How To Roast Coffee Beans At Home

If this is the first time you’re thinking about roasting coffee, well damn, you’re in for a treat. Roasting coffee at home is not only a load of fun, but you also get to make your own delicious coffee, and it’ll probably be the freshest brew you’ve ever had.

To do this, it’s helpful to know a little bit about the roast process, and what exactly is going on in that little green bean when it gets hot.

You’re also spoilt for choice with the amount of methods there are for at home roasting. So let’s get to it.

coffee beans cooling after roasting

Why Do We Roast Coffee In The First Place?

Coffee starts out as a little red berry that grows on the Coffea plant, and there are many stages this little fruit has to go through before it reaches your cup.

In this red berry sits two coffee beans (unless it’s peaberry coffee, but more on that some other time). Firstly, the coffee goes through a process to remove the outer skin, inner parchment skin, and pulp.

What’s then left is the coffee bean, which is dried out to become the green coffee bean that’s bought by the coffee roasters around the globe.

If we were to grind up these green coffee beans and brew a coffee with them, you wouldn’t recognise the drink you get as coffee. It’d be bitter, acidic, and full of flavour compounds we don’t find tasty.

This is where the magic of roasting comes into play. Roasting takes the somewhat 800 flavour compounds found in a coffee bean, and transforms them into the beautiful flavours and aromas we get to experience in our morning brew.

Now, we don’t need to understand the exact science behind the roasting process to roast our own coffee beans. But we do need to know how to manipulate the chemical reactions that roasting kick starts, in order to achieve the desired flavour.

Let’s dive into the roasting process a bit more.

How Roasting Coffee Works

Coffee beans go from a green, yellow colour, to that dark brown coffee bean colour we all love so much. But what’s going on? Why does making coffee beans hot make them delicious?

The Roast

There is a lot of water in a green coffee bean. It’s almost impossible to grind green beans up and brew a coffee with them. Roasting the coffee starts the chemical reactions inside the beans, transforming the flavour compounds into what we recognise as all those familiar tastes and smells.

When the beans first enter a hot environment, the water content starts to decrease. Known as the drying stage. The first stage of roasting.

Then you’ll notice the beans starting to change colour. Going from green, to yellow, then to a light brown. It’s when the beans begin to turn brown that the magic is really starting to happen.

The Maillard reaction. This is a series of chemical reactions that occur between amino acids and sugars, which changes the flavours, aromas, and colour of our food. Scientists have only recently begun to understand what the Maillard reaction is, as it’s that complex.

Other magic happens when roasting, like caramelisation and Strecker degradation. We don’t need to know the ins and outs of these complex reactions, but if you’re interested in reading more you can follow the links for further reading.

Soon after the coffee begins to turn brown, you’ll hear what’s known as the first “crack”. This is where the pressure from gases inside the coffee beans, causes them to crack open, allowing the moisture to escape.

You’ll know you’ve reached this stage due to lots of popping noises. This means you have now achieved a light roast.

Keep on roasting your beans for a little longer, and you’ll see the beans begin to turn even darker. Sugars will start to caramelise, the aromas will become more sweet, and the acidity will reduce.

Soon, all moisture from inside the bean will evaporate, bringing you to the second “crack”. A light to medium roast finishes somewhere between the first and second crack, whereas a medium-dark or dark roast will finish around, or just after the second crack.

coffee beans cooling on tray after roasting

The Post Roast Process And Degas

There are a couple of things to note once you’re finished roasting your coffee beans.

First, you’re going to need to let your beans “degas”. This is where the initial CO2 that your beans produce will be released from the beans.

This is important for a couple of reasons. If you decide to seal your beans up straight away, then there’s going to be a big build up of pressure in your container. This might make it go bang. Not what you want.

Also, coffee beans that contain too much CO2 will negatively affect the taste.

I’d say a good starting point is to leave them for 12 hours. You can play around with how long to leave your beans to degas, but make sure you don’t skip this step.

