Abstract:
A flexible package for storing and heating a precooked food product in a microwave oven includes an upper portion and a lower portion detachably connected to the upper portion. The lower portion includes a side defining a cavity adapted to hold the food product during heating and to serve the food product after the upper portion is removed. A vent is disposed in an aperture in the upper portion that operatively opens to release steam, and the vent is a valve that is initially closed and opens when a pressure within the package is greater than a predetermined valve opening pressure and stays open during heating in the microwave oven in order to completely exhaust the pressure formed in the package during heating.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional application of U.S. patent application Ser. No. 10/228,430 filed Aug. 27, 2002, which claims priority of U.S. Provisional Patent Application Ser. No. 60/315,207 filed Aug. 27, 2001. 
     
    
     FIELD OF THE INVENTION  
       [0002]     A package for cooking food in a microwave and a method of use. More particularly, a package having a vent.  
       BACKGROUND OF THE INVENTION  
       [0003]     Various types of disposable containers have been developed for use in heating or cooking foods in microwave ovens. 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.  
         [0004]     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 fresh food in the container heated by a microwave. However, such packaging is relatively expensive and the shell life of fresh foods is relatively short.  
         [0005]     Accordingly, it would be desirable to provide packaging which is inexpensive to produce, however can be used to eat the food after it has been heated. Additionally, it would be desirable to provide a method of providing prepared food in a microwave which provides a tasty meal and which has a long shelf life.  
       SUMMARY OF THE INVENTION  
       [0006]     Accordingly, a package for heating precooked food in a microwave and method of use has been devised. The package has a lower portion which is used for serving the food and ant upper portion having a vent. In one embodiment, the package is a flexible pouch having a bottom and a pair of sidewalls which are sealed at the top. The bottom is attached to the sidewalls with gussets so that the pouch stands up when rested on the bottom. A line of weakening extends from a notch in a side seam horizontally across the sidewalls to permit removal of the top portion after cooking by tearing the top and bottom portions apart. The top portion includes a vent for releasing steam generated by cooking from the package. The side walls of the bottom section have vertical reinforcement ribs formed to provide the sidewalls with sufficient rigidity to remain upright after the top is removed and form a serving dish for the food.  
         [0007]     A first embodiment of the package is suitable for use with two food portions requiring different preparation. The package is similar to the pouch of the preferred embodiment, but after a first food portion is filled in the bottom, the pouch is sealed below and above the line of weakening. A second food portion is filled in to the upper portion. The upper and lower portions are separated before heating, thus one portion may be heated for a different period of time than the second portion or not heated at all.  
         [0008]     A second embodiment includes a rigid tray having a cover formed of film. The cover includes a pressure relief device. The cover has a heat activated adhesive which may be peeled from the tray after the food portion is microwaved.  
         [0009]     A method of preparing food utilizing the package includes precooking a food product until the food has a water content of approximately 20%, filling a package with a portion of said food product, sealing said package, freezing said food product, microwaving said package and food product for a predetermined length of time at a predetermined power, venting steam from the package during cooking with a pressure relief device mounted in an upper portion of the package, and removing the upper portion of said package and serving the lower portion of said package containing said portion of food product. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a front view of a package in accordance with an embodiment of the invention;  
         [0011]      FIG. 2  is a cross-sectional view of a package in accordance with the invention,  
         [0012]      FIG. 3  is a front view of the package partially separated along the line of weakening in accordance with the invention;  
         [0013]      FIG. 4  is a perspective view of the package alter the top portion has been removed;  
