TREATMENT OF COFFEE AROMA GAS

Abstract: A process for drying coffee aroma gas. A stream of coffee aroma gas is contacted with a molecular sieve containing zeolite having pores sized for removing water molecules but a minimum of coffee aroma components from the coffee aroma gas. Water is thus removed from the coffee aroma gas. The coffee aroma gas may be dried to high levels with reduced loss of aroma components.

Description: Treatment of coffee aroma gas This invention relates to a process for drying coffee aroma gas and to apparatus for use in drying coffee aroma gas. Instant coffee powders which are obtained from commercial processes involving extraction, concentration and drying, are usually substantially aroma- less. However, it is important for coffee products to have aroma since consumers associate coffee aroma with quality coffee products. If a coffee product lacks coffee aroma, consumer perception of the product is adversely affected. For this reason, it is conventional to recover coffee aromas which are given off during the processing of the instant coffee and to later reincorporate these aromas into the instant coffee powder. The coffee aroma gases may be recovered at several points during processing of the instant coffee. However aroma gases are most commonly recovered during grinding of the roasted beans and by steam stripping of the coffee extract prior to concentration and drying of the coffee solids. Usually the coffee aroma gases which are recovered contain levels of moisture which, if not decreased, give rise to stability problems and complications in downstream processing of the aroma. For this reason, it is common to attempt to remove as much moisture as possible from the coffee aroma gases. Usually moisture is removed from the coffee aroma gases by running the coffee aroma gases through one or more condensers operated at temperatures sufficiently low to cause condensation of moisture but not low enough to cause condensation or freezing of the bulk of the aroma gases. Temperatures in the region of 0°C to 20°C are commonly used. The condensers are effective in removing most of the moisture but, in removing the moisture, the condensers also remove many aroma components which are soluble in aqueous solution. This may lead to some imbalance in the aroma ultimately recovered. US Patent 5,342,639 describes a process for removing further amounts of moisture by passing the coffee aroma gases through a desiccant bed containing calcium sulphate granules. The aroma gases leaving the bed are collected and combined. Once the moisture content of the granules rises to 4.3% by weight but before the moisture content of the aroma gases leaving the bed rises to 1000 ppm, the process is terminated. The granules must then be regenerated. The collected aroma gases are said to have a moisture content not exceeding about 200 ppm. There are three main drawbacks to this process: first, the adsoφtion capacity of the bed is low; secondly, the pressure drop across the bed is high, and thirdly, regeneration of the granules is energy intensive and requires long periods of time. These drawbacks lead to other problems. In particular, because the adsoφtion capacity is low, the process requires large amounts of desiccant, thus requiring expensive equipment. Further, to provide an adequate operation time, the US patent suggests that most of the water be removed using condensers prior to contacting the aroma gas with the calcium sulphate. As previously mentioned, this means that certain aroma components will be lost. Also, the high pressure drop means that the gas must be compressed, a process which can lead to damage of the labile aroma components. It is an object of this invention is to provide a process for drying aroma gas which is able to selectively remove moisture from the aroma gas. Accordingly, this invention provides a process for drying coffee aroma gas, the process comprising contacting a stream of coffee aroma gas with a molecular sieve containing zeolite having pores sized for removing water molecules but a minimum of coffee aroma components from the coffee aroma gas. Suφrisingly, the process permits a coffee aroma gas to be dried to high levels with reduced loss of aroma components. For example, more than 80% by weight of moisture in the coffee aroma gas may be removed with less than 20% by weight of aroma components being lost. This ratio of moisture removal to aroma loss is much better than may be obtained using condensers. Also the aroma obtained is of high quality and does not suffer from ill effects such as having musty notes or having an incomplete aroma profile. Also, because the molecular sieve has a high water load capacity, the molecular sieve may be used to remove moisture from the coffee aroma gas for extended periods without the need for regeneration. Preferably, less than about 20% by weight of coffee aroma components in the coffee aroma gas are removed by the