Once degased, you can store your coffee beans in an air-tight container, in a dry and dark space. I’d allow 24 hours from the time you stopped roasting before you grind and brew a coffee with your beans.

This lets your beans mature in flavour a little, and reach that full-bodied texture. Check out this article to get some killer tips on how to properly store your beans.

The Roasting Stages Summarised

Here are some roasting stages to look out for.

  1. Your beans will be green. Even when your beans start to heat up, they’ll keep their green colour for a little bit.
  2. Yellow beans. After a couple of minutes, you’ll notice your beans starting to turn yellow.
  3. Smoky. As the moisture starts to evaporate, steam will start to rise from your beans. Don’t panic! This is totally normal.
  4. Brown beans. As the moisture starts to evaporate, your beans will start turning that o’so familiar brown colour.
  5. First crack. Listen carefully. You’ll begin to hear the first popping sounds, indicating you’ve reached first crack.
  6. Light roast. Once you’ve reached first crack, the sugars will begin to caramelise, and with that, a light roast has been achieved.
  7. Second crack. This time, the popping will be a little more violent. Stopping between the first and second crack will put you somewhere around a light to medium roast.
  8. Dark roast. Maybe 30 to 60 seconds after the second crack, your beans will become a dark roast.
  9. Burnt. Don’t go much further past this point, or you’ll burn your beans. It’s okay to go to this point once, as you’ll then get a feel for how much roasting is too much.

To learn more about the different roasts, and which one might suit your fancy the most, you can find all you need to know towards the bottom of this article: Dark Roast Coffee vs Light Roast Coffee

Sourcing Your Green Coffee Beans

To roast your own coffee, you’re going to need some green coffee beans. They normally come in 60kg bags, but something tells me that’s a little more than what you’re wanting.

If you know somewhere local that roasts their own coffee beans, you’ll probably be able to get some from there. It’s definitely worth a visit. Plus you could pick up some top tips if you ask nicely.

Failing that, the internet is your best friend. A quick google search will bring up the most convenient ways to order beans to your front door. I’d research the beans you’re about to buy though, as each bean will bring with it its own unique flavours.

A little tip: two pounds of green coffee beans will produce around one pound of roasted coffee beans. 

green coffee beans in sack

4 Ways You Can Roast Coffee At Home

These methods are with a pan, an oven, a popcorn maker, and a home coffee roaster.

The first thing you want to do, before even thinking about turning on the pan, is open up some windows. Get some fans going. Or even roast your beans outside. Things are going to get smoky. 

Roasting Coffee Beans In A Pan

This is by far the most convenient way to roast you beans, as most households are going to have what you need already. So for a first attempt this could be the way to go.

Equipment needed:

  • Green coffee beans
  • Cast iron pan (make sure you’re not using a non-stick pan)
  • Stove/Hot plate
  • Metal colander and sieve
  • Wooden spoon or whisk
  • Airtight container
  • Oven mitts

Method:

  1. Ventilate. Yeah, do make sure the smoke has somewhere to go other than your lungs. That’s not the healthiest thing for you. Open a few windows.
  2. Put your pan on the stove and whack that baby up to 450F (230C). Don’t stress too much about getting this exact temperature, just make sure it’s around this mark. It could take a few attempts for you to figure out how far to turn the knob. You could get a laser temperature gun, if you’re feeling fancy.
  3. Add your beans. Don’t add too many that you can’t stir easily. You want a thin layer of coffee beans.
  4. Stir, and then stir some more. Don’t let your beans rest. Keep those bad boys moving. If they stay still for too long they’re going to roast unevenly. Or even worse, burn.
  5. Keep your ears alert for the first crack. The first crack should start to happen after 4 or 5 minutes. This means you’ve reached a light roast.
  6. Now listen for the second crack. This should happen after 6-7 minutes. But be careful not to leave them for much longer in the pan after the second crack. This could burn the beans. Maybe 30 seconds after you hear the second crack, you can then remove the beans from the heat.
  7. Remove the chaff. Do this outside, and be careful because everything will be hot hot hot. Take the beans and move them from the colander to the sieve, or whatever bowl you’re using. Just make sure to remove the beans from the pan. This will also get messy.
  8. Let the beans degas. For the next 12 hours, don’t seal your beans or else the pressure built up in the container could pop the lid. After 12 hours, store your beans as you would normally.

