At Chicago Coffee Roastery, Inc. we are dedicated to the use of a Sivetz Fluid Bed Roaster for the daily roasting of all of our coffee. A fluid bed roaster has many advantages over the conventional drum-style coffee roaster. It produces a cleaner, better developed coffee, without the tars and burnt tastes that can form in a conventional roaster.
A fluid bed roaster, in it's most simple form, works along the same principles as a hot air popcorn popper. Circulating the beans around the roaster with hot air, which propels them through the roasting process. It is called a "fluid bed" because the air flows through the roaster. The hot air moves the coffee, rather than the roaster moving the beans. A natural gas burner contained in the combustion chamber provides the heat for the roasting process. The pressure blower draws the hot air in and forces it up into the roast chamber. Hot air (at 550 degrees) is pushed through a perforated sheet of steel, lifting the coffee beans up along the vertical side of the roast chamber, the beans fall back down towards the perforated bottom of the chamber where they are again lifted.
The hot air continues to flow out the top of the roaster, to be vented outside. One of the greatest advantages of a fluid bed roaster is that hot air is what keeps the beans in constant motion. In a conventional roaster a large, hot steel drum is what moves the coffee beans, which tends to scorch the beans when they rest against the steel drum. A fluid bed roaster keeps the coffee moving, it never comes to rest against the hot steel of the roast chamber. Plus the agitation and circulation provided by the forced air more thoroughly and evenly heats the beans.
This process allows the beans to develop more evenly which makes better tasting coffee. Constant, forced air through the roast chamber also helps to carry out any foreign particles and chaff out of the roasting coffee. Chaff is the final layer of the coffee cherry pulp which remains on the bean until roasting. It is a thin, flaky layer of parchment which covers the bean. As the coffee beans swell in size from water within the beans turning into steam, the chaff comes off the beans and is carried out of the roaster.
A Sivetz Roaster is designed to collect the chaff in the chaff can. The chaff is dropped into the chaff can as the air exiting the roaster moves out through the vent. Roasting on a Sivetz Fluid Bed Roaster requires familiarity with both the roasting machine and the green coffee beans. The roasting process which coffee is put through is a very exact balance of time and temperature. As with any food product, coffee must be properly roasted to end up with the best possible flavor.
Coffee roasted too quickly, or with too much heat will not be evenly roasted throughout the bean. Likewise, coffee roasted too slowly or with inadequate heat will be completely void of the natural oils and compounds which give it taste. As coffee is circulated about the Roast Chamber, and as heat builds within the roaster, the beans are under constant observation by the Roastmaster through one of two sight glasses.
The coffee beans start from their raw pale green color, moving through shades of yellow and gold, into browns as they develop their character and taste. When they have reached their desired degree of roast within the required amount of time, the roasting process is stopped, the beans are allowed to cool and the roast is poured out of the roaster. This is another plus of the Sivetz Roaster, each batch of coffee begins at low temperatures, the coffee is built up to a certain degree (this varies with each roast), and then it is cooled down again.
With conventional roasters, the drum is heated up to very high temperatures (sometimes 800 degrees plus) then the coffee is dumped in, exposing it to scorching temperatures, immediately turning the water content of the coffee into steam before the carmelization of the sugars begins within the bean (carmelization is what gives the coffee it's brown color). The coffee is then dumped out at very very high temperatures into a cooling tray and the next batch of coffee is immediately dropped into the roaster.
While conventional roasters offer higher capacity as well as more batches per hour, a Sivetz Fluid Bed Roaster has smaller capacities with generally only three batches per hour possible. A Fluid Bed Roaster provides a better quality cup of coffee which is the cornerstone of the specialty coffee business.
Learn about our coffee roasting levels: Roast Levels