The Complete Guide To Coffee Roasting at Home

The fact that you find yourself reading this article says something quite significant about you! It probably shows that either you are really bored (!!!) or else you are a serious coffee enthusiast dedicated to the journey from bean to brew. Roasting coffee beans is a practice for the coffee lover who enjoys not just the end product but the actual process of extracting delicious flavour from this unassuming bean. And it is actually way easier than you think!

In this article we will take you step by step through both the theory and practice of roasting your own coffee beans from the comfort of your kitchen. After explaining the how of this process, we will give you three different methods of roasting coffee at home, two of which you could probably give a crack with what is in your kitchen today!  

why Roast your own Coffee Beans?

So why should you bother roasting your own beans? Isn’t it way easier and better just to buy pre-roasted? Well not necessarily! As with virtually every aspect of the coffee making process it comes down to flavour and intimacy in the bean to brew journey.

Bag of green coffee beans

Roasting your own beans means you can always have fresh roasted beans that have been roasted to your specific coffee palate. Depending on origin and storage method, roasted coffee beans usually have a peak flavour somewhere between one to two weeks of roasting. Home roasting allows you to produce small batches of coffee roasted to your preference and so with maximum freshness and flavour. While it can take time to master (along with just about anything worthwhile in life), this process allows you to customise the lightness or darkness of your beans exactly to your palate.

Finally, it is actually just a lot of fun and can be deeply satisfying. It is just another way to get more closely involved in that journey from bean to brew that we have all come to love. It is the reason that we love home brewing and are not satisfied with simply getting a latte from the local cafe. We love the process, we love learning and perfecting and experimenting on our journey to the perfect cup. It is also a nice added perk that green beans are significantly cheaper than pre-roasted 🙂

So give it a go! If it is not for you then nothing lost, but you may come to love it more than you expect!

What is Coffee?

People often don’t realise that coffee beans are actually the seeds of cherries from a coffee plant. These plants typically grow in a tropical climate producing the small red fruits that contain what will become our coffee bean. Once ripe, these cherries are picked and processed to remove the outer skin, pulp and inner skin. The seed (our coffee bean) is then dried resulting in a green coffee bean. These beans can last for one to two years if stored correctly and still be fresh when roasted.

Green coffee beans growing on a coffee plant

If you ever tried to grind or brew unroasted coffee beans you would would be quickly (and rather comically) convinced of the dire need for good roasting! Unroasted beans produce a bitter and acidic drink that is, to be honest, disgusting. When well roasted, however, the natural sugars of the green bean are caramelised into the complex smells and flavours we love.

What happens when we Roast Coffee Beans?

The almost magical transformation of flavour in the roasting process is what is technically called the Maillard reaction. It is a chemical reaction that occurs between amino acids and sugars that results in the browning of a range of food and the production of new aromas and flavours (this is also what is going on when you go to sear and cook that porterhouse steak). In this reaction over 800 compounds are transformed as our green bean is converted into a roasted bean full of delicious flavour and aroma. This reaction occurs at the beginning of roasting and is the reason the bean transitions from green to yellow or brown.

The Science of Coffee Roasting

This section will take you step by step through the stages of development as coffee beans are roasted. This will help you recognise how the roast is progressing and when to end it for various roast profiles. We recommend taking a look at this roasting guide that shows pictures of the beans at each various stage.

Showing 4 stages a coffee bean goes through when roasted

Stage 1: Drying

Green coffee beans start off with about 10-12% moisture (water trapped in the bean) that needs to evaporate before they can begin roasting proper. Hence, the initial heat applied acts to dry out the beans.The appearance changes in this step from light green to pale and a grassy smell is emitted.

Stage 2: Browning

This is the stage where the Maillard reaction begins to occur. The beans begin to change appearance from yellow to tan/orange colour. The beans begin to expand and shed the outer skin known as chaff. Caramelisation of amino acids and sugars begin to occur. At this stage it begins to smell like toasted bread.

Stage 3: First Crack

This is where the roasting process changes from endothermic to exothermic (basically in the earlier stages the bean is absorbing energy and now it releases that energy). The moisture in the beans evaporates into steam, forming pressure inside the bean which causes it to crack open. The beans audibly begin to crack which sounds very similar to the sound of popcorn popping.