molecular sieve; more preferably less than about 15% by weight of aroma components are removed; for example less than 10% by weight. The mean diameter of the pore openings in the crystalline lattice of the zeolite is preferably 0.5 nm or less: for example 0.4 nm or 0.3 nm. A zeolite which has a mean pore diameter of 0.3 nm. is preferred. Because water molecules have an estimated diameter of about 0.26 nm, by using a zeolite having a mean pore diameter of 0.3 nm. water molecules may be adsorbed but not larger aroma molecules. In this way, the loss of aroma components can be minimized. Preferably, the zeolite is a type A zeolite. A type A zeolite is an alumino- silicate of formula M2θ Al2θ3 xSiθ2-yH2θ in which x is 2; y, when fully hydrated, is 4.5 and M is a metal ion; preferably selected from Na, K, Mg, Ca, Sr, and Ag. A type 3 A zeolite, which has a mean pore diameter of 0.3 nm, is especially preferred. A type 5 A zeolite, which has a mean pore diameter of 0.5 nm, will operate perfectly adequately but the amount of aroma removed may be higher, but not unacceptably higher. The molecular sieve may be in the form of a powder, beads, moulded forms, or sintered forms. Preferably the molecular sieve is in bead form. The diameter of the beads is preferably about 1 to about 5 mm. more preferably about 2 mm to about 3 mm. Conveniently, the molecular sieve is arranged in the form of a packed bed through which the stream of coffee aroma gas flows. Preferably the stream of coffee aroma gas is contacted with the molecular sieve at a temperature in the range of about 20°C to about 80°C; more preferably 20°C to 60°C. The molecular sieve may be cooled while it is in contact with the stream of coffee aroma gas to maintain the molecular sieve at a substantially constant temperature. This has the advantage of preventing a decrease in the capacity of the molecular sieve to adsorb water; the water adsoφtion capacity otherwise decreasing with increasing temperature. The stream of coffee aroma gas preferably has a residence time in contact with the molecular sieve of about 0.5 seconds to about 20 seconds; for example about 1 second to about 5 seconds. Residence times of about 1 second to about 2 seconds are particularly preferred. The pressure drop across the molecular sieve is preferably from about 2 kPa to about 100 kPa; for example from about 4 kPa to about 6 kPa. Pressure drops of this magnitude are sufficiently small such that substantial compression of the aroma gases may be avoided. In a preferred embodiment, the stream of coffee aroma gas is caused to flow through the molecular sieve for a time less than that required to saturate the molecular sieve with water, the flow of the stream of coffee aroma gas through the molecular sieve then being terminated, and the molecular sieve is regenerated by causing a hot. dry gas to flow through it to drive off the water in the molecular sieve. The stream of coffee aroma gas is preferably caused to flow through the molecular sieve for a time sufficient to raise the moisture content of the molecular sieve to about 10% by weight to about 20% by weight; for example from about 15% by weight to about 20% by weight. The time may be about 1 hour to about 12 hours; preferably about 6 to about 10 hours; for example about 8 hours. The molecular sieve is preferably regenerated using gas heated to about 180° to about 220° C. The time required to regenerate the molecular sieve may be about 3 hours to about 6 hours. The regeneration of the molecular sieve may be terminated when the moisture content of the molecular sieve is reduced to about 2% by weight or less. Preferably at least two molecular sieves are provided and arranged in pairs in parallel; a stream of coffee aroma gas being passed through one molecular sieve of each pair while hot, dry gas is passed through the other molecular sieve of the pair to regenerate it. In this way, the process may be operated in a continuous fashion. In another aspect, this invention provides a system for removing moisture from a stream of coffee aroma gas, the system comprising: a pair of dryers each containing one or more beds of a molecular sieve, the molecular sieve comprising zeolite having pores sized for adsorbing water molecules but a minimum of coffee aroma components, and the pair of dryers having an inlet end and an outlet end; a cryogenic aroma condenser for condensing coffee aroma from the stream of coffee aroma gas and separating the condensed coffee aroma from non- condensing gas in the stream, the cryogenic aroma condenser having an inlet for receiving the stream of coffee aroma gas and an outlet for discharging the non- condensing gas; a first flow direction means at the inlet end of the pair of dryers for selectively directing the stream to one or the other of the pair of dryers for permitting flow of the stream through the dryer selected, the first flow direction means connecting the other dryer to an exhaust; and a second flow direction means at the outlet end of the pair of dryers for receiving the stream from the dryer through which the stream flows and the non- condensing gas from the outlet of the cryogenic condenser, and for selectively directing the stream to the inlet of the cryogenic aroma condenser and the non- condensing gas to the other dryer to flow through the dryer. Preferably the system further comprises a heating means for heating the non-condensing gas to a temperature of about 180°C to about 220°C prior to the non-condensing gas being directed to the dryer. The system may also comprise cooling means for maintaining the molecular sieve of the dryer receiving the stream of coffee aroma gas at a temperature in the range of about 20°C to about 80°C. Embodiments of the invention are now described, by way of example only, with reference to the drawings in which: Figure 1 is a schematic flow diagram of a drying process; Figure 2 is a partial cross-section of a drying column; and Figure 3 is a partial cross-section taken along line 2-2 of Figure 2. Referring to figure 1, coffee aroma gas, obtained from a coffee extraction system (not shown), is introduced through an aroma line 58. The coffee aroma gas may be obtained from any suitable source of aroma in coffee extraction; for example coffee aroma gas obtained by: stripping freshly ground roast coffee with an inert gas, flushing the grinder during grinding of the roast and ground coffee, steaming roasted and ground coffee, collecting gases evolved during the extraction of coffee, by gas stripping of coffee extract, and the like. Depending upon its source, the coffee aroma gas is usually made up of a mixture of an inert stripping gas (for example nitrogen, helium or carbon dioxide or mixtures of nitrogen and helium or carbon dioxide), coffee aroma, carbon dioxide and moisture. Depending on factors such as the source of the coffee aroma gas, the amount of water used in quenching the roasting process, the particle size of the coffee, the temperature of the coffee, and the ratio of the mass of the inert gas to the mass of the coffee, the water content of the coffee aroma gas entering through the aroma line 58 may vary widely; for example from about 3 to about 10 g- water/kg-dry gas. The aroma line 8 leads to a first four way valve 60. The four way valve 60 connects the aroma line 58 to either of two aroma inlet lines 21a, 21b. The other of the two aroma inlet lines 21a, 21b is connected to a gas vent 64. The drawing illustrates the aroma line 58 being connected to the aroma inlet line 21a while the aroma inlet line 2 lb is connected to the gas vent 64. By suitably turning the four way valve 60, the aroma line 58 may be connected to the aroma inlet line 21b while the aroma inlet line 21a is connected to the gas vent 64. The aroma inlet line 21a leads to a first drying column 20a while the ^aroma inlet line 21b connects to a second drying column 20b. Therefore the coffee aroma gas entering through the aroma line 58 is transported to the first drying column 20a. The drying columns 20a, 20b are identical and are best illustrated in figures 2 and 3 where the drying column is identified with the reference numeral 20. Referring now to figures 2 and 3, the drying column 20 is formed of a tubular shell 29 having an upper flange 32b at its upper end and a lower flange 32c at its lower end. A plurality of tubes 27 are positioned vertically in the tubular shell 29 to extend from the upper end to the lower end of the tubular shell 29. Each of the tubes 27 is filled with zeolite beads. The zeolite beads are commercially available and may be obtained, for example, from Degussa GmbH of Germany and CU Chemie Uetikon AG of Uetikon, Switzerland. An upper closure 25 is positioned over the upper end of the tubular shell 29 to seal it. The upper closure 25 has a flange 32a which may be fixed to the flange 32b, for example by means of bolts, to fix the upper closure 25 on the tubular shell 29. The upper closure 25 has an inlet aperture 30 for the input of coffee aroma gas from gas inlet line 21. Similarly a lower closure 26 is positioned over the lower end of the tubular shell 29 to seal it. The lower closure 26 has a flange 32d which may be fixed to the flange 32c, for example by means of bolts, to fix the lower closure 26 on the tubular shell 29. A perforated plate 28 is mounted in the lower closure 26, at its upper open face, to be positioned beneath and in contact with the tubes 27 when the lower closure 26 is sealed on the tubular shell 29. In this way, loss of zeolite from the tubes 27 may be prevented. The lower closure 26 has an outlet aperture 31 for the output of coffee aroma gas through aroma outlet line 22. The adsoφtion of water by zeolite is an exothermic process and therefore energy is released during the process. However, the adsoφtion capacity of zeolite decreases with increasing temperature. Thus, it may be desirable to cool