Abstract:
A process for producing an agglomerated instant coffee product having a roasted and ground appearance comprising; 
     a. milling spray-dried instant coffee to produce a milled powder of an average particle size of 30 to 75 microns; 
     b. adding oil to the powder so that it will bind together with slight compaction; 
     c. forming a regular shaped, loosely bound, structurally intact clusters from the powder with oil added, said cluster have a size of 800 to 2100 microns; 
     d. fusing the outer surface of the cluster to a depth of from 5 to 30 microns; and 
     e. drying and screening the fused clusters to produce an agglomerated instant coffee having a density of from 0.20 to 0.28 gms/cc, a hardness value of less than 8, a color of 17 to 24 Lumetron units and an average agglomerate size of from 800 to 1,300 microns. 
     When this process is employed, an agglomerate instant coffee is produced at commercially acceptable rates which has a dark color, a fused surface and a size giving the appearance of roasted and ground coffee. Furthermore, the product has a light density yielding about one cup of coffee per teaspoon of instant coffee.

Description:
TECHNICAL FIELD 
     This invention relates to a novel process for agglomerating an instant soluble coffee to achieve a final agglomerated product which has the appearance of roast and ground coffee. 
     BACKGROUND ART 
     Since agglomeration was first introduced, there have been many attempts to produce an agglomerated coffee product which has a roast and ground appearance. Such an appearance would have a beneficial impact on the consumer who equates the appearance of roast and ground coffee with the taste and quality of freshly brewed coffee. The product must, however, satisfy other criteria to be acceptable to the consumer. For example the product must have sufficient bulk density to produce about one cup of coffee per teaspoon of product. If the product is too dense, then too strong a cup of coffee will result and if the product is not dense enough the coffee will be too weak. The product must also possess sufficient structural strength so as not to produce a large number of fines and the product must have a dark pleasing look and suitably will have a vari-colored appearance. Furthermore, the product must be rapidly soluble without producing foam and the product should be of about the same size distribution of roasted and ground coffee. In addition, for the product to be commercially feasible, the product must be capable of being prepared at commercially acceptable rates. 
     An effort directed to agglomerating instant coffee is U.S. Pat. No. 2,977,203 issued to Sienkiewicz et al. entitled &#34;Agglomerating Process&#34; which is typical of the early teachings in the soluble coffee agglomeration field. The patent describes an agglomerating procedure whereby a plane of discretely arranged powder particles which are moving in a first direction preferably in the form of a falling curtain are contacted by a jet of steam, thereby redirecting the particles. As the particles in the curtain enter the path of the jet of steam, they immediately become wetted. By being directed in the path of the jet of steam, they are caused to contact one another. The opportunity for contact or collision results in a greater percentage of agglomeration. The turbulence created by the jet of steam allows a maximal opportunity for collision or contact of the wetted particles. U.S. Pat. No. 3,554,760 to Sienkiewicz et al. is an improvement of the above-described patent involving the use of upper and lower jets of steam which impinge against the falling curtain of powder. The upper jets of steam form agglomerates of varying size, density, and moisture content; the lower jets act to further wet the agglomerates and render them more uniform in density, size, and moisture content. This process, however, produces an irregular, jumbled agglomerate mass which does not have the surface appearance of roasted and ground coffee. 
     On the other hand, U.S. Pat. No. 3,716,373 issued to Rhodes et al. teaches a process for producing an instant coffee composition in the form of a free-flowing soluble agglomerated powder which comprises milling soluble coffee particles and forming clusters therefrom by feeding the milled particles into a vibrating distributor box. A sufficient depth of milled particles are maintained in the box, such that the particles are substantially compacted and form the desired clusters on release from the box. The resulting clusters are fed into a zone where they are moistened and heated thereby forming an agglomerated granular powder which is then dried; agglomerated powders having a bulk density of from 0.25 to 0.40 grams per cc and a color of from 28 to 40 Lumetron Units are then produced. Thus, this product is dense and relatively light in color. 
     British Patent No. 1,276,437 in the name of Rhodes and Clark teaches an improvement in this above-identified process; the agglomerate produced by this improved process can have a lower bulk density range if the feed material, likewise, has a lower density than the normal spray-dried coffee powder which was used in the process described in U.S. Pat. No. 3,716,373. The British patent to Rhodes et al. talks of drying a foamy product to produce a feed material which has a bulk density before milling of 0.05 to 0.18 grams per cc at a residual moisture content of from 2 to 7% by weight; the agglomerate is said to have a bulk density of from 0.22 to 0.34 grams per cc, a color of from 28 to 50 Lumetron Units and a hardness less than 10. This product is thus light in color. 
