This invention relates to a process for pre-wetting coffee grounds prior to extraction of soluble coffee solids from the grounds. Soluble coffee products are in general produced by roasting coffee beans, grinding the roasted beans, extracting soluble coffee solids from the ground coffee, and then drying the soluble coffee solids so extracted. Extraction ofthe soluble coffee solids from the ground coffee usually takes place in a counter¬ current extraction system made up of several colurnns or extraction cells. Hot water is introduced into one end ofthe system and flows from one column or cell to the next; contacting fresher coffee grounds in each succeeding column or cell. The last column or cell reached is that containing fresh ground coffee. Instead of columns and cells, some extraction systems use counter-current extractors in which the coffee grounds are transported in one direction by a screw while the water flows in the opposite directions.

In all ofthe extraction systems used, it has been postulated that there are advantages in wetting the fresh ground coffee which enters the system. There are many reasons for this; namely wetting is found to improve flavor, reduce the channelling of fines during extraction and in general improve extraction efficiency. One cause of a reduction of extraction efficiency may be attributed to foaming in the extraction system. The ground coffee particles contain absorbed gases and these are to some extent released upon contact with hot extraction liquid: causing foaming. The foaming in the extraction apparatus reduces contact between the extraction liquid and the coffee particles. Also coffee particles are often trapped at the top ofthe extraction apparatus in the foams. These effects contribute to extraction inefficiency. However, if the coffee particles are uniformly wet prior to contact with the extraction liquid, foaming is much reduced.

Unfortunately, uniform pre-wetting ofthe ground coffee is difficult to achieve. However, unless the coffee grounds are uniformly pre-wet, problems arise; in particular pressure drops across the extraction apparatus due to clogging may increase and irregular flow distribution may occur.

One attempt to overcome the problem is disclosed in International patent application WO 94/26126. This patent application describes a process in which an aqueous liquid is introduced into the base of a treatment tank and is discharged from the treatment tank adjacent the top of the treatment tank. Roast and ground

coffee particles are introduced into the treatment tank on the surface ofthe aqueous liquid. An auger draws the coffee particles below the surface to form a bed of coffee particles in the treatment tank. A mechanism is provided to counter-rotate the bed to facilitate the escape of gases from the coffee particles. The coffee particles are drawn off from adjacent the base ofthe treatment tank while the aqueous liquid leaving the treatment tank is collected as a coffee extract. The pre-wetted and semi-extracted coffee particles may then be fed to a conventional extraction system. This process operates adequately but the apparatus needed is large and complicated. It is therefore an objective of this invention to provide a relatively simple process for uniformly pre-wetting coffee grounds.

Accordingly, this invention provides a process for pre-wetting ground coffee particles, the process comprising: introducing the ground coffee particles into an elongated mixing zone; mechanically agitating the ground coffee particles in the elongated mixing zone while transporting the ground coffee particles through the elongated mixing zone; introducing an aqueous fluid into the elongated mixing zone to wet the ground coffee particles as the ground coffee particles are agitated and transported through the elongated mixing zone for causing gases to be released from the ground coffee particles; and removing the released gases from the elongated mixing zone. Surprisingly, the process permits ground coffee to be wet uniformly using relatively low ratios of aqueous fluid to ground coffee while achieving excellent levels of gas release from the ground coffee. It is believed that the mechanical agitation of the coffee ground particles softens the matrix structure ofthe particles and this promotes ingress ofthe aqueous fluid and release of the gases. Also, due to the agitation, the particles are continually raised out of any pools of aqueous fluid which may form. This reduces release ofthe gases into pools of aqueous fluid; in turn reducing foaming.

Preferably the ground coffee and the aqueous fluid are introduced into the elongated mixing zone in a mass ratio of about 1 :5 to about 5: 1 ; especially about 1 :2 to about 2:1 ; and more preferably in a mass ratio of ground coffee:aqueous fluid of about 1 : 1.5 to about 2:1. Particularly suitable is a mass ratio of ground coffee to aqueous fluid of about 1 : 1. The moisture content of the ground coffee is preferably increased to a level of about 15 % to about 60% by weight during

the process; especially about 40% to about 60% by weight. The aqueous fluid is preferably water or coffee extract but may also be steam or a mixture of steam and water or coffee extract.

