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 unlocking the complex flavors hidden within the humble coffee bean. And surprisingly, roasting coffee at home is easier than you might think!
In this guide, we’ll delve into the fundamentals of coffee roasting, offering practical steps and methods you can try at home. Whether you have specialized equipment or just a simple skillet, there’s a way to start your roasting adventure.
Why Roast Your Coffee Beans?
So why should you bother roasting your coffee beans? Isn’t it way easier and better just to buy pre-roasted coffee? Well not necessarily! As with virtually every aspect of the coffee-making process, it comes down to flavor and intimacy in the bean-to-brew journey.
Roasting your coffee beans means you can always have fresh roasted beans on hand that have been tailored to your taste. Depending on the origin and storage method, roasted coffee beans usually have a peak flavor around one to two weeks after roasting. Home roasting allows you to produce small batches of coffee roasted to your preference with maximum freshness and flavor. While it can take time to master (along with just about anything worthwhile in life), this process allows you to experiment with different roast levels giving you complete control over your coffee’s flavor profile.
Finally, it is actually just deeply satisfying and a lot of fun. It is just another way to get more closely involved in that journey from bean to brew. This is why 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 is lost, but you may come to love it more than you expect!
What is Coffee?
Many people are surprised to learn 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.
If you ever tried to grind or brew unroasted coffee beans you 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 caramelized into the complex smells and flavors we love.
What Happens When We Roast Coffee Beans?
The almost magical transformation of flavor in the roasting process is what is technically called the Maillard reaction. This is a chemical reaction that occurs between amino acids and sugars and results in the browning of a range of foods and the production of new aromas and flavors (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 coffee bean is converted into a roasted bean full of delicious flavor 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 recognize 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.
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 properly. Given this, 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 color from yellow to tan/orange. The beans begin to expand and shed the outer skin known as chaff. Caramelization of amino acids and sugars begins 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 beans, which causes them to crack open. The beans audibly begin to crack which sounds very similar to the sound of popcorn popping.
This is generally recognized as the point at which coffee beans become drinkable. 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 typically have higher acidity, bright and fruity flavors, and are lighter-bodied. They also have slightly 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 flavor 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 flavor 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.
As a general guide, this stage should be around 15-25% of the total roast time. During this stage the complex flavors start to develop; the acidity and sweetness of the bean decreases as the sugars and acids inside are caramelized. A medium roasted bean is stopped at this stage. In a medium roast, many of the unique origin flavors 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 its 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 color with an oily sheen and typically have low acidity and a high level of bitterness.
The flavor characteristics of the origin are dominated by bitter, roasty, and burnt flavors. If you like dark-roasted coffee you don’t need to be too concerned with the bean’s origins and can just go for cheaper 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 stage. You need to cool the beans down quickly to prevent the beans from roasting further and dulling the flavor 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 let freshly roasted beans rest for 3-4 days to de-gas, a process essential for achieving maximum flavor. Roasting coffee beans triggers chemical reactions that produce large volumes of carbon dioxide, which becomes trapped inside the beans. Over time, this gas gradually escapes. When hot water is added during brewing, the gas is released rapidly. If you brew coffee with beans that haven’t had enough time to de-gas, it can lead to improper extraction, especially when making espresso.
How To Roast Coffee Beans At Home
So now that we have explained a bit of the theory of coffee roasting it’s time to give it a go yourself. The first step is to select a coffee roaster.
Selecting A Coffee Roaster
Choosing the right coffee roaster is crucial for achieving an even roast. While it’s possible to roast coffee using basic equipment like a baking sheet in an oven, this method often leads to uneven roasting and scorched beans due to inadequate agitation and movement. Many beginners start with a repurposed popcorn maker, which is affordable and can quickly roast small batches in about 4-5 minutes. While a popcorn maker is a low-cost option, it often produces uneven results, particularly for lighter roasts, and is better suited for darker roasts.
