How to Roast Coffee Beans

Roasting coffee at home is fun and easy to learn. In no time you’ll be enjoying some of the most delicious coffee you’ve ever tasted, rivaling even that of your local coffee shop.

Roasting time may vary slightly depending on the roaster you have and the level of roast you’re aiming for. Consult your roaster’s manual for more details.

Midwest suggests starting with at least a couple of pounds of Guatemalan green beans, because they handle heat very well. This makes them great beans to learn the roasting process with. At this point you should only be concerned with understanding the capabilities of your roaster, not producing an award winning roast.

Roasting coffee does produce some smoke, so you should place your roaster near an open window or under a kitchen vent that exhausts outside. DO NOT use a kitchen vent that recirculates back into the kitchen! Whatever electrical outlet you use should be dedicated to the roaster while you are running it. The roaster may be affected by drops in voltage (i.e. someone is running a hair dryer which draws power, reducing the voltage going to your roaster). For the 10-15 minutes you’ll be roasting, it’s best to leave other appliances off.

For consistent results, measure and take notes. Measuring by weight is preferred. Measuring by volume is okay, but keep in mind that beans vary in size, so your roast volume may vary. Just be consistent in your measuring method. Have an oven mitt handy, as you’ll be dealing with steam at very high temperatures. You should also have a towel handy to collect any wayward chaff (the paper-like substance that will flake off the beans during roasting). Different beans have differing amounts of chaff, from a lot to none.

Taking notes is essential if you want to become a good home roaster. You don’t want to achieve the perfect roast and not be able to replicate it because you can’t remember what you did. For best results, take note of the following:

  • Country or Region of origin of beans used
  • Date beans were purchased
  • Date of the roast
  • Variety
  • Note the variables: weather, temperature, humidity; anything that may effect the roast
  • Whether you are working with a cold roaster (first roast of the day) or a warm one
  • The roast you are aiming for, and a space for the results and other notes

Before you continue, Midwest suggests that you take some safety precautions. Do not use an extension cord to plug your roaster in. If you have a fire extinguisher, have it handy. A fan can help clear smoke as it occurs. Open all the windows in the kitchen and place the roaster under the vented stove, and you’re ready to go! Once you’ve roasted a few times, you’ll know what to expect, but your first time can be a little daunting. The darker the roast, the quicker you’ll need to react-after first crack, even seconds can make the difference between a delicious roast and useless charcoal.

Consult your machine’s instructions to determine the amount you’ll be roasting, and fill the roaster.

There are 7 stages to the coffee roasting process. Knowing how the process works will help you understand how different levels of roast result in different flavors in the finished product.

Stage 1 - Yellowing: Initially, the beans will remain greenish in color. As they turn to a lighter yellow color, they will give off a “grassy” or “wet hay” smell.

Stage 2 - Steam: As the internal water heats up, the beans will start to give off steam.

Stage 3 - First Crack: Soon after the steam becomes fragrant, you will hear an audible “cracking” sound. This is where the actual roasting begins; the beans’ structure breaks down, the little pockets of oil migrate outward as more water escapes and the sugars begin to caramelize.

Stage 4 - First Roasted Stage: Following the first crack, the roast is considered complete at any time, depending on your personal taste. Determining what stage the roast is at is done by sight and smell. If you complete the roast now, this is what’s called a “City Roast”.

Stage 5 - Caramelization: Sugars continue to caramelize, oils continue to migrate, and the beans will expand in size. The roast becomes dark at this point. This is a “City + Roast”. Completing the roast just before second crack will result in a “Full City Roast”.

Stage 6 - Second Crack: This will often be more volatile than the first crack. At this point in the roast, the roast character begins to overtake the original character of the beans. If you complete the roast a few pops into second crack, this results in a “Full City + Roast”. If you complete the roast all the way through second crack, this is a “Vienna Roast”.

Stage 7 - Darkening Roast: The roast becomes very dark, the beans become shiny, and the smoke is more pungent because the sugars burn completely; the structure of the bean breaks down more. This is a “French Roast”.

If you smell charcoal, you’ve waited too long! Discard those beans and start over. Keep in mind that once you are past the first crack stage, even a few seconds can make a difference. Midwest suggests stopping the roast no later than after the first few pops of the second crack the first time you roast. It will likely be more delicious than any cup of coffee you’ve ever had, and you can always adjust to a darker roast your next time around.

Degassing: DO NOT make coffee with the beans you just roasted. It is important bleed off the CO2 produced during roasting, known as “resting” or “degassing”. You can store the beans in any lightly covered container, or zip baggies. At a minimum, they should rest for 4-12 hours. Understand that time is part of the recipe. Different coffee varieties and different roasts will be at peak flavor at different times. A coffee may taste good on day one, but may blow your mind on day three. It will be at its best between one day and two weeks, at most. Notes and consistent conditions will help you create the perfect roast for you; the variations are endless.

How to store roasted coffee beans:

Room temperature in a sealable glass jar like a mason jar works very well. Don't store coffee beans in the freezer. Roasted coffee beans give off CO2 up to 24 hours after roasting. This can be allowed to vent off by leaving the lid loose for the first 4-24 hours. After this period, the container should be sealed so as to prevent exposure to oxygen. The vented CO2 help create a barrier against oxygen which causes beans to go stale. Bags with one way vents are another good way to store coffee beans. They let CO2 escape without allowing exposure to oxygen.