Method of Dutching Cocoa

The present invention relates to the treatment of cocoa, and more particularly, to an improved method and system for dutching of cocoa for attaining a rich color, improved flavoring and other favorable parameters.

Heretofore, the process of dutching of cocoa has been a relatively long and expensive proposition. Basically, the same batch process wherein the cocoa is treated in large cooking vats has been used for at least 100 years without significant improvement. In most prior art processes, after roasting the beans and removing the husk or shell, the broken pieces of the beans, commonly referred to as the nibs, are crushed or ground to break the cells and form a smooth, creamy paste, known as chocolate liquor. Next the liquor is fed a hydraulic press whereby with the proper timing, temperature and moisture control and removal of a portion of the fat or cocoa butter, a press cake is formed. Typically, the press cake is next broken up and mixed with an alkalizing solution in the batch pressure cooker. The cooker then converts to a vacuum dryer to reduce the moisture content in the batch. The contents of the vat are then deposited in drums or other suitable containers for several days and allowed to cool. The cooled mass is then ground to a fine powder that can be used in devil's food cake, chocolate drinks, chocolate ice cream and chocolate cookies.

The standard batch process of the prior art suffers from several shortcomings. First, the conditions of treatment from batch to batch must be rigidly maintained in order to obtain proper moisture, pH, and low microbial flora content and uniformity of flavor and color. By the very nature of the non-continuous process, this has been found to be extermely difficult to do and requires the constant monitoring of people and machines. Secondly, the vat cooking and drying of the batch and the absence of significant mechanical working result in nonuniformity of heating of the cocoa so that parts are scorched and other parts are undercooked, giving a nonuniform product in terms of color and taste. The color obtained in the batch process is not as dark and rich in color with the same amount of alkali that is desired in many commercial products. In addition to requiring additional equipment and people to maintain the proper conditions, the large vats further financially burden the processor since the space required to house the equipment is substantial.

Problems of the prior art batch drying processes have resulted when previous attempts to depart from the above procedure have been made. First the danger of charring has arisen when the drying process has been attempted to be accelerated by employing a higher temperature. The prior processes have not included a necessary volume of working gas to distribute the heat to the end product efficiently and uniformly. The problem of case hardening of the individual cocoa solids is also a nemesis in the prior processes. This arises when the temperature of the product solid rises too rapidly thereby hardening the outer surface of the product. It is caused, in part at least, by not providing suitably small sized product solids, controlled heat, and large volume gas flow. Grinding and regrinding of the hardened solids thus becomes a trying necessity in an attempt to gain a satisfactory product.

In the past, the above overall "batch method" has been attempted to be replaced by a continuous method. Such attempts have, however, been unsuccessful and exemplary of those known in this art is shown by the U.S. Pat. to Walker No. 1,167,959. The failure of the continuous processes has keyed on the inability to find a way to successfully form the mixture of cocoa material and alkaline solution and cook the same and the failure to devise a method for efficiently drying and cooling the cocoa end product in a continuous manner.

A more recent process for preparing dutched cocoa may be found in U.S. Pat. No. 3,754,928, a patent issued on Aug. 28, 1973, or subsequent to the filing of applicant's parent application. This patent discloses a method for dutching cocoa by subjecting an aqueous alkaline solution of cocoa to frictional and compressive forces to rapidly raise its tempeature to 200-300.degree. F. within about 10 seconds and maintaining this temperature for about 45 to 75 seconds prior to cooling. The patent discloses that the frictional and compressive forces may be applied by extrusion of the mixture through a die. The mixture initially contains about 4 to 6 parts by weight of water and after drying contains about 4 parts by weight of water. However, this process requires high temperatures and careful control of temperatures and residence times in passing the mixture through the die as well as intense initial pressurization. Moreover, the low initial moisture content is detrimental to good working of the mixture because 4 to 6 parts of water saturated with alkali is an insufficient amount of liquid to wet out all particles of cocoa subject to frictional and compressive forces. The consequences of incomplete wetting is incomplete chemical reaction and unequal distribution of the alkali used. Therefore, because of this, poor control of production of varieties and intensities of color in the cocoa as well as in the finished product in which the cocoa is the result.

A second recently issued patent, U.S. Pat. No. 3,778,519, teaches that in the impregnation of cocoa seeds with alkali or water and eventual sterilization, requires that the moisture content be kept as low as possible because of subsequent difficulties in drying. The present invention provides a procedure where outstanding results are obtained using high initial moisture contents. Accordingly, the method of the present invention represents improvements in the art of dutching cocoa.

