Coffee Roasting Process And Basics: The process of roasting coffee, in some ways, often reminds us of hypocrisy. Although the first Ethiopians burned coffee hundreds of years ago, there is a microscopic scientific description of the roasting process.
Therefore, most roasters learn this technique from experienced roasters who have gone before. But often, young roasters learn from trial and error, roasting and tasting from countless different batches of coffee, thereby building their system of reasoning and experience. Let’s know about the basics of coffee roasting with Helena!
Roasting And Variations When Roasting Coffee
Roasting is the process of heating raw coffee to become coffee beans that we can puree brew – That is the simplest expression possible. In reality, however, things are a little more complicated than that. Coffee roasting has a lot to do with science, and understanding more about the Maillard reactions, caramelization, crack 1, crack 2, or the particle structure transformation mentioned in this article.
Coffee beans are green before roasting and have a fragrance similar to beans or grass; only after roasting do tastes and smells begin to develop in the seeds. The whole operation of a taste station is governed by two mechanisms: part science with physical responses and restart/inspiration.
As a result, the flavor we get from coffee originates from a brief journey in the previous few decades to convert from element to taste, with a variety of material modifications including:
- The seeds will change color from blue to yellow, brown, and finally black.
- The seeds grow increasingly porous and brittle as their size almost doubles and their mass virtually half.
- Between 800 and 1000 flavor compounds are significantly reduced if roasted for too long.
- Please turn on the crack as they release steam & other gases.
Some factors govern these changes and occur during certain roasting stages, which we will learn about shortly after.
Segments Of The Roasting Process
Various stages of the roasting process. The drying phase is commonly referred to as the first step in the roasting process (although coffee beans constantly lose moisture during roasting).
The breakdown of chlorophyll causes the color of the coffee beans to shift from blue to yellow at this early stage. When going on to the organization phase (flavor development stage), the Maillard reaction causes the coffee beans to transform from yellow to light brown.
As the roasting process progresses, the brown color of the coffee beans darkens as they approach the first crack (Frist crack), owing to the caramelization reaction that occurs. If the turn-out phase does not conclude on time, the coffee will be destroyed.
After processing, the raw coffee beans have 8 to 12% humidity. We need to dry it before we start developing new flavors. The drying phase usually lasts 4 to 8 minutes with a traditional drum roaster. The temperature at the end of the drying phase is usually 140–160⁰C. This is a critical time to collect the heat needed for coffee beans’ delicate taste development stage.
When you get used to the roasting process, you will know that we only put coffee in when the roaster has reached the required temperature. The roasting industry calls this charge temperature, i.e., the maximum temperature (or charging temperature).
And to determine the input temperature is how much you have to consider based on the origin & processing method of that type of coffee, the thickness of the roasting batch, more importantly, the type of roaster, and the total expected roasting time.
Why complicate the input temperature so much? Because the input heat is too high, the coffee will be explosive. But if the temperature is low, the coffee won’t get enough heat for the taste development process.
You are then forced to raise the temperature or extend the longer roasting time than expected, making the device hotter. The control is more difficult (due to the temperature difference between the grain core and the outside). Again, the coffee does not develop its potential flavors.
Middle Section – The Middle
A transition (though not necessarily a stage) is called ‘The Middle.’ While the drying process continues, green coffee will turn yellow or light brown, so some documents call this the ‘organization phase.’
From this stage, the natural sugars in the seeds will participate in the chemical reaction, along with the release of steam, causing the embryo to begin to expand and give off a pleasant aroma.
Changes in color and aroma are primarily the product of the Maillard reaction – they accelerate when the particle temperature reaches about 121°C – 149°C. By about 171°C, caramelization begins, degrading natural sugar levels so the Maillard reactions will slow down. The caramelization process will profoundly change the color of the seeds and create flavors of fruit, toast, or chestnuts.
Both the Maillard and caramel reactions reduced the sweetness of the already low amount of sugar in coffee to increase the bitterness significantly. Logically, the expansion of coffee beans and high temperatures also help free up the silver skin.
At the same time, the roasting process for this segment will release a large amount of smoke. The operator must ensure the airflow is high enough to suck all the dust and smoke out.
Many roasters have mentioned that the time from the start of the first crack until the discharge of coffee out of the machine is considered Development Time. This misleading term almost simplifies the roasting process with segmentation into steps 1, 2, and finishes while encapsulating the transformation of taste in a brief phase of the entire process.
According to Scoot Rao, most roasters often tailor the growing time separately from the rest of the roasting process. Still, such an approach will often lead to the possibility of coffee not achieving its delicate flavor formation, so how to make this stage proportional to the entire roasting process.
“Experience has taught me that the development-time ratio should be between 20%-25% of total roasting time. In other words, the timing of the first crack will start at 75% to 80% of the roasting time scale and vary slightly depending on the desired level of roasting.
The roasting level is just a name, a concept, and the most crucial key. Usually, lightly roasted coffee will show many “original flavors” derived from species characteristics, processing methods, altitude, soil & climate.
The darker the roast, the more the original taste of the seeds is overshadowed by the like produced by temperature. As it approaches the dark roasting area, the “roasting flavor” is so dominant that it is difficult to distinguish the origin of the coffees from one another.
