Food or edible material: processes – compositions – and products – Processes – Preparation of product which is dry in final form
Reexamination Certificate
1999-11-19
2003-08-19
Yeung, George C. (Department: 1761)
Food or edible material: processes, compositions, and products
Processes
Preparation of product which is dry in final form
C034S360000, C034S576000, C426S467000
Reexamination Certificate
active
06607768
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for roasting coffee and similar particulate vegetable materials.
BACKGROUND OF THE INVENTION.
Coffee beans are roasted to develop the characteristic flavor and aroma of the product as used by consumers. The flavor and aroma of green coffee are not desirable; but when green coffee beans are roasted, complex, thermally-induced chemical reactions convert compounds contained in the beans, such as sugars, amino acids, polysaccharides, proteins, trigonelline, chlorogenic acids, and others into more than 800 compounds that collectively provide the desirable, extractible flavor, color and aroma characteristic of roasted coffee. Some green coffee components that do not react during roasting, such as caffeine, contribute to roasted coffee's stimulatory action and flavor, but most of roasted coffee's flavor, color and aroma is provided by compounds generated in roasting-induced reactions.
Coffee roasting involves systems of interdependent chemical reactions that proceed along series and parallel reaction paths. Rates of these reactions increase markedly, but to different extents, as bean temperature increases. Because of reaction interdependence and the varying effects of temperature on individual reaction rates, the makeup and yield of products generated by roasting depend on bean temperature versus time history during roasting. Consequently, the flavor and aroma of roasted coffee depend on that history. Control of the temperature-versus-time history of the coffee during the roasting process would greatly enhance control of flavor and aroma.
Roasting initially is endothermic; i.e. heat transferred to coffee beans raises their sensible heat content, evaporates water and provides heat used in endothermic reactions. After bean temperatures reach 160° C., rapid exothermic reactions occur, bean temperatures rapidly rise and coffee's flavor changes very rapidly. Excessive weight loss and undesirable flavor changes occur if roasting is excessively prolonged. Therefore, to end roasting quickly and provide coffee of desired, reliably duplicated quality, beans most commonly are rapidly cooled (quenched) as soon as they reach a selected end-of-roast temperature. First, a controlled amount of water, is sprayed on the beans and largely evaporates, providing evaporative cooling. Then, the beans are cooled further by forced contact with ambient-temperature air.
Reflectance color is the fraction of incident light of selected spectral composition that is diffusely reflected from the surface of a suitable sample of compressed, ground, roasted coffee. The lower the reflectance color, the darker the coffee. End-of-roast temperatures correlate well with roast darkness, as measured by reflectance color. Roast darkness, in turn, roughly correlates with flavor. Some consumers prefer relatively dark and bitter roasted coffees; others prefer relatively light, somewhat acid coffees; and still others prefer coffee of intermediate character.
Roasting conditions also influence the bulk density (mass of coffee per unit volume) of the roasted coffee beans. As further explained below, under certain roasting conditions the coffee beans can be “puffed” by internal pressure of steam and other gasses when the walls of the beans soften at elevated temperature. Such puffing reduces the bulk density. The bulk density of the roasted beans in turn influences the bulk density of the ground product as sold to the consumer and the weight of coffee which fits into a standard coffee can or other container.
Coffee roasting thus requires careful control of numerous factors which influence the taste and appearance of the product. Because the coffee roasting business is competitive, economic factors such as capital costs, energy costs and coffee loss during the process are of great significance. Waste products discharged from coffee roasting processes can be a source of pollution. It is important to minimize such pollution while still maintaining an economical process and without comporomising the quality of the finished product.
All of the aforementioned factors together make coffee roasting a complex and difficult process. A vast number of methods and apparatus for roasting coffee have been proposed. Most commercial coffee roasting processes currently in use are performed at atmospheric pressure by contacting the coffee with hot gases such as a hot inert gas, typically nitrogen. The incoming gas heats the coffee beans whereas the outlet gas carries off waste products such as chaff and gases evolved in roasting. Traditional roasting methods can achieve only limited rates of heat transfer to the beans, and cannot provide full control of the bean time and temperature history. Further, traditional roasting methods and apparatus require significant effort and expense to minimize pollution.
Various proposals have been advanced for high-pressure roasting systems. Notably, numerous patents issued to Horace L. Smith Jr. describe batch or continuous systems for pressure-roasting of coffee in rolling fluidized beds or spouted beds. A “fluidized bed” system directs a gas or other fluid upwardly through a mass of particulates such as coffee beans, so that the particulates are held suspended in the rising fluid. Ideally, the upward flow is nearly uniform in all regions of the bed. A “spouted bed” system utilizes upward flow of the gas or other fluid concentrated at a few locations within the bed. The particles move upwardly at these locations and downwardly at other locations in the bed. Most of the Smith patents call for use of pressurized, low-oxygen-content gas circulating in a closed loop through: a heater, a bed of roasting coffee in a heavy-walled, cylindrical chamber and a cyclonic separator. The cyclonic separator removes small particles, commonly referred to as “chaff” from the gas. Some of the Smith patents use gas pressures up to 300 psig (2.1 MPa gauge). In a specific example, Robustas were roasted at 150 psig to improve their flavor. The roasting gas was heated by indirect contact with either a high-temperature, heatexchange fluid or hot gases produced in a fuel-fired furnace. To remove undesirable aromas, improve coffee flavor or puff roasting coffee, part of the roasting gas was bled off in some cases and replaced by inert gas produced by combustion of fuel. Certain Smith patents suggest that undesirable aromas also could be removed by condensation or scrubbing. Processes and methods disclosed in these patents suffer from certain fundamental limitations relating to the physical characteristics of the beds. If the gas velocity through the bed is increased, the fluidization becomes excessive. Beans can be entrained with the gas and carried out of the roaster into the remainder of the system. Moreover, the proper operation of the beds depends strongly on the depth of beans in the bed. Circulation of beans within the bed is suppressed if the bed is too shallow, whereas slugging and erratic spouting occur if the bed is too deep. Moreover, the Smith patents do not provide particularly precise control or repeatability in the process, inasmuch as these patents rely principally on control of gas inlet temperature to the roaster together with end-of-roast temperature or color measurements to indicate when the roasting procedure is complete.
Thus, despite these and other efforts in the art, there has been a significant need in the art for improvements in coffee roasting methods and apparatus.
SUMMARY OF THE INVENTION
The present invention addresses these needs.
One aspect of the invention provides methods of roasting coffee. The preferred methods according to this aspect of the invention include the steps of placing a charge of beans into a roasting chamber having a top and bottom, and directing a hot inlet gas through the beans from adjacent the bottom of said chamber and out of said chamber adjacent said top of said chamber to thereby form a fluidized or suspended bed of beans in said chamber and supply heat to the beans, whereby an exhaust gas inclu
Muserlian, Lucas & Mercanti, LLP
Praxis Werke, Inc.
Yeung George C.
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