How Coffee Roasters Work: The Complete Guide

How Coffee Roasters Work

You do know that cup of coffee in your hand was once a bunch of green beans, right? That remarkable transformation is the result of an essential process called roasting. If you’re an avid coffee consumer, you’ll probably know there are different roast levels of coffee. To achieve each level, the process is done differently. Here, I’ll tell you how coffee roasters work and the four types of roasters!

How Coffee Roasters Work – The 4 Stages of Coffee Roasting

Although there are only three primary stages of coffee roasting, drying, browning, and roasting, we can stretch the process to four stages if we include the cooling that occurs in the end. Here’s an overview of each step on how coffee roasters work.

Stage 1: Drying

Before starting the roasting process, the coffee beans need to dry out. They usually have a humidity level of 8–12%. For each roast level, the humidity reaches a specific level. For example, it should get 0% when making dark roast beans, so the beans completely dry out.

The drying stage doesn’t take long; it only takes around 4–8 minutes if you’re using a drum roaster. In the end, the coffee beans should reach a temperature of 160 C. If the temperature gets too high, the coffee beans may burn. That’s why dealing with a roaster should be done delicately. The starting temperature should be just right to avoid any inconvenience.

Stage 2: Browning

Coffee beans being poured out of a coffee roasting machine

Although the drying stage precedes the browning, it still goes on for some time during browning. When the temperature reaches 160 C, the coffee beans start to smell toasty. In this step, the aroma intensifies because it converts to compounds.

Author Note: The browning stage gets a chemical kickstart when the Maillard reaction begins. It happens when amino acids and reducing sugars react to result in melanoidin, which are color compounds responsible for the aroma.

During browning, the roasting slows down a bit to allow for flavor development. You can choose to keep it at the same speed, but most roastmasters decide to slow it down because it results in a much better flavor.

This stage ends when the coffee beans pop. That’s when you know the moisture took its way out and cracked through the outer wall. Roastmasters call it the first crack. Light roast coffee, for example, isn’t roasted beyond the first crack. That’s why it preserves its natural acidic taste.

Stage 3: Development

The development stage is when the reaction converts to exothermic, and the heat gets out. That’s when the coffee beans crack as a result of the collected energy in the previous steps.

So, you can think of the process that way: the first two steps work on collecting the energy, preparing for the exothermic stage. Then, in this stage, the coffee beans make a tiny explosion, getting the energy out. It takes around 25% of the whole process, making it an essential step.

This is also the stage when aroma compounds entirely develop, resulting in the desired scent. The roasting must slow down in the development step, or else the coffee beans will turn out ashy and too sharp for your liking. That’s what happens in extra-dark roasts, which typically taste like ash.

Stage 4: Cooling

The last stage of how coffee roasters work is the cooling process. However, many people skip it when listing the steps. That’s mainly because the roastmasters don’t have control over it. It’s the only stage in the process that’s done 100% automatically.

As soon as the roasting is done, the roastmaster throws the beans into the cooling sieve. He should do it immediately, so the roasting process halts. If the beans are left for 5 minutes without entering the cooling process, they’ll dry out.

Other Factors That Affect the Coffee Roasting Process

Aside from the process itself, some factors affect the coffee taste. These factors determine the labeling of coffee upon selling.

Roast Degree

The roast degree is the primary indicator of the coffee taste that results from the process. Roastmasters determine it by the taste or color meter. Light roasts tend to have a more golden color and a fruity flavor. Their taste also leans more toward being acidic. The fruity flavor results from the number of organic compounds in the beans, which don’t get masked by the roasting.

Meanwhile, the dark roast has an outright bitter taste and a dark brown color. The bitter taste is a result of the sulfuric compounds that increase when the roasting process takes longer. These compounds are responsible for the burnt flavor of dark roasts.

Roast Time

Coffee roster with cup of coffee having break during work

The total roast time determines which level you’re going to get. Although there are some other factors included, if the time fails you, the result will do the same. You can say it’s the winning card of the process.

The time you spend roasting your coffee will determine the flavor. Whether you want it nutty, ashy, fruity, or chocolatey, you’ll need to adjust your timing accordingly.

Top Tip: The time is also responsible for the aroma. If the roasting is done right, you’ll get your desired compounds. But if the roasting takes more time than it should, the smell will diminish.

The Different Four Types of Coffee Roasters

Although the four stages explained above go for most coffee roasters, different devices require other preparations. Here’s a brief description of each coffee roaster type.

Drum Roasters

Drum roasters are the classics of coffee roasting. Think of a modern Ford and a good old Cadillac. The drum roaster would definitely be the Cadillac. These roasters only consist of the rotating drum that you put the coffee beans in.

How do drum coffee roasters work? It’s as simple as it gets. The drum keeps rotating above the flame, roasting the coffee beans inside. The motion ensures that all the beans get roasted evenly. Additionally, the roaster includes a fan that gets rid of hot air inside. The air passes through the drum and gets out of the device.

Some drum roasters available have extra-thin walls, which is inconvenient for some people. The thin walls will deliver more heat to the beans, which may result in an ashy taste. Or, it might not get the flavor you’re aiming for. Meanwhile, double-walled drums do their jobs as they should.

Indirect Heat Drum Roasters

Although the four types share some qualities with the classic drum roasters, this one is the closest to them. Indirect heat drum roasters work by rotating, too. However, the process is totally different than that of drum roasters.

How do indirect heat coffee roasters work? Instead of rotating directly over the heat, the drum is placed far away from the burner. That’s not the only difference; the hot air also gets out without directly contacting the drum.

Although indirect heat roasters may result in a better taste, they need extra care while dealing with them. The process is delicate because of the airflow adjustment. You’ll need to have enough skills to adjust it correctly.

Recirculation Roasters

Recirculation roasters are made for people who want to save energy and cost. They’re the most energy-efficient type out of the main four. That’s simply because of the way they work, similarly to drum roasters, but with an exception.

Instead of getting rid of the hot air out of the roaster, recirculation roasters work on recycling the exhaust air. Hence, the naming. While that saves a lot of energy and reduces the carbon footprint, it may result in coffee beans with a smoky taste. It’s simple chemistry; the hot air passes through the beans twice, which ought to have its toll on the final taste.

Some roastmasters avoid that by reheating the air before recirculating it. They’re convinced that heating it to a higher temperature than that of the chamber will reduce the smoky effect.

Fluid Bed Roasters

Coffee beans in a roaster

Fluid bed roasters are the most unique out of the four. They work in a completely different way than drum roasters, although they give the same results. In these roasters, the coffee beans keep floating in a fluid bed full of hot air.

In other words, the roasting process is done by circulating hot air constantly over the beans. The idea here is roasting the beans without getting them in direct contact with the metal. That’s why the procedure depends on floating them in hot air.

Author Note: Needless to say that these roasters are the most expensive because of the fluidized beds. However, they result in evenly roasted coffee beans, and they allow for controlling each bean’s temperature. That’s why a lot of roastmasters prefer it.

Final Thoughts

Who would’ve thought such a simple cup of coffee goes through all these stages? Well, it’s justified. When the heavenly taste hits your buds in the morning, you’ll believe it’s worth every step the beans go through!

There are a lot of variations of the roasting process and hundreds of different adjustments to reach the desired roast levels. Not to mention that each roaster type may result in a different taste and color. However, each roasting process must go through the same steps mentioned above. And, they all result in incredibly flavorful beans! We hope you enjoyed learning how coffee roasters work!

Stay caffeinated friends!

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