         [0014]      FIG. 5  is a front view of another embodiment of the flexible pouch;  
         [0015]      FIG. 6  is a front view of the package after separation;  
         [0016]      FIG. 7  is a perspective view of a package according to a further embodiment of the invention; and  
         [0017]      FIG. 8  is a flow chart showing the method according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     Shown in  FIGS. 1-4  is a package  10  suitable for heating a precooked food portion  12  in a microwave oven. In this embodiment, the package  10  is a flexible stand-up pouch  14 . The pouch  14  has a tray-like lower portion  16  containing the food portion  12  and an upper portion  18  having a vent  20 .  
         [0019]     As shown in  FIGS. 1 and 2 , the pouch  14  is formed of a pair of panels  22  and a bottom  24 . As is known in the art, the panels  22  are welded together to form seams  28  and the bottom  24  is welded to the panels with gussets  30  so that the bottom of the pouch has a somewhat elliptical profile ( FIG. 4 ) which permits the pouch  14  to stand up on the edges of the bottom of the panels  22 . The pouch may be formed as known on a form-fill-seal machine. The pouch may be formed from a web of film of flexible material such as polyethylene, aluminum foil, VHOH, polypropylene. During the forming of the pouch, an embossed portion  33  is formed horizontally from seam  28  to seam  28  and a line of weakening  39  is formed with a laser through the embossed portion  33 . A tear notch  34  is formed through each seam  28  to facilitate separation of the upper portion  18  from the lower portion  16  along the line of weakening  32  after the food portion has been heated. As shown in  FIG. 4 , the embossment provides smooth edges along the line of weakening after separation.  
         [0020]     A plurality of spaced apart vertical ribs  36  are thermoformed onto the panels  22  of the lower portion  16  of the pouch  14 . The ribs  36  provide rigidity to the panel  22  of the lower portion  16  so that the lower portion  16  forms a tray  38  with sides  40  formed from the portion of the panels  22  having the ribs  36  for serving the food portion  12  after the upper portion  18  is removed.  
         [0021]     As shown in  FIG. 1 , the vent  20  is mounted on one panel  22  of the upper portion  18  of the pouch  14 . The vent  20  exhausts steam from the package during cooking. The vent remains closed tightly until pressure from gas in the pouch reaches approximately 3 mbar during microwaving. The vent then remains open to vent gas from the package. Although many suitable vents such as holes covered by tape may be used, in the preferred embodiment the vent  20  is a pressure relief device having a Model Number W009, manufactured by WIPF of Volketswll, Switzerland. The pressure relief device also is operable to respire gas formed in the package prior to heating from decaying food or during freezing. The vent device  20  is welded in an aperture formed in the panel  22  during the forming process.  
         [0022]     After the pouch is formed, the food portion  12  is filled through an opening formed between upper edges  42  of the panels  22 . The upper edges  42  are sealed as known in the art by a satisfactory method such as heat sealing.  
         [0023]     As shown in  FIGS. 3 and 4 , after the portion of food has been heated in the microwave, the upper portion  18  of the pouch is separated from the lower portion by ripping the pouch from the tear notch  34  on the seam  28  across the line of weakening  32 , forming the tray  38  for serving the portion of food  12 . The tray  38  sits on the bottom of the edges of the panels with the thermoformed ribs  36  supporting the sides  40 .  
         [0024]     As shown in  FIG. 1 , the package may be provided with a label  44  having bar coding  46  which is read by a scanner in the microwave, so that cooking time and temperature is automatically entered into the microwave. Additionally, a cooking temperature indicator  48  such as a strip of temperature-sensitive material which changes color upon reaching a certain temperature may be placed on the label so as to give an indication of when the food is properly heated.  
         [0025]     As shown in  FIGS. 5 and 6 , another embodiment of the pouch  14  is formed as discussed above. However, seals  50 ,  52  are formed on either side of the line of weakening  3  to permit the pouch to carry two different portions of food. After a first food portion  54 , such as a salad, is filled into the lower portion  16  of the pouch, seals are formed on either side of the line of weakening. The seals  50 ,  52  are formed with a heat seal. Thus, a top of the lower portion is sealed by seal  50  and a bottom of the upper portion  18  is formed by seal  52 . A second food portion  56 , such as chicken, is then filled into the upper portion  18  and the upper edges  42  of the upper portion are then sealed as before.  