This method is great for a first attempt. It’s fast, convenient, and no need to buy any equipment. However, it’s going to get very smoky, and it’s hard to get the right temperature to start with, and an even roast.

Roasting Coffee Beans In The Oven

This is another popular and convenient method to roast coffee at home, as you’ll probably have everything you need already.

Equipment needed:

  • Green coffee beans
  • Oven
  • Oven tray (preferably perforated, but not necessary)
  • Colander and sieve
  • Airtight container
  • Oven mitts

Method:

  1. Ventilate. Remember to open a few windows. Things are going to get smokier than a 70’s disco.
  2. Pre-heat the oven to 500F (260C). You might need to experiment with your oven to find the right temperature. It can vary depending on the oven and the beans.
  3. Place your beans evenly around the oven tray. Make sure not to stack them, you only want them one bean deep. If you’re a perforated tray, make sure no green beans fall through and get stuck, as the beans will expand during roasting.If you’re using a regular oven tray, place a sheet of baking paper on it first, and give them a little shake once or twice during the roast.
  4. Place the tray in the oven. Make sure they go on the middle runner, as this will create the most even temperature for the beans.
  5. Listen out for the first crack. This should happen after 5-6 minutes. You can stop roasting your beans now if you want. You have achieved a light roast level at this point.
  6. Listen for the second crack. This shouldn’t be too much longer after the first crack. I’d leave your beans for no longer than 30-60 seconds after the second crack.
  7. Place your beans into a colander to cool, and remove the chaff. Move the beans from the colander to the sieve to remove the chaff. Best off to do this outside. And make sure you’re wearing your oven mitts at this point. Everything will be hot.
  8. Leave beans un-sealed for 12 hours, to degas. After 12 hours, seal your coffee beans and store normally.

This method is great for a first attempt too, as you probably won’t have to buy anything other than the green beans. It tends to be a little slower than other methods, but the job gets done regardless.

Roasting Coffee In A Popcorn Machine

Firstly, this method comes with a warning. Popcorn machines are made for one purpose, and that is to make popcorn. That being said, they can also be great for roasting coffee at home.

Be careful though, your popcorn machine may break after a couple of roasts.

Equipment needed:

  • Green coffee beans
  • A popcorn machine with side vented heat
  • Wooden spoon
  • Colander and sieve
  • Bowl
  • Airtight container
  • Oven mitts

Method:

  1. Ventilate. Remember to get those windows open. It’s going to get smoky.
  2. Pre-heat your popcorn machine. Each model takes a different amount of time, usually around 30 seconds or so.
  3. Add your beans. I would add the same amount of beans as the machine recommends corn kernels. You don’t want to add too many coffee beans, as they should be agitated (rotated) by the machine.
  4. Give a helping hand with the stir. To get the beans moving around, take your wooden spoon and stir. You shouldn’t have to do it for the whole time. Once the beans are moving around on their own you should be able to stop and put the lid on. Keep an eye on the beans in case you need to lend a hand though.
  5. Collect the chaff. To avoid cleaning up a huge mess of chaff at the end, place a large bowl at the machine’s spout. This will collect all the chaff, before it ends up in every crevice of your kitchen.
  6. Listen for the first crack. This should be between 4-5 minutes, and once reached, you’ve achieved a light roast.
  7. Listen for the second crack. This should be between 6-8 minutes. Once you reach this point, your beans are at a medium roast. If you’re wanting to go darker, I wouldn’t roast your beans for more than another 60 seconds, as you run the risk of burning them.
  8. Cool and remove chaff. Pour your beans into the colander, and toss between colander and sieve. This will cool your beans and remove any excess chaff left on the beans.
  9. Allow to degas for 12 hours. Don’t seal your beans in the container just yet. Allow them to breathe for 12 hours before storing.