For those serious about home roasting, investing in a specialized coffee roaster is better for producing more consistent results. The two main types of home roasters are hot air and drum roasters.
Hot air roasters, which are essentially more powerful popcorn roasters, use jets of hot air to agitate and evenly roast the beans, typically taking 8-12 minutes. They offer some control over heat and fan speed, making them a good starting point, although they do produce smoke and odors, requiring a well-ventilated area.
Drum roasters closely resemble commercial roasters in design. They feature a metal drum that rotates over a flame, containing the coffee beans. This setup allows for precise control over temperature and airflow, enabling slower roasting times of 10-15 minutes. While drum roasters can replicate the consistency of commercial roasting, they are more costly and require a larger initial investment.
Method One: Roasting Coffee Beans On A Baking Sheet
The real benefit of this method is that it literally allows anyone who owns an oven and baking sheet (and let’s be honest, who doesn’t?) to give coffee roasting a shot. This method, while somewhat messy, is relatively easy to understand and master with time.
Equipment:
- 150g green coffee beans
- 2 medium metal sieves
- Timer
- Perforated baking sheet (ensure beans are no more than one layer deep)
- Kitchen scale
Instructions:
- Place a rack in the center of the oven and preheat the oven to 500°F (260°C) for 30 minutes. A longer preheat helps ensure the temperature remains stable when you open the door during roasting.
- Weigh out 150g (5.3oz) of green coffee beans and spread the beans in a single layer over the center of the perforated baking sheet.
- Place the baking sheet in the preheated oven, close the door, and start your timer.
Observation Tips: Try to observe the beans through the oven door without opening it frequently to maintain the oven temperature.
Roasting Stages:
2-3.5 minutes: Beans will appear brighter with a more intense green color.
3.5-4 minutes: Beans turn yellow. Note the time, then open the oven and gently agitate the baking sheet to move the beans around.
5.5 minutes: Beans will be a light brown color, still small and wrinkly. Agitate again if the outer beans are darkening faster than the center ones.
7-8 minutes: You’ll hear the first crack, similar to popcorn popping. Note the time of the first crack.
20-30 seconds after the first crack: Agitate the pan to ensure even roasting.
45 seconds after the first crack (around 9 minutes): the popping will begin to slow down, and there will be a brief moment of silence before the second crack starts. This stage is critical for flavor development; adjust the roasting time according to your taste preference. Remember to remove the coffee from the oven slightly before it reaches your desired roast level, as the beans will continue to cook from residual heat. - Take the roasted coffee beans outside and pour them into one of the sieves. Pour the beans back and forth between the sieves to remove the chaff and cool the beans down. Continue until the beans are warm to the touch.
Method Two: Roasting Beans In A Popcorn Maker
One easy and relatively cheap way to dip your toes into the roasting world is to repurpose a popcorn maker. Because this appliance isn’t designed for this use we don’t recommend using your kid’s favorite 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:
- 120g green coffee beans
- Hot Air Popcorn Maker
- 2 medium metal sieves
- Wooden spoon
- Timer
- Kitchen scale
Instructions:
- Measure the Beans: Use about 1/2 cup (approximately 120 grams) of green coffee beans. Avoid overloading the popper as it can prevent even roasting.
- Set up the popcorn maker in a well-ventilated area (under an extraction fan or outside). Position a bowl or colander under the chute to catch the chaff.
- Preheat the popcorn maker– this helps to achieve a consistent roast.
- Pour the green beans into the popcorn maker, start the popcorn maker, and begin the timer.
- Use a wooden spoon to stir the beans at the start of the roast. This helps to ensure an even roast.
- Monitor the Roast:
2-4 minutes: Beans will turn from green to yellow and emit a grassy aroma.
4-5 minutes: Beans enter the “first crack” phase, characterized by a cracking sound similar to popcorn popping. This stage indicates a light roast.
