Patent ID: 12256760

While the drawings do not necessarily provide exact dimensions or tolerances for the illustrated components or structures,FIGS.1-32are to scale with respect to the relationships between the components of the structures illustrated therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The Meat Dewatering Assembly

Turning first toFIGS.1-4, a meat dewatering assembly10is depicted, which generally includes an elongated bottom support frame12, a twin-screw dewatering unit14, a drive assembly16operably coupled with unit14, an endmost, swingable screw support18, and a water collection trough20. As illustrated, the frame12supports all of the foregoing components in an in-line manner, from right to left, as viewed inFIGS.1,3, and4.

In more detail, the support frame12has elongated, laterally spaced apart side members22,24, with intermediate connection structure26and spanning walls27extending between and interconnecting the side members. The drive assembly16includes an electric drive motor28having an output shaft30leading to gearbox32. The gearbox32has a pair of output shaft assemblies34,36, each including a first adjustment collar38, a first interconnected U-joint40, a short output shaft42from the first U-joint40to a second U-joint44, and a second adjustable collar46.

The dewatering unit14includes a pair of uniformly tapered, non-parallel, intermeshed, helically flighted screws52and54each having a central flighted region55, rearwardly extending drive section56extending into and supported within bearing housing50, and forwardly extending stub shafts58. As illustrated, the drive section56extends through the bearing housing50and is secured to adjustable collar46. In the illustrated embodiment, the center lines of the screws52,54have an included angle of 2° therebetween; more broadly, this angle would be from about 1-7°, more preferably from about 1-5°. Greater included angles of 10° or more would tend to degrade the performance of the assembly10by creating unduly high nip pressure conditions at the nip regions between the screws. The regions55of the screws52,54are of single flight design, with a uniformly decreasing pitch length from rear to front, and a uniformly varying flight depth from rear to front. The screw52is a left-hand lead, variable lead (from 3.937 in. at the rear end to 2.520 in. at the forward end), variable depth screw, whereas the screw54is a right-hand lead, variable pitch, variable depth screw having the same lead dimensions. Pinch points or nip clearances59are provided between the intermeshed flights along the length of the screws, which are adjustable in length. Importantly, the screws are designed and powered to rotate in a counter-rotating fashion, i.e., they rotate in opposite clock directions.

The nip clearances59between the intermeshed fighting of the screws52,54(seeFIG.7) can be varied using the adjustment structure described below between 0 and 0.161 inches at the large diameter ends of the screws, and from 0 to 0.086 inches at the small diameter ends of the screws. In alternate designs, multiple helix screws may be used in lieu of the screws52,54, or the screws could be of constant lead or constant pitch.

The overall unit14also includes a perforated, open-ended housing assembly60, which receives the screws52,54, with the drive section56extending rearwardly from the housing, and the stub shafts58extending forwardly therefrom. As best seen inFIG.6, the housing assembly60is made up of three end-to-end interconnected and tapered sections62,64,66, with each having an internal bore68,70,72of somewhat “figure-8” configuration so as to closely surround the intercalated screws52,54, i.e., the housing presents two elongated, side-by-side, communicating chambers, each surrounding and receiving a corresponding screw52or54. The rearmost housing section62is equipped with a tubular meat inlet74. The sections62-66have a series of elongated, water drainage slots76formed therein. In this embodiment, the slots76in section62are 1 mm in width and 9 mm in length; the slots76in the downstream sections64and66are smaller, with the slots of section64greater than those of section66. Also, in the embodiments ofFIGS.1-12, the slots76are provided about the entirety of the housing60and along the full length thereof. As best seen inFIGS.1and3, a series of upright mounts78are secured to the side members22,24, and extend upwardly for connection to the housing sections, thereby suspending the housing60above the support frame12. The open housing design ensures that the meat dewatering operation of the assembly10occurs at substantially atmospheric pressures in contrast to typical extruders which normally operate at superatmospheric pressures.

As depicted inFIG.6, use may be made of an alternate housing assembly60a, which is identical to the assembly60except that the bores68a,70a, and72ahave essentially flat intermediate sections and rounded ends. Consequently, the walls of the housing sections62a,64a, and66ado not closely conform to the configuration of the screws52,54at the intermeshed regions thereof.