This is generally recognised as the point at which coffee beans become usable. A light roasted bean is stopped at or just after this point. In a light roast the characteristics from the origin are most pronounced. Light roasted beans are generally higher acidity, bright and fruity flavoured, and lighter bodied. They also (obviously) display less roast flavours than some darker roasts. They have more caffeine than darker roasted beans. Lighter roasts are also known as: Half City, Light City or Cinnamon roasts

Stage 4: Roast Development

This stage of the roast is really when the art of roasting comes in as this is where the flavour profile of the roast is developed. Roast development is the time from the first crack until you decide to end the roast. The coffee changes in appearance and flavour quickly after the first crack so you have to carefully monitor the time and temperature. Faster roasts generally have a brighter profile, while longer, darker roasts tend to be less acidic and have more body.

It is generally recommended that this stage should be 15-25% of the total roast time. During this stage the complex flavours start to develop; the acidity and sweetness of the bean decreases as the sugars and acids inside are caramelised. A medium roasted bean is stopped at this stage. In a medium roast many of the unique origin flavours are preserved alongside a fuller body, less acidity, and a more balanced, sweeter taste. Medium roasts are also known as City, Full City, Breakfast and American roasts.

Stage 5: Second Crack

If left long enough, coffee beans go through a second crack where the structure of the bean begins to break down and it’s oils are released. The second crack is similar to the first but is softer sounding. Roasting to this point will result in a dark roasted coffee bean. The beans are a dark brown colour with an oily sheen and typically have low acidity and a high level of bitterness. The flavour characteristics of the origin are dominated by bitter, roasty, burnt flavours. If you are wanting to produce a dark roast you don’t need to be too concerned with the beans origins and can just go for cheap green beans. Roasting past the second crack will result in burnt, undrinkable coffee. Dark roasts are also known as French, Italian, Vienna or Continental roasts.

Stage 6: Cooling

This stage is almost as important as the roasting stages. You need to cool the beans down quickly to prevent the beans from roasting further and dulling the flavour of the coffee. Some automatic home roasters blow cool air through the roasting chamber to do this or you can dump the beans on a cooling tray. Another easy and effective method is to pour the hot beans back and forth from one colander to a second until they cool.

Stage 7: Resting

It is recommended to leave freshly roasted beans for 1-2 days so they can de-gas (essential for maximum favour). Using beans that haven’t had time to de-gas can result in an uneven extraction.

How To Roast Coffee Beans

Method One: Roasting Beans in a Pan

The real benefit of this method is that it literally allows anyone who owns a skillet (and let’s be honest, who doesn’t own a skillet!?) to give coffee roasting a shot. This method, while somewhat messy, is relatively easy to understand and master with time.

Equipment Needed:

  • ¾ cup of green beans
  • 12 inch or so skillet (Cast Iron is best)
  • Cooktop
  • Stirring utensil: we recommend a whisk
  • 2 Colanders/ cookie sheet
  • Oven mitts
  • Air tight container

Method:

  1. Preheat the skillet on a medium heat to around 300F (any higher than this may cause the beans to scorch)
  2. Turn extraction fan on as roasting produces a lot of smoke
  3. Add the green beans and immediately begin whisking, continue this throughout the entire roasting time to prevent scorching and to get an even roast
  4. Adjust temperature accordingly to control roast level
  5. Listen for the first crack which indicates your beans are now at a light roast level
  6. Continue roasting until beans reach desired roast level (usually around 12-14 min for a medium roast), remove from heat and pour onto a cookie sheet or into the colanders to cool. Agitate in colander (or between 2 colanders) to cool quickly and remove chaff. Do this outside as it can be messy and produces a lot of smoke and wear oven mitts to prevent getting burnt!
  7. Pick out any really under or over roasted beans which can be very bitter
  8. Once beans are cool pour into an airtight container and leave to degas for one to two days before using. We recommend not sealing the lid for the first 24 hours.

