Abstract:
The present invention relates in general to methods and apparatus for processing expandable food materials, and more particularly to methods and apparatus for low shear thermo-mechanical processing of food materials. The invention can include cooker and extruder apparatus for the customized production of food products, including a compression module, a dryer module, and a control unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to and the benefit of U.S. provisional patent application Ser. No. 60/672,902, filed Apr. 19, 2005, the entire disclosure of which is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to methods and apparatus for processing expandable food materials, in particular methods and apparatus for low shear thermo-mechanical processing of food materials. Additionally, the invention relates to a self-actuating die and poppet valve combination for use with the aforementioned methods and apparatus.  
       BACKGROUND OF THE INVENTION  
       [0003]     Mass-produced breakfast cereals, some of which use expandable food materials, have several disadvantages, for example, high cost, the inclusion of preservatives and other unwanted ingredients, and a lack of choice of ingredients. A consumer with allergies, for example, is limited to certain selections and types of products. Similar disadvantages exist for other mass-produced food products, such as, for example, snack foods, croutons, bread crumbs, and other types of puffed foods.  
         [0004]     Various examples of methods and apparatus for processing food materials can be found in U.S. Pat. No. 2,858,218, U.S. Pat. No. 2,858,219, U.S. Pat. No. 4,187,727, U.S. Pat. No. 4,465,452, U.S. Pat. No. 4,317,842, U.S. Pat. No. 4,503,127, U.S. Pat. No. 4,517,204, U.S. Pat. No. 4,537,786, U.S. Pat. No. 4,547,376, U.S. Pat. No. 4,608,264, U.S. Pat. No. 4,615,894, U.S. Pat. No. 4,756,916, U.S. Pat. No. 4,820,470, U.S. Pat. No. 6,511,309, U.S. Pat. No. 5,198,239, U.S. Pat. No. 4,569,848, U.S. Pat. No. 4,276,800, U.S. Pat. No. 4,405,298, U.S. Pat. No. 4,801,258, U.S. Pat. No. 4,859,165, U.S. Pat. No. 5,773,043, U.S. Pat. No. 4,555,407, U.S. Pat. No. 5,577,410, U.S. Pat. No. 4,778,365, U.S. Pat. No. 4,460,611, U.S. Pat. No. 4,548,571, U.S. Pat. No. 4,528,900, U.S. Pat. No. 4,578,027, U.S. Pat. No. 4,648,821, U.S. Pat. No. 4,656,039, U.S. Pat. No. 4,698,000, U.S. Pat. No. 4,715,803, U.S. Pat. No. 4,743,458, U.S. Pat. No. 4,882,185, U.S. Pat. No. 4,882,172, U.S. Pat. No. 4,469,475, U.S. Pat. No. 4,372,734, U.S. Pat. No. 5,403,603, U.S. Pat. No. 4,251,201, U.S. Pat. No. 5,333,538, U.S. Pat. No. 4,406,603, U.S. Pat. No. 5,993,188, U.S. Pat. No. 4,268,532, U.S. Pat. No. 4,900,572, U.S. Pat. No. 4,966,542, U.S. Pat. No. 4,456,446, U.S. Pat. No. 4,659,580, U.S. Pat. No. 5,198,257, U.S. Pat. No. 5,449,281, U.S. Pat. No. 4,886,441, U.S. Pat. No. 4,999,206, U.S. Pat. No. 4,685,877, U.S. Pat. No. 6,764,701, U.S. Pat. No. 5,464,642, U.S. Pat. No. 5,304,055, and U.S. Pat. No. 6,120,360, the disclosures of which are hereby incorporated by reference in their entirety.  
         [0005]     Apparatus for processing expandable food materials typically utilize screw-type extruders that can impart excess shear on the food material, thereby degrading the food material and the finished product. Some of the methods and apparatus used for processing food materials can negatively impact the taste and texture of the finished product. For example, shear can degrade starch molecules forming dextrin, an undesirable by-product, and degrading product quality. Additionally, shear is also responsible for substantial wear of screws and barrels, thereby shortening the life of the equipment.  
