An alternate to the drum coffee roaster was developed by Michael Sivetz for which he was given US patent 3,964,175 on June 22, 1976. It involves roasting the coffee beans while they are levitated on a cushion of heated air. The process is called a fluidized bedand is commonly used in other food processing applications.
Many people who roast coffee prefer to follow a "recipe", or roast profile, when bringing out the flavor characteristics they wish to highlight. Any number of factors may help a person determine the best profile to use, such as the coffee's origin, varietal, processing method or desired flavour characteristics. A roast profile can be presented as a graph showing time on one axis and temperature on the other, which can be recorded manually or using computer software and data loggers linked to temperature probes inside various parts of the roaster.
Indirect-fired roasters are roasters in which the burner flame does not contact the coffee beans, although the combustion gases from the burner do contact the beans. Direct-fired roasters contact the beans with the burner flame and the combustion gases. At the end of the roasting cycle, the roasted beans are cooled using a vacuum system. Roasted coffee beans are also cooled using fine water mist, which is known as "quenching" and is considered inferior to air cooling as the water soaks the fresh beans with moisture and oxygen particles making it stale almost instantly. Following roasting, the beans are cooled and stabilized. This stabilization process is called degassing. Following degassing, the roasted beans are packaged, usually in light-resistant foil bags fitted with small one-way valves to allow gasses to escape while protecting the beans from moisture and oxygen. Roasted whole beans can be considered fresh for up to one month. Once coffee is ground it is best used immediately.
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PackagingExtending the useful life of roasted coffee relies on maintaining an optimum environment for the beans. The first large scale preservation technique was vacuum packing. However, because coffee emits CO2 after roasting, coffee to be vacuum packed must be allowed to degas for several days before it is sealed. To allow more immediate packaging, pressurized canisters or foil-lined bags with pressure-relief valves can be used.
DarknessAs the bean absorbs heat, the color shifts to yellow and then to varying shades of brown. During the later stages of roasting, oils appear on the surface of the bean, making it shiny. The roast will continue to darken until it is removed from the heat source.At lighter roasts, the bean will exhibit more of its "origin flavor" - the flavors created in the bean by the soil and weather conditions in the location where it was grown. Coffee beans from famous regions like Java, Kenya, Hawaiian Kona, and Jamaican Blue Mountainare usually roasted lightly so their signature characteristics dominate the flavor. As the beans darken to a deep brown, the origin flavors of the bean are eclipsed by the flavors created by the roasting process itself. At darker roasts, the "roast flavor" is so dominant that it can be difficult to distinguish the origin of the beans used in the roast.
A note on flavor: Describing the tastes of different roasts is as subjective as putting a wine into words. In both cases there’s no substitute for your own personal taste. As a guide, if you can see the oil on the beans as in the image above, you are more likely to taste the roasting flavours than the individual characteristics of the beans.
Roast levelNotesSurfaceFlavorLightCinnamon roast, half city, New EnglandAfter several minutes the beans “pop” or "crack" and visibly expand in size. This stage is called first crack. American mass-market roasters typically stop here.DryLighter-bodied, higher acidity, no obvious roast flavourMediumFull city, American, regular, breakfast, brownAfter a few short minutes the beans reach this roast, which U.S. specialty sellers tend to prefer.DrySweeter than light roast; more body exhibiting more balance in acid, aroma, and complexity.Full RoastHigh, Viennese, Italian Espresso, ContinentalAfter a few more minutes the beans begin popping again, and oils rise to the surface. This is called second crack.Slightly shinySomewhat spicy; complexity is traded for heavier body/mouth-feel. Aromas and flavours of roast become clearly evident.Double RoastFrenchAfter a few more minutes or so the beans begin to smoke. The bean sugars begin to carbonize.Very oilySmokey-sweet; light bodied, but quite intense. None of the inherent flavors of the bean are recognisable.Grades of coffee roasting; from left: unroasted (or "green"), light, cinnamon, medium, high, city, full city, Italian, and French.
Particulate matter emissions from the roasting and cooling operations are typically ducted to cyclones before being emitted to the atmosphere. Gaseous emissions from roasting operations are typically ducted to a thermal oxidiser or thermal catalytic oxidiser following PM removal by a cyclone. Some facilities use the burners that heat the roaster as thermal oxidisers. However, separate thermal oxidisers are more efficient because the desired operating temperature is typically between 650°C and 816°C (1200°F and 1500°F), which is 93°C to 260°C (200°F to 500°F) more than the maximum temperature of most roasters. Some facilities use thermal catalytic oxidizers, which require lower operating temperatures to achieve control efficiencies that are equivalent to standard thermal oxidisers. Catalysts are also used to improve the control efficiency of systems in which the roaster exhaust is ducted to the burners that heat the roaster. Emissions from spray dryers are typically controlled by a cyclone followed by a wet scrubber.