a batch type coffee roaster 10 employing the principles of the present invention is illustrated in fig1 - 4 and requires four basic elements : a roasting chamber 12 , a heater system 14 , a heated air plenum 15 and a blower 16 . other elements such as a cyclone collector 18 , air recirculation duct 20 , and thermal insulation 22 are preferably utilized but are not an essential part of the invention . a charge of coffee beans 24 undergoing roasting is shown in fig2 and 3 . the roaster 10 may be sized to process several pounds of beans , or it may be enlarged to batch roast bags of coffee beans in commercial quantities . regardless of the size of the roaster , the principles of apparatus design and processing method disclosed herein remain substantially the same . in the batch roaster embodiment shown in fig1 - 4 , the roasting chamber 12 is an elongated rectangular box - like housing 26 having a long front wall 28 , an outer back wall 34 , two short sidewalls 30 , 32 , and a hinged top loading cover 36 . unloading access to the chamber is achieved through a bottom hinged drop down unloading door 38 extending across the lower front wall 38 and flush with an air distributor plate 42 . the door 38 has sidewalls 39 to form a chute enabling rapid loading and unloading of the chamber 12 . above the door 38 is a sight glass 40 through which bean movement and color change of the beans 24 from green to brown may be observed during a drying and roasting operation cycle . the perforated airflow distributor base plate 42 extends across the width of the chamber at the bottom and is considerably narrower than the width of the sidewalls 30 and 32 . the plate 42 is inclined toward the front wall 28 at about 30 °. a multiplicity of orifices 44 are spaced throughout the distributor plate 42 and are aligned to create an airstream ( shown by light arrows in fig3 ) substantially tangential to the front wall 28 and door 38 . the orifices 44 are typically in excess of three sixteenths inch in diameter which represents the usual size of the smallest type of coffee bean found in export trade of good quality coffee beans . the particular orifice size is selected to achieve an economical balance in air lifting capacity between blower capacity and air flow rates which are directly influenced by the depth of green coffee beans in the roast chamber . in the event that the size selected for the orifices 44 approaches or exceeds the size of the beans 24 that will be roasted , a screen 45 having a suitable mesh may be placed over the distributor plate 42 to prevent the beans from lodging in , or falling through , the orifices 44 , without unduly impeding the air flow . an inner inclined plate 46 is joined to the distributor plate 42 along the back edge thereof and forms the inner back wall of the roast chamber 12 and the inclined plate 46 extends upwardly and toward the outer back wall 34 so that it diverges away from the front wall 28 , and functions to guide the descending portion of the recirculating beans 24 back into the air lift stream adjacently above the base plate 42 so that a dense recirculating fluidized mass thereof is achieved . the inclined air distribution plate 42 is joined along its upper edge to the outer back wall 34 . bean temperatures are indicated by a dial thermometer 48 mounted in the roast chamber left sidewall 30 . the thermometer 48 is joined to a thermocouple sensor probe end 50 which extends horizontally into the chamber above the distributor plate at a location where the fluidized beans are very densely packed and out of the airstream so that the true bean temperatures within the mass of moving beans 24 is continuously indicated during roasting . a chart recorder may also be employed to record the bean temperatures during each roast cycle . in addition the probe 50 may be connected to provide automatic thermostatic temperature control of the heater system 14 . thus , shut down of the heater system may be controlled automatically when a predetermined maximum set bean temperature is reached within the roast chamber 12 . the roast chamber housing 26 is joined at its base to a heater system 14 comprising an enclosure forming the heated air plenum 15 for conducting heated air through the multiple orifices 44 of the distributor plate 42 . the heater system 14 contains a heater element 52 capable of imparting sufficient temperature rise to an airflow stream passing through the heater box to enable the airstream to heat the beans to the desired roast temperature range of 450 ° to 530 ° f . air . the heater element 52 may be an electric heating element 54 or it may be a direct fired natural gas burner positioned before or after the blower . in smaller roasters , the electric heater element 54 after the blower is preferred , whereas in larger commercial roasters , the gas burner before the blower may be more practical . other forms of heater elements may be employed so long as no undesirable combustion gases or coffee reaction products are brought into contact with the beans 24 being roasted . vented air may be recycled through the air recirculation duct 20 to conserve heat . a heater enclosure thermometer 58 in conjunction with a probe 60 is positioned to indicate the plenum air temperature after the heater element . the heater system 14 is joined at its base to the blower assembly 16 which forces air upwardly through the heater element 52 and the perforated air distributor plate 42 and into the bean roast chamber 12 with sufficient air velocity to move the beans 24 therein up the front wall as a dense and constantly recirculating fluidized bean mass . the preferred air volume and velocity developed by the blower 16 and distributed by the plate 42 will expand the volume of the bed of beans 24 only about twenty to thirty percent over the volume of the beans at rest in the chamber before and / or after roasting . in practice a single stage multiblade 3600 r . p . m . centrifugal pressure blower 62 in an enclosed housing 64 has been found to provide ample air flow and pressure . an electric motor 66 is usually used to drive the fan . an exhaust duct 68 is connected to the roast chamber at the top of the right sidewall 32 to enable outflow of the still warm air after it has passed through the mobilized beans 24 . the spent air may be recycled through the recirculation duct 20 to conserve heat . a chaff collection cyclone 18 typically forms a necessary part of the vented air or recirculated air roast system . the cyclone employs well known principles and does not form a part of the present invention . thermal insulation 22 such as fiber glass wool is placed around the roast chamber 12 , inlet plenum 15 and the recirculation duct 20 to minimize heat losses and conserve temperature thereby reducing fuel costs and sustaining needed temperatures in the system . the loading cover 36 is opened upwardly and a charge of green coffee beans 24 is dumped into the roasting chamber 12 . the cover 36 is closed and the blower 16 is turned on , followed by the heater system 14 . heated air with progressively higher temperatures then passes into the roasting chamber 12 through the orifices 44 as indicated by the light arrows in fig3 and heats the beans 24 as they are simultaneously moved into a densely fluidized and constantly recirculating mass . because of the acute angle of the distributor plate 42 with respect to the front wall 28 , the hot air is directed upwardly along the inside of the door 38 causing a somewhat higher level of beans adjacent to the front wall 28 . the beans roll out of the airstream by gravity and move toward the inner back wall 46 and are then guided downwardly by the inclined wall 46 to the base plate whereupon the beans reenter the hot airstream and are elevated as before , thereby completing a cycle of recirculation . after about 10 to 20 minutes of roasting time and when the bean temperature has reached the range of 410 ° to 430 ° f ., as indicated by the dial thermometer 48 , depending upon whether the particular desired roast will be light or dark , roasting is terminated by cutting off the heater element 52 . cooling ambient air from the blower 16 is then circulated through the roasted beans for several minutes to lower the beans to room temperature . water spray cooling may also be employed . the blower is then stopped . the bean discharge door 38 is swung open whereupon the roasted and cooled beans slide out of the chamber and into a suitable transfer container . the discharge door sidewalls 39 serve to guide the beans out of the chamber 12 . continuous coffee roasting apparatus 80 employing the principles of the present invention is illustrated in fig5 - 8 and comprises three separate vertically descending stages : a dryer stage 82 , a roaster stage 84 and a cooling stage 86 . unroasted coffee beans 24a are continuously fed into the dryer stage 82 via an inlet hopper 88 while roasted and cooled coffee beans 24b are discharged from the cooling stage 86 through a discharge chute 90 which is positioned over a moving horizontal conveyor belt 92 . rotary valves may be utilized to achieve air pressure differential seals at the inlet hopper 88 and discharge chute 90 if desired . each stage 82 , 84 , 86 of the continuous roaster 80 is very similar in design and operation to the box - like roasting chamber 12 of the batch type roaster 10 except for the