         [0026]     When the meal is prepared, the upper portion  18  is separated from the lower portion  16  by way of the tear notches and line of weakening. As shown in  FIG. 6 , the upper portion  18  is placed in the microwave and heated. After heating, the seal  50  at the top of the lower portion is opened to form the tray  38  and access the salad  54 . After the second food portion  56  is heated in the upper portion  18  of the pouch  14 , the bottom seal  52  of the upper portion is opened and the second food portion  56  may be placed in the tray  38  for service as a meal. Alternatively, two different food products may be placed in the upper and lower portions  18 ,  16  and a second vent  20  is also mounted in the lower portion  16 . In this way two food types which require different cooking times may be utilized. Both food portions may be served in the tray  38 , as discussed above.  
         [0027]     As shown in  FIG. 7 , a further embodiment is illustrated which includes a package  60  having a lower portion consisting of a tray  62  and a removable upper portion consisting of a heal sealable/peelable film cover  64 . The film cover  64  includes a vent device  20 . The tray is filled with a portion of food (not shown). The tray  62  is preferably produced of a clear plastic such as cast polypropylene. The tray  62  has a bottom  66  and a side  70  having a top edge  72 . The tray should remain stable to −72° Celsius. The tray  62  has an oval shape and fibs  74  are formed in the side  70  to provide strength to the sides. A handle  76  is disposed at each end of the tray in order to facilitate moving of the tray  62  after the portions of food  12  have been heated.  
         [0028]     The cover is formed of a film laminate having a polyester layer, a polypropylene layer, and an adhesive layer. The polyester layer has a thickness of 12.0 micrometers and a weight of 16.8 grams/m 2 . The polypropylene layer has a thickness of 90.0 micrometers and a weight of 81.0 grams/m 2 . The adhesive layer has a thickness of 2.5 micrometers and a weight of 2.5 grams/m 2 . Such a film laminate has a low oxygen permeability and water vapor permeability. The sealing medium of the adhesive layer has a melting point of 165° Celsius and a sealing range of 180°-230° Celsius depending upon sealing time and pressure. Suitable adhesive layers are a mixture of a cast polypropylene and polyethylene. The film must be able to withstand a minimum of 120° Celsius heat. Film of this type is available from WIPF of Volketswll, Switzerland.  
         [0029]     The film is supplied as a web. The web is unrolled and apertures are formed in the web at predetermined spaced apart locations. The vent device  20  is heat welded to the film and the apertures formed in the web. The portion of food  12  is filled into the tray  62  and the trays  62  are then delivered by a conveyor to a station where the web of film which is then sealed on the edge  72  of the tray and cut to the shape of the tray  62  and handles. After heating, the cover may be peeled from the tray and the food is served in the tray. Alternatively, the covers may be cut to the shape of the trays and supplied separately with the trays to small scale production facilities such as delis. At the deli, the food is filled in the tray as before, but the precut covers are placed on the tray and heat sealed on the tray in a machine which heats the adhesive to seal the cover to the tray.  
         [0030]     As shown in  FIG. 8 , the method of food preparation using the packaging includes first filling  80  a portion of precooked food having a moisture content which is generally 20% into a package. The food portion can be a single food item or can be a dish prepared to a recipe. The precooking prevents rapid decomposition of the food. Thus, food which has been at least partially precooked will have a shelf life of up to seventeen days whereas raw food will have a shelf life of approximately seven days. In the precooking or blanched state, the food is cooked until it reaches a temperature of 125° Celsius. Satisfactory temperature ranges for partially cooked food are set forth as follows:  
                                                       Temperature           Food   Celsius                           Chicken   125           Beef   130           Fish   110           Pork   125           Green beans   105           Carrots   105           Broccoli   100                      
 
