Coffee Technology Sivetz Pdf
Coffee Roasting History – an abridged versionWhile coffee has been around for centuries the act of buying roasted coffee did not come about until the mid to late 1800’s. This was because the buying of green, unroasted coffee was the only way to ensure you were getting only coffee and not coffee mixed with cereal substitutes. There were many devices available to roast coffee beans at home; a job that typical fell to the children of the household. It was a hot, smelly job consisting of holding a pan-like enclosed skillet over the fire while rotating the beans within.“Coffee roasting is essentially a process of exposing the green coffee beans to a warming process that is sufficiently fast to drive off the free and bound moisture of the bean and the dried bean residue is heated to more than 400 F. At about this temperature, pyrolysis, or thermal decomposition and chemical change, occurs within the bean.” -Sivetz, Coffee TechnologyLaws guaranteeing roasted coffee purity opened the stage for the transfer of roasting in the home to factory roasting.
Sivetz Air Roasters
These laws were first enacted in Germany in 1875 and as a result many of the earliest industrial size roasters began there. These early roasters were simply large cylinders placed over a heat source. The main problem was emptying and cooling the coffee beans. The American Carter Roaster of 1846 allowed the entire cylinder to be pulled out of the flame and doors mounted on the drum walls allowed the coffee to be dumped onto the floor or into trays to cool.In 1864 Jabez Burns of New York introduced a roaster with two main improvements. The first was an opening mechanism to empty the beans without removing the cylinder from the flame and the second was a double screw inside the cylinder that would evenly distribute the beans. They would later invent add a cooling tray to the front of the roaster with a fan mounted below to draw air through the just emptied beans.
The modern roasting machine was beginning to take on a recognizable shape.Beginning in the early 1880’s manufacturers began experimenting with introducing hot air into the roasting cylinder to take away some of the smoke and gasses. The German manufacturer Van Gulpen introduced a roaster with an exhauster to draw the hot air through holed walls in the drum or through the drum from one end to the other. It also featured a fan that delivered fresh air to the beans while roasting, representing the biggest change in coffee roaster design. From this point forward coffee roasters went from being closed cylinders to keep the air out to vented cylinders to let air. The Probat roaster took its name from one of these Van Gulpen models.In 1889 Carl Salomon of Braunschweig introduced the principle of hot gas ventilation and with it quick roasting. He determined the number of revolutions needed per minute so that the beans would tumble off the wall into the hot air stream being blown into the roaster.
Coffee Technology Sivetz Pdf Download
As a result roasting times fell to around twenty minutes. By the early 1890’s many other manufacturers followed suit, making improvements with their own designs.
For nearly the next hundred years all roasting machines would employ some variation to this design. Cylinder roasters to this day employ one of two basic design modes: one using heat under the drum and sucked through holes at the end of the drum, and two, using hot air blown directly into the drum:As Ian Bersten notes in Coffee Floats, Tea Sinks: “The conventional coffee roaster is operated by combining the mechanical movement of the beans with a hot air stream.
All conventional coffee roasting machines can be classified according to whether the drum is singe or double-walled or even perforated, whether the heat is direct of indirect against the drum, or hot air direct into the drum, or even a flame on the drum.”Mike Sivetz was not the first to devise the fluid-bed roaster, an electric version designed for storefronts appeared in 1926. In 1954 the Aerotherm Roaster was introduced by the Lurgi Company blowing air straight up through the bean mass. Due to design limitations the roaster was considered too small for commercial applications and required a high degree of attention monitoring the airflow so that the beans would not blow out the top.
It would not be until 1976, when Mike filed patent for his roaster that a practical fluid-bed roaster would become available.Courtesy of The Coffee Heretic (unpublished), 2012.
A coffee bean roasting system is disclosed wherein coffee beans in a box-like chamber are levitated as a dense, uniformly recirculating mass by an upwardly directed airstream. The air is heated to a temperature not in excess of 530°F., and the heat is transferred to the beans primarily by convection and secondarily by conduction from bean to bean. Heat transfer continues until after a thermally induced pyrolitic reaction has occurred within the bean mass and the desired roast has resulted whereupon the roasted beans are cooled. The system may employ batch type or continuous roast apparatus. Coffee bean processing comprising:a. BACKGROUND OF THE INVENTIONThe present invention is an improved processing apparatus for efficiently transferring heat from air to coffee beans to secure a uniform roasting thereof.Accepted commercial coffee bean roasting methods have not undergone any significant recent improvements in efficiency or simplification.
The principles employed in widely utilized coffee roasters are virtually the same as used over 50 years ago. One exception is that about 40 years ago a continuous rotary cylinder roasting machine was developed by the Jabez Burns & Sons, Inc. Company in the United States. The commonly utilized prior art roasters employed rotating steel cylindrical roast chambers which held the coffee bean charge occupying only about 15 percent of roast chamber volume, and which cylinder was rotated about a horizontal axis at rates of typically 60 to 90 revolutions per minute. Hot recirculatory gases are passed about and through the cylinder, but not necessarily through the beans therein, at temperatures from 650° to 700°F., or even higher. Coffee roasting times varied from 10 to 30 minutes, and uniform roasting of each bean was not routinely achieved.Smoke, smog, organic fumes and aerosols of fine oil were abundantly liberated during roasting operations in such prior art coffee roasters. With the enactment and enforcement of air quality control standards by federal, state and municipal authorities, coffee roasting firms have become obligated to make large capital expenditures for air pollution control devices such as 'after burners,' the operation of which has doubled fuel consumption and operating costs.The movement of hot gases through the roasting beans has not been positively controlled.
