Patent Application
20110262609
1. Field of the Invention
The present invention is broadly concerned with improved preconditioners for use with downstream extruders, wherein the majority or all of the thermal energy input to the preconditioner is in the form of heated non-steam gas, such as ambient air. More particularly, the invention is concerned with such preconditioners, as well as methods of processing using the preconditioners, wherein high meat content pet feeds can be produced without creation of excess moisture conditions within the feeds, which can plug conventional preconditioners.
2. Description of the Prior Art
A large volume of pet feeds, such as cat or dog feeds, is produced by extrusion. Generally speaking, a dry ingredient mixture containing respective quantities of grain protein, starch, and fat is fed to an extrusion system which serves to fully cook and form the starting ingredients as a complete feed. The extrusion systems typically include a preconditioner, such as that shown in U.S. Pat. No. 4,752,139, which serves to moisturize and partially pre-cook the starting ingredients, as well as a downstream extruder. During processing with such preconditioners, steam and/or water are injected into the preconditioner housing, and mixing shafts supporting paddles are rotated at a constant speed and at a preset rotational direction.
The extruder includes an elongated barrel presenting an inlet coupled with the outlet of the preconditioner, and a downstream, restricted orifice die. One or more elongated, axially rotatable, helically flighted screws are situated within the barrel in order to move the preconditioned ingredients along the length of the barrel, towards and through the outlet die. Generally, the extruder serves to heat and subject the ingredients to increasing levels of shear within the barrel, with the final cooking and shaping occurring at the die. A rotating knife is normally used to cut the extrudate into an appropriate size.
Premium pet food manufacturers increasingly wish to add fresh meat to the dry ingredients during extrusion processing. These types of feeds command higher prices in the marketplace. In the past, the practical maximum level of meat addition was about 40% by weight. If greater quantities of meat were used, the preconditioner would tend to plug up, making processing difficult or impossible.
A new generation of preconditioners is disclosed in U.S. Pat. No. 7,448,795. These preconditioners include an elongated housing with a pair of internal mixing shafts with outwardly extending paddles. The shafts are powered by individual variable speed drive mechanisms allowing infinite adjustment of the rotational speed of the shafts, as well as the ability to rotate the shafts in the same or opposite directions. With these improved preconditioners, much higher levels of meat can be added to feed formulations, on the order of 40-60% of the dry ingredients, by weight. However, it has been found with such high-meat mixtures that the native moisture content of the meat precludes addition of enough steam to the preconditioner to achieve the desired levels of cook. Thus, while higher meat quantities can pass through the preconditioner without plugging, insufficient cook levels are achieved for proper downstream extrusion.
There is accordingly a need in the art for modified preconditioners, extrusion systems, and methods which can not only handle high meat feeds, but also achieve a sufficient level of cook for efficient downstream extrusion.
The following references are pertinent: U.S. Pat. Nos. 4,028,030, 4,659,299, 4,812,324, 4,929,136, 6,344,228, 7,396,151, and 7,404,262; U.S. Published Applications: 2006/0251791, 2006/0093718, 2008/0075808, 2008/0260913, 2008/0118607, 2008/0069926, 2008/0069927; and EP Publications: 1027836 and 0610789.
The present invention overcomes the problems outlined above, and provides an improved preconditioner especially adapted for use with a downstream extruder. Broadly speaking, the preconditioner is operable to precondition material for subsequent processing thereof by heating and/or moisturizing the material and achieving a level of cook of the material. The preconditioner includes an elongated housing presenting a material inlet and a material outlet and having at least one elongated, rotatable mixing shaft therein. Apparatus is coupled with the preconditioner housing in order to introduce non-steam heated gas into the housing during passage of material therethrough, as a partial or complete replacement for steam and/or water conventionally used with preconditioners.
As used herein, “non-steam heated gas” refers to a gas, which is not wholly in the form of steam and preferably having an absolute humidity of up to 50%, more preferably up to about 25%. The gas may be a mixture of gases such as air or a relatively pure gas. The non-steam heated gas may contain some steam, up to about 25% by volume, and more preferably up to about 15% by volume. Most preferably, the heated gas contains essentially no steam. In practice, the gas is ambient-derived air free of steam at any ambient absolute or relative humidity and is heated to a level of from about 350-700° C., more preferably from about 450-600° C.
