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What is Coffee Roasting?

  • by Justin Lim
  • 5 min read

Coffee beans are the seeds of coffee cherries that have been developed. They are then transformed and dried to coffee beans after being processed. Coffee beans are green in color and possess a somewhat earthy smell before being roasted.

Man holding coffee beans from a roasting machine

Green coffee beans, on the other hand, do not have a strong aroma of coffee. There are hundreds or even thousands of aroma chemicals in coffee. These substances give the coffee its flavor. We can modify the amount of these fragrance chemicals in coffee and also influence its taste via roast profile analysis.


The Process

Roasting is the process of turning green coffee beans brown. It may be done in a number of ways, and each method has its own set of benefits and drawbacks. I'll go through the fundamentals of roasting and commercial roasting.


Roasting stages

Roasting is divided into three phases: drying, browning, and development.

1. Drying

The relative humidity of the coffee bean is between 8 and 12 percent. Before we begin roasting, it must be dried out. The drying process takes between 4 and 8 minutes in a conventional drum roaster (see below for different types of roasters). The end temperature of drying is generally 160 ⁰C. With drum roasters in particular, you must be cautious not to burn the beans by putting too much heat into the beginning. The drying stage is essential for gathering energy in the bean since the last phase of roasting is endothermic (heat absorbing).


2. Browning

The coffee will begin to smell like toasted bread and hay after being heated to 160°C. At this time, the aroma precursors are beginning to convert into aroma chemicals. Browning occurs even though drying takes place throughout the browning phase.

The Maillard reaction, which causes browning, begins at the end of the first stage. The Maillard reaction is a chemical process in which reducing sugars and amino acids react to produce hundreds of distinct aroma and color compounds known as melanoids. The roast is now at its highest temperature and is slowing. -Some roastmasters also want to slow it down (and some don't) in order to aid flavor development. The coffee begins to pop near the end of the browning phase. This is known as the first crack, and the coming stage starts.


3. Development

The coffee cracks in the early development stage, and the reaction becomes exothermic. The bean has gathered energy throughout the drying and browning processes, leading to an explosion. Time is the process in which desirable aromas are developed. If we don't slow down the roast at development time, we risk producing coffee with a smoky flavor and an unpleasant taste.

Depending on the desired flavor profile and roast level, the development stage might last anywhere from 15 to 25% of the total roast time.


Roast Degree

The roast degree is one of the most significant criteria when it comes to roasting. It can be determined by a colorimeter or by taste. Roasters typically want to accentuate coffee's natural qualities and control the roast degree. Lightly roasted coffees are generally more acidic, while dark roasted coffees are generally more bitter. In general, the more fruity tastes are found on light roasts, whereas roasted and burnt tastes are common on dark roasted coffee. Due to the presence of a organic chemical called 5-hydroxymethylfurfural, light roasted coffee is more fruit-flavored. When roasted beans are roasted further, this compound breaks down to fewer fruity chemicals. The mixture acquires a toasted and charred flavor when the amount of sulfuric compounds in it increases. We can assume that light roasted coffee helps to bring out the raw coffee's taste better than dark roasted coffee. It is simpler to tell apart light roasted coffees from each other than dark roasted coffees.


Roasting Time

Despite the fact that roast degree has the most significant impact on coffee flavor, overall roast duration and time of each step are also important variables. You'll produce more odor chemicals if you roast quickly. However, don't over roast the beans! The overall taste of coffee (fruity, berry-like, chocolatey, and nutty altogether) is better. Additionally, the amount of fragrant chemicals created in the early development phase is greater with rapid roasting.

In certain situations, however, rapid roasting is not desirable. It might be owing to the shape of the roaster (see next paragraph) or to coffee's characteristics. Fast roasting accentuates all of the coffee's tastes. We can adjust the roast profile if we don't want some tastes in the coffee. For example, acidity is generally desired flavor in espresso beverages, yet low acidity is sometimes sought after. When organic acids have more time to break down while roasting, the coffee gets less acidic. This is when slow roasting might be beneficial.


Coffee Roaster Designs

There are numerous roaster designs available. The thermodynamics of roasting are affected by the design, and different tastes of coffee can be produced with various machines.Smaller roasters frequently use drum roasters, which rotate beans in a drum below either a direct or indirect fire. This results in big energy volume for the roaster. Roasting with these apparatus is quite consistent, but the roastmaster should be able to anticipate up to minutes ahead of time. Drum roasters are ideal for slow roasting since a too high temperature at the outset of the roast may cause beans to be burned from the outside.

For ages, there have been fluidized bed roasters in the business. In a fluidized bed roaster, the roaster is heated by hot air flowing through it. That allows for smoother operation of the machine. It's also possible to roast beans faster and add more aroma with fluidized bed roasters since the outside of the bean isn't burned. There are also some Loring Roasters, for example, in which a drum is used to heat the coffee indirectly.


Filter or Espresso Roasting?

Have you ever tried to figure out what the difference is between filter and espresso coffee? Gravity distillation is used for filter extraction, which makes it extremely gentle. Filter may be used with aromatic, more acidic coffees. Espresso is produced with a 9 bar pressure, whereas coffee is extracted at a lower pressure. That means the flavor of the beverage is superior. When brewed, some coffee roasted for espresso may not be as good as filter coffee, and vice versa. Roast masters strive for a golden middle ground between too light and too dark, ensuring that coffee is suitable for both brewing and drinking.

Espresso is a beverage prepared from dark roasted coffee with a low acidity and a high body. Filter coffee is roasted differently in various countries, although the roast degree is generally lower than that of espresso. Today's roasts are more adaptable than they were in the past. On the other side of the spectrum, we want some of our espresso to be more robust. Then we roast a bit longer and extend the development period to develop flavor and lessen acidity.

In the end, becoming a roaster is an ongoing learning process. You may always learn more about the bean. I hope you enjoyed reading this article and found it useful in your coffee journey!

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