Your favorite bag of coffee starts its life as green beans, the seed from the fruit of coffee cherries. Green is color and full of moisture, these beans need to be roasted in order to become the toasty flavorful brown beans everyone loves. Roasting is a process where green beans are heated to specific temperatures to remove moisture and cause chemical reactions within the beans that develop the delicious aroma and flavors that we look for in a great cup of coffee. We will be covering general roast profile guidelines, the phases of roasting where the chemical reactions take place, the steps in our roasting process and the differences between drum and fluid bed air roasting.
Time, temperature and airflow are the defining variables that make all the difference when roasting. Green bean moisture content or a slight temperature change or extra few seconds passed can result in a completely different roast or even leave you with a burnt batch. Accurate control of these variables allows us to precisely dial in our desired flavor profiles that we get from each bean, and let the origin characteristics meld perfectly with the characteristics the roasting process imparts. We want to bring out the best of each bean by adjusting our roast to what we think is the optimum flavor profile for each coffee. The roasting guidelines we will cover are general classifications that are frequently adjusted by those in the industry in attempts to find the optimal roast.
These roast types are broken down into 3 main categories: Light, Medium and Dark. Each main category has various sub-roast profiles that blend together and overlap between categories at times. It’s important to remember that these are not hard rules that are universally used.
Cinnamon: roasted at 385F, toasted grain taste, sharp acid, sweet, “grassy”
New England: roasted at 401F, toasted grain taste, sharp acid
American: roasted at: 410F muted acid, displays origin characteristics.
City: roasted at 426F, smooth flavor, less acidic than light roasts, characteristics are displayed.
Full City: roasted at 437F, slight oiliness, roast characteristics have strong presence balanced with origin characteristics
Vienna: roasted at 446F, oily, strong flavor, roast characteristics start dominating
French: roasted at 464F, shiny, oily, dominant roast characteristics, rich and bittersweet
Italian: roasted at 473F bittersweet, entirely reflects roast
During the roasting process there are a series of chemical changes that determine the roast characteristics listed above. They are split into 5 Phases called: Endothermic, 1st Crack, 2nd endothermic, 2nd crack and Dark. Things can get pretty detailed here, so we’ve cut it down to the basic ideas here and skipped the chemistry lecture.
The beans enter the roaster and the temperature drops because of the cool beans. Heat is applied and the air temp starts to rise, evaporating moisture. Next is the turning point, at which the bean’s internal temp starts to rise after tumbling in the hot air. They begin to brown close to 350F as the Maillard Reaction takes place and soon after caramelization of the sugars occur. 370F-410F is where the Light Roast profile is found in this phase. American Roast, roasted at 410F, is at the end of this phase and is used for cupping because the origin characteristics still dominate the flavor profile with little to no flavor chances from the roast.
The beans continue to darken, sugars caramelize and the Maillard Reaction occurs. The beans continue to darken, sugars caramelize and the Maillard Reaction occurs. The Maillard Reaction is responsible for turning a few dozen compounds inside the coffee bean into hundreds, even thousands of aromatic compounds that make up the unique flavors of coffee. These compounds include the organic acids (citric, acetic, and malic acids to name a few) that give coffee its brightness. Other compounds like aldehydes, furans, and pyrazines give coffees their range of flavors like sweet, earthy, caramel, butterscotch.
As their sugars caramelize, the beans expand and make a popping noise similar to popcorn. They eventually can double in size and have become much less dense than the green beans they started as. When the 1st Crack stops, you have a City Roast at 426F and have approached the Medium Roast category.
2nd Endothermic Phase:
The beans continue to absorb heat. At 437F Full City Roast is achieved and you are on the border about to exit the Medium Roast category. The flavor profile continues to become more influenced by the roast characteristics over the origin characteristics, and the beans’ oils start extracting to the surface.
At 446F there is a 2nd cracking phase, this time caused by the cellulose structure of the beans beginning to break down and excess CO2 building up. Dark Roasts begin here with Vienna Roast achieved at 446F, and the roast characteristics start to dominate origin characteristics.