       SUMMARY OF THE INVENTION  
       [0006]     The invention generally relates to a low shear food cooker/extruder for the customized production of breakfast foods (such as cereals) and similar food products. In one embodiment, the invention relates to a counter-top breakfast cereal apparatus targeted for the consumer (home use) market. The cooker/extruder can be used to freshly produce ready to eat (RTE) breakfast cereal for the consumer. The cereal would be made on demand and, if preferred, preservative-free, with ingredients tailored to particular taste and texture preferences. Some of the advantages of a apparatus and related processes in accordance with the invention are that batches are made fresh and on demand; preservatives are not required in the recipes; cost per batch is economical, whereas, overhead costs passed on by commercial cereal manufacturers are eliminated; consumers with allergies to specific food materials control ingredient content of their recipes; and better overall output quality due to minimized starch damage within the final food product.  
         [0007]     In one aspect, the invention relates to a very low shear cooker/extruder utilizing a piston to extrude the expandable food material. In one embodiment, the piston can include a rotating mechanism to introduce a minimum amount of shear as may be necessary to aid the cooking of the food product, but not enough to damage the food product. Additionally, the cooking can be performed under pressure as high as about 500 psi. A variety of dies or nozzles can be used with the extruder to produce different finished products and to accommodate different viscosity food products.  
         [0008]     Generally, the cooker/extruder apparatus includes three basic modules: a compression module, a dryer module, and a control unit. The apparatus is capable of cooking, forming and puffing a food product, such as, for example, cereals, snack foods, breadsticks, croutons, pet foods, and textured vegetable proteins, without the use of oil, hot air or gun-puffing, for example, to puff the product. Additionally the apparatus could be used to produce non-puffed foods, such as pellets or other half-product made for later processing by other means, e.g., frying. Furthermore, the apparatus could also be used as an analytical test machine to measure properties, for example viscosity, of materials. The apparatus can vary in size and configuration to suit specific applications. For example, a relatively small manually operated unit could be produced as a home appliance. A larger version could be manufactured for in-store production, such as might be found in supermarket bakeries or health-food stores. A larger and more sophisticated automated machine may also be produced.  
         [0009]     In one embodiment, the compression module includes a chamber for inserting and processing raw food materials, a quick-release sealed chamber cover for maintaining high pressure during the cooking/extrusion process, a heating element that surrounds the chamber, a variable speed piston for ejecting processed food materials from the chamber, a piston drive mechanism, and an adjustable pressure-activated nozzle for controlling the expansion rate of food materials ejected from the chamber. The piston drive mechanism could be mechanically (e.g., a screw), electrically, hydraulically, or pneumatically driven.  
         [0010]     The dryer module, in one embodiment, includes a variable speed blade for cutting extruded/expanded food material to desired lengths, a bin for capturing and containing said food material, a heater for drying and toasting said food material, a blower for circulating said food material during the drying/toasting process, and an enclosure that houses the blade, bin, heater and blower. In one embodiment, the control unit includes electro/mechanical hardware and circuitry, which controls all electrical, mechanical, and physical aspects of the cooking, extrusion, drying and toasting processes. All of the necessary hardware and circuitry is housed inside a grounded enclosure.  
         [0011]     In another aspect, the invention relates to methods of producing food products with low or very low shear. The methods involve thermo-mechanically processing the food products. The methods include introducing a raw or partially processed food product into a compression module, heating and/or pressurizing the food product to cook the product, and extruding the product under minimal shear.  
         [0012]     In another aspect, the invention relates to a food product as produced by a method in accordance with one embodiment of the invention, such as, for example, cereal or a puffed cheese snack. The methods and apparatus of the invention can be carried out with a variety of raw ingredients to suit a particular user&#39;s tastes. For example, prestressed or pregelatinized ingredients could be used, such as melted starches. The apparatus can include additional modules for modifying the extruded food product, for example for flavoring or combining with other food products.  