5-7 minutes: As the roast progresses, the cracks will subside. The beans will darken in color, and you may notice the “second crack,” a fainter and quicker series of pops, indicating a medium to dark roast. - Continue roasting until the beans reach your desired roast level. For a medium roast, this typically takes around 4 minutes. Once achieved, turn off the popcorn maker.
- Quickly pour the beans into a metal colander or sieve to cool. Agitate the beans in the colander or between two colanders to speed up cooling and remove the chaff. This step can be messy and produces smoke, so it’s best done outside. Use oven mitts to protect your hands from the heat.
- Pick out any under-roasted or over-roasted beans, as they can impart bitterness to your brew.
- Once cooled, transfer the beans to an airtight container. Leave the container partially open for the first 24 hours to allow the beans to degas. After that, seal the container to preserve freshness.
Helpful Tips
- Experiment with Time and Temperature: The roasting process can vary depending on the popcorn maker and bean type. Note the times and temperatures that work best for your taste.
- Adjust the amount of beans based on the movement in the roasting chamber. If the beans are not moving much, you may have added too many; if they move too freely, consider adding a few more beans.
- Place a damp cloth in the colander to make it easier to remove chaff, place a damp cloth in the colander. The chaff will stick to the cloth as you pour the roasted beans into it.
- Safety First: Always supervise the roasting process to avoid overheating and potential fire hazards.
- Ventilation: Proper ventilation is crucial as the roasting process produces smoke and chaff.
Method Three: Roasting Beans In An Automatic Coffee Roaster
For those of you who are serious about roasting beans, we recommend buying a home coffee roaster. These machines yield a more consistent roast and are simple to use and easy to clean.
Equipment:
- Automatic coffee roaster
- Green coffee beans
- Scale
- Airtight container for storage
- Timer
Instructions:
- Place the recommended amount of beans into the roasting chamber. Most roasters have a recommended capacity—typically between 100-300 grams (3.5-10.5 oz). Do not exceed the recommended amount to ensure even roasting.
- Adjust settings- some automatic roasters allow you to choose a roast profile (light, medium, or dark). Others have options to adjust the temperature, fan speed, and roasting time.
- Start Roasting: Turn on the roaster and start the roasting process. The machine will typically agitate the beans and control the temperature automatically.
- Monitor the Process: Even with an automatic roaster, it’s good practice to observe the process. Listen for the “first crack” (sounds like popcorn popping) to gauge the roast level. If aiming for a darker roast, you may also hear a “second crack.”
- Cool the beans: Once the roasting cycle is complete, the roaster should enter a cooling phase. This cools the beans quickly to stop the roasting process. Some roasters have built-in cooling systems; if not, you may need to manually cool the beans using a colander or a dedicated cooling tray.
- Degas the beans: Once cooled, transfer the beans to an airtight container. Freshly roasted beans release carbon dioxide gas. Leave the container loosely covered for the first 24 hours to allow degassing before sealing it tightly.
Helpful Tips
- Experiment with Roast Levels: Different beans and roast profiles can yield a variety of flavors. Experiment to find what you like best.
- Consider Ventilation: Roasting coffee produces smoke and odors. Ensure your roasting area is well-ventilated or use an exhaust system.
- Keep Records: Note the settings and outcomes of each roast to refine your process over time.
How To Store Coffee Beans
Once roasted, coffee beans should be stored in an airtight container to maintain freshness and flavor. Allow the beans to degas overnight with the container loosely covered before sealing it tightly. It is best to use the beans within one month of roasting, as their flavor can deteriorate over time.
Green (unroasted) coffee beans have a longer shelf life and can be stored in an airtight container for up to six months. Proper storage ensures that both roasted and unroasted beans remain fresh and flavorful for your coffee brewing needs.
Roasting Coffee Beans At Home- In Summary
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 flavor and experience. And the best part is, you can roast coffee beans at home without the need for expensive, specialized equipment. So give it a go and we would love to hear from you how you found the experience.
Happy Roasting!
