Mar 15, 21

How Is Coffee Actually Roasted?

March 15th, 2021

How + Why Coffee Beans Are Roasted.

Why do we roast coffee?

In a nutshell, we roast coffee beans because nobody in their right mind wants to drink a brew made from raw coffee beans. It’s undrinkable.

Fresh off the plant, once the beans have been de-shelled from the sherry fruit surrounding them, those lil’ seeds (which is what they technically are) look, smell and taste NOTHING like coffee. In fact, they’re green and smell a tad grassy. Funky.


So, roasting these alien nugs is the only way you’re going to get an enjoyable cuppa from these unique plants.


What does roasting do?


Roasting is an age old technique, and it’s highly likely to have developed from a happy accident (careless 15th century chefs knocking them into the fire + rescuing them, only to discover it made them 100 x better!).


Essentially, ROASTING = FLAVOUR.


I mean, you’ve gotta start off with some awesome beans in the first place (we source top quality Arabica + fine Robusta stock). Roasting is all about coaxing some specific flavour characteristics out of these beans. Your coffee can be totally made or destroyed during the roasting. You are literally playing with fire.


When you roast coffee beans, chemical reactions occur, developing 800-1000 different aroma compounds which create the flavour of the drink. There’s an obvious colour change as the beans turn from green to brown and a lot of acidity is removed, allowing an enormous array of exciting + delicious flavours to unfold.


You might be thinking, ‘so all you need to do is roast those little green buggers til they’re brown, right’ - yep, it doesn’t sound any harder than cooking a sausage, right?




Coffee roasting is a science in itself, there are whole books on the various nuances of the process!

How do you roast coffee beans?


The way in which we roast coffee beans today is still evolving, as scientific advances are made and our knowledge deepens.


To begin with, roasting techniques were very basic. A pan, above an open flame, toasting coffee beans; simple, (very) small batch and (very) inconsistent flavour wise. Burnt beans were a thing.


In the 17th century, drums were created to house coffee beans whilst roasting. This was a safer and much more practical method, as a smaller flame could be used and the heat could be regulated (to an extent) inside the drum.


In the 19th century, coffee roasting was given the industrial revolution treatment. Patents for larger machinery came flooding in and commercial roasting became common.


As we said hello to electricity in the 20th century, big improvements were made to the drum roasting technique as we could then replicate conditions - leading to super consistent roasting results. Fluid-bed (or hot-air) roasters also entered the scene in the 1970s. These purely use convection to roast, rather than the combination of convection, conduction + radiation which a drum roaster creates - therefore they’re often deemed not as good.


Nowadays, roasting is highly scientific and pretty much everything is sensor based, so that the entire process can be controlled and we can end up with super batches that taste exactly how we want every time.

The Roast Curve


The perfect roast comes down to two factors: the roasting time and the temperature.


These define the colour and subsequently the flavour of the beans. As we all well know, taste is massively subjective, but it’s widely agreed that lighter roasts have fruity + floral aromas and are usually more acidic, medium roasts are balanced, have complex aromas with only a mild acidity, and dark roasts have low acidity but strong toasty aromas and a heavy body.


The roast curve shows this relationship between the roasting time and the temperature. It’s a really useful guideline for reproducing the same roast over + over - for a coffee company, it’s basically the fingerprint of their coffee. Which is why we can’t show you our exact roast curve, but something that gives you an idea of what it shows!


The classic roast curve looks like a tick and directly relates to what’s going on in the roaster. Roasting is a real art form and the roasters need to be experienced enough to successfully adapt the roast curve to compensate for things like unusually cold days, or humid periods, or very dry spells, which can all influence the roast.  


Check out our example roast curve here, detailing what happens at each stage of the roast:

Roasting Black Insomnia Beans


Our green Arabica + Fine Robusta beans arrive at our roastery in North Bavaria where our expert roasters then take charge. We use large scale traditional drums to roast the Black Insomnia blend in, as we mind this to be the most consistent + efficient method.


The maximum temperature reached in the roast is 200°C and then they are cooled back to room temperature relatively quickly, as leaving the beans hot for too long means the roast ‘develops’ and the flavours will actually lessen. In total, the roast is only a 14 minute process, but an eagle eye needs to be focussed on the drum throughout.


Basic Science


It may come as a shock, but this blog just skims the surface of what there is to know about coffee roasting. It’s a complicated art, and it just shows you how much science goes into producing your favourite brew. In conclusion; roasting coffee is worlds apart from browning bangers.

By Black Insomnia

Test out our roast for real!

Check out Black Insomnia Whole Beans

Nutty aromas, caramel sweetness and a dark chocolate aftertaste will make your palate sing, while our extraordinary caffeine kick works its magic.

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