         [0013]     In another aspect, the invention relates to a self-actuating poppet valve. The poppet valve is used in the compression module to trigger the extrusion process. In one embodiment, the valve is a pressure-actuated poppet valve that connects the chamber to the die or nozzle when a pre-determined pressure is reached within the chamber.  
         [0014]     These and other objects, along with advantages and features of the present invention herein disclosed, will become apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:  
         [0016]      FIG. 1  is a schematic side view of a compression module for an apparatus for processing expandable food materials, in accordance with one embodiment of the invention;  
         [0017]      FIG. 2A  is a schematic perspective view of the compression module of  FIG. 1 ;  
         [0018]      FIG. 2B  is a second schematic perspective view of the compression module of  FIG. 1 ;  
         [0019]      FIG. 2C  is a third schematic perspective view of the compression module of  FIG. 1 ;  
         [0020]      FIG. 2D  is a fourth schematic perspective view of the compression module of  FIG. 1 ;  
         [0021]      FIG. 3  is an exploded schematic perspective view of the compression module of  FIG. 1 ;  
         [0022]      FIG. 4  is a table of parts for the compression module of  FIGS. 1-3 ;  
         [0023]      FIG. 5A  is a schematic perspective view of a dryer module for an apparatus for processing expandable food materials, in accordance with one embodiment of the invention;  
         [0024]      FIG. 5B  is a second schematic perspective view of the dryer module of  FIG. 5A ;  
         [0025]      FIG. 6A-6I  are schematic perspective views of the dryer module of  FIG. 5A , in various stages of construction;  
         [0026]      FIG. 7  is a table of parts for the compression module of  FIGS. 5A-6I ;  
         [0027]      FIG. 8  is a schematic view of a control unit for an apparatus for processing expandable food materials, in accordance with one embodiment of the invention;  
         [0028]      FIG. 9  is a schematic view of three positions descriptions for the toggle switch of  FIG. 8 ;  
         [0029]      FIGS. 10A-10F  are schematic views of a housing and valve for a self-actuating die and poppet valve combination, in accordance with one embodiment of the invention;  
         [0030]      FIG. 11  is a schematic view of a piston and valve for a self-actuating die and poppet valve combination, in accordance with one embodiment of the invention; and  
         [0031]      FIG. 12  is a schematic view of a spacer and spring for a self-actuating die and poppet valve combination, in accordance with one embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0032]     Embodiments of the present invention are described below. It is, however, expressly noted that the present invention is not limited to these embodiments, but rather the intention is that all equivalents and all modifications that are apparent to a person skilled in the art are also included. In particular, the present invention is not intended to be limited to any specific food material or end product.  
         [0033]     The compression module includes the components listed and arranged as shown in  FIGS. 1-4 .  FIGS. 8 and 9  show an electrical schematic representing one embodiment of a control unit for operating the apparatus. The dryer module includes the components listed and arranged as shown in  FIGS. 5A-7 . The operation of the various modules and components are described hereinbelow.  
         [0034]     The invention also relates to a variety of methods of producing food products. Generally, the operation of the apparatus includes the following steps. Food materials of a particular recipe are inserted into the chamber of the compression module and the chamber cover is attached and sealed to the chamber and locked. The heating element is activated to begin the cooking process. As the closed-volume cooking process proceeds, the pressure and boiling point of the food materials continuously elevate above their atmospheric levels, and the starches within the food material transform to a plasticized state. After a specified elapsed cooking time (dependant on recipe and ingredient quantities, for example), the heating element is deactivated to terminate the cooking process. The piston is then activated to begin the extrusion process by decreasing the volume of the chamber and, thereby, further increasing the differential pressure between the food materials within the chamber and atmospheric pressure outside of the chamber.  