The swingable screw support18is mounted to the forward end of support frame12by means of a pivot assembly80, allowing the support18to be selectively moved from a closed position, illustrated inFIGS.1-5, to an open position, illustrated inFIG.6. Appropriate latching structure (seeFIGS.6and12) is provided to hold the support18in its closed position, with an attach/detach crank82. When it is desired to open the support, the crank82is actuated, and the support is swung outwardly to theFIG.6position. The support18is provided with a fixture84having a pair of side-by-side bearing supports86, which receive the forwardly projecting stub shafts58of the screw52,54; thus, the screws are supported at both ends thereof during operation of the assembly10.

The water collection trough20positioned under housing60is of generally U-shaped configuration and is designed to receive water expressed through the housing slots76. Suitable water take-away structure (not shown) is provided for draining of the trough20during operation of the assembly10.

As indicated previously, the nip clearances between the screws52,54can be varied. In order to do this, use is made of one or more of the adjustment collars38. Referring toFIGS.8-10, the adjustment collar/U-joint46/44is illustrated. Specifically, the rearmost end of drive section56of screw54is secured to the collar46. The collar46has a first radially expanded segment88having a pair of opposed lugs90. The collar46also has a second segment92having a pair of opposed lug-receiving recesses94. The segment92is secured to U-joint44by means of screws96. The recesses94are defined by a pair of projections98, each carrying an adjustment screw100; the screws100engage the lugs90as shown. When it is desired to change the relative position of the screw54relative to the screw52, and thereby change the nip clearances therebetween, it is only necessary to turn one of the adjustment screws100, which affects a slight rotation of the collar46, and thereby the entirety of the screw54. Of course, such adjustments can only be made when the assembly10is not in operation.

FIG.13illustrates a modified embodiment in the form of a meat dewatering assembly102. In this embodiment, a screw assembly housing104is provided made up of first, second, and third end-to-end interconnected housing sections106,108, and110. The initial housing section106is equipped with a surrounding steam-heating jacket112, which serves to heat the emulsified meat introduced through the inlet114. Moreover, in this embodiment, the intermediate housing section108is equipped with water-drainage slots76, which cover the full surface area of the section108. The final section110has slots76only on the bottom half thereof, as best seen inFIG.14.

It is desirable that meat to be processed in the assembly10be first mechanically conditioned into an emulsified form, which may be optionally preheated to a temperature of from about 40-80° C., before delivery to the inlet74. The meat then passes along the length of the housing60during counter-rotation of the screws52,54, the latter powered by means of drive assembly16. As the meat traverses the length of the housing at substantially atmospheric pressures, the intermeshed screws serve to press or squeeze the meat particles within the emulsified meat, to thereby expel water through the housing slots76for collection within and take-away from trough20. The fully dewatered meat then passes through the open forward end of the housing60where it is collected, by a suitable conveyor or other apparatus (not shown) separately from the expressed water. In normal practice, the screws52,54are counter-rotated at a speed of from about 30-200 rpm, more preferably 50-150 rpm, which differs from typical twin-screw extruders equipped with high rotational speed, co-rotating screws.

The Hollow Core Screw Extruder

Turning now to the drawings, and particularlyFIGS.15-19, a processing device220is illustrated. Broadly speaking, the device220includes an elongated, tubular barrel222having a material inlet224and an opposed processed material outlet226, with a twin-screw assembly228within the barrel222.

As illustrated, the barrel is made up of a plurality of end-to-end interconnected barrel sections230,232,234, and236. An internal liner assembly238is located within and extends along the length of the sections230-236and presents a pair of elongated, juxtaposed communicating arcuate passageways240,242, which receive the twin-screw assembly228. The sleeve further presents the rearmost opening244, as best seen inFIG.18. An apertured front wall246is located at the opposite end of the barrel and is secured thereto. Additionally, a forwardly projecting bearing housing248is attached to the outer face of front wall246, and has a pair of side-by-side tubular bearings therein.

