Home coffee roasting, 101

Yes, you can roast coffee in your home! While home roasting cannot, unfortunately, save you from an “I’m out of coffee” meltdown (the beans need to rest for at least 12-hours post-roast), it can be a fun, satisfying way to learn about your favorite beverage.

The roasting tool kit

Before you begin, it is important to have all the tools needed for a successful roast. The entire process takes rough 15-20 minutes and you cannot pause in the middle to fetch a forgotten tool. You will need:

  • Fresh green beans: beans of any origin will do but be sure they are fresh, processed, and ready to roast.
  • A roaster: this could be anything from a cast iron skillet or a stovetop popcorn maker to a home fluid bed or drum roaster. For those of you devoted home roasting, we recommend a drum roaster as it creates the most even, controlled roast.
  • A laser or inferred thermometer capable of reading up to 500 degrees Fahrenheit (260 degrees Celsius).
  • A colander to remove and collect the chaff, a paper-thin leaf-textured material that falls off the bean during roasting.
  • A baking sheet or rack for cooling your beans post-roast.
  • A wooden spoon for stirring your beans if you are using a skillet.

Let’s roast!

Roasting is as much a skill as it is an art of balance, instinct, and control. For the home roasting newbies among you, on the most basic level roasting is the process of removing moisture from the bean until you achieve the desired balance of sugars, acids, and carbonization. As the beans roast they darken, drop water weight, expand, and generate natural CO2.

If you are working with a fluid bed or drum roaster, your machine should have heat and roast settings. It is best to follow the manufacture’s instructions. If you are using a cast iron skillet or stovetop popcorn maker, fire up the stove or grill and let’s begin! To start, you want your green beans at room temperature and your roasting apparatus heated between 370 and 500 degrees Fahrenheit (180 and 260 degrees Celsius). Once at an appropriate temperature, add 3 to 4 ounces of green beans to your roaster, bearing in mind that they will at least double in size as they roast. It is best to stick to a maximum of two layers of beans to ensure an even roast. Once the beans have been added and start to heat (this is referred to as the “charge”), stir them constantly. If the beans aren’t in constant motion, thus receiving equal heat, you will end up with an uneven, unpleasant roast. Now, the fun begins!

While it is essential to listen for the first “crack”, which signifies you’ve reached a medium roast (generally a City roast), it is helpful to know the colors and stages of the roast prior to the first crack:

  • Green beans indicate that the beans are raw and moist.
  • Yellow steaming beans indicate that moister is leaving the bean. The beans may also start to emit a grassy, earthy odor at this stage. As the beans continue to yellow they will turn a deeper mustard color and the odor will shift from earthy to more of a toast scent.
  • Pale brown beans signify that you are close to the first crack! At this stage, the beans may start to accentuate their central line.
  • The first crack means you’ve reached a medium, generally a City roast. The beans should have a lovely medium brown shade, no oil sheen, and a rich, full aroma. The beans are considered roasted and can be removed from the heat at this stage.

If you continue roasting, the beans will quickly darken, expand, and almost shine as oil begins to develop within the bean. Next comes the second crack and development a slight oil sheen, which indicates you’ve entered dark roast territory. Beans roast very quickly following the first crack, moving from a Full City to an Italian roast within a matter of minutes. It is vital you use all of your senses to determine when the beans have reached your desired roast profile and then to promptly remove them from the heat. Beans left on the heat for too long will darken to the point where they look (and taste) like charcoal. To learn more about roast profiles, click here.

Once the roasting is complete, transfer the beans to a colander and gently shake the colander to remove the chaff (there is no harm in drinking the chaff but it may impact the flavor of the roast). Next, spread the beans out on a backing sheet to cool and degas for at least 12 hours (for best results, we recommend degassing for at least 24 hours). Degassing, the release of CO2 from the bean, is an essential step. Brewed, gassy beans taste sour and ripe. We know you are anxious to taste the beans of your labor but trust us and wait! Once your beans are cooled and degassed, transfer them to an airtight, light-blocked container. Properly stored beans should remain fresh for up to 6 weeks.

Finally, be sure to remove and dispose the chaff from your roaster post-roast. Chaff left in the roaster is likely to catch on fire the next time you roast. Chaff can be thrown out or added to a compost pile.

Technical point: understanding airflow and Rate of Rise (RoR) are vital to perfecting a consistent roast. Airflow because it is the convection setting that creates even, consistent roasts and RoR because it allows you to gauge and control the roasting speed. Without sufficient airflow or a low RoR, your beans may taste dull and flat having effectively been baked. Too much airflow or too high an RoR and your beans char quickly.

Closing notes

While we’ve highlighted the basics of home roasting, we feel compelled to stress that roasting is an art of balance — between sugars, acids, and origin and roast profiles — and practice. While it isn’t essential to know where you want to end with your roast, it is imperative that you, to quote Dave M. from Mills Coffee “listen to the beans. They talk to you.” They talk to your eyes, your nose, your ears, and your instinct.

As with coffee tasting, the fastest way to improve your roasting is by document your findings in a roasting journal. With each roast, take note of every small and meaningful element — from the beans used to the RoR, aroma, texture, color, cook time, wether (temperature and humidity can impact roasting), flavor, and anything else that will help you prefect your roast.

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