The gas introduction apparatus is preferably in the form of a burner and a blower operably coupled with the preconditioner housing. Advantageously, the apparatus is designed to introduce relatively large volumes of gas into the housing, normally at a cubic meter/hour rate of from about 60-240 times (more preferably from about 125-200 times) the cubic meter volume of the preconditioner housing. Thus, if a given housing had a volume of 100 cubic meters, the broad range of introduction rates would be from about 6,000-24,000 cubic meters/hour. In order to obtain adequate preconditioning, it is also desired to add from about 100,000-200,000 (more preferably from about 140,000-180,000) kJ/hr of thermal energy to the preconditioner. In the context of the present invention, at least about 60%, and more preferably from about 70-100%, of the total thermal energy input is derived from the introduced non-steam hot gas. The preferred preconditioner of the invention is also very efficient in terms of energy transfer. That is, the preconditioner should be operable to transfer from about 60-90%, and more preferably from about 80-88%, of the total thermal energy input to the material being preconditioned.
In particularly preferred forms, the preconditioner should be of the type described in U.S. Pat. No. 7,448,795 incorporated by reference herein. Such a preconditioner includes a pair of elongated, laterally spaced apart, axially rotatable shafts each having a plurality of outwardly extending mixing elements or paddles, with a drive assembly operably coupled with the shafts and capable of individually adjusting the speed and/or rotational direction of the shafts during passage of material through the preconditioner. The drive assembly is advantageously in the form of a pair of variable speed drives so that the respective shaft speeds can be infinitely varied. Also, the mixing elements of the shafts are axially offset and intercalated for maximum material mixing and self-wiping of the shafts and mixing elements.
The invention also provides extrusion assemblies made up of a preconditioner as described above with a downstream extruder, the latter including an elongated barrel separate from the preconditioner housing and having an inlet and a restricted orifice die outlet. At least one (and preferably two) elongated, helically flight, axially rotatable screw assemblies are located within the barrel and are operable to move the material from the inlet toward and through the outlet. In such emulsion assemblies, the preconditioner material outlet is coupled with the barrel inlet. During extrusion, the material being processed is subjected to increasing levels of temperature, pressure and shear in order to create formed and cooked final extrudates.
The preconditioners and extrusion assemblies of the invention are particularly suited for the production of food or feed products having relatively high quantities of meat therein. A typical example would be pet foods having large amounts of fresh, uncooked meat as a part of the starting recipe. Thus, the invention provides a method for extruding such products by providing a starting material including respective quantities of protein, starch, and fat and containing at least about 30% by weight meat (more preferably, at least about 40% by weight, and most preferably from about 42-60% by weight), based upon the total weight of the dry ingredients taken as 100% by weight. This starting material is then preconditioned by passing the material through a preconditioner in accordance with the invention with the simultaneous introduction of non-steam heated gas into the preconditioner housing. This serves to heat and at least partially cook the material before downstream extrusion.
The protein content of the starting material is typically derived from a variety of sources, such as the meat as well as grain proteins (e.g., soy, wheat, corn, milo). The total protein content is usually between about 5-60% by weight, more preferably from about 20-45% by weight. The starch content of the starting feed material would normally be from about 0-45% by weight, whereas the fat content would usually be from about 5-25% by weight, where all of the foregoing percentages are based upon the total weight of the material taken as 100% by weight.
The meat content of the starting material may be selected from the group consisting of beef, pork, mutton, horse, venison, fowl, fish, and mixtures thereof, but in principle any meat could be used.
While the preconditioners of the invention make use of heated non-steam gas as a thermal energy source, other types of thermal energy may be used as well. For example, steam could be introduced into the preconditioner along with the non-steam gas, but it is preferred that at least about 50%, and more preferably at least about 70%, of the thermal energy to the preconditioner be derived from the non-steam gas. This is particularly the case where high meat concentration starting materials are used, and in many of these instances, the preconditioning is carried out without the introduction of water or steam into the preconditioner housing.
Turning now to the drawings, an extrusion system 10 is illustrated in
The preconditioner 12 is of the general type disclosed in U.S. Pat. No. 7,448,795, and includes an elongated mixing vessel or housing 16 with a pair of parallel, elongated, axially extending mixing shafts 18 and 20 extending along the length thereof. The shafts 18, 20 are operably coupled with individual, identical variable drive devices 22, the latter in turn connected with a digital controller (not shown).