         [0031]     Examples of satisfactory recipes are set forth below.  
       EXAMPLE 1 
       [0032]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                   
               
               
                 Seared Chicken and Rice with Vegetables 
               
             
          
           
               
                   
                 INGREDIENT 
                 NOTES 
               
               
                   
                   
               
             
          
           
               
                 AMOUNT 
                   
                   
               
               
                 135 g.  
                 90% cooked rice 
                 Parboiled long grain rice 
               
               
                 40 g. 
                 Blanched broccoli florets, 
                 Blanched in salted water 
               
               
                   
                 small 
               
               
                 25 g. 
                 ¼ inch sliced and seared 
                 Seared in canola oil 
               
               
                   
                 button mushrooms 
               
               
                 25 g. 
                 ¼ inch sliced, blanched 
                 Blanched in salted water 
               
               
                   
                 and half moon cut carrots 
               
               
                 10 g. 
                 Prepared chicken stock 
                 Prepared from chicken base 
               
               
                   
                   
                 paste and water 
               
               
                 120 g.  
                 Seared and ¼ inch slight 
                 Seasoned with kosher salt and 
               
               
                   
                 bias-sliced chicken breast 
                 fresh ground black pepper; 
               
               
                   
                   
                 seared quickly on both sides. 
               
               
                   
                   
                 Trimmed of all fat and 
               
               
                   
                   
                 cartilage. 
               
               
                   
                   
                 Seared in canola oil 
               
               
                 355 g.  
               
               
                 METHOD 
               
               
                 1. 
                 Place rice, vegetables and 
               
               
                   
                 chicken stock in base of 
               
               
                   
                 container 
               
               
                 2. 
                 Place chicken, slightly 
               
               
                   
                 shingled, in one line across 
               
               
                   
                 top of rice and vegetables 
               
               
                 3. 
                 Place top on container and 
               
               
                   
                 seal 
               
               
                 4. 
                 Microwave at 800 watts for 
               
               
                   
                 4 minutes or until chicken is 
               
               
                   
                 just cooked through 
               
               
                   
               
             
          
         
       
     
       EXAMPLE 2 
       [0033]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                   
               
               
                 Penne Pasta Primavera with Seared Chicken 
               
             
          
           
               
                   
                 INGREDIENT 
                 NOTES 
               
               
                   
                   
               
             
          
           
               
                 AMOUNT 
                   
                   
               
               
                 125 g.  
                 90% cooked penne or farfalle 
                 Cooked in salted water. Real 
               
               
                   
                 pasta 
                 Torino brand, 100% durum 
               
               
                   
                   
                 semolina 
               
               
                 30 g. 
                 Blanched broccoli florets, 
                 Blanched in salted water 
               
               
                   
                 small 
               
               
                 25 g. 
                 ¼ inch sliced and 
                 Seared in canola oil 
               
               
                   
                 seared button mushrooms 
               
               
                 25 g. 
                 ¼ inch sliced, blanched 
                 Blanched in salted water 
               
               
                   
                 and half moon cut carrots 
               
               
                 20 g. 
                 Frozen peas 
               
               
                 60 g. 
                 Prepared alfredo sauce 
                 Digiorno brand 
               
               
                 10 g. 
                 Prepared chicken stock 
                 Prepared from chicken  
               
               
                   
                   
                 base paste and water 
               
               
                 100 g.  
                 Seared and ¼ inch 
                 Seasoned with kosher salt and 
               
               
                   
                 straight sliced chicken breast 
                 fresh ground black pepper; 
               
               
                   
                   
                 seared quickly on both sides. 
               
               
                   
                   
                 Trimmed of all fat and 
               
               
                   
                   
                 cartilage. 
               
               
                   
                   
                 Seared in canola oil 
               
               
                 395 g.  
               
               
                 METHOD 
               
               
                 1. 
                 Combine pasta with 
               
               
                   
                 vegetables and alfredo sauce 
               
               
                   
                 and toss to coat well. Place 
               
               
                   
                 entire contents in base of 
               
               
                   
                 container 
               
               
                 2. 
                 Top with chicken slices in a 
               
               
                   
                 single layer 
               
               
                 3. 
                 Place top on container 
               
               
                   
                 and seal 
               
               
                 4. 
                 Microwave at 800 watts for 3 
               
               
                   
                 minutes 30 seconds, or until 
               
               
                   
                 chicken is just cooked through 
               
               
                   
               
             
          
         
       
     
         [0034]     Once the food has been precooked, it is then cut in portions and then placed into a lower portion of the package. Total volume of the food must not exceed 500 grams for a container having a volume of 700 grams. The package has an upper portion having the vent device as discussed below. The oxygen may be purged from the package with a nitrogen bath. The package is sealed.  
         [0035]     The next step is a freezing step  82  where the food in the package is then flash frozen and stored until meal time. The vent device may be of the type which respires during the freezing. If desired, the valve may be covered with a seal which is removed before cooking.  
         [0036]     The next step is a heating step  84  where the package is then heated in a microwave at a predetermined power level and time as required for the recipe. While the food portion is being heated, steam is vented  86  from the package. The vent device  20  opens at a predetermined pressure, such as 3 mbar and remains fully open through the heating process.  
         [0037]     The next step is to remove  88  the upper portion of the package. Finally, the heated food is served  90  in the lower portion  16  of the package  10 .  
         [0038]     It is understood that while certain embodiments of the present invention have been illustrated and described, the invention is not to be limited to specific forms or arrangements herein described and shown.