Basic Knowledge of Coffee Roasting
Coffee Roasting is a process that plays an important role in coffee processing until served. The scents, flavors, aftertastes, and magical flavors of coffee are caused by this process. Roasting coffee beans isn’t such a simple thing, it’s not only putting it in the roaster and then waiting until the color is changed and ripe.
The coffee roasting process has an impact on the quality of taste and coffee aroma until 30%. This number is gained from the assumption that 55% of aroma forming and coffee flavors comes from “farms” like climate, natural conditions, altitude, varieties, and post-harvest process. at the same time, another 15% occurs when the brewing process.
Coffee has a taste and aroma which we can enjoy in the form of a drink initially is a green coffee bean that has a scent like grass. Then, coffee beans that have been through the post-harvest process will be roasted with different methods. Through the roasting process, the aroma compounds present in the coffee beans will increase, and coffee beans will experience quite drastic changes. Actual coffee beans will produce different coffees if roasted in different heats even though the result is the same color, its because the coffee roasting technique is an art.
Color and Water Content Changes
The first change that will experience the coffee beans is the color display. The green color of the coffee will change to brown with different levels of color depending on the profiling roasting selected by the roaster. Generally, three roast profiles affect the color change on green coffee beans, specifically Light roast, Medium roast, and Dark roast.
Next is the reduced water content contained in coffee beans. The roasting process will reduce the water content included in coffee beans by around 2,5%. During the roasting process, water that appears because of a chemical reaction will vaporize. As the water content lowerings, the mass of coffee beans shrinks by around 12-20%. That’s why roasted coffee beans’ weight is lower than green beans.
Coffee beans also contain oil because of the high internal pressure. The compound migrates from the center of the cell to the coffee beans’ surface. This oil will keep the chemistry compound whose role is to produce the taste and aroma in coffee.
The Purpose and Function of Coffee Roasting
Of course, the purpose and function of coffee roasting are for the coffee beans to be ripe, killing germs and bacteria on coffee, and fit for consumption. More than that, the purpose and function of the roasting process is exposing the potential of coffee:
- The potency of aroma/smell on coffee beans
- The goods of a kind of flavors and aftertastes included on coffee beans, like sweet, fruity, etc.
- Body
- Balance ratio between aroma, taste, and body
The Process Phases of Coffee Roasting
There are several steps or phases during the roasting process. The time taken for coffee beans to go through each phase side by side to beans temperature is generally known as Roasting Profile.
1. Drying Phase
Uncooked coffee beans usually contain water evenly split into every dense structure of coffee beans. When green beans get put into the roasting machine, the first step that occurs is the coffee beans will absorb the heat, then start to evaporate the water content. This drying process tends to need large enough heat and energy.
2. Yellowing Phase
After the remaining water content was “drained” from the coffee beans, the color change reaction began. This phase is commonly called the yellowing phase or Maillard or often called the caramelization phase. In this phase, coffee beans will expand, and coffee beans’ thin skin or chaff will peel off. The chaff will separate from the roasted beans through the airflow system in the roaster. The collection of coffee beans’ chaff will stored in the chaff collector to prevent fire risk (on the machine) given by its thin and flammable.
The first two steps (drying and yellowing) include a meaningful phase of the roasting process. The mixing process should be regulated to get even heat on every part of the coffee beans.
3. First Crack Phase
When the coffee beans start to change brown after the yellowing process, there is a mixing between carbon dioxide gas and water that evaporates from the coffee beans’ core. When the pressure of those two elements reaches its peak, The coffee beans will begin to open, and at this phase, the coffee beans will cracking. This process we can recognize through the crisp sound, like the sound of cracking nuts. In this step, all the characteristics and familiar tastes of the coffee beans will begin to develop and “form”.
4. Development Phase
After the first crack, the coffee beans tend to have a softer texture in the surface but not in its entirety. This roasting phase determines the final color of coffee beans. In this phase, the roasters decide the final result (body, aroma, aftertaste) of roasted beans according to what they want.
5. Second Crack Phase
In this phase, coffee beans start cracking for the second time, but the sound is lighter and softer. When coffee beans reach this phase, The coffee oil usually will appear on the beans’ surface. Much of the coffee’s acidity character has been lost in this phase, and a new kind of taste also grows in this step.
6. Cooling Phase
Once it feels correct with the wanted specification, coffee beans will be discharged from the drum, then quickly cooled in a coolant tray to lock the taste, aroma, and body of the coffee beans.
7. Resting Phase
After the roasting process, coffee beans are kept somewhere. Giving pause around 1 to 3 days relies on the coffee beans type. This process is purposed to give time to the coffee beans to release the carbon dioxide that formed during the roasting process.
It is not just the color that’s experiencing the change when the coffee beans get into the roasting process, but also the structure. After the roasting process, the next coffee beans will through many processes by the serving method, for example, brewing, espresso, etc.
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