The twin-screw assembly228includes identical, complemental first and second intermeshing, double-flight screws250and252, which are designed to directionally co-rotate during the operation of device220. Referring toFIGS.16and18, it will be seen that the screws250,252each have an elongated shaft254with outwardly extending, helical fighting256along the length of the shaft254, having a pitch length of 1, based upon the screw diameter. An elongated central bore258extends substantially throughout the length of the shaft254, thereby creating a hollow core260therein. As best seen inFIG.17, the fighting256is divided into two sections, namely a first section262operable to convey material from the inlet224toward and through the processed material outlet226, and a second section264operable to retard the flow of material therepast. To this end, the flighting sections262,264are of reverse hand, respectively. The rearmost ends of the screws250,252are provided with drive and bearing structure266,268, having rearmost, splined connector ends270,272; the ends270,272are designed to mate with suitable drive structure (not shown) for axially rotating the screws. The forward ends of the screws are equipped with elongated extensions274,276, which are received within the tubular bearings of housing248(FIG.17).

The screws250,252are equipped with structure278to supply heat exchange media to the internal cores thereof. Specifically, elongated, stationary steam delivery tubes280and282extend from a point outside of housing222adjacent front wall246and into the bores258. The tubes280,282extend through the endmost tubular fixtures284,286located at the forward ends of the extensions274,276. The outermost ends of the tubes280,282connect with identical rotary unions288,290. Each such union includes a block292having a media inlet opening294, a liquid removal outlet296, and a rotatable sleeve298disposed about the corresponding tube280or282. To this end, the sleeves298are secured to the corresponding tubular fixtures284,286.

The screws250,252are preferably fabricated from metal using normal machining techniques and are normally case-hardened.

In operation, material to be processed (which may be preconditioned, as explained hereafter) is delivered to inlet224during co-rotation of the screws250,252, which serves to advance the material during processing thereof to deliver processed material to outlet226. During this operation, heat exchange media (normally steam) is directed from a delivery conduit (not shown) coupled with the media inlets294and into the tubes280,282to the open cores260of the screws in order to provide thermal energy required for processing of the material. Additional energy input is provided by means of pressure and shear conditions developed within the barrel222. During processing, steam condensate passes from the cores260and through the sleeves298, exiting the system via the removal outlets296. In order to prevent leakage of material past the wall246and the fixtures284,286, the reverse flight section264comes into play by creating a retardation force against the flow of material created by the opposite hand fighting of the section262. The product emerging from the outlet226may then be passed through a restricted orifice extrusion die and cut, in order to form the final product, although in practice, the elongated delivery pipe is normally secured to the outlet226and a final die and knife assembly are located at the opposite end of the pipe.

FIGS.20-25illustrate another embodiment of the invention, in the form of a processing device300. The device300is in many respects similar to the device220, having a tubular barrel302with a twin-screw assembly304therein, and having an inlet224and an outlet226, as in the case of the first embodiment. Again, the barrel302is made up of tubular, interconnected barrel sections306-312with an internal liner assembly314defining side-by-side passageways316,318. The forward end of barrel302is equipped with a front wall320, which supports a forwardly projecting bearing housing322.

The screw assembly304has a pair of identical, intermeshed, single flight, helical screws324,326, which are received within the passageways316,318. Each of the screws has an elongated central shaft328,330, as well as outwardly extending helical flighting332,334along the length thereof. As in the case of the first embodiment, the screws324,326have rearmost drive and bearing structures336,338, equipped with splined drive connection ends340,342. The forward ends of the screws have bearing extensions344,346, which are received within the bearings of housing322.

The principal differences between the first and second embodiments are the configuration of the helical screws324and326. Specifically, each such screw includes a primary central section348operable to move product along the length of the barrel302towards and through the outlet226, an inlet section350operable to deliver incoming material to the section348, and a forward, material flow retarding section352. The inlet section350is advantageously a machined part having a central shaft354with an internally splined bore356, and outwardly extending fighting332,334. As best seen inFIG.24, the bore356is designed to receive the forward end of the corresponding drive and bearing structure336,338. The screw sections348and350have a pitch length of 1, based upon the screw diameter, and denoted by D1ofFIG.24. The forward section352of each screw is likewise a machined part and has a central, bored shaft360with outwardly extending helical flighting362. Notably, the pitch of the flight362is opposite that of the pitch of the flighting358of screw section348, and has a pitch length of 0.3, based upon the screw diameter, denoted by D2ofFIG.24. Preferably, the pitch length D1should be from about 0.4-1.2, more preferably 0.5-1.0, whereas the pitch length D2should be from about 0.2-1.1, more preferably 0.3-1.