The mechanical agitation ofthe ground coffee preferably causes the ground coffee particles to travel in directions substantially perpendicular to the overall direction of transport through the elongated mixing zone. To achieve this, the ground coffee may be mechanically agitated by rotating one or more shafts in the elongated mixing zone; each shaft having a plurality of beating elements projecting from the shaft to agitate and transport the ground coffee. Preferably two shafts are rotated in the elongated mixing zone; one shaft rotating faster than the other. The elongated mixing zone may comprise two elongated mixing chambers which are in fluid communication along their length; one shaft rotating in one mixing chamber and the other shaft rotating in the other mixing chamber. Preferably the mixing chamber containing the shaft which rotates at a slower speed has a diameter larger than that ofthe other mixing chamber.

Preferably the released gases are removed from the elongated mixing zone by sweeping a carrier gas through the elongated mixing zone. The carrier gas is preferably an inert gas; for example nitrogen.

Preferably the aqueous fluid is heated to a temperature of about 50°C to about 120°C prior to being introduced into the elongated mixing zone. More preferably the temperature ofthe aqueous fluid is about 70°C to about 90°C.

The mean residence time ofthe ground coffee particles in the elongated mixing zone is preferably in the range of 30 seconds to about 4 minutes.

In another aspect, this invention provides homogenously wetted, ground coffee produced by the process defined above.

Embodiments of the invention are now described, by way of example only, with reference to the drawings in which:

Figure 1 is a schematic cross-section of an apparatus for pre-wetting coffee grounds; and Figure 2 is a cross-section of line AA' of figure 1.

Referring to figures 1 and 2, ground coffee is introduced into a feed hopper 2. A screw feeder 4 transports the ground coffee from the bottom ofthe feed hopper 2 to the top of a vertical feed column 6. The lower end ofthe vertical feed column 6 is connected to an upwardly-opening solids inlet 30 of a preconditioner 8. Hence the ground coffee falls down the vertical feed column 6 and into the preconditioner 8. The preconditioner 8 comprises an elongated

conditioning vessel 10 defining a first frustocylindrical mixing chamber 12 and a second frustocylindrical mixing chamber 14. The first and second mixing chambers 12, 14 are in communication with one another along the length ofthe elongated conditioning vessel 10. The second mixing chamber 14 has a diameter which is larger than the diameter of the first mixing chamber 12. The solids inlet 30 is positioned at the upstream end ofthe preconditioner 8 while a downwardly- opening solids exit 32 is positioned at the opposite, downstream end ofthe preconditioner 8.

A first mixing shaft 16 extends along the longitudinal axis ofthe first mixing chamber 12 and supports several beating elements 18 which project radially from the first mixing shaft 16. The beating elements 18 are spaced from one another along the length ofthe first mixing shaft 16 and about the circumference of the first mixing shaft 16. Each beating element 18 has an elongated blade portion 20 which extends to just short ofthe inner surface 22 of the first mixing chamber 12. Each elongated blade portion 20 is inclined so that it advances the ground coffee along the elongated conditioning vessel 10 as the first mixing shaft 16 is rotated.

A second mixing shaft 24 extends along the longitudinal axis ofthe second mixing chamber 14 and supports several paddles 26 which project radially from the second mixing shaft 24. The paddles are spaced from one another along the length of the second mixing shaft 24 and about the circumference ofthe second mixing shaft 24. Each paddle has a large flat portion 28 at its tip which is inclined so that it advances the ground coffee along the elongated conditioning vessel 10 as the second mixing shaft 24 is rotated. Each mixing shaft 16, 24 is connected to a drive (not shown) to rotate the shafts. Preferably, the first mixing shaft 16 is rotated at a speed greater than the speed of the second mixing shaft 24. Also, the first mixing shaft 16 preferably rotates in a direction opposite to that ofthe second mixing shaft 24.

