Abstract:
A flexible pouch for cooking a food item using microwave energy. The pouch includes a base configured to retain hot gases above atmospheric pressure within the pouch to heat and cook the food item when the package is exposed to microwave energy. The pouch also includes a cover comprising a sealant layer and a score layer. The score layer includes a weak portion which ruptures and vents the pouch at a predictable location when pressure within the pouch due to the hot gasses exceeds a predetermined pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. 119(e)(1) of a provisional patent application Ser. No. 60/771,243 filed Feb. 8, 2006 which is incorporated herein by reference in its entity. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to cooking by means of microwave energy, and more particularly relates to a system utilizing a flexible pouch for containing and cooking a food product which regulates and maintains an elevated internal heat and pressure during the microwave cooking process. 
     BACKGROUND OF THE INVENTION 
     Preparing food products in a pouch is generally desirable. It permits the food product to be hygienically handled without direct contact with the food and it typically reduces or eliminates the need for cleaning cooking utensils. For example, it is known to boil a variety of foods including rice and pastas in net pouches. In doing so, the net pouch with rice or pasta is immersed into boiling water. After the food is cooked, the pouch is lifted out of the water. The pouch then acts as its own colander as the water drains from the food and out of the pouch through the spaces in the net. 
     The pouches described above are typically not used for certain types of food like vegetables or fish because cooking these types of food directly in water can result in the loss of vitamins and color from the food. The uptake of water can also result in a change in the structure of the product as well as in the product&#39;s overall flavor. 
     In response to the drawbacks caused by the direct exposure of certain foods to water during the cooking process, the “boil-in-bag” process has been developed. A boil-in-bag is a closed pouch which prevents contact between the food contained in the bag and the water along with the loss of vitamins and color described above. Moreover, boil-in-bag meals are often previously prepared cooked dishes in sauce which makes them unsuitable for being placed directly into water without any protective package. Such bags are very difficult to handle after boiling because the heat imparted due to the boiling is retained within the bag and may cause burns or other injury to the consumer when the bag is opened to access the food. 
     In response to the drawbacks of the boil-in-bag process described above, various types of disposable containers have been developed for use in heating or cooking foods in microwave ovens. For example, U.S. Pat. No. 4,961,944 to Matoba et al discloses a flexible pouch for use in cooking frozen foods. The food is filled into the pouch which is sealed and then frozen. The pouch has a number of holes covered by an adhesive strip. The adhesive strip is removed before microwaving to provide a vent for steam which is generated during the microwave cooking process. 
     Plastic containers having lids with pressure relief valves are also known such as disclosed in PCT Application PCT/CH98/00546. This application discloses use of a container having a tray and rigid cover. The cover has a pressure relief valve which opens and closes to maintain a predetermined pressure range for pressure cooking for fresh food in the container headed by a microwave. However, such packaging is relatively expensive and the shelf life for fresh foods is relatively short. 
     In view of the foregoing, there is a need for a low cost, low waste article and method of steaming frozen food products without encountering the drawbacks inherent in the prior art. 
     SUMMARY OF THE INVENTION 
     The invention generally includes a flexible pouch for use in microwave heating of frozen food that enables the product to be steamed during preparation. The pouch provides a predictable venting location, and is easily handled and opened when heating is complete. More specifically, the invention includes a flexible pouch for cooking a food item using microwave energy. The pouch includes a base configured to retain hot gases above atmospheric pressure within the pouch to heat and cook the food item when the package is exposed to microwave energy. The pouch also includes a cover comprising a sealant layer and a score layer. The score layer includes a weak portion which ruptures and vents the pouch at a predictable location when pressure within the pouch due to the hot gasses exceeds a predetermined pressure. 
     In an alternative embodiment, the invention includes a pouch meal including, a plurality of pieces of frozen food, a flexible pouch having an inner surface containing the food and an outer surface. The inner surface is defined by a base and a sealant layer. The base is configured to retain hot gasses above atmospheric pressure within the pouch to heat and cook the food when the pouch is exposed to microwave energy. The pouch also includes a score layer disposed over the sealant layer. The score layer includes a weak portion configured to rupture and vent the pouch at a predictable location when the pressure within the interior of the pouch due to hot gasses exceeds a predetermined pressure. 
     In yet another alternative embodiment, the invention includes a method of cooking a food item using microwave energy. The method comprises the steps of obtaining a pouch meal having a plurality of pieces of frozen food. The pouch has an inner surface containing the food and an outer surface, wherein the inner surface is defined by a base and a sealant layer. The pouch further includes a score layer disposed over the sealant layer. The score layer includes a weak portion configured to rupture and vent the pouch at a predictable location when the pressure within the interior of the pouch due to hot gasses exceeds a predetermined pressure. 
     The method also includes the step of cooking the food item with steam and hot gasses generated by heating the food item with microwave energy during a first phase of the cooking process. During this first phase of the cooking process, the sealant layer expands to hold the increased volume of hot gases until the sealant layer forms a permeable membrane. At this point, a second phase of the cooking process begins. 