The central section348is preferably formed by casting (e.g., sand or investment casting) with a plurality of sections which are butt-welded together to form the entirety of the central section. As best seen inFIG.24, the central section348has a central shaft366, which is hollow along the length thereof to define a central core367, as well as outwardly extending flighting368, which is likewise hollow to define a helical core369. In this regard, the flight368is defined by outwardly extending, opposed, spaced apart sidewalls370and372, with a flattened outer wall374. As such, it will be observed that there is a helical transition376between the innermost ends of the sidewalls370,372, which provides full, open communication between the central core367and the helical core369, without any blockage or narrowing whatsoever; stated otherwise, the transition376presents an area which is open throughout the length and width thereof in order to afford unobstructed communication between the hollow regions of the shaft and helical screw. Inasmuch as the section348is of cast construction, it will be seen that the thickness of the shaft366is essentially identical with the thicknesses of the sidewalls370,372, and outer wall374. In preferred forms, the length of the central screw section348is at least about three times, more preferably at least about five times, greater than the length of the forward screw section352. The screws324,326receive elongated media delivery tubes378,380, which are designed to deliver media such as steam to the interior of the screw sections348and352. The forward ends of the tubes378,380are received within rotary unions288,290, identical to those described in connection with the first embodiment, and like reference numerals have been applied (FIG.24). The rotatable sleeves298are supported by couplers284, again as described in the first embodiment.

The innermost ends of the tubes378,380are each supported by a tubular, open-sided diffusion cage382. The latter includes a mounting screw384, which extends through the end of the primary screw section348and is received within a threaded bore386in the forward butt end of bearing and drive structure336.

The rearmost end of the screw section348has a splined portion388, which receives the forward end of the structure336ahead of inlet screw section350. The forward end of the screw section348is secured to the rearward end of screw section352by butt welding or any other appropriate technique. Hence, driving rotation of the structures336serves to rotate the entire screws324,326.

The operation of device300is similar to the device220. However, owing to the completely open hollow core structure of the screw section348, better heat transfer from the injected steam is afforded, as compared with the device220.

FIGS.26-32illustrate another hollow core screw embodiment of the invention in the form of helical extrusion screw390. The screw390is designed for use in a twin-screw extruder so that a mating screw (not shown) will be used in conjunction with the screw390to make a screw set. Generally, the screw390includes an elongated central shaft392with a continuous helical flighting394along the length thereof.

The shaft392has a rearmost splined section396to afford a driving connection with a motor/gear reducer assembly and a forward bearing extension. The shaft392is a machined, case-hardened part and has a solid rear section398and a hollow core forward section400presenting an elongated, axially extending, central core402. The forward end of the core402is equipped with a coupler404designed to receive a rotary union288(FIG.28). A stationary steam delivery tube408(shown fragmentarily inFIG.28) extends substantially the full length of the core402and has an open end410.

The fighting394includes a rear section412of relatively narrow flight width, which extends the full length of the solid section398. Additionally, the fighting394has a wider flight width forward section414presenting an outermost flight surface414a, which extends from the end of section412to a point close to the forward end of the shaft392. However, as in the case of the earlier embodiments, the screw390has a reverse flight section416between the end of section414and coupler404.

In the manufacture of the screw390, the fighting394is machined as a solid protrusion from the shaft392, with a continuous, helical, open-top groove418in the wide flight section414, extending from the outermost flight surface414ainwardly to an inner wall420close to the core402. Thereafter, a series of spaced apart apertures422are formed along the length of the inner wall420, in order to communicate the core402with groove418. Next, a helical cover piece424is positioned over the upper end of the groove418, and is welded to the fighting section414. In the final step, the screw390is machined to provide the proper outside diameter for the flighting394. This creates a unitary construction, as illustrated in the drawings.

The operation of the screw390, with its mating, intermeshed screw within an extruder barrel, such as barrel222, is the same as described in connection with the embodiment ofFIGS.15-19. That is, co-rotation of the screw set serves to advance material during processing thereof from the barrel inlet to the barrel outlet. Simultaneously, steam or other heat exchange media is directed into the core402through the union288and the extension of shaft392beyond the end of the extruder barrel. This media flows through the core402and groove418owing to the communicating apertures422. This provides an increased level of thermal energy to the process. The reverse flight section416also serves to retard the flow of material at the forward end of the screw390.