Thus, it is one object of the present invention to provide an improved method of dutching of cocoa that is continuous and results in improved color in an infinite variety of shades and tones and other favorable parameters of the end product.

It is another object of the present invention to gain maximum color using the legal amounts of alkali.

It is another object of the present invention to provide a process for dutching cocoa that is considerably faster, takes up less room in a plant for the processing equipment and is more economical to operate and properly control.

It is another object of the present invention to provide a continuous dutching process that gives uniform cooking of the cocoa without scorching or undercooking the product.

It is still another object of the present invention to provide a continuous dutching process wherein the product is under continuous mechanical working during premixing and cooking.

It is still another object of the present invention to provide a process for dutching cocoa wherein pellets of the finished product are dried and cooled by jet streams impinging on a moving bed to lift and tumble the pellets.

It is still another object of the present invention to produce a finished product that is virtually sterile.

It is still another object of the present invention to fully gelatinize the product so as to produce a better suspension of cocoa when used in cocoa drinks.

According to the present invention, the cocoa material, such as a prepared press cake or nibs, is pulverized while at the same time an aqueous alkaline solution is being prepared in a separate tank. The powdered material and the solution are combined and subjected to vigorous mechanical working to form a homogeneous resultant product mixture. Immediately after this premixing step has been completed, the product mixture is placed in a combination cooker-extruder where it is continuously cooked under pressure and mechanically worked to further obtain uniformity of product. The cooker-extruder is preferably of an auger type wherein the pitch of the auger gradually decreases toward the discharge end to progressively subject the mixture to greater and greater pressure. This compression of the product mass permits efficient extruding through suitable die means positioned directly on the end discharge face of the cooker and to form a product rod that is readily divided into pellet size lengths. Drying of the pellets takes place in accordance with the invention on a fluidized bed by a plurality of jet streams that lift and tumble the pellets in an inert atmosphere.

The premixing of the ground press cake with the alkaline solution enhances the interaction between the molecules within the product mixture to gain the desired color and also leads to a more homogeneous product mixture for reaction in the cooker-extruder to produce a more uniform color and taste. The mechanical working during the cooking step is also of great importance since the molecules of the mixture are constantly being stirred and mixed to prevent scorching and undercooking. Preferably, the cooking is performed in the range of approximately 150-230.degree. F. while the pressure maintained in the final stages of pressurization is between approximately 500-1300 pounds per square inch.

The drying and cooling steps are of substantial importance since it is possible for the first time insofar as I am aware to rapidly dry cocoa product without the previous hazards, such as scorching and degrading the flavor or color, and then drastically cool the product. However, for uses in certain areas the drying step may be omitted and the product used in the form exiting the extruder. The 20-35 percent total moisture content of the material at the entrance to the premixer is reduced to approximately four percent at the end of the drying and cooling steps. The 20-35 percent moisture content has been found to provide an easily workable mixture and one conducible to forming a homogeneous mass and to be particularly suited to causing the rod to be easily broken by acting against a stationary plate as it leaves the die means of the extruder. The 20-30 percent moisture content has also been found to provide a product which has a rich homogeneous color and to provide a product of high sterility. In some cases, notably with the fat content in the range of 10 to 12 percent, the moisture may be reduced to the neighborhood of 27 percent and no plate is needed to effect breaking off to form the pellets. The pellets, being in lengths of approximately 1/4 to 1 inch long and the rod being approximately one-eighth inch in diameter, give excellent drying action. The drying is carried out in an inert atmosphere in the temperature range of 350-450.degree. F. for approximately 2.5 to 3 minutes. The inert atmosphere may be any of the well known inert gases, e.g. nitrogen, argon, etc. as well as any gas which would not react with or affect the product. In the continuous procedure, air which has been burned to consume all the oxygen compounds and thus consists primarily of nitrogen, is suitable. The drastic cooling step lowers the temperature to approximately the ambient temperature in the same length of time.

Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein I have shown and described only the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by me of carrying out my invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modification in various obvious respects, all without departing from the invention.