     In the second phase of the cooking process steam and hot gasses are retained within the pouch by the base and score layer. Next, the pouch is ruptured at the weak portion of the score layer during a final phase of the cooking process. 
     During the final phase of the cooking process, the internal pressure of the pouch exceeds the predetermined pressure required to break the score layer at the weak portion to allow for release of excess pressure. Next, the method includes the step of venting some steam and hot gasses through the permeable sealant layer and weak portion of the score layer. Finally, some steam and hot gasses are retained within the pouch to complete the heating and cooking of the food item. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
         FIG. 1  shows an isometric view of the pouch of the present invention. 
         FIG. 2  shows a top view of the pouch of the present invention. 
         FIG. 3  shows a side cross sectional view of the pouch of the present invention before the heating process. 
         FIG. 4  shows a side cross sectional view of the pouch of the present invention during a first phase of the heating process. 
         FIG. 5  shows a side cross sectional view of the pouch of the present invention during a second phase of the heating process. 
         FIG. 6  shows a side cross sectional view of the pouch of the present invention during a final phase of the heating process. 
         FIG. 7  shows a top view of the pouch of the present invention during a final phase of the heating process. 
         FIG. 8  shows an isometric view of the pouch of the present invention in an opened position. 
         FIG. 9  shows an isometric view of an alternative embodiment of the pouch during a final phase of the heating process. 
         FIG. 10  shows an isometric view of an alternative embodiment of the pouch of the present invention in an opened position. 
     
    
    
     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A flexible pouch  10  in accordance with the invention is shown in  FIG. 1 . Pouch  10  is generally defined by a base  12  and a cover  14 . Base  12  includes a sidewall  18  and a bottom  20 . Sidewall  18  extends upwardly from bottom  20 , defining an interior  22  for containing a food item  24 . Flange  26  extends radially outwardly relative to sidewall  18 . 
     As shown in  FIG. 1  base  12  generally forms a rectangular bowl, although a variety of shapes including round, triangular, irregular, or flat could be used while falling within the scope of the invention. Base  12  may also be fabricated from a variety of materials. In one embodiment, base  12  is an integrally thermoformed plastic material, such as polyolefins (e.g., polypropylene, polyethylene), blends of polyolefins, polystyrene—HIPS, or polyester resin-based materials—CPET, foamed polypropylene, polyethylene, paper and paper laminations with polypropylene, polyester, etc. In an alternative embodiment, base  12  may be fabricated using known injection molding or compression molding techniques. 
     With reference to  FIG. 3 , the details of cover  14  will now be discussed. Cover  14  includes score layer  28  and sealant layer  30 . In a preferred embodiment, score layer  28  and sealant layer  30  include a laminated film such as PET/PE. 
     The combination of sealant layer  30  and base  12  defines interior  22 . Score layer  28  is disposed against sealant layer  30 . In one embodiment, score layer  28  is attached to sealant layer  30  with adhesive. In another embodiment. Score layer  28  may be thermally bonded to sealant layer  30 . 
     Score layer  28  includes score  16 . Score  16  does not extend to the sealant layer  30  of the cover  14 , resulting in a completely sealed and enclosed pouch  10  containing food  24 . In one embodiment, score  16  extends from a flange  26  on one side of the pouch  10  to another flange on an opposing side of the pouch. Score  16  may be mechanically formed in score layer  28 . In alternative embodiments, score  16  may be chemically or thermally formed in score layer  28 . By weakening the tensile strength of score layer  28  along score  16 , score  16  provides a predictable rupture location along the score layer  28 . In a one embodiment, the tensile strength of score layer  28  along score  16  is less than half the tensile strength of score layer  28  without score  16 . In a preferred embodiment, the tensile strength of score layer  28  was measured to be approximately 17 lbs/in and the tensile strength of the score layer  28  along score  16  was measured to be approximately 7 lbs/in. 
     As shown in  FIG. 3 , bottom  20  of pouch  10  is generally flat. A flat bottom  20  promotes stable placement of the pouch  10  on a table top, in a microwave oven, or on another flat surface. In an alternative embodiment, bottom  12  may be concaved upwardly or inwardly relative to interior  22  of the pouch  10  to enhance microwave interaction with food items contained within pouch  10 . 
     As shown in the drawings, sidewall  18  is continuous, extending radially outwardly and upwardly from bottom  20  until terminating at flange  26 . It should be recognized however that, in a preferred embodiment, the components of base  12  and cover  14  are highly flexible and can form a wide variety of shapes. 
     With reference to  FIGS. 3-10 , the details of pouch  10  will now be discussed. When a user desires to heat the food  24 , excess packaging material (not shown) is separated from pouch  10  and pouch  10  is placed in a microwave. The user then programs the microwave to heat for a desired cooking time. Although cooking time is dependant on a variety of factors, including quantity of food  24  and microwave power. Typical cooking times range from about 1 minute to about 10 minutes, preferably about 2 minutes to about 6 minutes, more preferably about 3 minutes to about 5 minutes. 