FIG.33schematically illustrates a system426for the production of high-meat content pet foods, and broadly includes an upstream meat dewatering assembly10operably coupled with an extrusion system generally having an optional preconditioner428, an extruder430, and a post-extrusion terminal assembly440including a drying assembly446. The extruder430is a modified version of the devices220or300, using any of the hollow core screws described above. The extruder430includes a generally L-shaped conduit or pipe432affixed to barrel outlet226and extending to the terminal assembly440. The use of pipe432permits attachment of steam lines to the previously described rotary unions288,290(FIG.20).

The meat dewatering assembly is designed to treat high-moisture meat products, such as emulsified poultry (e.g., chicken or turkey) products to substantially reduce the moisture levels thereof and create low-moisture meat cakes. Such emulsified products typically contain from about 60-80% by weight moisture, and treatment in the assembly10serves to reduce the moisture content such that the final meat cakes usually have a moisture content of from about 45-60% by weight, more preferably from about 48-55% by weight, based upon the total weight of the dewatered meat taken as 100% by weight.

The system426in further detail includes a conveyor434and dewatered meat cake delivery line436leading to the input224of the extruder430. In some cases, it may be desirable to use emulsified meat along with dewatered meat cake and, to this end, an optional emulsified meat inlet line438is provided, which leads to extruder input224. If desired, the preconditioner428may be used, and in such a case the meat inlet lines436a,438awould direct the meat products through the preconditioner428before entering the extruder inlet224. In preferred practice, the preconditioner428is operated without any injection of moisture by way of steam or water, and thus the preconditioner would principally serve as a means of uniformly mixing the ingredients to be processed in the extruder430.

As noted, the output end of pipe432is operably coupled to a terminal assembly440made up of an adjustable back pressure valve442and an extrudate hood444, with a restricted orifice die (not shown) located at the entrance to the hood444. These components are fully illustrated and described in U.S. Pat. No. 9,320,298, which is incorporated by reference herein in its entirety. The valve442is designed to provide a selective degree of restriction of flow of material from pipe432as the material passes through the endmost die. The extrudate hood444serves to facilitate the spread of extrudate issuing from the die to prevent agglomeration or clumping of the extrudate. The hood444includes a shiftable conveyor belt (not shown), in order to move the product from the die area to the hood exit.

The dryer assembly446is made up of a relatively short pre-dryer448and a final dryer450of conventional design. In some instances, it has been found that high-meat extrudates issuing from the die are delicate and prone to fragmentation. Accordingly, in these case, the extrudate from the hood444passes immediately into the pre-dryer, which serves to “set” the products and preserve the integrity thereof, prior to passage to the final dryer.

The system426is designed to produce extruded products using mixtures of meat including dewatered meat, with the optional presence of full-moisture meat or meat emulsion, together with other conventional pet food ingredients such as grains, starches, and fats, with optional minor ingredients such as vitamins and emulsifiers.

In general, the products should contain from about 5-50% by weight starch, from about 3-12% by weight fat, and a preferred moisture content of from about 6-12% by weight, all of the foregoing percentages based upon the total weight of the product taken as 100% by weight.

The total meat content can consist essentially of dewatered meat, or a mixture of such dewatered meat with whole meat and/or meat emulsion(s). Where the total meat content is made up of a combination of dewatered meat and other meat sources such as emulsified meat, the dewatered meat should be present at a level of from about 50-100% by weight, more preferably from about 85-100% by weight, based upon the total weight of the meat content taken as 100% by weight; correspondingly, the meat emulsion, if used, should be present at a level of from about 0-50% by weight, more preferably from about 1-15% by weight, again based upon the total weight of the meat content taken as 100% by weight.

Advantageously, the total meat content of the products consists essentially of dewatered meat, because adding untreated meat or meat slurry emulsions increases the moisture content of the mixture to be extruded, which is to be avoided.