the zeolite during the adsoφtion process; particularly if the temperature increase would be greater then 10°C. Therefore the tubular shell 29 has a coolant inlet 33 adjacent its lower end and a coolant outlet 34 adjacent its upper end. A coolant inlet line 23 is connected to the coolant inlet 33 and a coolant outlet line 24 is connected to the coolant outlet. In this way, a coolant may be introduced into the tubular shell 29 to flow around and cool the tubes 27 containing the zeolite. Baffles 38 and the like may be positioned in the tubular shell 29 to obtain optimum flow conditions. Although the coolant flow as described is intended to be counter-current to the coffee aroma gas, the system may be readily altered to be co-current. Any suitable fluid, gas or liquid, may be used as the coolant. Water is particularly suitable because it is inexpensive and easy to handle. The temperature of the coolant should be such that the temperature of the adsoφtion process is held between 20° and 80° C. In particular, it is desirable that the zeolite be maintained at a temperature above the dew point of the coffee aroma gas to prevent condensation which is a non-selective manner of removing water. The water content of the dried aroma gas leaving the drying column 20 through the aroma outlet line 22 is a function of the length of the zeolite bed in the tubes 27, the velocity of the coffee aroma gas in the tubes 27. the temperature of the zeolite, the operating pressure, and moisture content of the coffee aroma gas entering the drying column 20. Therefore these variables may be adjusted to give any desired water content of the dried aroma gas. This may be done routinely by the person skilled in the art. Typically however, the water content of the dried aroma gas varies from about 0.1 to about 2 g-water/kg-dry gas. The pressure drop across the zeolite beds may be readily maintained within acceptable limits: for example from about 4 kPa to about 6 kPa. For most commercial applications, the drying column is preferably from about 0.5 m to about 2 m in length. Also the drying column 20 preferably contains about 5 kg to about 20 kg of zeolite for each kilogram of water to be removed. Referring again to figure 1. the aroma outlet line 22a from the first drying column 20a and the aroma outlet line 22b from the second drying column 20b each lead to a second four way valve 62. The second four way valve 62 connects either of the two aroma outlet lines 22a, 22b to either an aroma feed line 66 or a regeneration line 68. The drawing illustrates the aroma outlet line 22a being connected to the aroma feed line 66 while the aroma outlet line 22b is connected to the regeneration line 68. By suitably turning the second four way valve 62, the aroma outlet line 22a may be connected to the regeneration line 68 while the aroma outlet line 22a is connected to the aroma feed line 66. The aroma feed line 66 extends to a cryogenic aroma condenser 70 in which the dried aroma gas may be condensed. Many suitable aroma condensers 70 are known and have been reported in the literature. Preferably however, the aroma condenser 70 has a housing formed of an upper cylindrical section and a lower conical section. The lower end of the conical section terminates in a discharge opening. Several cylindrical filters 72. preferably porous stainless steel, extend vertically within the upper cylindrical section. The inner bore of each cylindrical filter is connected to a gas manifold 74. An inert gas in liquid form is sprayed into the housing from a liquid gas source (not shown) through a gas input line 76. The liquid inert gas is preferably the same as the inert gas in the aroma line 58; more preferably nitrogen. Sufficient liquid inert gas is sprayed into the housing to maintain the housing at a temperature below about -80°C or lower, but sufficiently high such that the liquid inert gas vaporises in the housing. Therefore most aroma components of the dried aroma gas introduced into the cryogenic aroma condenser 70 condense into a frost while the inert gas carrying it. as well as carbon dioxide, does not. The aroma frost falls to the bottom of the housing and out of the discharge opening. The inert gas passes through the cylindrical filters 72 and into the manifold 74. Some entrained aroma frost may collect on the cylindrical filters 72 but this may be removed by pulsing inert gas back through the cylindrical filters 72 at regular intervals to dislodge the frost. The frost falling through the discharge opening may be recovered by mixing it into a suitable substrate; for example coffee oil. Further details of the operation of the cryogenic aroma condenser 70 may be obtained from US patents 5,182.926 and 5,323,623; the disclosures of which are incoφorated by reference. Plainly other cryogenic aroma condensers may be used: for example that disclosed in US patent 5,030,473. The inert gas passing into the manifold 74 is drawn out of the