In more detail, the housing 16 has an elongated, transversely arcuate sidewall 26 presenting a pair of elongated, juxtaposed, intercommunicated chambers 28 and 30 (see
Each of the shafts 18, 20 has a plurality of radially outwardly extending mixing elements 42 and 44, which are designed to agitate and mix the starting materials fed to the preconditioner, and to convey the material from inlet 32 towards and out the outlet 34. The elements 42 are axially offset relative to the elements 44 and the elements 42, 44 are in intercalated (i.e., the elements 42 extend into the cylindrical operational envelope presented by shaft 20 and elements 44, and vice versa). Although the elements 42, 44 are illustrated as being substantially perpendicular to the shafts 18 and 20, the invention is not so limited; rather, the elements 42, 44 are adjustable in both length and pitch at the discretion of the user. Again referring to
The drives 22 are identical in terms of hardware, and each includes a drive motor 46, a gear reducer 48, and a coupling assembly 50 serving to connect the drive to a corresponding shaft 18 or 20. The drives 22, 24 also have variable frequency devices 52, which are designed to permit selective, individual rotation of the shafts 18, 20 in terms of speed and/or rotational direction independently of each other. In this way, each of the shafts 18, 20 can be individually rotated through an infinite range of speeds.
In preferred forms, the preconditioner 12 may be conventionally supported as indicated at 54, or if desired may be mounted on weighing devices such as load cells which are coupled with the digital controller. The use of load cells permits rapid, on-the-go variation in the retention time of material passing through the housing 16, as described in U.S. Pat. No. 6,465,029, incorporated by reference herein.
The use of the preferred variable frequency drives 22, 24 allow high-speed adjustments of the rotational speeds of the shafts 18, 20 while avoiding any collisions between the intercalated mixing elements 42, 44.
The preconditioner 12 further includes apparatus 56 for the introduction of non-steam hot gas into housing 16. In this case, the apparatus 56 includes a fuel-fired burner 58 operably coupled to an inlet 60 on housing 16. This apparatus thus serves to heat and introduce large volumes of ambient air into housing 16 where, owing to the rotation of the mixing shafts 18 and 20, the hot air comes into intimate thermal contact with the material being processed. Thereafter, the air passes outwardly through downstream vent 62. It will thus be observed that the flow of hot air is in co-current relationship relative to the flow of material being processed within housing 16. Of course, countercurrent flow of such hot air could also be employed.
The extruder 14 is itself entirely conventional and well-known to those skilled in the art. Generally speaking, an extruder of this type includes an elongated, multiple-section barrel with a material inlet and a restricted orifice die outlet. One or more elongated, axially rotatable, helically flighted screw assemblies are located within the barrel and serve to subject the preconditioned material from preconditioner 12 to increasing levels of temperature, pressure, and shear to create the final products.
The following examples set forth preferred apparatus and methods in accordance with the invention. It is to be understood, however, that these examples are provided by way of illustration only, and nothing therein should be considered as a limitation upon the overall scope of the invention.
In this example, a series of test runs were carried out using the modified preconditioner of the invention, as illustrated in
In each run, standard dog food dry recipe ingredients were fed to the preconditioner and extruder, along with fresh chicken meat in the amounts set forth below. In Runs 1-3, steam was added to the preconditioner, whereas in Runs 4-5, no steam was used.
In this series of runs, additional high meat pet feed products were prepared. The dry recipe included 53% by weight corn, 22% by weight poultry meal, 15% by weight soybean meal, and 10% by weight corn gluten meal. The added meat was fresh MD chicken meat having a moisture content of 72.83% by weight, fat 14.54% by weight, and protein 12.63% by weight. The extruder was a standard Wenger TX760, as set forth in Example 1. Two Wenger Model 450 preconditioners were used. The first precondition was of the type described herein, including hot air introduction. The second preconditioner was downstream of the first and was a standard preconditioner. The output from the second preconditioner was fed into the extruder.
Run 6 was a control with the dry recipe, heated air, and water only to the first preconditioner, with steam introduction to the downstream extruder. Runs 7-10 were similar, with Run 7 including 38% by weight fresh heated meat (23° C.) Run 8 including 38% by weight cold meat (5° C.); Run 9 including 50% by weight fresh cold meat; and Run 10 had 76% by weight fresh cold meat.
