In teaching a young adult the fine art of roasting green coffee beans sourced from around the world, I realized that the roasting process was all about the sensory input and the true artisan touch is in assessing the beans at every stage.
Assessment
The green coffee beans are analyzed visually for defects:
Aged/Floaters (Ripe green coffee beans that are ready for roasting are dense and sink in water. The first step in coffee production separates the floaters from the sinkers, roasting the floaters and allowing the immature sinkers more time to ripen.)
Full Sour (These defects are caused by waiting too long between picking and de-pulping, an overly long fermentation process, or storing the beans with a high moisture content.)
Damaged Beans (Green coffee beans may become damaged from fungus, insects, and overexposure to light.)
Wrinkled (Typically a result of drought during the growing process.)
Cherry Pulp (The pulp/rind of the coffee berry should always be removed during the first stage of coffee processing, before drying, and before the green beans are shipped to be roasted.)
Broken, chipped, or crushed beans
Foreign Material (nails, rocks, wood)
Before I began my coffee roasting journey, I had no idea I would be visually analyzing for defects like these! At Cody Coffee Roaster, any defect and the Green Coffee Broker is informed and the beans are returned.
About the Coffee Roaster
Coffee roasters come in all shapes, sizes, models, and from a multitude of vendors. Cody Coffee Roaster uses a 10kg Mills City Roaster allowing us precision control in every batch, perfect for our growing coffee demand.
Let's begin by highlighting a few key parts of a coffee roaster:
High voltage electrical source
A heat source, natural gas
Hopper (Where the beans are initially dumped into the machine)
Drum (Rotates the coffee beans and heats them during the roasting process; this is where most of the magic happens.)
Viewing port (Window on the end of the drum where beans can be viewed throughout the roasting process.)
Viewing port (left) and sampling port (right)
Sampling port (Allows for beans to be pulled out while being roasted, looking for color changes and aroma.)
Thermocouples (Measures how the probes react to environmental and bean temperature to determine the roasting temperature.)
Cooling agitator (Stimulates cooling after roasting)
Fans, Motors
Chaff collector barrel (Collects the dry skin, known as the chaff, that comes off during the coffee roasting process.)
Smokestack (Similar to a wood-burning stove, roasters have a smokestack to allow the smoke and heat to escape the drum.)
The complexities of a coffee roaster can be intimidating for both the beginner and the novice.
Before every roast, a visual inspection is performed and all parts are cleaned for safety purposes and quality control at Cody Coffee Roaster.
The Roasting Process
The actual roasting is where all of the senses are used. First, the green coffee beans are weighed according to the batch. Next, the charge temperature is dialed in, this is the temperature of the drum before the beans are added. The charge temperature is responsible for a lot of the roast's flavor profile. For our roasting purposes, the charge temperature is 375 degrees Fahrenheit. The green coffee beans are then dropped into the drum and the gas is shut off for 60 seconds, known as the soak, allowing the green beans to absorb the surrounding heat energy. After 60 seconds, the gas is turned back on and the convection air is set. Two roasting processes are going on in green roasting: convection heat (the temperature of the air in the roaster), and conduction heat (energy transfer from the metal the green beans come in contact with.)
Monitoring of the Roasting Process
The Roaster has thermocouples, thermometers that measure the bean, environment, and exhaust temps. We connect ours to an interface called a Phidget which is connected to our computer running the software program “Cropster.” During the roast, measurements are taken every 15 seconds and all are integrated to get the RoR. This provides quality control for our tasting profiles.
Dehydration and Turning Point
The roasting begins with the dehydration process as soon as the green beans are dropped into the drum. To roast, the moisture needs to evaporate from the green beans which requires heat energy. The Turning Point is when the green beans reach the coolest temperature, around 160 degrees Fahrenheit and start to heat up, entering the dehydration process. This slow rise in temp through the roasting is called the Rate of Rise (RoR). Maintaining the RoR consistency for each roast helps keep the roast and the taste profiles. Many factors affect the roasts: humidity, wind, and ambient temp (thus artisan roasting.)
The senses now really come into play. When sampling, the green has a grassy, alfalfa smell. As the dehydration proceeds the green starts to turn yellow and the smell is more like baking bread. When all the green has turned yellow, at about 270 degrees F, the actual roasting begins!
The Maillard Reactions or Browning
The next stage of roasting coffee is the Maillard or Browning reaction. Hundreds of reactions take place in any cooking or roasting process, these are chemical reactions that take place between the sugars and proteins in the coffee (or whatever else is being cooked.) Visual, smell, and hearing are predominately used for this stage of roasting. The Maillard starts at the color change and goes until the first crack, a temp of about 380 degrees F for our roaster at Cody Coffee. The yellow beans slowly turn to light brown and the smell takes on a more pronounced roasted smell. The first crack is a significant part of the coffee roasting process. The coffee beans expand as they take on heat and at that critical temp and time they audibly crack or pop like popcorn which ends the Maillard stage.
The Development
The next stage of the roast is roast development, from the first crack to the end of the roast with potential for other substages. The Development is when the actual flavors of the coffee are coming out, the coffee is getting darker, and the smells are starting to become caramelized to charred. For a medium roast such as our Pilot and Index Roast, Signal Peak Roast, Spirit Mountain Blend, and Bliss Creek Roast, the end of the roast is a little past first crack, before the second crack. The second crack is when the coffee has lost the heat it absorbed at first crack, has then taken on some more heat, expanded, becomes darker, and cracks again (a much more subtle crack.) Our machine’s second crack comes around 410 degrees F, signifying a dark roast. The coffee at this point has to be watched carefully, there's a fine line between dark roast and charred or burnt. Espresso and Vienna roasts are quite dark. Once the roast has been achieved, the coffee is dropped into a cooling tray with agitation and a fan for the cooling to go faster, as the coffee is still roasting.
References:
Hoos, Rob, Modulating, The Flavor Profile of Coffee "One Roasters Manifesto". Jan 2015