cryogenic aroma condenser 70 through an outline line 78 and on to a compressor 84 which drives circulation of the gas through the system. Compression of the gases at this stage will not damage aroma components since they have been removed in the cryogenic aroma condenser 70. From the compressor 84. the inert gas is directed to a flow splitter 80. The flow splitter 80 directs a portion of the inert gas to a heater 82 in which it is heated to a temperature suitable for regenerating zeolite: for example from about 180°C to about 220°C. The heated inert gas leaving the heater 82 is fed into the regeneration line 68 which leads to the second drying column 20b through the second four way valve 62. The remainder of the inert gas leaving the flow splitter 80 in an inert gas line 56 is purged or recovered for further use, or used to strip coffee aroma from a suitable source. Prior to introducing the heated inert gas into the second drying column 20b, the coolant is conveniently drained from the tubular shell 29 to enable more rapid heating of the zeolite. The heated inert gas flows through the second drying column 20b, driving off the moisture adsorbed by the zeolite and regenerating the zeolite. The moist inert gas leaving the second drying column 20b is led through gas line 2 lb to the first four way valve 60 and hence on to the gas vent 64. In use. the first drying column 20a which receives the coffee aroma gas may be operated until the moisture content of the dried aroma gas leaving the first drying column 20a begins to rise rapidly with time. This is referred to as break-through. At this point, the zeolite has begun to reach its maximum water capacity and no longer operates adequately as a molecular sieve. The time taken to reach break-through will depend upon many factors such as the initial moisture content of the zeolite and the incoming coffee aroma gas, the amount of zeolite, the mass flow rate of the coffee aroma gas, and the like. However it may be readily determined for any application. Also, suitable detectors may be placed in the aroma outlet line 22 to detect the onset of break-through. Usually, under industrial conditions, a drying column 20 may be operated for about 3 to about 10 hours before break-through. The time taken to reach break-through in the first drying column 20a is sufficient time for the zeolite in the second drying column 20b to be regenerated. Usually about 3 to about 6 hours is sufficient to regenerate the zeolite in the second drying column 20b. Once regenerated, the zeolite in the second drying column 20b is ideally cooled to a temperature from about 20°C to about 80°C. This may be achieved by turning off the heater 82 and permitting cold inert gas to flow through the second drying column 20b. Also, if desired, a coolant may be passed through the tubular shell 29 of the second drying column 20b. Therefore the system may be operated in a semi-continuous mode. Once the first drying column 20a which receives the incoming coffee aroma gas begins to reach break-through, the first four way valve 60 is switched to direct the incoming coffee aroma gas to the second drying column 20b. Also, the second four way valve 62 is switched to connect the second drying column 20b to the aroma feed line 66 and the regeneration line 68 to the first drying column 20a. The incoming coffee aroma gas is then dried in the second drying column 20b and the first drying column 20a is regenerated as described above. Clearly numerous modifications may be made to the embodiments described without departing from the scope of the invention. For example, it is not necessary to have two drying columns 20. If it is feasible to operate in batch mode, one drying column 20 may be used. Similarly, more than two drying columns 20 may be used. It is also not necessary for the drying columns to be aligned vertically; they may be aligned horizontally or at any desired angle. The drying columns 20 also need not be in the form of shell and tube columns; any form of fixed bed system may be used. Further, if under the flow conditions chosen, the temperature rise of the zeolite during drying is small, the need to provide for cooling is reduced or may be eliminated completely. If the moisture content of the coffee aroma gas is very high, for example if the coffee aroma gas is obtained from the steam stripping of coffee extract, it may be desirable to partially condense moisture from the coffee aroma gas prior to introducing it into a drying column. In this way. rapid saturation of the drying column with water may be avoided. Some aroma may be lost in the condensers but this may be maintained within acceptable limits. Example 1 A batch of 270 g of roasted and ground coffee is placed in a bench-scale tumbler. The drum of the tumbler is held in a water bath at about 38°C ( 100°F). Nitrogen gas at a flow rate of 0.5 litres/minutes is introduced into the tumbler to strip coffee aroma from the roast and