         [0035]     Once the pressure of the food materials within the chamber reaches a pre-determined level, the nozzle or valve opens, allowing the pressurized food material to flow from the chamber. The piston remains in motion until all food materials within the chamber have been ejected. Approximately ninety five percent of the water content within the food material instantaneously boils upon exit from the nozzle, causing the ejected food material to expand. Expansion rate is dependant upon original water content of the recipe and is controlled by multiple mechanical parameters, such as nozzle orifice size and piston speed. At ejection, the plasticized starches throughout the food material go through a glass transition, that is, they form cellular structures that cool rapidly to maintain the size, shape and texture of the expanded food product.  
         [0036]     The expanded food product flowing from the compression module nozzle optionally enters the dryer module through an opening in the enclosure wall thereof. After exiting from this opening, the food product is cut into equal length sections by a spinning blade. Section length is selected based on the desired size and/or shape of the finished food product. Section length is determined by the speed of the blade. Depending on the type of food product produced, the dryer module may not be needed as the product can be air dried and manually cut or otherwise manipulated. Additionally, other processes can be carried out to sweeten, flavor, color, texturize, enrich, and otherwise treat the finished food product.  
         [0037]     After being cut, the food sections are gravity fed into a perforated holding bin. Once the complete batch of food product has been sectioned and is in the holding bin, a heater and a blower unit are both activated. In one embodiment, the heater is located directly beneath the holding bin and has an output of approximately 400 watts and is toggled on and off by a thermostat control. The heater&#39;s function is to toast the food product for added flavor and decrease its moisture content to, for example, between about three percent and about five percent. The desired resultant moisture content will depend on the food product being produced. In one embodiment, the blower unit is located directly beneath the heater, has an output of approximately 20 cfm, and remains on throughout the drying/toasting process. The blower&#39;s function is to promote even heating and to prevent burning of the food product by circulating the food sections within the bin during the drying/toasting process.  
         [0038]     The size of the apparatus and the size and arrangement of the various components of the apparatus will be selected to suit a particular application. In one embodiment, a cylinder having a diameter from about 0.25″ to about 4″ is used. The cylinder stroke can be from about 0.5″ to about 18″. The apparatus can be scaled up or down to suit the particular application, for example as a home appliance or for an industrial application. For example, in the compression module, the cylinder size and quantity will be selected based on the amount of product to be produced, the heat transfer requirements, and the desired cycle time. For example, better heat transfer permits the use of raw feeds and higher temperatures that will allow operation at reduced moistures for better product quality.  
         [0039]     One of the considerations when selecting the size of the cylinder is the time required to achieve a desired level of heat penetration, which is approximately proportional to the square of the cylinder&#39;s diameter. For example, if it takes one hour to heat a 2″ cylinder, we expect the same results in 15 minutes with a 1″ diameter cylinder. And, using the same piston stroke, the production rate will remain constant. Each shot will have ¼ of the original quantity, but will happen four times more frequently. Moreover, multiple cylinders (like in a reciprocating engine) can be used to increase the product output. A description of thermal penetration can be found in Heldman and Singh,  Food Process Engineering , pp. 124-130, the disclosure of which is hereby incorporated by reference in its entirety.  
         [0040]     In another embodiment, an annular piston can be used. Although a more complex design, converting from a circular cross-section to an annular cross-section vastly increases the heat transfer area (heating inside and outside the annulus) with a dramatic decrease in cycle time and improvement in product uniformity. For example, replacing the solid  2 ″ cylinder with a hollow  3 ″ cylinder would require an inner diameter of 2.24″ for the same volume with the same stroke. But the heat transfer area would increase by a factor of about 2.6, and the relative distance that the heat would have to penetrate would be only about 38% of that in the 2″ cylinder. A one-hour heating cycle could be reduced to about 8.8 minutes with this design. With that reduced cycle time, the production rate would increase about 6 times.  