In all cases, whether the total meat content is made up entirely of dewatered meat or a combination of dewatered meat and untreated meat emulsion and/or meat slurry, it is important to understand the basis for determining the meat content of the products. For example, (1) the total meat content may be expressed as a percentage of the dry recipe components, i.e., the dry components are taken as 100% by weight; or (2) the total meat content may be expressed as a percentage of the total recipe, i.e., the total recipe including the total meat content is taken as 100% by weight; or (3), similar to (1), the total meat content may be expressed as an equivalent meat slurry level, i.e., as if the total meat content were present as meat slurry, with the meat slurry level expressed as a percentage of the total dry recipe components; or (4), similar to (2), the equivalent meat slurry level may be expressed as a percentage of the total recipe components taken as 100% by weight. From a commercial perspective, current labeling laws and regulations allow the pet food manufacturer to advantageously express the meat content as in (4).

The following Table 1 sets forth approximate broad and preferred ranges in the case where the meat content is entirely in the form of dewatered meat and expresses those ranges as set forth in (1)-(4) above. It should be understood in this respect that the data in columns (3) and (4) are, correspondingly, the values of columns (1) and (2) multiplied by 3.33; this reflects the fact that each pound of dewatered meat was made from 3.33 pounds of starting meat slurry. Moreover, the values of column (2) are equal to the values of column (1) divided by the values of column (1) plus 100, and the values of column (4) are equal to the values of column (3) divided by the values of column (3) plus 100.

TABLE 1(3)(4)(1)(2)Equivalent meatEquivalent meatDewatered meatDewatered meatslurry levelslurry levelexpressed as %expressed as % ofexpressed as %expressed as % ofProcessof the dry recipethe total recipeof dry recipethe total recipeRangecomponentscomponentscomponentscomponentsBroad range85.0-120.046.0-54.5156.0-400.060.9-80.0Preferred85.0-105.046.0-51.2156.0-350.060.9-77.8range

The above Table 1 represents preferred implementations of the invention wherein the total meat content is in the form of dewatered meat. If the total meat content includes untreated meat emulsion or meat slurry, such will normally reduce the total meat content which can be employed in the products, inasmuch as meat or meat slurry will have a greater moisture content than the dewatered meat. As noted above, the total moisture content of the mixture fed to the extruder is important, in order to permit proper extrusion processing of the mixture. Typically, this moisture content should be from about 25-48% by weight, more preferably from about 35-43% by weight, based upon the total weight of the mixture fed to the extruder taken as 100% by weight.

During extrusion processing, the ingredients passing through the extruder should be heated to a minimum temperature of 70° C., or more preferably ≥90° C., in order to meet feed safety requirements. The rotation of the extruder twin screws should be in the range from about 100-600 rpm, more preferably from about 300-450 rpm; pressure within the extruder barrel is normally from about 200-600 psi, more preferably from about 300-400 psi. Pressurized steam is directed into the hollow core screws usually at a level of 30-120 psi, more preferably from about 45-90 psi, depending upon the size of the extruder. Although not illustrated in the drawings, it is possible to employ extruder barrels which are externally jacketed for receiving steam or other heat exchange media in order to indirectly heat the materials passing through the extruder. The jacket steam would likewise be pressurized to a level of about 30-120 psi, more preferably from about 45-90 psi.

In the drying assembly446, the pre-dryer448is of multiple-pass design and employs heated air at a temperature of from about 100-240° C., more preferably from about 140-180° C., with a total retention time of from about 3-12 minutes, more preferably from about 5-10 minutes. The final dryer450is likewise of multiple pass design and employs heated air having a temperature less than that utilized in the pre-dryer, namely from about 70-140° C., more preferably from about 85-110° C., with a total residence time of from about 6-20 minutes, more preferably from about 8-15 minutes.

The optional preconditioner428may take a variety of forms, so long as the starting mixtures are substantially uniformly mixed prior to delivery to the inlet224; it is also possible to add moisture during preconditioning, but this is normally minimized or eliminated, owing to the high moisture content of the meat fraction of the mixtures. For example, commercially available Wenger DDC or HIP preconditioners (see U.S. Pat. Nos. 4,752,139, 7,448,795, and 9,028,133) may be used in this context. Such preconditioners may provide steam and/or water injection in order to heat and pre-cook the starting mixtures, or in some instances hot air may be used as a heating medium (U.S. Pat. No. 7,963,214). In such instances, it may be necessary to provide only a portion of the meat fraction of the mixture during passage through the preconditioner, with separate introduction of the remainder of the meat fraction directly into the input224of the processing device, along with the preconditioned materials, to achieve the desired total percentage of meat.