Some beans were always scorched (tipped) or burned due to remaining in contact with the very hot metal cylinder walls more than a few seconds. The high temperature of the gases used permitted shortened roasting times, for example, 5 minutes, with the concomitant drawback that the beans were less uniformly roasted, many beans were scorched and excessive volatiles, vegetable oils, char and degraded organics were liberated from the beans which in turn degraded coffee flavor as well as generated abundant air pollutants.Coffee volatiles are rich in aromatic aldehydes and ketones, chemical constituents which are very unstable at the temperatures typically found within these prior art roasting cylinders. In seconds, oxidized and polymerized byproducts were formed from liberated aldehydes, and these chemical byproducts became smokey, and by contact contaminated the clean beans being roasted, thereby adversely affecting the produced flavor quality. And, in combination with loosened chaff, these organic byproducts coated the cylinder walls and other apparatus with which they came into contact. Frequent cleaning and removal of the charred oily encrusted coating has been essential in order to minimize coffee bean contamination and fire hazards. In addition, high temperature roasting produced harmful insolubles such as the carcinogens noted in the 1974 U.S. 3,809,775 to Ganiaris.Further details and drawbacks of widely used commercial roasting methods and machines may be found in Volume 1, pages 203 to 226, 235 to 238, of my two volume work entitled Coffee Processing Technology, published by the AVI Publishing Co.
Inc., Westport, Conn., in 1963.There have been a number of prior art efforts directed to a process of fluidization of coffee bean mass to achieve an improved roast. One such effort may be found in the 1958 U.S. 2,859,116 to Heimbs et al. This reference teaches the roasting of a coffee bean type material by a fresh upward hot air suspension of the beans in vertically conical roasting chamber. However, the patent does not disclose how to control the bean fluidization and the chamber temperature to produce a uniform bean roast without burning. The undesirable roasting vapor organic byproducts generated by the Heimbs method had to be purified before recirculation of the heating gas, a limitation overcome with the present invention.In a 1962 U.S.
3,060,590 to Brown, a complicated continuous flow apparatus achieving fluidization of a thin sheet of solid particles by a plurality of downwardly directed air blast tubes is shown. The apparatus therein is vastly different from the present invention, and it is not particularly directed to roasting coffee beans. The process disclosed therein is incapable of creating a dense cubic floating bed of coffee beans in recirculating fluidized mass. Also, heat is lost by conduction from the bottom metal conveyor.
An even more complicated downdraft apparatus is shown in Brown's 1966 U.S. 3,263,339 wherein baffles and deflectors are employed in an effort to thicken the fluidized particulate mass being processed. The complications and disadvantages of the Brown devices are made unnecessary by the present invention.Another prior art reference disclosing a species of fluidization is the 1954 U.S. 2,876,557 to Ducatteau. That continuous processing apparatus reference discloses only in general terms a complex series of baffled compartments in which various upward air currents lift particles from one processing location to another, but gives no details to cover the processing of coffee beans therein. It is doubtful from the information actually supplied that successful coffee bean roasting could be accomplished by such an apparatus.
The present invention is vastly different in both method and apparatus from that shown in the Ducatteau reference.A 1964 U.S. 3,149,976 to J. Smith, Jr., assigned to Blaw-Knox Co. Of Pittsburgh, Pa., shows a columnar roasting apparatus wherein fluidized particles cascade downwardly from plate to plate while warm air passes upwardly through the particles. That process and apparatus bears no resemblance to the present invention.A 1969 U.S. 3,486,240 to Nowak et al, also assigned to Blaw-Knox, discloses a complicated multi-level and radially extending multi-chamber carousel type roasting device employing a heated gaseous fluid updraft to fluidize particles.
Baffle members and carefully aligned gas nozzles are utilized in the device to create an involved mushroom spraying effect within the particulate material being treated. The complications of apparatus and method disclosed therein are avoided in the present invention.In another patent assigned to the Blaw-Knox Company, the 1968 U.S. House of the dead 3 full pc game. 3,370,522 to Anderson et al, a high speed fluidization of roasting coffee beans is achieved in a complicated pressurized environment involving humidified heated gas and a pressure release.
Such complicated processing apparatus and complicated processing requirements are shown to be unnecessary by the present invention.Finally, several patents issued to H. Smith, Jr., U.S. 3,189,460, (1965); 3,328,894 (1967); 3,329,506 (1967); 3,345,181 (1967); 3,385,199 (1968); 3,447,338 (1969); 3,615,668 (1971 ) and 3,724,090 (1973) disclose pressurized roasting methods that employ a form of bean fluidization.
The pressurized inert gas processes disclosed in those patents are of primary usefulness only in the roasting of the lower grades of Robusta coffee beans, wherein it is desirable to increase the acidity of the coffee bean to improve taste acceptance.