         [0041]     In one embodiment, the cylinder head is insulated to, for example, minimize condensation at the cold spot in the center of the product and the loss of heat to the atmosphere. Additionally, the cylinder wall thickness can be varied to alter the heat transfer properties. The material of the cylinder can be, for example, stainless steel, an aluminum/stainless sandwich (as used in waterless cookware), or normal mild steel with a stainless liner.  
         [0042]     The apparatus of the present invention is an improvement over the prior art at least because of its lack of shear until the product enters the final die orifice, which is an inherently high-shear operation required to create the desired product characteristics. Shear earlier in the process (for example in the screw of a standard extruder where it is responsible for generating most of the heat required to cook and puff the product) does little to build texture, and can be detrimental to product quality by damaging, or dextrinizing, the starch molecules. The present invention utilizes external methods of heating, such as conduction heating, thereby eliminating the damaging shear.  
         [0043]     The size of the die should be selected to optimize discharge speed, but will also vary depending on the raw materials used and the food product to be produced. There is an optimum extrusion flow rate for any particular die size. For larger product size, requiring a larger die hole, the piston speed can be increased. The die orifice itself can be streamlined for better product formation.  
         [0044]     Moisture is another operating parameter that affects the final food product produced. In one example, the mix used in the test was formulated to be at 25%, which is higher than normally used for expanded products. After mixing for about 1 hour, the moisture was measured by loss-of-weight in a microwave oven to be about 17%, which is about ideal for standard corn-based snack extrusion.  
         [0045]     The following test data is included to be illustrative only.  
         [0046]     I. Power Input and Shell Temperature:  
         [0047]     In one test, the power to the electrical heater was adjusted to maintain an average shell temperature of about 453 deg. F., starting with an initial power setting of about 100% and dropping as the sample heated up to avoid overheating the outer surface of the product within the cylinder. Applying an exponential model, a final power setting of about 51% is expected at equilibrium. Assuming that the potentiometer setting is proportional to the actual power delivered, about half of the total coil power at that temperature is lost to the atmosphere. 
         
 
         [0048]     II. Heat Penetration—Pressure and Product Temperature:  
         [0049]     Moisture migrates from the outer portions of the cylinder to the center due to the temperature gradient. The center portion remains cool for a period of time required for the heat to diffuse inward, and then its temperature starts to rise, eventually coming to equilibrium with the outer portion. This picture is complicated somewhat by the head space above the product which allows the moisture to move quickly to those cooler portions, and the effect of the unheated cylinder head which prevents that top-center portion from coming to equilibrium. Some of the energy loss noted above would be through the head. 
        Center Temperature Estimation: It was assumed that the temperature at the top center was that which would be in equilibrium with the pressure measured in the head space (steam, created by the hot outer portion, would condense in the center at a temperature in equilibrium with the pressure).     Equilibrium Temperature: Using the exponential model, an equilibrium final temperature for the top center position was estimated at about 249 deg. F., considerably lower than the shell temperature, and much lower than the normal temperature range usually required for good expansion. An additional point on this curve was generated by extrapolating the pressure curve backward in time to zero pressure (one atmosphere absolute) where the temperature would be about 212 deg. F. This occurred at about 43 minutes. 
         
       
 
         [0052]     Dimensionless Format: Unsteady-state heat transfer data are usually converted into dimensionless form for analysis. Knowing the initial and final temperature, the conversion is:  
       UTC   =         T   f     -   T         T   f     -     T   i             
 
         [0053]     where: 
        T i =initial temperature     T f =final temperature     UTC=unaccomplished temperature change        
 
         [0057]     UTC goes from 1 to zero at infinite time. 
         
 
         [0058]     Penetration Time: The resulting curve fit the exponential model well, and was extrapolated back to UTC=1 for an initial temperature of about 70 deg. F. That occurred at about 25.6 minutes, which is about how long it took for the first heat to penetrate to the center of the cylinder.  
         [0059]     Having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein can be used without departing from the spirit and the scope of the invention. Accordingly, the described embodiments are to be considered in all respects only as illustrative and not restrictive.