A liquid inlet 34 to the elongated conditioning vessel 10 is positioned a small distance downstream from the solids inlet 30 and above the mixing shafts 16, 24. More than one liquid inlet 34 may be provided and the inlets 34 may be spaced along the length ofthe elongated conditioning vessel 10. An aqueous liquid feed line 36 is connected to the liquid inlet 34. Gas inlets 38 for steam may be provided along the length of the elongated conditioning vessel 10 beneath the mixing shafts 16, 24. The gas inlets 38 are connected to a steam supply line

Further details ofthe construction ofthe preconditioner 8 may be obtained from US patent 4,752.139; the disclosure of which is incoφorated by reference. The preconditioner 8 is commercially available and may be purchased from Wenger Manufacturing, Inc. of Sabetha, Kansas, USA. Upon entering the preconditioner 8, the coffee particles making up the ground coffee are immediately subjected to the action ofthe rotating beating elements 18 and paddles 26. The beating elements 18 and paddles 26 cause the coffee particles to move in a general direction towards the solids outlet 32. The rotation ofthe beating elements 18 and paddles 26 also causes the coffee particles to move from one mixing chamber 12, 14 to the other mixing chamber 12,14; and back again. Hence, due to the agitation, the coffee particles are also transported in directions substantially perpendicular to the overall direction of transport through the preconditioner 8; causing the particles to be continuously raised and lowered. The particles in the first mixing chamber 12 are subjected to relatively severe beating and mixing while those in the second mixing chamber 14 are subjected to much less beating and mixing but have a longer residence time in the mixing chamber 14.

While the coffee particles are being subjected to the action ofthe beating elements 18 and paddles 26, aqueous liquid (usually in the form of water or coffee extract) is sprayed onto the coffee particles through the liquid inlets 34. If desired, steam at pressures of about 101 kPa (0 psig) to about 170 kPa (10 psig) may be introduced into the preconditioner 8 through gas inlets 38 to supplement the aqueous liquid. In this case, the mass flow rate of steam is suitably 5 to 10 times less than the mass flow rate ofthe ground coffee into the preconditioner 8. Alternatively, sufficient steam may be introduced into the the preconditioner 8 to totally replace the aqueous liquid.

The aqueous fluid may be at any desired temperature; especially in the range of about 20°C to about 120°C. It is found, however, that better results can be obtained if the temperature is above about 50°C; for example from about 70°C to about 90°C. The ratio of ground coffee to aqueous fluid fed into the preconditioner 8 is suitably in the range of about 1 :5 to about 5: 1, more preferably about 1 :2 to about 2:1 ; with about 1 : 1 being particularly suitable. One advantage of the preconditioner 8 illustrated in Figures 1 and 2 is that very small amounts of aqueous fluid may be uniformly distributed throughout the ground coffee. However the preconditioner 8 is also able to adequately process slurries having large amounts of aqueous fluid. This provides excellent flexibility.

Due to the action ofthe beating elements 18 and paddles 26, the ground coffee and the aqueous fluid are well mixed. Also, due to the beating or striking action ofthe beating elements 18 and the paddles 26, the matrix structure of the coffee particles appears to soften; facilitating release of trapped gases and ingress ofthe aqueous fluid. As the aqueous fluid enters the softened matrix structure of the coffee particles, the coffee particles swell. Further, due to the transport ofthe coffee particles in directions substantially perpendicular to the overall direction of transport, the coffee particles are constantly raised out of any pools of aqueous fluid which may form in the preconditioner 8. Hence the trapped gases are in general not released into pools of aqueous fluid and foaming is reduced. This is a substantial advantage.

The gases evolved from the coffee particles may be removed by sweeping a carrier gas through the system or by drawing them off using vacuum. To achieve this, the preconditioner 8 may be provided with a gas outlet (not shown) adjacent the solids outlet 32. Alternatively, the gases may be removed through the solids outlet 32 and separated from the pre-wetted coffee particles at some point downstream from the preconditioner 8. Preferably, the gases are removed by introducing a sweeping gas into the feed hopper 2 or the vertical feed column 6 which then sweeps through the preconditioner 8. The gas used as the sweeping gas may be any suitable gas which is sufficiently inert that it does not degrade the coffee or coffee aromas. Nitrogen gas is particularly suitable although gases such as helium, carbon dioxide, etc may also be used.

