What Does a Coffee Roaster do?

There are many people and equipment involved in getting coffee from a seed in the ground 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? At its most basic, a coffee roaster cooks coffee beans. Green beans are loaded into the roaster’s top then dropped into a very hot (around 200c) drum, where they are then heated, causing a series of reactions altering the taste of the bean from an almost tasteless green bean into coffee as we know it.

The person working the coffee roaster can control how hot the coffee gets, how long it is roasted for, and ultimately 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).

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 vent at ton and down, which for smooth airing of inner housing.

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 are looking 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

The Journey of Coffee Beans Through the Coffee Roaster

The coffee beans are loaded into the roaster via the hopper. They are then held until the coffee roaster is at 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 first start to dry out, then roast (when the milliard reaction occurs). Once the coffee has begun to roast, the first crack will happen. This sounds a little like popping popcorn. Not long after this, there will be a similar second crack.

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 are monitored throughout the process via a computer system.

Whoever is operating the roaster will have to 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 do you 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 tasted a sample (in a process known as 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 upon 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 out 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.  

The role of the person operating 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, but 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, and 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 to roast delicious coffee ready for you to brew!

Final Thoughts

Depending on your level of enthusiasm for coffee roasting, the coffee roaster recommended above may be a bit much for what you are interested in. If you are new to coffee roasting and want a simpler one, 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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