     Still another process is that set forth in the British Patent No. 2,006,603 issued to Morgan et al. teaching a coffee product consisting of free-flowing agglomerates which comprise soluble coffee particles and finely ground roasted coffee, the finely ground roasted coffee being present in an amount of from 2 to 20% by weight. A product with a roasted and ground appearance is not described. 
     While the coffee art is thus replete with numerous examples of ways to agglomerate coffee products, there is still a need for a process of producing an agglomerated instant coffee which will result in a product possessing a truly roast and ground coffee appearance while at the same time having an acceptable density, be sufficiently strong, have suitable dark color appearance, and be produceable at commercially acceptable rates. 
     SUMMARY OF THE INVENTION 
     This invention relates to a process for preparing an agglomerated instant coffee product having a roasted and ground appearance. Spray-dried instant coffee is milled to produce a powder of an average particle size of 30 to 75 microns with a standard deviation of from 35% to 75%. From 0.01 to 1.0 weight percent oil is added to the powder before or after milling. Next the powder with oil added is formed into regular shaped, loosly bound, structurally intact clusters. The clusters have a size of from 800 to 2100 microns. The outer surface of the clusters are fused to a depth of from 5 to 30 microns and the clusters are then dried and screened to produce an agglomerated instant coffee product having a density of from about 0.20 to 0.28 gms/ cc, a hardness value of less than 8, a color of 17  to 24 Lumetron units and an average agglomerate size of from 800 to 1,300 microns. 
     When this process is employed, an agglomerate instant coffee is produced at commercially acceptable rates which has a dark and varied color, a fused surface and a size giving the appearance of roasted and ground coffee. Furthermore, the product has a light density yielding about one cup of coffee per teaspoon of instant coffee and is rapidly soluble in water. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In order to achieve an agglomerate with the proper product attributes, spray-dried instant coffee is milled to an average particle size of from about 30 to about 75 microns and preferably 35 to 45 microns with a standard deviation of 35% to 75%. The mill used preferably should be combined with an air classifier which will produce size particles with a minimum degree of variation from this desired micron size. The air classified powder will have a size standard deviation of 35% to 55% and preferably 40% to 50%. The spray-dried product is produced from extracts of 20 to 65% soluble solids. Spray-dried product resulting from lower concentration of extracts are generally hollow spheres having a diameter of about 150 to 300 microns with a wall thickness of about 4 to 30 microns. When these spheres are milled, they produce platelet shaped particles. Spray-dried material produced from higher extract concentrations generally yield porous irregular shaped particles. The size of these particles are about 60 to 110 microns. When these irregular shaped particles are milled they produce cubical shaped particles. Cubical particles tend to form less dense clusters. 
     After milling, the powder may be cooled to a temperature of from 40° to 70° F. Cooling aids in producing a darker final product. An example of equipment which will accomplish this cooling is a Rotex brand cooler. With this equipment the powder is channeled through the unit and is indirectly cooled by a circulating liquid medium which may be water or preferably propylene glycol. Other means for cooling the powder will be readily apparent to those skilled in the art. 
     Up to 40 percent by weight of unmilled spherical soluble coffee material may be added to the milled material. The unmilled spherical coffee materials include unmilled, spray-dried instant coffee (reseed). These unmilled powders have a size range of from about 5 to 280 microns but preferably are from about 25 to 65 microns. 
     It has been found that the of the milled and classified powder do not form clusters with suitable properties to yield the product of the instant invention at commercially acceptable rates. The powder requires too much compaction to form structurally intact, loosely packet clusters. Hence, the ultimate product will be too dense or will lack proper color or adequate strength. 
     According to the present invention oil is added to the coffee powder. The oil may be any suitable oil or lipid capable of coating the powder such as coffee oils, vegetable oils and the like. The amount of oil added should be in the range of about 0.01 to about 1.0 weight percent and preferably in the range from 0.05 to 0.1 weight percent based on the weight of the powder. The oil may be added to the powder in a variety of ways, such as mixing with or spraying onto the spray dried coffee before or after milling. Preferrably the oil is added prior to milling so that it becomes thoroughly mixed with the powder. 
     When oil is added to the powder, the powder will form a loosely packed cluster which holds together during further processing. Thus, a cluster may be formed which will ultimately result in a product having a proper density with suitable color and friability. Furthermore, it will be possible to process these clusters at high commercial rates. Suitable commercial rates are at least 400 pounds per hour, preferably at least 800 pounds per hour and more preferably at least 1,000 pounds per hour. 