ground coffee. The resulting gases are led through a cartridge containing either 1 g or 2 g of type 3 A zeolite. The zeolite is held at a temperature of about 22°C (72°F) or about 88°C ( 190°F). The gases entering and leaving the cartridge are sampled for analysis of moisture content even-' 10 minutes and aroma content every 5 minutes. The process is continued for about 1 hour. Zeolite Amount Temperature Water removal Aroma Loss (g) (°C) mass % mass % 1 88 66 4.5 1 22 76 - 2 88 80 14.3 The dried aroma gas leaving the cartridge is collected and sniffed. Undried eas leaving the tumbler is also collected and sniffed as a control. No difference is perceived and the dried aroma gas has a well balanced aroma profile. The test is repeated with type 4A zeolite and the results are similar although a little more moisture is removed and aroma loss is higher. Example 2 A drying column of diameter of 50 mm and length of 800 mm is loaded with 1 kg of type 3A zeolite. The drying column is insulated and installed vertically. Coffee aroma gas is collected by stripping of the freshly ground roast coffee with nitrogen gas. The coffee aroma gas has a moisture content of about 20g-water/kg dry gas. The coffee aroma gas is directed to the drying column at a flow rate of about 4.4 kg/hr for about 4 hours. Samples are taken from the coffee aroma gas entering the drying column and the coffee aroma gas leaving the drying column. The amount of water removed from the coffee aroma gas is about 65% by weight. The aroma loss could not be determined. Example 3 The process of example 2 is repeated using various types of zeolite, and for various different durations. The results are as follows: Run Zeolite Duration Water removal Aroma Loss (Minutes) (mass %) (mass %) 1 Type 3A 155 67 13 2 Type 3A 215 91 22 3 Type 5A 160 87 31 4 Type 3A 475 82 14 The aroma loss value is an integrated value. For each run. the aroma loss initially decreases rapidly with time before reaching a "steady-state" asymptote. In runs 1 to 3, the "steady-state" asymptote is just reached which means that the results obtained are higher than would be obtained if the runs were carried out for a longer time: as would occur in practice. In run 4. break through is reached after about 350 minutes and this has reduced the water removal value. Prior to break through, water removal is better than 90% by weight. Example 4 Two drying columns of diameter of 40 mm and length of 1000 mm are each loaded with 10 kg of type 3 A zeolite. The drying columns are insulated and installed vertically. Coffee aroma gas, which has a moisture content of 4g- water/kg dry gas. is directed to a first of two drying columns at a flow rate of 30 Nm^/hr at an inlet gauge pressure of 7 kPa (Nm^ indicates volume at normal conditions of 0°C and 101.3 kPa). The coffee aroma gas has a velocity of 0.6 m/s in the drying column; providing a residence time of about 1.7 seconds. The dried coffee aroma gas leaving the first drying column has about 82% to about 93% by weight of the initial moisture removed. The amount of aroma lost in the drying column decreases over time as the selectivity of the zeolite improves. The dried coffee aroma gas is directed to a cryogenic condenser as described and operated in US patent 5,182,926. The condensed coffee aroma is collected and captured in coffee oil. The non-condensing gases are collected, heated to about 200°C, and then directed through the second of the two drying columns at a flow rate of 32 Nm^/hr and at an inlet gauge pressure of 8 kPa. Upon leaving the second drying column, the gas is vented. After about 6 hours, about 98% of the water in the second drying column is removed. The drying column is then allowed to cool for about 2 hours. The system is operated in this fashion for a cycle of about 8 hours. Then the incoming coffee aroma gas is directed to the second drying column and the non-condensing gases from the cryogenic condenser are heated and directed to the first drying column. The system is operated in this cyclic manner for a total of 48 hours; each drying column having an adsoφtion period of 8 hours before being regenerated again. The average aroma loss during each cycle is determined by gas chromatography to be less than about 10% by weight. It is noted that aroma loss decreases with time during each cycle and from one cycle to the next as the selectivity of the zeolite improves. Example 5 The process of example 4 is repeated except that type 5 A zeolite is used in the drying columns. The process is run for 48 hours with each drying column undergoing an 8 hour adsoφtion cycle followed by 8 hours of regeneration and cooling. The dried coffee aroma gas leaving the first drying column has about 65% to about 78% by weight of the initial moisture removed (average about 77.8%). As compared to zeolite 3 A, the water loading capacity of zeolite 5 A is diminished (from 86 to 76%). Average aroma loss is about 20% or less by weight.

