, we heat the roaster. At temperatures between 20 and 130 degrees Celsius, the coffee beans dry until the water has completely evaporated. The drying step is a prerequisite for the coffee beans to turn brown as the roasting process continues. If this does not happen, they roast less inside, with the result that an unpleasant, grassy taste develops.

Phase 2: Yellowing – The Maillard reaction – the browning process begins

Once we reach a temperature of around 130 degrees Celsius, the actual roasting begins, during which the coffee bean changes color. It slowly turns yellow and then takes on a beautiful caramel-like brown tone. The color change is also due to chemical processes and, in particular, to the Maillard reaction, which takes place between 145 and 200 degrees Celsius. The smell also changes and changes from a hay-like to a slightly buttery scent. The delicate skins of the coffee beans loosen, making them considerably bigger. Depending on the roasting process, the detached skins will be removed in different ways.

The Maillard reaction, named after the French natural scientist Louis Camille Maillard refers to a browning reaction. This reaction you can similarly observe at the frying and deep-frying of other foods. It is not a specific chemical reaction, but rather the entirety of reactions taking place next to each other and succession, which are the cause of a large number of reaction products.

Phase 3: First crack or the first crackle

The first crack is the name of this third phase of the roasting process because carbon dioxide and steam develop inside the bean. Said processes cause the pressure to increase so that the seed finally cracks along its middle notch and doubles in size. You can recognize this process by a cracking or crackling sound. The beans are already drinkable from this event onwards. The coffee nuances develop so that the roasting process can be stopped at this earliest stage for filter coffee. This point in time occurs regularly 30 seconds to one minute after the first crack. The duration of the roasting process also determines the intensity of the brown color, while the balance between acidity and bitterness in the coffee depends on the degree of roasting. The acidity decreases as roasting continues, while the bitterness increases.

Light roasting stages

Be aware that every roaster can interpret the roasting stages his/her way. The following images of roasting stages only should give you an idea.

Coffee roasting stage - light roast to cinnamon roast

Light roast to cinnamon roast

Coffee roasting stage - medium roast

Medium roast

Coffee roasting stage - medium roast - city roast

Medium roast / City roast

Phase 4: Second crack or the second crackle

At 200 degrees Celsius, sugar in the bean starts to caramelize, resulting in the typical roasted flavor. At around 230 degrees Celsius, the seeds begin to lose pieces from their cell wall, which are simply broken off. This second crack is much quieter than the first crack. This produces a continuous crackling sound that slowly increases and then flattens out again. When the second crack starts, the roasting depth is sufficient for espresso and darker roasts. In this phase, the acids are almost entirely broken down, which gives rise to the typical roast aroma and makes the coffee much more bitter.

Once 245 degrees Celsius are reached, the second crackling ends. Already during this process, the beans have taken on a slightly oily shine. These oils, fats, and other cell constituents are driven out of the seed by the heat. The coffee bean has now taken on a very dark, almost black color. Now, at the latest, is the time to stop roasting. If the roasting process continues, the coffee will still taste like charcoal, with substantial smoke development.

Dark roasting stages

Be aware that every roaster can interpret the roasting stages his/her way. The following images of roasting stages only should give you an idea.

Coffee roasting stage - dark roast - full city roast

Dark roast / Full city roast

Coffee roasting stage - dark roast - french roast

Dark roast / French roast

Coffee roasting stage - dark roast - italian roast

Dark roast / Italian roast

Phase 5: Cooling the roasted beans

Cooling the roasted beans is also an essential step in roasting. The seeds must be cooled down quickly so that the coffee does not roast any further, and the reactions are stopped.

cooling roasted coffee beans

Roasting coffee – the different roasting processes

Several critical processes are set in motion during coffee roasting. The coffee beans lose water and weight due to rising temperatures and water vapor forms, which increases their volume. Between 160 and 190 degrees Celsius, the sugar contained in the beans caramelizes, while between 165 and 210 degrees Celsius the roasting aroma is created. The combination of sugars and amino acids leads to the development of new flavors. The way the coffee is roasted also influences the taste of the coffee prepared later. Small roasting plants particularly prefer long-term roasting. It ensures an intensive taste experience and a distinct aroma. Traditional drum roasters are used, in which an externally heated drum rotates around its center and whirls the coffee beans around. The roasting of the coffee beans regularly takes between eight and 25 minutes.

In contrast, industrial roasting is completed in two to seven minutes. In industrial coffee roasting, scorching air between 400 and 800 degrees Celsius is used. Due to the high temperature, the coffee beans may be nicely brown on the outside but not yet sufficiently dried on the inside, so burnt roasting aroma can develop.

Finally, it should be noted that the degree of roasting determines the taste of the coffee. A distinction is made between light and dark roasts when roasting coffee. Light roasting produces a grassy or bread-like aroma that is acidic, although this roasting process is particularly suitable for filter coffee. Dark roasting takes longer and takes place at higher temperatures. As a result, the coffee contains more bitter substances and less acid, so these beans are used primarily for espresso.

Find out how the coffee of KX ORAIO is roasted with a unique method.

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