The process of roasting coffee revolves around heating the beans to release their aromatic oils and caramelize sugars. Home roasters use several methods to go from green beans to ready-to-brew coffee, but they all rely on the senses, rather than specific measurements of time or temperature, to tell when the beans are done.
The roasting method that’s right for you depends on your budget, how much coffee you want to roast and how picky you are about your coffee.
- Use what you have. People have been roasting coffee beans using nothing more than a cast-iron skillet and a campfire for generations. You can roast beans on the stove, in the oven or in a hot-air popcorn popper. Any of these methods will produce roasted coffee beans, although they will not come out as evenly roasted as beans prepared in a purpose-built roaster. These methods have the advantage of being inexpensive and easy to try.
- Buy an air roaster. These entry-level coffee-roasting appliances are similar to hot-air popcorn poppers except that they have a filter to collect the chaff from the beans. Some models also have a smoke-control feature. They are more expensive than a popcorn popper, and they produce evenly roasted beans in about 10 to 15 minutes. Air roasters typically feature small batch sizes, so you’ll need to roast every day or two depending on how much coffee you drink.
- Invest in a drum roaster. If you want to roast larger batches, or like being able to control every aspect of the roasting process, a drum roaster is the tool you need. Commercial roasters and independent coffee shops use this type of roaster to keep up with demand, but smaller ones designed for home use are also available.
After you start the roasting process, keep an eye on the beans. You’ll need to watch for a change in color from green to yellowish to light brown. At the same time, you will smell a difference in the odors coming off the warming beans, going from a grassy scent to a toasty aroma. The final clue that the beans are beginning to roast is the sound of the first crack, when the crease in the bean opens up releasing trapped moisture.
After the first crack, continue to roast the beans until they reach the stage you prefer. There are three primary roast levels, traditionally called City, Full City and Vienna or French Roast. Each level has several gradations within it. The darker or more roasted end of the spectrum is denoted by a plus(+) after the name of the roast level. Choose the roast you prefer – or make several batches of the same bean to different levels to compare them.
- City to City+: The lightest roast. This level allows the characteristics of the bean to take prominence in the cup, but it can be sour or astringent at the very lightest stages. City to City+ occurs just after the first crack. Flavors at this stage can be floral, nutty or malty, depending on the characteristics of the coffee bean.
- Full City to Full City+: At this stage, the characteristics of the roast begin to overwhelm the bean varieties. Most commercial beans are roasted to Full City or beyond for uniformity. At this stage, you can expect deeper chocolate, raspberry, and roasted notes in the final cup.
- Vienna or French Roast: These roasts are very dark and are left on the roaster up to the second crack. At this stage, the roast characteristics completely overwhelm the coffee varietal. This stage can be tricky to achieve without burning the coffee beans.
Let the beans rest for 12 to 24 hours in a loosely covered container. This will allow the flavors to develop and the beans to release pent-up carbon dioxide.
After the rest, your coffee will stay fresh for about a week if stored in an airtight container away from heat, light and moisture. If you’ve roasted a large batch, you can store unused beans in the freezer for up to a month. Once you’ve removed coffee beans from the freezer, do not refreeze. Instead store them just as you would freshly roasted beans.