Roasting coffee beans at home isn’t common any more, but before large scale coffee producers came along in the 1920s, it was the only way to do it. Roasting coffee beans at home has been done for centuries with methods as simple as roasting in cast iron skillets over an open fire. Although it is not necessary anymore, many people have been roasting their own beans both as a hobby and as a way to get even fresher roasted coffee. It also gives you the opportunity to have different coffee every day of the week.
For the most part, roasting coffee beans is very simple. Apply heat to green coffee beans until you achieve your desired roast. The beans will become hotter during the roasting and will achieve different roast types as the temperature changes. The hotter the beans get, the darker the roast will be. To achieve that temperature or roast, there are different methods used. The roasting methods are not difficult and some can be done with very little money. Let’s take you through the process by reviewing the roasting process, different methods, and buying green coffee beans.
The Roasting Process
Roasting coffee beans is simply the application of heat over time to green coffee beans. Beans are heated to a temperature up to 450°F, although the specific temperature they reach will vary depending on the desired roast. How quickly the beans are brought to this temperature affects their flavor. In general, it takes somewhere between 8 to 30 minutes to roast. Once the roasting part is done, you need to cool the beans and let the beans de-gas for 24 to 48 hours to release CO2.
Regardless of the method used to roast, there are some key stages during roasting that you need to be aware of. Understanding the different stages of the roast will help you control the flavor. Many people compare it to popping corn.
Stages of the Roasting Process:
Beginning – Unroasted coffee beans are green. The will remain so for a few minutes as the beans are being heated.
Yellowing – After a couple of minutes, the beans will become a light yellow color and begin to emit a grassy smell.
Steam – After a few more minutes, the beans will begin to steam as the water in the bean begins to dissipate.
First Crack – The beans at this stage are at about 385 °F which typically takes from 3 minutes to 15 minutes to begin and should last from 1 minute to 3 minutes. The steam will begin to have a smell and you will hear a crack. At this stage, the sugars in the beans begin to caramelize and the bound-up water inside the bean is trying to escape. This causes the bean to break down and the oils of the bean will begin to come out of the bean. After this point, the beans can be used for coffee. This would be considered a light roast.
First Roasted Stage – At this stage, cracking becomes louder and the beans become a medium brown color and there is a strong aroma. This is what is called a City roast. The beans are at about 426 °F.
Caramelization – As caramelization continues, the oils in the bean are coming out and the bean is becoming darker and expanding. At this stage, the coffee is going from a City+ roast and onto a Full City roast.
Second Crack – Once the beans begin to crack again, you are at the second crack stage. This begins 15 seconds to 2 minutes after first crack ends, when your beans have reached about 435°F. The cracks are usually louder than the “first crack” stage. At this point, you have a Vienna roast and the beans are starting to lose their origin character. Pieces of the shell of the bean will start to break off.
Darkening Roast - As the roast becomes very dark, the smoke will become stronger and the beans will continue to break down. As the end of second crack approaches you will achieve a French roast. If you leave a little longer, you will achieve an Italian roast and later a Turkish roast. This is as far as you can roast beans. Any longer will break down the beans and they will begin to resemble charcoal.
As soon as you reach your desired roast, you will want to remove the beans from the heat source. Cool in colander or roasting pan over small fan or just shake to remove chaff, outdoors or near a sink helps as this stuff floats off in almost any air current. If you have an electric machine, they will often have a cooling method.
Note that there will also be a large amount of smoke from the beans. Make sure you are in a well-ventilated area. Otherwise, you could set off your fire alarm. Also, as you roast, keep notes such as date, time, climate, method used to roast, time to reach first Crack, duration of first crack, time and duration of Second Crack, total roast time, taste, etc. This way you will be able to remember next time one what was done and if anything should be changed.
Once the beans have cooled, you want to store the beans in containers that will be air-tight but still allow gases to escape with one-way valves. It will take up to 3 days for the gas to slow down. The time will vary based on the coffee, roasting method, and roast level.
For the most part, the roasting coffee bean basics is the same regardless of the equipment used. Let’s look at each of the most popular types of equipment.
Coffee Roasting Methods and Equipment
There are four common methods used for roast coffee beans at home: in the oven, on the stovetop, in a hot-air popcorn maker, and in a coffee roasting electrical appliance. As previously described, all of the different types of equipment use the same basic principle to roast coffee beans by applying even heat to the raw coffee beans until you are at the desired roast level. Commercial machines have various sensors and gauges to monitor the roasting process and make it easier while other methods will require more monitoring and practice to perfect.
Roasting in the oven method
One of the easiest ways to roast coffee beans is to roast them in the oven. To do so, you spread green coffee beans evenly into a single layer on a perforated baking tray with raised sides. Simply preheat the oven to 450°F and roast the beans to the desired roast as previously mentioned in the “roasting process”. This method will take about 15 to 20 minutes. There are a couple of problems with this method. Because the beans are not stirred, the beans will not roast evenly. Also, roasting the beans will make a lot of smoke. Therefore, the oven area should be well ventilated.
The stovetop method is the way roasting coffee beans used to be done. To do so, use a cast-iron skillet, a frying pan, or a wok. Layer the beans evenly with the green coffee beans in the pan at medium-high heat. Cover the pan and stir the beans occasionally. Continue until the desired roast is reached. When done, remove the beans from the burner and separate the chaff from the beans using a colander and then cool. The process should take about 7 minutes depending on your roast.
Another stovetop option is to use a stove-top popcorn maker such as a "Whirley Pop" where there is an integral crank and agitator system to keep the beans in motion as they roast.
Popcorn maker roasting method
Another method is to use a hot-air popper. These poppers used to be popular a while back for popping popcorn. Now many people find them very practical for roasting coffee beans. To use it, simply turn it on and put a cup full of beans into the popper. After about a minute, the beans will begin to change color. Follow the “roasting process” mentioned previously to achieve your desired roast.
There are numerous issues with this method. First, these machines are not designed for roasting coffee beans. Therefore, it is not designed to withstand the longer heat cycle required by coffee beans. This may cause the popper to break from heat damage. Also, it blows chaff off of the roasting coffee beans. So it will require some cleaning up.
Electrical Coffee Roaster
In the last few years, home-roasting machines have become more popular. There are basic kinds: fluid-air bed and drum. Fluid-air bed machines will roast and agitate the beans by floating them on a “bed” of hot air. These machines will roast faster than a drum machine. But, they are smaller due to limits on the fan size. Drum machines roast by heating a rotating chamber. The rotation prevents burning of the beans. Drum machines are often used in very large commercial roasting operations, but there are smaller versions for home roasting. Operating machines will vary based on the specific machine. So, we cannot give you specific directions. But, these machines are typically very easy to operate by setting a few options and starting the machine. Therefore, if you are nervous about roasting coffee beans, this is a great option for getting more consistent roasts. A couple nice features to look for in an electric roaster are a smoke filter and a chaff filter.
Getting Good Unroasted Coffee Beans (Green Coffee)
As a home roaster, you can select any green coffee beans you desire. You can even mix if you like. It is best to purchase small quantities of various high quality beans so you can see what your preferences are. You have a wide variety available from numerous countries around the world. Like wine, you will find specific countries, regions, and orchards, and years that will become your favorite. Once you have found a type that you like, you can buy in a larger quantity. Green coffee beans will store well for over a year.