Light, medium, or dark… The flavour and aroma of your coffee is significantly altered by the roasting process. How does roasting work and why does it have such an impact?
Why do we roast coffee beans?
Straight from the plant, coffee beans are green. At a glance, they look a little more like shelled pistachio nuts than the coffee we’re used to grinding.
If you try to grind green coffee beans, even in a premium Niche grinder, all you’re going to end up with is a mess. The wetter coffee beans will leave your grinder needing a thorough clean, while the end result will not produce anything drinkable. Brave taste testers describe the drink made by brewing green coffee beans as bitter, tasting like wheaty, yeasty, bread dough, or even like Play Doh and crayons. We recommend that you avoid this entirely!
Roasting turns these raw green beans into flavourful coffee, reducing moisture, unlocking the aromas, and changing the chemistry of the coffee so it is properly soluble in the water. After roasting, the coffee is grindable and brewable, smells enticing, and takes on the rich brown colours we associate with a pleasant drink.
Roasting forms part of the chain of coffee production that begins with location and planting. For an insight into how environment also dictates the final flavour of your favourite drink, why not read our article on how rainfall and temperature affect your coffee?
How does roasting coffee beans work?
Roasting is not a long process. Compared to the lengthy stages of planting, growing, harvesting, and drying, it can seem almost inconsequential; yet this stage is essential to turn the coffee bean into the drink we love.
Over eight to fifteen minutes, the coffee changes from a barely-usable green bean to a rich and heady temptation.
- Stage 1 : the drying phase (up to ~160°C) - As the bean warms, the moisture content is slowly cooked off. The beans start to yellow, releasing a grassy smell.
- Stage 2 : the Maillard reaction (~160–200°C) - Here the sugars and amino acids react with each other, developing the flavour as hundred of different chemical compounds are formed. As the beans move past 160°C and towards the first crack, they brown and their unique aromas are released, giving off scents of nuts, chocolate, or toast.
- Stage 3 : the first crack (~196°C) - Steam and CO₂ build-up push through the outer shell of the coffee bean, causing it to split and audibly crack, similar to popcorn popping. This is a key moment as now the beans can be brewed for a flavourful coffee (though at this stage it would be a very light roast).
- Stage 4 : development - After the first crack the flavours continue to develop. Roasting experience is necessary to balance the flavours, ensuring that the resulting coffee isn’t sour and underdeveloped, but neither does it become flat or burnt.
- Stage 5 : the second crack (~224°C) - Now, the internal bean structure breaks down; cell walls fracture and the natural oils rise to the surface. A second cracking noise, similar to twigs breaking, announces that the coffee has passed into dark roast territory.
- Stage 6 : cooldown - To halt the roast, the beans are cooled rapidly, locking in the desired flavours.
Selecting when to stop the roasting period, either after the first crack for a light roast, just before the second crack for medium roast, or post-second-crack for a dark roast is part of the skill of coffee roasters.
How do roasters know when each stage has happened?
Centuries ago, roasting lacked the modern technology that we use today and roasters relied on listening for the cracks, timing, and experience. Today we have sensors and thermocouples that can detect the temperature of the bean and surrounding air, and complex software that ensures consistency with the roast process.
Nonetheless, the best indicators for coffee roasters remain auditory and visual - expert roasters will still listen to the beans and watch as they brown. It’s no less an art today than it was when coffee was first discovered.
Do different beans roast differently?
Is roasting just a generic process or do you have to tailor it to different beans? With something as finely nuanced as coffee, it comes as no surprise that roasting beans from one region is subtly different to that from another.
Consider beans from Brazil vs. those from Kenya, for example. A Brazilian bean has been grown at a lower altitude in a warm climate. They are typically processed through sun-drying for a sweeter cup. These soft beans respond well to medium-to-dark roasting, though if pushed too far they can become bitter and flat.
A Kenyan coffee, however, grows at high altitude, with cool nights and warm days that lead to a dense bean with complex flavours. Kenyan coffee is washed for clarity and has a keen acidity to it. These are best when lightly-to-medium roasted, allowing the bright acidity to emerge, bringing with it the lighter fruity tones.
What determines a coffee’s roast level?
Roasting coffee beans means paying attention to many different qualities of the coffee. Expert coffee roasters will choose the level of roasting considering:
- The natural character of the bean - As described above, the bean’s growing environment and nature will have an impact on the length of roast.
- The desired flavour - Through roasting it’s possible to adjust the final flavour profile. This itself is affected by a range of influences: What does the end customer prefer? What is the brand identity of the coffee? Where will the coffee be used and which flavours need to be highlighted?
- The final brew method - Roasting beans intended for espresso is different from those aimed at the filter aficionado, and different again for Moka pot lovers, or those seeking the perfect French press.
The same bean can be roasted in different ways to control its final taste, though some beans do shine brightest and best when roasted in a certain way. Nonetheless, it’s possible to get excellent results roasting the same bean as a light, medium, or dark roast. Roasters will test all three levels, ultimately choosing the one that results in the most enticing brew for their market and audience.
The types of coffee roasts and how to best use them
How does this affect your coffee brewing method? Consider the following levels of roast to match your desired drink:
| Roast type | Flavour | Suggested brewing method |
| Light roast | Bright, acidic, floral, fruity | Pour-over, AeroPress, Chemex |
| Medium roast | Balanced, chocolaty, smooth | Machine drip filter, French press, Espresso |
| Dark roast | Bold, smoky, low acidity | Milk based drinks, Moka pot |
Which roast should you choose? It all depends on your taste preference and favoured brewing methods. At Niche we encourage experimentation, so why not try a variety of methods, note the results and how you feel about the end brew, and hone in on your favourites? Do you find you prefer the greater acidity and more floral hints of a light roast manually filtered with a V60 setup, or are you pushing for a deeper flavour that’s bold for your daily espresso shot, perhaps tempered with milk for a rich latte?
The personalisation of coffee is one of its wonderful traits, allowing you to tailor your cup to meet your exacting requirements - and there’s no rule saying you can only love one coffee, so why not let your mood drive you?
Why a good grinder matters with your roast level
Do different coffee roast types need different grinder settings? Actually, yes, though this is secondary to considerations based on brew method.
- Light roasts are denser and benefit from a finer grind when brewed under pressure to allow the release of all the flavours.
- Dark roasts are more brittle and a coarser grind will mean you avoid over-extraction.
Adjusting your grind level is effortless with a Niche grinder, meaning you can switch roasts from one cup to the next. Virtually zero retention means each grind is clean and fresh, avoiding any flavours carrying over from the previous brew, while the unparalleled accuracy means consistency is guaranteed.
When you’re aiming for the very best in coffee taste, a Niche Zero or Niche Duo grinder is the perfect choice for your home coffee setup.
Making the most of coffee roasts
The roast level is one of the biggest decisions you will make when it comes to finding the coffee that excites you. It may be a quick process, but the decisions that go into roasting are complex and important, with a major impact on how to get the best out of each coffee bean.
Shape your coffee experience by considering each link in the coffee chain, from the growing climate, through drying process, roasting, home setup and care, fresh grind, and brew method. Experiment with beans from different places on the coffee belt, a range of roasts, finely-tuned grind settings, and alternative brew methods to discover the taste that truly inspires you.
Choose a Niche grinder to make the most of your beans. Even though some owners have proven the Niche Duo can grind green beans, we recommend you make sure they’re roasted