What Does a Coffee Roaster do?

Many people and equipment are involved in getting coffee from a seed in a cherry to a drink in your cup. There are endless videos on youtube of baristas brewing coffee in filters or on espresso machines. There is much less information on the most magical equipment—the coffee roaster. 

Without the coffee roaster, the beans would be green, not brown, and coffee as we know it would not exist. This blog post will give an overview of what happens, from the coffee beans going into the roaster to them coming out roasted and smelling delicious.

What does a coffee roaster do? A coffee roaster cooks coffee beans. Green beans are loaded into the roaster and dropped into a very hot (around 200c) drum. When heated, a series of reactions alter the taste of the bean from an almost tasteless green bean into coffee as we know it.

The person working the coffee roaster controls a handful of roasting variables, including how hot the coffee gets and how long it is roasted. Ultimately, they control the flavors we taste in the coffee we drink. Coffee roasters come in all sizes, from sample roasters that can roast less than 20g to large commercial roasters, which can roast batches of 500kg.

Types of Coffee Roaster

The two main types of coffee roaster are a drum roaster and a fluid-bed roaster (other types include a centrifugal roaster and a tangential roaster). A third, less common, type is called air roasters.

In an air roaster, each bean is suspended in air to ensure a nice even roast, each and every time. The chaff of the bean is then vacuumed away from the final product, leaving you with a smooth cup of coffee.

Drum Roaster 

A drum roaster heats the coffee through the conduction of heat. Imagine a cement mixer with a flame underneath it. The flame heats the drum, which continually rotates with the coffee beans inside it ensuring they’re evenly roasted. The gas can be turned up or down to control the flames, which controls the temperature and speed of the roasting process.

A drum roaster I would recommend is the Kaldi Home Coffee Roaster. This is a motorized Coffee Roaster that requires a gas burner. 

It comes with the body, thermometer, hopper, probe rod, and chaff holder.

It’s designed for effective circulation and warming of fresh air and hot air through arranged vents at a ton and down for smooth inner housing airing.

Fluid-Bed Roaster

Fluid-bed roasters use convection rather than conduction to heat the beans. Imagine blowing a hot hairdryer up into a drum. The airflow heats and moves the beans around the drum. Roasting coffee this way is quicker than roasting in a drum roaster.

If you want to purchase a fluid-bed roaster, I recommend the Fresh Roast SR800.

It has nine levels of heat and fan settings and can roast up to 4 ounces / 120 grams.

With its real-time temperature display and manufactures 1- year warranty, it is a great at-home fluid-bed coffee bean roaster. 

Parts of a Coffee Roaster

How do Coffee Roasters Work?

When making a batch of coffee, the beans are loaded into the roaster via the hopper. They are then held until the coffee roaster reaches the designated start temperature (usually just under 200c). The beans are then released through the loading chute into the drum.

When the room-temperature beans drop into the drum, it immediately brings down the temperature inside the drum, and heat (gas) is turned up to increase the heat and roast the beans.

As the temperature rises, the beans start drying out, then roast (when a chemical reaction called the mailliard reaction occurs). Once the coffee has begun to roast, the first crack will happen. Not long after this, there will be a similar second crack. This sounds a little like popcorn popper.

Some coffee will reach its end temperature before the second crack (but after the first) and will be released from the drum with the bean release lever and into the cooling tray. It will be released after the second crack occurs for darker roast coffee.

Coffee must cool down quickly to avoid further roasting. So, in the cooling tray, a revolving arm moves the beans around the tray to ensure they get as much air as possible. Some roasters also spray the coffee with cold water at this point to aid cooling.

Once the coffee is cooled, it is released from the cooling tray into a bucket, ready to be weighed and bagged.

A Recipe for Roasting

Once the coffee beans have entered the roaster, the person operating the roaster will have a roasting recipe called the roast profile. This will involve following a pre-set roast curve. The temperature of the drum and beans is monitored throughout the process via a computer system. 

Whoever is operating the roaster must make tiny adjustments to the gas flow to ensure correct temperatures are reached at the proper time to achieve the desired roast curve. Looking at a roast curve graph, you can follow the roast journey. 

The charge temperature is 200c, and once the beans are released from the hopper into the drum, the temperature dramatically reduces. After a minute, heat is applied by incrementally turning the gas up and sometimes down throughout the rest of the roast. 