loading cover and unloading door . sight glasses 94 are positioned in the front walls of each stage 82 , 84 , 86 to enable operator view of the operations occuring therewithin . a bean sampling tube 95 communicates with the chamber of each stage 82 , 84 , 86 . indicating thermometers 96 , 98 , 100 have sensitive thermocouple probes 97 , 99 and 101 respectively extending into and transversely across the chamber of each stage so that bean process temperatures can be constantly and progressively monitored . air distributor plates 102 , 104 , 106 having multiple spaced apart orifices 108 , form the bottom walls in the chambers of the respective stages 82 , 84 , 86 and are aligned to form an acute angle with the front walls 103 , 105 , 107 of the stages as shown in fig8 . heated air plenums 112a , 112b , 114 , 116 form the bottom portion of each stage 82 , 84 , 86 and have inlets 113a , 113b , 115 , 117 which receive heated air from a source utilizing well known principles . the plenums deliver heated air to the distributor plates 102 , 104 , 106 of each respective stage at a controlled velocity sufficient to levitate the beans 24 into a dense and constantly recirculating fluidized mass of beans as with the batch roaster 10 . the dryer stage 82 has two separate adjacent plenums 112a and 112b feeding air to the distributor plate 102 . in the first plenum , the air may be warm spent air recirculating from the roaster stage 84 whereas the second plenum 112b may be hot air being supplied directly from a heating source . in this way the beans are gradually heated to drying temperature and heat is conserved through recirculation . however , the two dryer plenums 112a , 112b are not essential and could be replaced by a single plenum . by adjusting the size and spacing arrangements of the orifices 108 in each distributor plate 102 , 104 , 106 and the velocity of the supply of heated air delivered to the inlets 113a , 113b , 115 , 117 of the plenums , the beans 24 are moved by gravity longitudinally through each stage 82 , 84 , 86 as they recirculate in a vertical plane as a dense fluidized bed . in order to minimize &# 34 ; batch mixing &# 34 ; of beans from the discharge side to the inlet side of each stage , the length thereof is considerably more than the width . a length to width ratio of about six to one is satisfactory . a discharge weir 122 , 124 , 126 forms the lower sidewall of the discharge end of each stage , and continuous longitudinal bean flow occurs in each stage only as beans are discharged over the weir at the same rate that beans are added from the preceding stage or inlet hopper . the dryer stage 82 is positioned above the roaster stage 84 which is likewise positioned above the cooling stage 86 . this staggering arrangement enables gravity flow movement of beans from stage to stage via the interconnecting chutes 116 and 118 . the dryer to roaster chute 116 communicates with the dryer chamber at a discharge port above the weir 122 and with the roaster stage 84 at an inlet port ; and the roaster to cooler chute 118 forms a like connection . alternatively , bean transfer from stage to stage may be accomplished mechanically as by bucket elevators employing well known principles . the cooling stage 86 may include water spray apparatus 120 near the cooler inlet port to provide a quenching water spray for rapidly cooling the beans . green , unroasted coffee beans 24a having a typical moisture content of twelve to thirteen percent are admitted to the dryer stage 82 through the inlet hopper 88 . the warm recycled air from the first plenum 112a levitates and heats the beans which are slowly moving longitudinally into the airstream coming from the second plenum 112b which is heated to an inlet temperature around 450 ° f . during the drying cycle , which averages about nine minutes , the beans are heated from ambient temperatures to about 400 ° f . and the moisture content in each bean is reduced to about 1 percent . at the discharge end of the dryer 82 , the beans pass over the dryer weir 122 and fall down the transfer chute 116 and pass into the roaster stage 84 . the inlet temperatures in the roaster plenum 114 are higher than those in the dryer stage and are typically in the range of between 450 ° and 500 ° f . a temperature profile of the beans ranges from 400 ° to 425 ° f . and this profile is monitored by the thermometers 98 or by a chart recorder employing well known principles ( not shown ) attached to sensor probes 99 extending into and transversely along the fluidized mass of dense recirculating beans . the beans remain in the roaster stage for only about 11 / 2 minutes . during this short roasting period , the beans swell , release chaff and undergo density reduction to about half that of green beans . the removal of chaff is accomplished conventionally with chaff cyclone separation apparatus such as the cyclone 18 shown connected in fig2 to the batch roaster 10 . since chaff is only released during actual roasting , the continuous roaster apparatus 30 is actually simplified by having three separate stages . also , processing temperatures are more easily controlled in three stages than in only one or two . at the discharge end of the roaster stage the beans pass over the roaster weir 124 and flow downwardly into the cooler stage 86 via the transfer chute 118 . the roasted beans are met by a water spray at the inlet to the cooling chamber which removes most of the heat within the beans by evaporation of water . cooling air of ambient temperature in the cooler plenum 116 continues to fluidize the beans and enables rapid cooling down to about 100 ° f . during the cooling cycle which has a typical duration of about 5 minutes . the water spray can be adjusted by the operator by reference to a longitudinal temperature profile from probes 101 positioned longitudinally along the cooling section and registering on dial thermometers or a chart recorder ( not shown ). thereafter , the cooled beans pass over the cooler weir 126 and down the discharge chute 90 to a conveyor 92 where they are carried to a packaging or grinding operation . fig9 sets forth in graphical format the detectable thermal rises or bumps occuring within each coffee bean undergoing roasting in accordance with the present invention . during approximately the first 12 minutes of heating of coffee beans 24 the bean temperature rises gradually and virtually linearly from about 100 ° to 400 ° f . during this initial stage , the coffee beans are drying ; they are not being roasted . starting at about 400 ° f ., true bean temperature , pyrolitic chemical reactions begin to occur within each bean and the bean temperature climb rate accelerates , resulting in the charted thermal bumps a , b and c of fig9 . these thermal bumps a , b and c may be detected during roasting to enable precise roast time control . in addition it has been found that the magnitude of the thermal bump indicated the nature of coffee beans being roasted and the flavor of the coffee beverage ultimately produced therefrom . in fig9 the charted bump a indicated that new crop wet processed mild coffee grades are being roasted . curve b is indicative of roasting of wet processed older crop milds . curve c indicates dry processed brazils , and curve d , having virtually no thermal bump , is indicative of the low grade dry processed robusta coffee beans . if the roasting process is terminated before the pyrolysis bump occurs , the beans will not have developed their peak flavors . if heating stops during the thermal bump , only some of the flavor will have been developed . if heating of the beans continues more than about 3 minutes after completion of the thermal bump period , the flavor and aroma producing aldehydes , etc ., will be altered and driven off and the resultant beans will produce a dark roast taste which is lacking in aromatics . a heat cut off point within the range between point e and point f on the curve of fig9 may be selected to control the flavor characteristics of the final coffee product . cutting off the heat at point e produces a light medium roast whereas cut off at point f results in a dark or italian roast . a chart recorder may be attached to the probe 50 of the batch roaster or the probes 99 of the roaster stage 84 of the continuous apparatus so that the phenomena displayed in fig9 may be permanently recorded for each bath of beans , and such records are commercially useful in disclosing the quality of coffee roasted and the degree of roast achieved . thus , the thermal bumps are indexes which document green coffee quality scientifically and objectively , as opposed to commonly employed subjective tasting procedures which are most difficult to document reliably . as previously explained , the magnitude of the thermal bump is directly related to desirable coffee flavor , that is , the greater the bump , the better tasting and more aromatic is the final coffee product . sensing and recording inlet air temperatures , as with a chart recorder connected to the probe 60 of the batch roaster 10 , enables control and optimization of processing times and conditions . to those skilled in the art to which this invention relates , many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention . the disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting .
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 .