Roasters are often free to decide how much roasting is needed for their coffee (on a spectral scale) and even named after their own, even as Counter Culture Coffee calls roasting levels by their boldness Apollo, Big Trouble, and Forty-Six. Stark bucks, meanwhile, have Blonde roast, Full city, Italian roast, and French roast.
It may seem complicated, but they’re different from light roasts, medium roasts, or dark roasts. Or at a smaller level of division between them.
Although most experts rate roasting levels based on grain color, there has never been an exact consensus on the names of these specific levels. There is no universal system that exists to name roasting levels. – Scott Rao
Agtron Color Scale
The most common, but perhaps most accurate, a method for determining the level of roasting is to evaluate the color of the coffee beans on the Agtron scale. In principle, the Agtron coloring machine will shine an ultraviolet light on the ground or whole-grain coffee sample. Then the sensor will measure the level of reflection to analyze the color, thereby giving a number indicating the status of roasting.
An Agtron coloring machine will have two scales: M-Basic (or Commercial Scale) and Gourmet Scale (similar to the centimeter and inch scales), each of which was developed to meet the needs of each roaster, at different scales:
- Commercial Scale: from 0 to 100 (dark to light), commercial is the original roasting classification scale developed for commercial roasters. Over time, the commercial has been adopted by many other measuring devices as a critical scale for the development of coffee beans.
Both scales use the same reference point of 0, equivalent to pure carbon, without aroma and taste. At the top of the Scale with Commercial 100.0 and 133.0 with Gourmet is the equivalent of green coffee. The roasting levels on the Agtron Gourmet scale regulated by the SCA include:
- Light: > 70
- Medium Light: 61-70; Medium: 51-60; Medium Dark: 41-50
- Dark: 35-40; Very Dark: 25-34
However, Agntron is not the only way to track the transformation of coffee throughout the roasting process. Most roasters use a combination of temperature, smell, color, and sound to follow the roasting process.
There are two crucial temperature thresholds called “cracks” that we have mentioned before – At a temperature of approximately 196 °C, coffee will sound due to the spread of the grain. This point is called the “first crack,” marking the beginning of the “light roast.” At the first crack, a large amount of the moisture of the coffee has evaporated, and the coffee beans will increase in size.
Next, when the coffee reaches approximately 224°C, it emits a “second crack,” which indicates that the structure of the coffee begins to break. If roasting is allowed to go further, the coffee will soon be fully carbonized and eventually burned.
Roast Profile And Consistency Of Roasting
Roast profiles are a collection of data that affect the coffee roasting process. Based on input data and settings during roasting, Roast profiles will be recorded manually or using computer software connected to the probes inside the roaster.
The Roast profile will provide an approach to the desired taste and be the basis for maintaining consistent quality on an industrial scale.
We often say that life is not a destination, but a journey. Coffee as well, coffee can be roasted to the same brown color but the taste is completely different. As a result, another trend has dominated the coffee roasting industry, in which the roasting process has shifted its focus from focusing on color, temperature, or end time to recording roast profiles with large amounts of data to ensure product consistency. – Rob Hoos – SCA
Temperature And Equipment (roaster)
Not only does temperature caramelize sugar and brown coffee during roasting, but it also catalyzes a variety of changes. Otherwise, each coffee bean is also created by temperature when done correctly.
Most fundamentally, heat peeling can take place in a variety of ways, including three main heat transfer mechanisms: thermal conductivity (contact heat); Convection (like a dryer), and Radiation (like heat from the sun). And each different type of roaster will prevail in one of the three ways above, which is not considering the ability to stabilize temperature, automation, or Scale.
Here are some of the roasters that are commonly used in the coffee industry:
- Classic drum roasters: Coffee is heated directly due to contact with the empty surface and the process of hot air convection through a suction fan.
- Fluid-bed roasters: The machine uses hot airflow with high temperatures that constantly blow into the roasting chamber to heat the coffee while mixing them instead of the rotation of the drum.
- Recirculation roasters: Instead of smoking – exhausting the whole as the above machines, recirculation uses a system to circulate hot air in the device, making it more fuel-efficient.
Each roaster design has its advantages and disadvantages (you can see more coffee roasting history or the coffee roaster revolution), but no new design has ever overshadowed the popularity of traditional roasting drums – with techniques that haven’t changed much in the last century.
Finally, the Agtron, Roast profile, and roaster scales are never decisive enough for a coffee’s ability to develop the expected taste. As mentioned from the beginning, quality depends on the combination of essential insights in the personalization phase of each roaster.
“The best roasters always know how to operate according to how they feel and only use data and technology as a backup to their instincts,” said Jim Kelso, head of quality control at Stumptown Coffee.
Therefore, Prime has pursued this topic relentlessly, with a modest accumulation to provide a total reliability overview of the roasting process. May you carefully share, with complete sources, to ensure originality and orthodoxy – Thank you for taking the time.!
- The Coffee Roaster’s Companion (Scott Rao, 2014)
- www.thekitchn.com/ What Actually Happens During Coffee Roasting?; www.baristahustle.com/ Let’s Talk About Roasting; www.scanews.coffee/ The Impact of Roasting on Coffee’s Flavor; www.coffeereview.com/ Roast Definitions; www.baristainstitute.com Coffee Basics: How do you roast coffee?