It will be appreciated that in extrusion technology there are two principal sources of energy input, referred to as specific mechanical energy (SME), and specific thermal energy (STE). SME is primarily derived from the heat, friction, and shear forces developed by the extrusion screw(s), whereas STE is generated by the addition of heat exchange media, typically steam. In existing extrusion technology, STE is most commonly added by means of direct injection of steam into the mixture being processed, either in the preconditioner, the extruder, or both. However, as indicated above, direct injection of steam can be problematical when high-meat recipes are being processed. The present invention provides a distinct improvement, in that indirect heating is achieved in the extruder, which avoids direct steam addition and the consequent excess moisture problems attendant thereto.

Example

In this example, a series of pet food runs were carried out using the apparatus ofFIG.33, with a Wenger HIP preconditioner428, and an extruder430equipped with the hollow core screws illustrated inFIGS.27-32. In addition, the extruder was provided with jacketed barrel heads allowing introduction of steam for the indirect heating of the material passing through the extruder barrel.

In each run, a dry recipe was used made up of 26% poultry meal, 36% whole potato flour, 26% yellow pea flower, 8% beet pulp, 3% flax meal, and 1% salt, all percentages based upon the total weight of the dry recipe taken as 100% by weight. The moisture content of the dry recipe was 8.6%. Two different meat sources were used in the runs, specifically mechanically separated chicken (MSC) in the form of a high-moisture emulsion, and dewatered MSC meat cake (having a moisture content of about 50% by weight) derived from initial processing of MSC using the meat dewatering assembly10(333 kg of MSC yields 100 kg of MSC meat cake). In general, the process involved directing the dry ingredients and the meat sources to the preconditioner428for mixing therein prior to delivery to the extruder430; however, no moisture was added during preconditioning. When emulsified meat was used, it was preheated to 40° C. prior to delivery to the preconditioner. Thereupon, the preconditioned mixtures were passed through the extruder430, and then through the assemblies440,446to complete the process.

In greater detail, a total of five runs were carried out, using the following meat ingredients, as set forth in Table 2:

TABLE 2MSC DewateredRun No.MSC %Cake %160026057.236041409050103weight percentage based upon the total weight of the dry ingredients in the mixture taken as 100% by weight

In carrying out the runs, the extruder heads and hollow core screws were fully heated with injected steam. In particular, the steam was injected at a pressure of 120 psig into both the extruder heads and hollow core screws, with the steam flow through the heads at a level of about 20-45 kg/hr, with a steam flow of about 40-45 kg/hr through the hollow core screws. It can be appreciated by those skilled in the art of extrusion, that steam flow rates can be varied depending on the size of the extruder and the throughput capacities of the extrudate.

The extrusion mixtures made up of the dry recipe and meat sources were initially passed through a Wenger HIP preconditioner428without any injection of steam or water into the mixtures; accordingly, the preconditioner428thoroughly mixed the ingredients prior to introduction of the mixtures into the extruder inlet. As the product emerged from the extrusion die and entered the hood444, fan air was blown onto the products in order to prevent them from adhering to the hood.

The following Table 3 sets forth data collected in these runs.

TABLE 3Dry feedMeatMoisture % by wtBulk Density (g/l)RunrateCook %MSCcakeOffOffNo.(kg/hr)OE1kg/hrkg/hrCVR2OE1OD3OE1CVR2OD3150089.2300016.732.32.4555444402250095.730028633.243.36.9540514421350092.430020524.940.34.8580505436450096.4045034.338.74.4580472376550097.4051431.846.91.65825283701OE means the cook, moisture, or bulk density values of the product off of the extruder prior to any drying thereof2CVR means the moisture or bulk density values of the product taken off the pre-dryer prior to any final drying thereof.3OD means the moisture and bulk density values of the product after complete drying thereof.

The following Table 4 sets forth the proximate analysis of the final, dried products:

TABLE 4Proximate analysis (% by wt)RunNo.ProteinFat4MoistureAshFiber130.99.05.17.04.6237.111.47.48.73.6334.810.36.68.13.7439.912.46.28.34.8540.012.86.98.72.94The fat level was based upon the extruded and dried product, before any downstream coating thereof.

The cook values for the extruded products were all satisfactory, and the products after drying were of acceptable bulk density and product integrity. That is, the products were commercially acceptable as extruded pet feeds.