Helpful Tips

  • A cast iron skillet is best for this technique as it has a more even distribution of heat
  • If possible use a smaller skillet as it makes it easier to keep the beans moving evenly
  • A colander does tend to be more effective at cooling the beans down than a cookie sheet. As an added bonus, it helps to get rid of the chaff at the same time.
  • A whisk is the best stirring utensil to agitate the beans
  • Use a timer and journal so you can record what temperature and roasting times you used to duplicate your favourite roasts (or avoid those inevitable less than perfect batches :))

Pros:

  • Inexpensive method
  • Great for beginners to learn different stages of roasting
  • Roast level and temperature relatively easy to control

Cons:

  • If not done carefully can produce an uneven roast
  • Easy to scorch
  • Very smoky, messy process

Method Two: Roasting Beans in a Popcorn Maker

One easy and relatively cheap way to dip your toes into the roasting world is to recommission a popcorn maker which heats from the sides as opposed to the bottom (very important!) . Because this appliance isn’t designed for this use we don’t recommend using your kids favourite popcorn maker! So either use an old popcorn maker you don’t really care about or pop into your local shop/thrift store, find a cheap secondhand one and hey presto! You’re good to go!

Equipment Needed:

  • ½ cup of Green beans
  • Popcorn maker
  • Metal Colander
  • Wooden spoon
  • Airtight container

Method:

  1. Set up popcorn maker in a well ventilated area (under extraction fan or outside)
  2. Preheat machine according to manufacturer’s instructions
  3. Place metal colander under popcorn maker spout to collect chaff and beans that come out
  4. Turn on popcorn maker and add green beans (do not overfill as will scorch coffee). We recommend starting with half a cup and adjusting quantity based on action in roasting chamber
  5. Stir beans with a wooden spoon at the beginning of the roast to ensure an even roast
  6. Listen for the first crack which indicates your beans are now at a light roast level
  7. Continue roasting until beans reach desired roast level (usually around 4 minutes for a medium roast) then turn popcorn maker off and quickly pour beans into a colander or onto a cookie sheet to cool. Agitate in colander (or between 2 colanders) to cool quickly and remove chaff. Do this outside as it can be messy and produces a lot of smoke and wear oven mitts to prevent getting burnt!
  8. Pick out any really under or over roasted beans which can be very bitter
  9. Once beans are cool pour into an airtight container and leave to degas for one to two days before using. We recommend not sealing the lid for the first 24 hours.

Helpful Tips

  • Try to use a popcorn maker that has a flat bottom and heats from the sides rather than the bottom
  • If you put a damp cloth in the colander, when the roasted beans are added the chaff sticks to it and is easier to remove
  • Initially use a larger bean as it takes a bit longer to roast and so is easier to control roast level.
  • Adjust quantity of beans depending on level of movement in the roasting chamber – if there is little or no movement of the beans you may have put in too many and vice versa.

Pros:

  • Inexpensive
  • Simple to use
  • Automatically agitates beans
  • Able to produce a pretty even roast
  • Average roast time 4 min (very fast)

Cons:

  • Messy and smelly
  • Not built for roasting coffee so could damage machine
  • Small roast capacity

Method Three: Roasting Beans in an Automatic Coffee Roaster

For those of you who are serious about roasting beans we recommend buying a coffee roasting machine (if you need some help deciding which one to buy you can read our top five review here). These machines yield a more consistent roast and are simple to use and easy to clean.

Equipment Needed:

  • Green beans
  • Roasting machine
  • Colander
  • Airtight container

Method:

  1. Place the recommended amount of beans into the roasting chamber
  2. Close the roaster and turn it on
  3. Allow the coffee to roast until you reach the desired stage
  4. Cool the coffee down (some machines do this for you by blowing cool air through the roasting chamber), otherwise cool using a colander
  5. Once beans are cool, pour into an airtight container and leave to degas for one to two days before using. We recommend not sealing the lid for the first 24 hours.

Helpful Tips

  • Get a notebook and record your temperature, fan or drum speed, roast times and the outcomes. This means you can duplicate roasts you love and tweak ones you’re not so pleased with
  • Don’t overload the roaster or you will get an inconsistent roast

Pros:

  • Purpose built
  • Simple to use and clean
  • Have functions such as chaff collection and smoke suppression
  • Able to vary temp, air flow
  • Larger roast capacity

Cons:

  • Expensive
  • Can be large machines

Takeaway

So while roasting beans can seem both unnecessary and daunting, we hope we have persuaded you that as well as being doable it is a great way to maximize your coffee flavour and experience. So give it a go and we would love to hear from you how you found the experience.

Happy Roasting!

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