This can be done quickly or slowly, depending on the desired taste of the coffee. Once the first crack has occurred and the end temperature is reached, the coffee is released into the cooling tray. 

How to Decide what the Best Way to Roast Coffee is?

The person who roasts the coffee often decides how the coffee should be roasted. Before the coffee is bought, they will have a sample roast(in a process known as coffee cupping), so they will probably already have a good idea of what flavors they would like to bring out of it and a roast profile in mind.

They will then continue to roast samples (usually on a sample roaster, a miniature version of a coffee roaster) and cup with a person responsible for coffee quality. They will decide which roast showcases the flavors in the coffee best and use that one moving forward. The roast profile can be adjusted at any point.

What do I mean by showcasing the best flavors? In specialty coffee, the aim is always to hit the highest point of sweetness while balancing bitterness and acidity.

The longer you roast coffee, the less acidic it will be. But as the acidity decreases, it is a case of adjusting the length and temperature of the roast profile to hit the perfect balance of all these things.

What are the Different Roast Levels?

Roast level significantly impacts how coffee tastes. There are three primary roast levels, but the coffee roaster can roast anywhere between them.

Roast Levels
  • Light Roast Coffee: Coffee beans are in the roaster for the least amount of time. As a result, they are the lightest color of brown. They are also the most acidic bean and don’t have any oil on their surface. Concerning taste, lighter roasts highlight the actual distinct flavor of the coffee bean while having a mellow body.
  • Medium Roast Coffee: A well-rounded and less acidic cup of coffee. The coffee beans are browner in color, and seldomly have an oily surface. When it comes to taste, medium roasted beans create a more bold and more balanced cup of coffee. While the coffee’s origin’s distinct flavors can still be tasted, you also start to taste more of the sweetness and bold flavors that come through as the beans are roasted longer.
  • Dark Roast Coffee: The most intense flavors out of all the roast levels. Dark roasted coffee beans will be the darkest brown of the roast and will most often have an oily surface. Dark roasts will have the least acidity and the heaviest body compared to the other roast levels.

To read more on each roast level, check out, “Differences Between Light, Medium, and Dark Roast Coffee.”

What is the Job of a Coffee Roaster?

Firstly, the person operating the coffee roaster is also called a coffee roaster for this blog post. Their role can vary massively from just watching a screen in an office in a huge commercial production to doing every job from sourcing the coffee right through to bagging it.

Smaller batch roasters also involve a lot of lugging around heavy coffee beans and meticulous cleaning and maintenance of the roaster. If you want to try out being a coffee roaster and roasting your beans at home, you can get small home roasters or use a sample roaster.

While commercial roasters use gas to heat them, there are small sample roasters like the Ikawa. You can plug it in and link to your phone through an app to select and change your roast profile. Some people even try roasting their coffee beans in the oven.

Doing so would turn green beans brown. They probably wouldn’t be very tasty as you couldn’t continually turn the beans to ensure they were evenly roasted. Some would likely be burnt by the time they had all cracked.

You would also need very accurate control of the temperature. You could not change the temperature of a domestic oven quickly or accurately enough. 

To conclude, if you’re looking for delicious coffee, you have three options.

  1. Do some research
  2. Buy a roaster and become an expert
  3. Buy ready roasted beans from a coffee roastery who employs an expert roaster.

What is a Master Roaster?

A Master Roaster is a highly experienced coffee professional with a certification and a passion for coffee.

They are responsible for taking green coffee beans grown in various places and seasons and implementing roasting techniques to produce specific roast and flavor profiles. Much work is involved with the tasks of a Master Roaster.

Every batch of beans requires a different temperature and time of being roasted. While some beans need to be roasted a little darker, others have to be roasted a bit lighter. This is so the knotty characteristics of the bean are not lost. Small changes to roasting can make all the difference.

Their primary objective is to create a stable and consistent blend. A Master Roaster often needs to make split-second decisions on the roast. If the wrong decision is made, it can ruin the entire batch of roasted coffee beans.

Click the link to read more about Master Roasters.

Final Thoughts

Depending on your enthusiasm, the coffee roaster above may be a bit much for what you are interested in. If you are new to coffee roasting, I would check out this Electric Coffee Roaster by JIAWANSHUN. It has a 0-240 adjustable temperature and is reasonably priced. 

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