This is an easy method, where the machine will do most of the work for you. It’s easy to monitor the roast level, and to achieve the desired roast. However, these machines aren’t built for roasting coffee, and will void the warranty if they break.

Roasting Coffee In A Home Coffee Roaster

If you’re wanting to get a little more serious about roasting your own coffee beans, then get yourself a decent at home coffee roaster. There are some great small coffee roasters on the market, ideal for this purpose.

(You can check out our coffee roasting machine reviews here if you’re interested)

Equipment needed:

  • Green coffee beans
  • Coffee roasting machine
  • Oven mitts
  • Colander and sieve (if your roasting machine doesn’t have it’s own cooling process)

Method:

  1. Ventilation. Open a few windows and make sure the room you’re roasting in is well ventilated.
  2. Turn on your roaster, and add your beans. Each machine will come with it’s own instructions, so I recommend following them.
  3. Keep an eye on your beans. Although each machine will say they’re fully automatic, there are other variables that will affect the roast time. Such as bean size and type, the age of the machine etc.
  4. Listen for the first crack. When you hear the first crack, this means you’ve achieved a light roast. If you want a darker roast leave the beans in the roaster.
  5. Listen for the second crack. This indicates you’ve achieved a medium roast. Leave in the roaster for a little longer for a dark roast.
  6. Cool and remove the chaff. Your roasting machine may have it’s own cooling process. If not, remove your beans from the roaster and into the colander. Pass the beans from the colander to the sieve to remove the chaff. Best off doing this outside to avoid the inevitable mess.
  7. Allow beans to degas. Leave for 12 hours unsealed.

This method definitely has the highest up front cost, and you need to find space to put your roaster somewhere. I’m sure in the long run you’ll save money on coffee though. Plus, roasting your own beans is fun, and you’re learning a new skill too. Can’t put a price on that.

roasting machine roasting coffee beans

Some Common Home Roasting Errors To Avoid

Roasting your own beans is a lot of fun. Don’t be afraid to make some mistakes along the way. This is how you’ll learn to refine your roasting process, and produce beans that suit your taste buds.

For your first attempt, use the times in the methods above as a guide, but don’t stick to them if your beans didn’t come out how you wanted them to. There are so many variables at play here, you’re going to need to find your own roasting rhythm.

For example, the type of bean will affect the roasting process. Where they’ve grown, soil composition, altitude etc. As well as this, the actual temperature surrounding your beans might differ to what you told the machine to sit at.

So don’t be afraid to play around and hone in on the right roasting process for your machine and beans.

Don’t leave your roaster unattended too. If you’re distracted or multitasking, your roast can change in the blink of an eye and before you know it, the batch is ruined. Keep an eye on your beans.

Cleaning your roasting machine is important too, even if it’s not the most fun. Chaff can build up, as well as oils, which will affect the taste of your beans. So give it a clean out every now and then.

Be careful not to add too many coffee beans to your batch too. It could mean your beans won’t be evenly agitated and that results in an uneven roast. If your beans aren’t all around the same colour, try reducing the size of your batch.

Check out this video of a first attempt at roasting coffee beans at home! Maybe you can learn a thing or two:

To Sum Up

Have fun! Go experiment! Home roasting may seem like a challenge, but I’m sure you’ll find it easier than you might expect.

Getting involved in the processes that our food goes through brings another level of appreciation, and I’m sure you’ll find it rewarding.

Happy roasting!

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Tom Bolland

Tom Bolland

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