     After the oil has been added to the powder it must be formed into clusters. Lower density clusters may be achieved employing larger size milled powder but more oil is necessary to bind the longer particles. Furthermore, it is desired to produce clusters having a regular shape. By regular shape it is meant substantially cubical, spherical or similarly shaped. Clusters may be formed by compaction which may be achieved by subjecting the powder to vibration. A vibratory trough or a vertical bin which vibrates can be used to produce the necessary forces for compaction. It is desired to concentrate the powder flow through the vibrators in order to avoid problems associated with transmitting vibration over long distances. Suitable the powder will flow through the vibrator at the rate of 25 lbs per minute per inch of vibrator feed port opening preferably at the rate 75 lbs per minute per inch. Increasing vibration forces effect an increase in compaction. Too much compaction yields a cluster well formed but very dense, while too little compaction will not allow the particle to only hold together during processing. Since it is desired to make a product of low density, it is preferred to only operate at minimum compaction energy necessary to keep the powder together. A proper amount of added oil allows the use of minimum compaction energy. Uniformity of the clusters is enhanced by passing the clusters through a vibratory formation screen. This screen produces uniformly sized clusters and smooths out the edges of the clusters. The screen size, amplitude of vibration, mesh size and wire diameter must be carefully matched to the throughput and cohesiveness of the powder to prevent breaking of the fragile clusters. Preferably the screen will vary from 6 to 12 mesh. 
     Furthermore, the screen will control the size of the clusters which suitably will range from about 800 to 2100 microns and preferably from about 900 to 1900 microns. The bulk density of the formed clusters will suitably be from about 0.5 to 0.9 gm/cc and preferably from 0.6 to 0.8 gm/cc. 
     Once the clusters are formed, it is necessary to fuse the surface of the clusters to produce the desired color and appearance and to minimize breakage during handling. Steam may be used to melt a thin film of the cluster surface which upon drying forms a strong crust. The crust thickness ranges from 5 to 30 microns and preferably from 10 to 15 microns. Furthermore, the amount of steam used will affect the color and density of the particle form. Using more steam results in a darker color and stronger product but a smaller and denser product. 
     The clusters are contacted with steam in a free-fall condition. The free-falling clusters may be in single curtain pattern or multiple parallel curtain patterns. When three parallel curtain patterns are employed it has been found that the rates may be greatly increased with little increase in steam usage. The steam for agglomeration can be either saturated or superheated. The relative quantity of steam used simply must be sufficient to form the aforesaid crust only. Steam velocity should be such that it is insufficient to break the clusters once they are formed, and yet the amount of steam present must be sufficient to partially liquify the exterior surface of the clusters without penetrating the interior core thereof. Suitable steam velocities are less than 50 ft/sec and preferably less than 40 ft/sec. Steam contact will produce an agglomerate wherein the exterior of the cluster is hardened and is of a darker color than the interior, the interior being of approximately the same color as the feed stock material undergoing clustering. Suitably the steam to powder ratio will vary from approximately 2:1 to 12:1. 
     After contact with the steam, the fused clusters are dried in an atmosphere which minimizes possible cluster-to-cluster agglomeration. Such drying is suitably practiced in the lower section of a tower while the agglomerates are still in free-fall. A dryer air temperature (inlet) above 200° F. and below 450° F. will be common, typically 290°-400° F. inlet and an outlet temperature in the order of 200° F. Eventually, this material will further dry and cool by passing from the tower onto a vibrating trough at the discharge from the tower, as is well-known in the art. 
     After drying the agglomerates may be screened to remove undersized and oversized particles. The average size of the agglomerates of the present invention range from 800 to 1300 microns and preferably from 1,000 to 1,150 microns. Furthermore, the fused agglomerates will have a bulk density of from 0.20 to 0.28 grams per cc. and preferably from 0.22 to 0.26 grams per cc. and are rapidly soluble in water. Up to 60% of the agglomerates may be undersized or oversized material which may be fed to the feedstock material to the mill and co-milled with the spray-dried powder. 
     Approximately 5% of the agglomerate surface, will be lighter colored than the remainder resulting in a varied color or speckled appearance. This product speckling is due to the presence of some minor amounts of broken agglomerates formed by attrition throughout the process after steam agglomeration. As previously stated, the interior core of the agglomerate maintains its lighter color. Thus, an overall speckling will be produced because of the contrast of the darker particles represented by the fused outer crust and the lighter material representative of those agglomerates which are fractured. 
