How to roast coffee beans
The smell of freshly roasted coffee is enticing, alluring, and intoxicating. It’s almost worth learning how to roast your own coffee just for the smell! But we want great tasting coffee too. Read our guide to help you become an expert at roasting coffee beans at home.
We’ve split this guide to home coffee roasting into a number of sections. We’d love you to read the whole lot but if you’re short on time here are a number of quick links.
How to roast your own coffee
If you want to know how to roast coffee beans then this guide is for you, particularly if you’re roasting coffee beans at home. Mastering the skill of coffee roasting can be a lifelong pursuit, nonetheless that doesn’t mean beginners can’t pick up the main skills quickly and within a short time be producing amazing roasts at home. Even with a little skill you will be able to take a green coffee seed with hardly any meaningful flavour or taste and transform it into something magnificent.
We’ve always said that there are four crucial stages to making the perfect cup of coffee; selecting the best beans, the right roast, a good grind, and finally a barista brew.
Roasting Coffee is the second stage of this process. So, if you really want to know how to roast coffee beans AND get a wonderful brew then before you rush in it is worth having a quick think about the bean you want to use. As a rule of thumb make sure you are buying 100% arabica (avoid robusta) ideally from a single source. Whatever you do don’t buy old or cheap beans.
If you just want to get going then for anyone starting with home coffee roasting we suggest these Nicaraguan coffee beans, they have loads of good reviews and with a medium roast will produce a medium body, low acidity, smooth coffee with citrus notes.
What equipment do I need?
It is possible to roast your own coffee beans with a baking tray or even a popcorn maker. However, in order to get a quality and consistent roast you the more you can control the temperature and keep the beans moving the better. That’s why we recommend buying a coffee roaster of some sort. You can either get a stove top roaster or a more sophisticated drum roaster. Stove top roasters are usually £40-£60 whereas more sophisticated electric roasters range from £60 to £500.
Read our guide to home coffee roasters if you want to know more.
The 7 stages of home coffee roasting
If you want to learn how to roast coffee beans then it is crucial that you understand what happens to the bean during the roasting process. This understanding will only help you improve your home coffee roasting.
We’ve added some guide times to each stage, though it is important to remember that these are only guides. The actual time each stage takes will depend on a combination of the bean you select, your equipment (particularly stove top roaster or electric roaster, stovetop will take longer), and the temperature you are roasting at. Learning how to roast coffee does involve an element of trial and error, playing with these variables will be how you become good at home coffee roasting. We always keep notes so that we know how to replicate a particularly good roast, or avoid another disaster!
In summary though expect roasting coffee beans at home to take between 10 and 20 minutes. Any less and the coffee will not be cooked, anymore and it may just be bitter.
Stage 1: Drying
Raw coffee beans contain about 10% water and during the first stage the water starts to evaporate. This will take a few minutes to start as the green beans absorb the heat. As the beans dry they will start to turn from green to yellow and it may well smell like popcorn, don’t worry this is normal. This stage takes around 3-4 minutes.
Stage 2: Colouring
As the beans continue to heat water is forced out. The beans start to expand their skins, known as the chaff, flake off. Although during the drying phase the beans turned yellow you will now start to see them turning brown. Acids within the bean are now starting to react with each other and there may be more aromas, in addition to popcorn they may also smell like toast or basmati rice. This stage takes about 3-4 minutes.
Stage 3: First Crack
The force of the steam as water evaporates as well as a build-up of other gases will eventually cause the bean to crack. The cracking will sound like popcorn popping. The bean is now smooth and has almost doubled in size, it may also start to smell a bit like coffee. Expect the first crack at any point between 6 and 9 minutes after the start of the roast, it will last anywhere between 30 seconds and 2 minutes.
Stage 4: Roast
The first three stages are common to all coffee roasts, how long you continue after becomes more about what type of coffee you are looking to make. Broadly the longer the roast the darker the beans and the more bitter the taste.
After the first crack this stage is typically 5 minutes long for a dark roast, for a lighter less bitter roast remove the beans after about 1-2 minutes. As a rule of thumb to produce a medium roast the first crack should be at about 80% of the total roast time or put another way once the first crack has happened roast for a further 25% of time.
Stage 5: Second Crack
Many expressos are roasted to the beginning of what is known as the second crack. This second crack is quieter than the first crack and is caused by a build-up of gasses in the bean. It will start between 2 and 5 minutes after the end of the first crack.
Once the second crack is over very little of the original flavour of the coffee will be left, it will be extremely bitter. If you are after a dark bitter roast it is important that you don’t let the roast go on too long, remove from the heat before the second crack has finished.
Stage 6: Cooling
After the roast the coffee should be cooled as quickly as possible, otherwise it will continue to roast. Spreading the beans out on a room temperature baking tray should be fine, make sure to leave enough space between the beans.
Stage 7: De-Gas
For a few hours/days after the roast gases will continue to escape from the bean. If you use your coffee too soon these gases (mainly carbon dioxide) will badly affect the flavour of your coffee.
We recommend that you leave your freshly roasted beans to de-gas for at least 24 hours after they have been roasted (longer for light roasts as they de-gas slower than dark roasts.
What type of roast do you want?
You should have worked about from above that the key stage for determining the style of coffee is the roast.
It is this stage that has the most impact on the final flavour. If you really want to learn how to roast your own coffee then we recommend paying close attention to this stage of the roast.
Dark roasts take longer and are often referred to as Italian or French roasts. They are usually done at a higher temperature and produce stronger tasting coffee. Coffee roasted like this is better suited for expresso or stove top coffee makers.
Lighter roasts are best for a French press or filter coffee. Although bear in mind that this is absolutely about your personal preference, personally I prefer a lighter roast with my expresso as it is less bitter and retains more of the fruit flavours.
As we said above home coffee roasting is not just about following a rigid set on rules. To perfect your coffee, you will need to experiment with the temperature at different stages as well as the timings. Do make notes as you go.
Top tips for roasting coffee beans at home
There will be times when it all goes wrong, that’s OK. Remember that in learning how to roast coffee it is equally important to learn what to avoid when roasting coffee beans at home. We’ve made mistakes along the way, here is what we’ve learned.
Preheat the roaster – make sure the roaster is properly heated before you start, otherwise it is difficult to record and replicate a roast.
Smoke – roasting can involve a lot of smoke, just be aware and when home coffee roasting make sure the area is well ventilated.
Keep the beans moving – electric drum roasters will do this for you but if you have a stove top roaster you will need to keep shaking the beans. Otherwise you will end up with a mixture of burnt and undercooked beans.
Fire risk – in the colouring stage as the beans expand their skins shed and chaff is produced. These can easily catch fire, be aware and make sure you have a plan in case this happens. Also note that if you roast to the second crack and beyond fire risk increases.
Too many or few beans – make sure you don’t overfill or underfill your roaster. Most roasters give an indication of the amount of beans the roaster will take, we recommend you consistently add the same amount.
Do batches and make notes – if you’re all set up to roast then why not do a few batches? Make notes on each batch and when ready brew a few cups and compare. That way you will learn what you like and take an important step towards brewing your perfect cup of coffee.