The wet coffee particles which are transported to the solids outlet 32 fall through the solids outlet 32, from where they may be transferred to an extraction system. At flow rate ratios of aqueous fluid to ground coffee of about 1 :1 or less, the wet coffee particles contain very little or no free fluid. Therefore the coffee particles may be transferred directly to the extraction system without an intermediate solids-liquid separation step. Samples of the wet coffee particles are found to release little or no gas in gas-release tests; indicating that most gases were released in the preconditioner 8 and that the wet coffee particles retain very little gas.

The mean residence time ofthe ground coffee particles in the elongated mixing zone is sufficient to achieve uniform wetting of the coffee particles; for example in the range of 30 seconds to about 4 minutes. Although longer times are acceptable, they are not neccessary and provide no advantage. For a given volume ofthe elongated mixing zone, the mean residence time may be selected

by appropriately altering the rate at which the ground coffee particles are introduced into the elongated mixing zone. Also, the mean residence time may be adjusted by suitably adjusting the blades ofthe beating elements 18 and paddles 26, the angle of inclination ofthe preconditioner 8. and the like. When the wet coffee particles are used in the extraction system, foaming in the extraction system is also found to be decreased. Also, no undue clogging, channelling or pressure drop increases occur in the extraction system.

Although the process was described with reference to a particular apparatus in which the ground coffee is pre-wetted, the process is not limited to such an apparatus. This apparatus is merely preferred. For example, it is not necessary for the elongated conditioning vessel 10 to have mixing chambers of different diameters; instead the chambers may have the same diameter with the mixing shafts and paddles being ofthe same size. Further, the mixing shafts may rotate at the same speed. Also it is not necessary to have two mixing chambers; one mixing chamber would be adequate. Similarly the apparatus need not have two mixing shafts; one mixing shaft or more than two mixing shafts would operate adequately. It is also not essential to have the number and arrangement of beating elements 18 and paddles 26 illustrated in figures 1 and 2. What is required, however, is an apparatus which includes beating elements which are able to agitate the coffee particles while transporting them. It is the agitating action which assists in release ofthe trapped gases from the coffee particles and which is essential. Other suitable apparatus may be obtained from Wenger Manufacturing, Inc.; Extru-tech Inc. (of Sabetha, Kansas. USA) and the like.

Example 1

A batch of about 550 kg of roasted and ground coffee is placed in a feed hopper. The average particle size ofthe ground coffee is about 2 mm. A sample ofthe ground coffee is taken and labelled sample A. The ground coffee is fed to a Wenger 7DDC preconditioner (obtained from Wenger Manufacturing, Inc. of Sabetha, Kansas, USA) at a rate of about 2.3 kg/minute (5 lb/minute). The diameter ofthe smaller mixing chamber ofthe preconditioner is about 0.25 m (10 inches) while that ofthe larger mixing chamber is about 0.35 m (14 inches). The mixing shaft in the smaller mixing chamber is rotated at 350 φm while that in the larger mixing chamber is rotated at 170 φm.

A coffee extract containing about 11 % by weight of soluble coffee solids is sprayed into the preconditioner at a rate of about 2.3 kg/minute (5 lb/minute) through three nozzles. The temperature ofthe coffee extract is about 82°C ( 180°F). Nitrogen gas is swept through the preconditioner to remove evolved coffee gases.

The coffee particles leaving the preconditioner are uniformly wet and sticky but with almost no liquid visible. The particles appear swollen. A sample ofthe ground coffee is taken and labelled sample B. Sample A and sample B are analyzed for moisture and sample A is found to have about 1% moisture by weight while sample B has about 41% moisture by weight. This indicates that adequate wetting is achieved.