     As indicated previously, the agglomerate will possess a hardened value of less than eight, i.e. less than 8% fine produced during measurement. A hardness value of under eight would correlate to an agglomerate possessing a good mechanical strength both in the jar and during use by the consumer. Hardness value is arrived at by the following simple tests set forth in the aforesaid Rhodes patent; 100 grams of sample to be tested is first gently screened to remove fine particles below 36 mesh. The samples are then subjected to more intense vibration using a further screening for a standard time of five minutes, and a sieve analysis is carried out to determine the amount which passes through the 36 mesh sieve. The comparative hardness of the granule, which gives a measure of a particle mechanical strength is expressed as the percentage by weight which passed through the 36 mesh sieve in the second screening. As product hardness increases the hardness value decreases. A hardness value of 10 or more is considered to be unsatisfactory for subsequent handling and packaging operations. Products made by the process of the present invention have comparative hardness value generally of less than 8. Preferably the products made by the present invention will have a hardness value less than four. 
     The agglomerates of the present invention have a dark appearance which ranges from 17 to 24 Lumetron units. The color of the coffee composition is herein quantified in so-called Lumetron units which are a measure of the reflectance color of the agglomerated powder from a tristimulus light source. For this purpose, the powder is placed in a small flat dish and measurements are taken by a Photovolt Reflection meter manufactured by the Photovolt Corporation of New York and used as described in their brochure for Model 575, a Reflecting and Gloss meter. For the purposes of interpreting the figures quoted herein, commercial roasted and ground coffee powders normally available in the United States have a Lumetron value of from 45 to 70 units (light colors), whereas expresso type coffees have a Lumetron value of 20 to 30 units (dark colors) at similar particle sizes. 
     The following example is presented to further illustrate this invention. 
    
    
     EXAMPLE I 
     An agglomerated instant coffee of the desired form was made by the following process. Spray dried powder having a moisture content of about 3.0% was obtained by spray drying coffee extract containing about 55% solids. Four hundred pounds per hour of powder was then fed to a 12&#34;×20&#34; horizontal vibrating trough manufactured by Eriez Magnetics Corporation. As the powder flowed over the trough, 0.075% by weight coffee oil was sprayed onto the powder using a 1/4 J air atomizing nozzle manufactured by Spraying Systems Co. The oil coated powder was then milled utilizing a model 10 ACM Mikro Pulverizer manufactured by the Pulverizing Machinery Division of the Mikropul Corporation. The powder was milled to a particle size of 40 micron with a variation from the mean of 53.6%. 
     The powder was then transported to a Siletta® feeder, manufactured by Solids Flow Control Corporation. The feeder used was a vertical bin which had a cylindrical top section and a conical bottom section. Suspended from the bottom of the bin was a 6&#34; by 6&#34; tray with 3 vanes positioned 33° above the horizontal. Flow through the tray was induced by an Eriez vibrator attached to the side of the tray housing. Horizontal vibrations effecting displacement of 0.02&#34; at 60 cycles per second provided powder compaction within the bin, and also powder flow from the bin. Three distinct curtains of powder at flow rates of about 500 pounds per hour were obtained from the feeder (the 500 pph was made up of the feed stream plus a recycle stream). A powder head within the bin of about 1 foot was used. 
     The falling clusters of powder then passed through an 8 mesh-0.028&#34; (wire diameter) vibrating screen positioned horizontally which served to size the clusters. The screen was vibrated at a displacement of 0.03&#34; at 60 cycles pwer second. The screen was positioned approximately 1/2 inch below the 3  slot tray and vibrated perpendicularly to the curtains of powder. 
     The falling curtains of uniform clusters were then contacted with steam directed from three nozzles. The first two nozzles utilized low velocity steam at 2 psi and 4 psi respectively, to wet only the surface layer of the particles. This enabled a crust to form around the particles. The third nozzle used high velocity steam to project the particles into a drying tower. The high velocity steam did not have sufficient turbulence to break the crust. A total steam to powder ration of 3/1 was used. 
     The wet powder was subsequently dried within a tower. Tower conditions included an air flow of 2100 CFM, an inlet air temperature of 400° F. and an outlet air temperature of 220° F. 
     After drying, the powder was screened with a 6 mesh - 0.035&#34; wire diameter screen to remove oversize particles and a 14 mesh -0.032&#34; wire diameter screen to remove the undersized particles. The final product had a density of 0.27 g/cc, a moisture of 3.7%, a color of 22.0 Lumetron units, a hardness of 3 and a roasted and ground appearance.