Claims: Claims: 1. A process for drying coffee aroma gas. the process comprising contacting a stream of coffee aroma gas with a molecular sieve containing zeolite having pores sized for removing water molecules but a minimum of coffee aroma components from the coffee aroma gas. 2. A process according to claim 1 in which the molecular sieve removes less than about 20% by weight of coffee aroma components in the coffee aroma gas. 3. A process according to claim 1 in which the zeolite has pores of a mean diameter of about 0.3 nm to about 0.5 nm. 4. A process according to claim 1 in which the zeolite is a type A zeolite of formula M2θ Abθ3 xSiθ2 yH2θ in which x is 2; y, when fully hydrated. is 4.5 and M is a metal ion selected from Na, K, Mg, Ca, Sr, and Ag. 5. A process according to claim 1 further comprising cooling the molecular sieve while the molecular sieve is in contact with the stream of coffee aroma gas to maintain the molecular sieve at a substantially constant temperature. 6. A process according to claim 1 in which the stream of coffee aroma gas has a residence time in contact with the molecular sieve of about 0.5 seconds to about 20 seconds. 7. A process according to claim 1 in which the stream of coffee aroma gas is caused to flow through the molecular sieve for a time less than that required to saturate the molecular sieve with water, the flow of the stream of coffee gas through the molecular sieve then being terminated, and the molecular sieve is then regenerated by causing a hot, dry gas to flow through the molecular sieve to drive off the water in the molecular sieve. 8. A process according to claim 7 in which the stream of coffee aroma gas is caused to flow through the molecular sieve for a time sufficient to raise the moisture content of the molecular sieve to about 10% by weight to about 20% by weieht. 9. A process according to claim 7 further comprising providing at least two molecular sieves arranged in pairs and in parallel: a stream of coffee aroma gas being passed through one molecular sieve of each pair while hot, dry gas is passed through the other molecular sieve of the pair to regenerate the other molecular sieve. 10. A system for removing moisture from a stream of coffee aroma gas, the system comprising: a pair of dryers each containing one or more beds of a molecular sieve, the molecular sieve comprising zeolite having pores sized for adsorbing water molecules but a minimum of coffee aroma components, and the pair of dryers having an inlet end and an outlet end; a cryogenic aroma condenser for condensing coffee aroma from the stream of coffee aroma gas and separating the condensed coffee aroma from non- condensing gas in the stream, the cryogenic aroma condenser having an inlet for receiving the stream of coffee aroma gas and an outlet for discharging the non- condensing gas; a first flow direction means at the inlet end of the pair of dryers for selectively directing the stream to one or the other of the pair of dryers for permitting flow of the stream through the dryer, the first flow direction means connecting the other dryer to an exhaust; and a second flow direction means at the outlet end of the pair of dryers for receiving the stream from the dryer through which the stream flows and the non- condensing gas from the outlet of the cryogenic condenser, and for selectively directing the stream to the inlet of the cryogenic aroma condenser and the non- condensing gas to the other dryer to flow through the dryer.

Inventors: SASAKI TAKUYA, TSAI CHUN-DAR, WESTFALL SCOTT, SASAKI, TAKUYA, TSAI, CHUN-DAR, WESTFALL, SCOTT
Applicants: NESTLE SA, SASAKI TAKUYA, TSAI CHUN DAR, WESTFALL SCOTT, SASAKI, TAKUYA, SOCIETE DES PRODUITS NESTLE S.A., TSAI, CHUN-DAR, WESTFALL, SCOTT
Application year: 1996
Main classification: A23F5
IPC codes: A23F5, B01D53