Introduction to Coffee Roasting

The last six weeks we have covered all sorts of information about how coffee is grown, how it is processed, and even how it is shipped. Today in our From Farm to Cup blog series, we are going to look at the next step for the beans: coffee roasting. 

Roasting is an incredibly complex science, one that takes lots of practice to learn and understand. While the subject cannot be covered in one small explanation, this post will look to answer some questions and correct some common misconceptions about coffee roasting. 

The process of roasting is fascinating and also is always evolving and changing with upgrades to technology and techniques. Roasting is a trial by error craft. Many factors have to be analyzed and considered before a roast and during the roast. Every coffee shop goes about roasting coffee with their own slight variations as well, which adds intricacy and uniqueness to the roasts. Every type, variety, and origin of the coffee beans will taste better by roasting them light, medium, or dark depending on doing a test batch. Different coffee roasts will also taste better than how the coffee is brewed.

Roasting can be done through a fast process or a slow process. Fast roasting will usually be done around 12-14 minutes per batch and slow roasting is around 14-20 minutes. Some roasters choose to do one or the other depending on the type of beans, the quality of the beans, or based on what roasting machinery they have equipped. Most commercial coffee roasters have a double-wall insulated drum that spins continuously and is fueled by natural gas.

Once the coffee is put into the roaster at the chosen starting temperature, the heat from the flame begins to dry up the liquid moisture remaining in the green beans. Visible effects are not seen but once all the water has dried due to the gas flowing the flame around the drum, the coffee will start to yellow, then brown from the heat. After the coffee starts browning it will start to crack (called first crack) around from the carbon dioxide gases being released. The first crack sounds like popcorn popping and indicates to the roaster that the coffee is roasted enough to be dropped out, which makes a light roast. Any additional time left in the roaster means that flavor is being further developed in the beans.♦1

The longer the beans are left in the roaster the darker they will appear. The acidity and caffeine are also burning off the beans the more the beans are roasted. Roasts that are darker than a light roast will actually have less caffeine and be more bitter. Roasters can wait until a second crack but the beans could catch fire, become bitter, and lose flavor. However, if the coffee is roasted to a second crack, which sounds like rice krispie cereal, it is considered a medium roast. Waiting thirty more seconds to one minute after the second crack would bring the coffee to a dark roast. The roaster chooses the best moment to drop the beans into a mixing tray, which then cools the beans down to a room temperature in two to five minutes.♦2

So much effort and skill come with roasting coffee. It is one of the most complex processes of the From Farm to Cup experience. Although this post is just a brief introduction to roasting, I hope it was helpful and enjoyable to learn a little bit about the work that goes into making your coffee taste good and flavorful!

◊ Written by Andrew Watson, Manager at Ntaba Mellwood, v60 lover, and Interstellar‘s #1 fan

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♦1 – Hoffman, James. “The World Atlas of Coffee.” Octopus Books, 10.4.2018.
♦2 – Rao, Scott. “The Coffee Roaster’s Companion.” 2014.