In this phase, the roast characteristics completely dominate the flavor profile. Sugars are heavily caramelized, oils are heavily present, there is a very strong Maillard reaction and the beans’ cellulose begins carbonizing. We choose to combine the precision of our air roaster with a slightly lighter roast profile for our espressos that prevents any level of carbonizing (aka burning) from occurring. 464F equals French roast and 473F will yield an Italian roast. Anything roasted beyond Italian roast begins carbonizing quickly and results in a strong burnt chemical flavor profile.
Our Roasting Process
1. To start the roasting process, we weigh the green beans on a precision scale so each batch is consistent. Repeatable consistency is one of the most important qualities of a good roaster because small changes can make the difference between a perfect batch or a ruined one.
2. Second, the bean temperature and air temperature are set on our Sivetz air roaster. Each type of bean we import is always run through a series of sample roasting to determine the exact temperatures that will yield our desired roast characteristics and end flavor profile. We use a color spectrometer to visually calculate the color preference and maintain consistency between roasts.
3. Third, the beans are vacuumed up into the roast chamber from the barrel they were weighed in and the roasting can begin.
4. Next we roast the beans for roughly 13-15 minutes. The time each batch of beans requires is determined by the final characteristics we are seeking. The type of machine we use, discussed in detail below, allows us to dial in the exact time and temperature without having to constantly check the roast process. During the roasting process, chaff is blown away from the beans during the roast. This is important because if the chaff stayed attached to the beans, it would burn and smoke, giving the coffee a somewhat bitter smoky flavor. The hot air that tumbles the beans also lifts any chaff and debris to the top of the roast chamber where it is collected and later disposed of in an afterburner.
5. Following the roasting phase, the beans are dumped from the roast chamber into the cooling tray, which has a large stirring arm to help cool the beans. Fresh air is circulated from above the cooling tray downward through the tray, cooling the beans as it passes over them. The beans have to be cooled quickly to prevent the continuation of the roasting process.
6. Finally the beans are dumped from the cooling tray into bins, and taken to our processing room where they are either bagged as single origin or blended with other coffees.
Why We Use A Fluid Air Bed Roaster
Since 1983 we have used Sivetz fluid bed air roasters. The air roaster was invented in the early 1970’s by the renowned chemical engineer and coffee industry maverick, Michael Sivetz. The Sivetz Roaster is unique in its use of hot air instead of a hot surface to heat the coffee beans. A traditional drum roaster uses direct heat applied to the drum to roast the coffee. Sivetz invented and patented this method for roasting coffee which was a revolutionary way to transfer heat to roast the coffee beans.
Air roasting produces great tasting coffee, and allows for more precise adjustments to the roast characteristics. The fluid air bed produces a vortex which allows each individual bean to be roasted evenly and to perfection. No tipping or hot spots occur, because the rapid air flow tumbling the beans in suspension keeps the roast chamber’s walls cooler than the beans and applies heat evenly.
Air roasting is different from a drum roaster. In a drum roaster the walls of the roast chamber are much hotter because they conduct the heat into the beans. This means there are hot spots that can unevenly roast beans and uneven temperatures in the roast chamber that cause tipping, when steam inside a bean escapes rapidly and breaks the bean. It is important to note that the fluid air bed method does not allow carbonizing to occur which causes burnt flavors as opposed to drum roasters that constantly need to be monitored via the sampling spoon to prevent burning.
Air roasters essentially solve many of the problems of traditional drum roasters, while increasing precision and accuracy and most importantly consistency. With digital temperature settings for both the bean and air temperature, fluid air bed machines allow us to maintain precise temperature control and formulate our roasts in a more predictable manner that yields extreme consistency. Air roasting is known for producing a brighter, cleaner, better tasting and more aromatic coffee.
If you would like to try it for yourself and see the difference, you can order our coffee at https://www.passportcoffee.com