The wet coffee particles leaving the preconditioner are fed into an extraction cell of an extraction system having 6 extraction cells. Hot extraction water at about 180°C is fed into the extraction system and flows from one cell to another; reaching the cell with the wet coffee last. Very little foaming is observed in the extraction cell. The extraction yield is about the same as if ground coffee which had not been pre-wetted is used.

Upon completion ofthe extraction cycle, the extraction cell which contains the freshest coffee grounds is opened. Five samples of coffee grounds are taken from various points in the extraction cell. The samples are then analyzed for the amount of extractable coffee solids which still remained in the coffee particles. By comparing the amounts of extractable coffee solids remaining, a measure of the extraction uniformity can be obtained.

An extraction cell containing fresh coffee grounds which had not been pre- wetted is then connected to the extraction system. The extraction cell containing the most expended coffee grounds is removed from the extraction system. The extraction cycle is repeated and the extraction cell which contains the freshest coffee grounds is opened and five samples are taken at substantially the same points as previously. The samples are analyzed for the amount of extractable coffee solids remaining. The results are presented in table 1 :

Table 1 : Extraction Uniformity

Sample Extractable coffee solids % Extractable coffee solids % Pre-wetted Ground Coffee Dry Ground Coffee

1 17.6 21.9

2 18.4 16.2

3 19.5 30.0

4 17.0 35.4

5 15.6 13.4

The results indicate that pre-wetting ofthe ground coffee greatly improves extraction uniformity; a very significant advantage. Also, extraction efficiency of the first cell is improved.

Example 2

Example 1 is repeated except that the ground coffee is fed into the preconditioner at a rate of 4.5 kg/minute. Water at 85°C is fed into the preconditioner at one of fiverates; about 6.8 kg/minute (15 lb/minute), about 4.5 kg/minute (10 lb/minute), about 3.2 kg/minute (7 lb/minute), about 2.3 kg/minute (5 lb/minute) and about 1.7 kg/minute (3.7 lb/minute). No steam is introduced into the preconditioner in each case.

Water Flow Rate Wet Coffee kg/minute Appearance

6.8 sticky - up to 4% free liquid - swollen

4.5 sticky - almost no free liquid - swollen

3.2 moist - no free liquid - swollen

2.3 moist - no free liquid - swollen

1.7 dry to touch - no free liquid

Again excellent and uniform wetting is obtained.

Example 3

Example 1 is repeated. Coffee sample A (taken prior to entry into the preconditioner) and coffee sample B (taken upon leaving ofthe preconditioner) are analyzed for gas release. Fresh, dry ground coffee contains significant amounts of gases while completely wetted ground coffee contains no gas. Hence a determination ofthe gas release over time provides an indication ofthe degree of wetting.

The samples are analyzed by placing 100 g ofthe ground coffee in a flask and the flask sealed. 200 g of water at 82°C is added from above through an inlet. Gas released from the ground coffee is conducted to an inverted cylinder and the volume of gas released is determined as the displaced volume in the cylinder. The amount of gas released from the each sample over time is given in table 1 :

Table 1 : Gas release over time

Time Gas Release - Sample Gas Release - Sample B minutes A ml g ml/g

0.5 0.45 0

1 1.05 0

1.5 1.3 0

2 1.7 0

3 2.1 0

4 2.35 0

5 2.56 0

6 2.65 0

7 2.81 0

10 2.98 0

15 3.1 0

The results indicate excellent removal of gases from the ground coffee.

Example 4

The procedure of example 1 is repeated except that water at 34°C is used. The wet coffee obtained is acceptable but more free liquid is observed than in example 1. Also the particles are not as soft and swollen as the particles of example 1. However the particles are uniformly wet.

Example 5

Example 2 is repeated except that steam, at pressures of about 101 to 170 kPa, is injected into the preconditioner in place ofthe water. For injecting the steam, a series of steam nozzles located along the bottom ofthe preconditioner are used. The temperature ofthe ground coffee entering the preconditioner is about 20°C.

The ground coffee leaving the preconditioner has a temperature of about 90°C, is very dry to the touch, and has a moisture content of 20%. Again excellent and uniform wetting is obtained.