Although coffee roasting is one of the last steps in the coffee production journey, it is also one of the most important ones when it comes to flavour and aroma.
Roasting helps develop flavour. It can hide flavour notes as well as reveal them in completely different ways, of course, if correctly done. In fact, without roasting coffee would not smell like coffee at all! Roasting is directly responsible for the smell of your coffee, not only taste. That’s why it’s important to understand what happens during roasting and how it affects the taste, whether you’ve decided to give a go at roasting yourself, or if you simply wish to make a wiser choice when shopping, the knowledge you’re about to learn will be very valuable.
What happens during roasting?
Unroasted coffee beans are green and smell a bit like peas – far from your regular coffee. This means that roasting helps them develop not only flavour and aroma, but the visible factor, too – their dark brown colour. According to Barista Institute, there are three main stages in roasting: drying stage, browning stage and development stage or roasting stage.
Stage 1 – Drying
Once added into a roasting machine, coffee beans enter the drying stage – it‘s especially important since green beans have around 12% humidity, according to a study on roasting profiles conditions and coffee flavour. Drying stage typically lasts for about 4–8 minutes, depending on the bean and the roasting machine. Roasters have to control the temperature during this entire stage to ensure the beans are only dried, but not beginning to actually roast or even worse – start burning. The temperature at the end of the drying stage is typically 160 ⁰C, and that’s when the browning stage starts.
Stage 2 – Browning
It’s not hard to guess that the bean will start developing colour at this point. Natural sugars and amino acids within the coffee beans start to react and create specific colour and flavour characteristic to the coffee bean. During this stage, the beans usually crack – meaning the development has begun.
Stage 3 – Roasting
It’s the final stage of the roasting cycle and is also known as the actual roasting. This is when the beans collect enough of energy from the heat and start cracking, in other terms exploding from the heat. It’s important to carefully control this stage and stop the roasting process before the beans develop a smoky, burnt-like flavour and smell, which is really what we’re all trying to avoid in a cup of coffee.
Different roast degrees and their effect on taste
What’s really important when shopping for coffee is understanding roast degrees, or in other words – knowing how to read the label. So you should have in mind that coffee beans are usually roasted in main three degrees (or profiles): light, medium or dark. There are variables in between of them, too, but let’s start with the basics. The lighter the roast, the lower number you’ll see on the packaging. Sometimes it can be indicated by colour or simply by the word ‘light’ or ‘lightly roasted’.
This means that your coffee spent less time in the heat, it will usually have a lighter brown colour and taste lighter, too. Many single origin or specialty coffees are roasted lightly, just as much as it’s needed to give the coffee it’s flavour, but without hiding the natural taste notes. Lightly roasted coffees tend to be more fruity, have hints of herbal flavours, also usually described as acidic. Light roast also impacts the body of your coffee – it will be more watery, thinner, almost like a strong black tea in terms of texture and mouthfeel.
Dark roasted coffees are the opposite – stronger in terms of taste and smell, more rich and creamy, thicker body and richer crema on top (espresso-style), yet more single-note in terms of flavour, so not as complex and diverse as lightly roasted. The dark roast also hides acidity, so coffee seems sweeter, nutty, buttery, or even develops notes of chocolate. Some dark roast can seem slightly bitter, too. So think of what you want to experience in your cup and choose a roast degree accordingly. Knowing that you will always know what to expect.
Can roast degree dictate a preparation method?
Yes, and it should! A well-prepared coffee depends on correct extraction levels. When you add water – extraction starts and several chemical compounds are extracted into the drink. The compounds responsible for fruity taste notes and acidity are extracted first, then extraction continues to sugars, and ends with compounds that create bitterness. Under extracted coffee can taste sour because the sugars haven’t yet extracted, and over extracted coffee can be bitter.
Lightly roasted should be brewer slower, because the compounds are extracted more slowly in that case, so to reach sweeter, or even bitter notes for such coffee you would need more time during extraction, therefore methods like pour-over, chemex and such are more typical here. Alternatively, for dark roast – usually an automatic coffee machine or espresso coffee machine with pressure, which can quickly extract coffee ensuring it’s not too bitter.
Next time you shop for coffee, keep an eye on the packaging – not only the beautiful pictures, but also the roast degree – this will guide you towards the preparation method and also give you an idea of what flavours to expect. The more different roasts of coffee you try, the better understanding you’ll have of what is your favourite, or where to look for it.