     When the microwave begins the cooking process, the pouch  10  generally comprises the cross sectional configuration shown in  FIG. 3 . During a first phase of the cooking process, steam and hot gasses are generated in the interior  22  of the pouch. The pouch then expands to hold the excess volume created by the steam formation as shown in  FIG. 4 . As the steam and hot gasses are generated cover  14  begins to bow in an upward direction as sealant layer  30  pushes against score layer  28 . 
     As the cooking process continues, sealant layer  30  begins to stretch and deform to allow for increased volume on the interior  22  of the pouch  10  due to additional steam generation. At a second phase of the cooking process shown in  FIG. 5 , the sealant layer  30  fractures to form a permeable membrane that allows the steam to vent through various apertures  32 . As the steam initially vents through apertures  32  sealant layer  30  may separate from score layer forming one or more pockets  34 . The formation of pocket  34  increases the pressure on score layer  16  causing further deformation as steam and hot gasses are retained within the pouch by the base and score layer. 
     During a final phase of the cooking process, the pressure in the interior  22  of the pouch  10  exceeds a predetermined pressure causing the pouch to rupture at the weak portion of the score layer  28  as shown in  FIG. 6 . Because the weakest portion of the score layer is along the score  16 , the pouch  10  will rupture along the score resulting in a predictable venting location near the end of the heating. In this configuration, some steam and hot gasses are permitted to vent through the permeable sealant layer and weak portion of the score layer while other steam and hot gasses are retained within the pouch to complete the heating and cooking of the food item. 
     Once the cooking process is completed, the pouch  10  is removed from the microwave. In a preferred embodiment, the user removes the pouch  10  from the microwave by grasping the flange  26  on opposing sides of the pouch  10 . The flange  26  provides a convenient and intuitive location on the pouch  10  for the user to hold. The location of the flange  26  relative to the food  24  enables the flange  26  to cool at a relatively rapid rate allowing the user to remove the pouch  10  from the microwave without discomfort. 
       FIG. 7  illustrates a top view of the pouch  10  after the cooking process is completed but before the food  24  is removed from the pouch. In a preferred embodiment, score  16  remains identifiable. However, score  16  contains apertures  36 ,  38 , and  40  which allowed the steam and hot gasses to escape from the interior  22  of the pouch  10  during the cooking process. Although three apertures  36 ,  38 , and  40  are shown in  FIG. 7  for purposes of illustration, it is important to note that any number of apertures can be formed along score  16  while remaining within the scope of the invention. 
     With reference to  FIG. 8 , the removal of the food  24  from the pouch  10  will now be discussed. The configuration of score  16  upon completion of the cooking process provides a natural location for removal of the food  24 . However, in most instances the apertures  36 ,  38 , and  40  need to be combined into a single opening  50  to facilitate easy removal of the food. 
     To create opening  50 , the user grasps the flange  26  at locations transverse to the score  16 . Using one hand to grasp point  42  and another hand to grasp point  44 , the user pulls point  42  and point  44  apart. As the distance between point  42  and  44  increases, apertures  36 ,  38 , and  40  expand to form a single opening  50 . This configuration also provides a convenient location for the users hands away from the heat of any remaining steam that may be escaping from pouch  10 . At this point, the food  24  can be easily removed from the container. 
     It is important to recognize that score  16  can be located in a variety of locations along score layer  28  while remaining within the scope of the invention. For example, in  FIGS. 7 and 8 , score  16  is centrally located between points  42  and  44 . However, it may desirable to position score  16  closer to point  44  to facilitate the removal of large or elongated foods from pouch  10 . In a preferred embodiment, pouch  10  incorporates an easy peel material to enable the cover  14  to be removed from the base  12  without a scissors or a knife. This aspect of the invention further allows for the removal of large items from the pouch  10 . 
     With reference to  FIGS. 9 and 10 , an alternative embodiment of pouch  10  will now be discussed.  FIG. 9  shows two apertures  52  and  54  that are formed along score  16  upon completion of the cooking process. Again, it is necessary to combine apertures  52  and  54  along score  16  to create a single opening  50  to facilitate easy removal of some food products. 
     To create opening  50 , the user grasps handles  56  and  58 . Handles  56  and  58  are disposed near the flange  26  at locations transverse to the score  16 . Using one hand to grasp handle  56  and another hand to grasp handle  58 , the user pulls handle  56  and handle  58  apart. As the distance between handle  56  and handle  58  increases, apertures  52  and  54  expand to form a single opening  50 . This configuration also provides a convenient location for the users hands away from the heat of any remaining steam that may be escaping from pouch  10 . At this point, the food  24  can be easily removed from the container. 
     In another embodiment, pouch  10  may consist essentially of a cover  14 . A score  16  is disposed in cover  14  to provide a predictable venting location. This embodiment has the advantage of simplifying the manufacturing process as only a single material is used to make the pouch  10 . 
     Pouch  10  may be used for a variety of food items, including individually frozen predominately carbohydrate ingredients, individually frozen predominately vegetable ingredients, individually frozen predominately meat based ingredients, and combinations thereof, although a wide variety of food items may be used while remaining within the scope of the invention. 
     Although the invention has been described with reference to preferred embodiments, workers of ordinary skill will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention.