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Intro to Coffee Roasting

Posted by Matt Chitharanjan on

Note: We are lucky to have Simon Frank working with us over the summer. Simon recently graduated from the University of Toronto and wanted to spend some time exploring his interest in coffee before going back to grad school in the fall.  Over the coming months, Simon will be sharing his experiences with roasting, brewing and other coffee experiments on our blog and social media pages.   His first post below looks at coffee roasting, but if there are questions you’d like him to explore, you can email him at



The path that a coffee bean takes from green, to roasted, to your cup seems fairly straightforward, but the details of this process are mystifying unless you take a close look. A few weeks ago, I knew almost nothing about roasting, except that is was complex and could profoundly affect the flavour of a coffee. Through observation and a little hands-on experience I’ve found answers for some of the initial questions I had. If you’re curious about roasting, this might answer some of your questions too.


How long does roasting take?


On Blue Tokai’s erstwhile rugged Taiwanese roaster, it’s a quick process. A batch of beans take 12 to 15 minutes, depending on whether you’re going for a lighter or darker roast. The beans are placed in a rotating drum over a gas flame and go through three stages.

Our handmade Huky sample roaster. Source: Blue Tokai Coffee Roasters


The first, around 3-5 minutes into the roast, is the drying phase, when all remaining moisture evaporates from the green bean. Then at around 7-9 minutes there’s the first crack, when the silver skin, a thin flaky layer on the bean’s exterior, starts to pop off, making a sound akin to popcorn. Later, about 10-12 minutes in, the second crack occurs. As another outer layer of the bean falls off, there’s a quiet sound more like the subtle pop of Rice Krispies in milk. For a medium roast, you’d let out the coffee and cool it around the time of the second crack, but darker roasts can go on a bit longer. Light roasts on the other hand barely reach the second crack.


Don’t worry if this makes little sense. We’ll create a more detailed roasting post soon. Image source:


How does roasting affect a coffee’s flavour?


At a fundamental level, a coffee’s flavour profile is shaped by its origin and how it’s grown. However, roasting determines which elements of this latent flavour will be emphasized in your cup. A lighter roasted coffee will emphasize citrus or fruit-like acidity, with a pleasant sourness. Medium roasts can offer a sweet, chocolaty flavour. Dark roasts boast strong, bitter flavours, what we might associate with a classic coffee flavour. You might be surprised that despite their taste, dark roasts actually contain the least caffeine — extended roasting burns off caffeine, so light roasts are actually the most likely to wake you up.


How precise is roasting?


Coffee roasting is not without its Zen and Sufi elements. Chicago’s Intelligensia Coffee describes their Black Cat Project for espresso beans as “a pursuit of something we’ll never catch: the perfect espresso in all of its manifestations.” In roasting there’s always another detail, be it timing, heat or airflow, that can be changed, taking you incrementally closer to the ideal coffee. That being said, Blue Tokai rigorously controls and records roasts so we can recreate experiments later and consistently make you the coffee you want. We monitor our roaster with a temperature probe synced to the computer program Artisan, which charts temperature and its rate of change against time. Following the data on Artisan, we are able to ensure that a roast works out as planned, guiding it along with minute adjustments.


What a simplified roasting graph on Artisan looks like. Image source:


What are the advantages of freshly roasted coffee?


Although in the right conditions green coffee can stay fresh for months, roasted coffee is best enjoyed up to two weeks after its roast date. Leave the beans sitting around and they’ll start to go stale. When in sealed bags, carbon dioxide released during roasting protects the beans from oxidization, which would damage its flavour. But after two weeks, many of the flavor and aroma compounds will have dissipated, resulting in less than ideal brew. That’s why Blue Tokai roasts your coffee specifically for your order and ships to you immediately. You can learn more about freshly roasted coffee from our earlier post on the topic.

Carbon dioxide is released in freshly roasted coffee (above, left) which makes it bubble and foam. Source: Blue Tokai Coffee Roasters

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