The steps of the process begin with the grinding of a press cake that has been formed in a press from roasted cocoa beans. While use of a press cake of cocoa is preferred as the starting material, it is obvious that other cocoa forms such as nibs may also be used. However, regardless of the physical form at this stage it is subsequently pulverized and formed into a homogeneous mass. The press cake is then ground in a conventional grinder and pulverized into a coarse, free-flowing powder. Sufficient size reduction is attained that the resultant particles will be easily workable and will pass through the die. A preferred particle size is one in which the particles have a diameter of about one-eighth inch or less. Thus, it should be understood that the particles need only be ground so that they will subsequently pass through the die without plugging the opening. It is usually preferred to effect grinding until the particles will pass through a suitable screen. As to the screen through which the particles are passed, it is preferably of such size to provide particles having a size of about 50 to 150 mesh. The resulting powder is then passed through a magnet grate to remove any small metal particles that may have escaped previous cleaning steps. The ground cocoa material is then stored until mixed with alkali solution. The preferred fat content of the cocoa is about from 0 to 16 weight %.

An aqueous alkaline solution is prepared in accordance with accepted practice using compounds of alkali and alkaline earth metals. A suitable alkali compound, such as sodium hydroxide, sodium carbonate (soda ash), sodium bicarbonate (NaHCO.sub.3), potassium carbonate, potassium hydroxide, potassium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonium hydroxide, ammonia gas, magnesium carbonate, magnesium oxide, and mixtures thereof may be used. The alkaline solution should have a concentration of about 3 to 12 weight percent, and preferably about 5 to 12 weight percent. The solution is well mixed and then diluted as necessary with water. Dilution should be sufficient to provide a maximum of 3% anhydrous K.sub.2 CO.sub.3 or its alkaline equivalent in the final product. With low fat nibs, up to 6 percent alkali can be present. Supplemental colors, sugars, malts or the like may also be added at this stage. The alkaline solution additive is then mixed with the proper proportion of powdered cocoa material and good mixing achieved. At this stage the mixture shoud have a moisture content of about 20-35 weight percent.

The resulting damp mass or mixture is then subjected to continuous mechanical working. Mixing may be effected using one or more rotating shafts with mullers, paddles and ribbons mounted on the shafts for thoroughly mixing the product mixture into a homogeneous state. This is particularly advantageous since upon next entering the cooking step, the cooking may thus be performed in a uniform manner without creating hot spots or uncooked portions that might otherwise result due to a non-homogeneous mixture. A suitable piece of equipment to perform this step is a "Double Shaft Continuous Mixer" manufactured by Paul O. Abbe, Inc. of Little Falls, New Jersey. While this is the preferred manner of carrying out this step of the process it is to be understood that any type of mechanical working can be utilized, it being only necessary that the mixture be subjected to such thorough mixing that a homogeneous mass will be provided prior to the cooking step.

The product mixture is now ready to enter the next important step of the process of the present invention. This step continues the mechanical working of the product mixture and concurrently cooks the mixture under pressure that progressively increases. The preferred equipment used is the cooking extruder manufactured by The Bonnot Company of Kent, Ohio, although it is to be understood that equivalent equipment may be utilized in accordance with the broad aspects of the invention. In the preferred equipment, the increase in pressure is provided by a variable pitch screw. It should be understood that other types of mechanical working may be used within the extruder. Suffice it to say that the product mixture is continuously worked by the screw and is progressively pressurized while at the same time being heated to cook the product. The exit end of the extruder is provided with an extruding die head from which the compressed product mass is extruded. The extruding step forms a product rod that is divided into relatively short lengths to form product pellets.

In the cooker-extruder, the temperature is maintained at about 150.degree. to 230.degree. F., preferably about 180.degree. to 212.degree. F., while progressively increasing the pressure to a final stage of pressurization of about 500 to 1300 pounds per square inch, preferably about 700 to 1100 psig. In general, the homogeneous mixture is heated substantially by the frictional forces or mechanical working taking place within the extruder which can operate adiabatically but additional heating means is provided if it is necessary to maintain the indicated temperature range. Temperatures above those indicated may result in charring of the product.

The residence or cooking time within the cooker-extruder will vary over a limited range with limitations being placed thereon by the size of the die opening and the speed of the screw. Suitable die openings range from approximately 0.100 inch to about 1.150 inch. Larger opening may be used but the product quality and economies of operations may be adversely affected. Much larger openings would also be unsuitable because the required pressures could not be produced. In general, it may be stated that in operation of a continuous process with continuous introduction of cocoa material, for a die having a diameter ranging from about 0.100 inch to about 0.150 inch, the cooking or residence time can range from about two and one-half nimutes to about five minutes. A preferred residence or cooking time within the cooker-extruder is about four to five minutes. The time within the cooker is important, the time within the die being only about one second or less.

The head of the extruder includes any number of suitable extruding dies or passageway out of which come the lengths of product rod. The composition of the product is gauged by moisture content of about 20-35 weight percent, preferably about 27-33 percent, in order to facilitate breaking off of the rod cleanly as it leaves the extruder head. This breaking off process is facilitated by providing a stationary plate across the path of the exiting rod. The plate breaks the rod into pellets.

At this stage the pellets may be used as desired or they may be dried by any desired process. A particular method of drying is disclosed herein. Prior to drying, the pellets still contain about 85-97 percent of the initial water added to the press cake.

In the preferred drying procedure the pellets are dried in a fluidized bed dryer and cooler unit wherein a bed of the pellets if formed by directing a plurality of downwardly extending streams of heated gas into a bed to lift and tumble the pellets. The gas is preferably an inert gas such as nitrogen or argon. The jet streams of gas are provided from a heating plenum and a cooling plenum or other desired source. The bed of pellets may be oscillated or vibrated in order to effect feeding along in a continuous fashion. At the exit end of the dryer, the dried and cooled pelletized end product is recovered for further processing and forwarding to the converter or maker of the final cocoa product. A particular fluidized bed dryer is sold as the "Jetzone" and manufactured by Wolverine Corporation, Methuen, Massachusetts. Other equivalent euipment may also be used of course.

Thus having described the equipment and the steps of the process, a more particular example of the process and the results can be set forth in the following Example. Particular attention should be directed in this Example to the operating conditions placed on the equipment that greatly enhance the efficiency and desired results of the process.

Cocoa material in the press cake form was obtained having preferably 10 to 16 percent fat. The press cake was comminuted through a pulverizer or grinder so as to form the product into a coarse, free-flowing powder of sufficiently small size that it would not plug the one-eighth inch die opening. A particle size of about 60 mesh was suitable. The powder was metered into a mixer at a rate of approximately 972 grams per minute. A final diluted solution of 22.35 grams of anhydrous sodium ash (Na.sub.2 CO.sub.3) in 390 grams of water was prepared and fed into the mixer at a predetermined rate to give a 33 percent moisture basis. The mixer was operated in a continuous fashion to completely combine and mix the soda ash solution with the powdered cocoa material, and the resultant homogeneous product mixture was then introduced into the cooking extruder at a continuous rate. Temperatures within the extruder were controlled in the range at 190.degree. F. and the pressures were progressively increased and in the final stage were controlled to 900 pounds per square inch. The product was thus continuously mechanically worked by an auger as the cooking was carried out. Total time within the cooker-extruder was four and one-half minutes. The compressed product mass was continuously fed from the extruding head and formed into approximately one-eighth inch diameter rods as the mass was extruded through the one-eighth inch die holes. This rod contained approximately 29 percent moisture; a loss of 4 percent moisture occurring as the rod emerges from the extruder 40. This moisture content allowed the rod to be freely broken into the pellets by the presence of a stationary plate.

The pellets formed were from 1/4 inch to 1 inch in length. Because of the control of the moisture content and the equipment used, there was no need to employ a cutter in order to cut the rod. These pellets were particularly suitable for drying and cooling because of the large surface area exposed to the gas of the fluidized bed unit.

The plenum of the fluidized bed unit was provided with a heated inert gas (nitrogen) that was injected into the bed of pellets in the drying section to lift and tumble the pellets for approximately 2.5 to 3 minutes as the bed moved continuously along a support. The heating element raised the temperature and maintained the same in the range of 350.degree. to 450.degree. F. Finally, the pellets were cooled to about ambient temperature under the gas nozzles in about 2.5 to 3 minutes. The product had a rich dark color and a moisture content of about 4 weight percent.

In summary, dutching of cocoa is performed by grinding the pressed cake made from cocoa beans, converting to powder, mixing with alkaline solution, and cooking the product mixture under pressure and continuous mechanical working. The compressed product of critical moisture is passed through die means to form pellets by breaking into relatively short lengths. The drying and cooling of the pellets is performed in an efficient manner on a fluidized bed with the pellets being lifted and tumbled by downwardly directed jet streams of inert gas.

In the process of this application the initial moisture content, preliminary mixing to a homogeneous mass and residence time within the cooker-extruder are especially critical in order to provide a final cocoa product having a rich homogeneous color, improved flavor and high sterility. By use of the term "rich color" is meant a dark uniform color whether brown, red or black.

In this disclosure, there is shown and described only the preferred embodiment of the invention, but, as aforementioned, it is to be understood that the invention is capable of use in various other combinations and environment and is capable of changes or modifications within the scope of the inventive concept as expressed herein.