Packaged food item and method for achieving microwave browning thereof

• US 4,267,420 A
• Filed: 10/12/1978
• Issued: 05/12/1981
• Est. Priority Date: 05/30/1978
• Status: Expired due to Term

• Current Assignee: General Mills Incorporated
• Original Assignee: General Mills Incorporated
• Inventors: Brastad, William A.
• Primary Examiner(s): GRIMLEY, ARTHUR
• Application Number:
  US05/950,757
• Time in Patent Office: 943 Days
• Field of Search: 219/10.55 E, 219/10.55 M, 219/10.55 F, 219/10.55 R, 426/107, 426/234, 229/3.5 MF, 229/87 F
• US Class Current: 219/730
• CPC Class Codes: B65D 2581/3466 Microwave reactive material applied by vacuum, sputter or vapor deposition
• CPC Class Codes: B65D 2581/3472 Aluminium or compounds thereof
• CPC Class Codes: B65D 2581/3494 Microwave susceptor B65D2581/3487 takes precedence
• CPC Class Codes: B65D 81/3461 Flexible containers, e.g. bags, pouches, envelopes

Abstract

A food item is wrapped with plastic film or other dielectric substrate having a very thin coating thereon which controls the microwave conductivity when the package is placed within a conventional microwave oven. The plastic film or other substrate and its coating conform to a substantial surface portion of the food item. The coated plastic film or other substrate converts some of the microwave energy into heat which is transmitted directly to the surface portion so that a browning and/or crispening is achieved. The coating has the additional capability of modifying the microwave field configuration so as to further enhance the heating of the food surface immediately adjacent the film in which the food is packaged. The microwave energy not converted into heat by the coated film passes through the film to dielectrically heat the single food item as is normally done when cooking with microwaves.

Claims

1. In combination with a food item capable of having its color changed or being crispened by thermal energy, said food item to be heated in a microwave oven, wrapping material conforming generally to the shape of said food item comprising a flexible dielectric substrate having a thin semiconducting coating thereon residing in a close proximal relation to a substantial surface portion of said food item, said thin semiconducting coating having the property of being able to convert a proportion of the microwave energy of a microwave oven into heat in the coating itself to thereby change the color or crispness of the surface of the food item while permitting the remainder of the said microwave energy to pass through the wrapping material to dielectrically heat the food item.

2. The combination of claim 1 in which said semiconducting coating has a specific surface resistance of from about 1 to 300 ohms per square.

3. The combination set forth in claim 2 in which said semiconducting coating has a specific surface resistance of from about 1 to about 10 ohms per square.

4. The combination set forth in claim 2 in which the coating is evaporated aluminum.

5. The combination set forth in claim 2 in which said dielectric substrate constitutes a polyester film.

6. The combination set forth in claim 5 including a second plastic layer constituting a polyethylene film, said coating being sandwiched between said polyester and polyethylene films.

7. In combination with a food item capable of having its color changed or being crispened by thermal energy, said food item to be heated in a microwave oven, flexible dielectric material having a substantial portion thereof conforming generally to the shape of the food item, and a relatively thin flexible layer of metal carried by said dielectric material, said metallic layer also conforming generally to the shape of said food item and residing in a proximal relation thereto and having the property of being able to convert a proportion of the microwave energy of a microwave oven into heat in the metallic layer itself to thereby change the color or crispness of the surface of the food item adjacent thereto while permitting the remainder of the said microwave energy to pass through the metallic layer and the flexible dielectric material to dielectrically heat the food item.

8. The combination set forth in claim 7 in which said metallic layer has a specific surface resistivity between about 1 to 300 ohms per square.

9. The combination set forth in claim 8 in which said metallic layer has a specific surface resistivity between about 1 to 10 ohms per square.

10. The combination set forth in claim 7 in which said flexible dielectric material constitutes a polyester film, said metallic layer having been evaporated onto said plastic film.

11. The combination set forth in claim 10 in which a second plastic film is included said second plastic film confronting the other side of said metallic layer.

12. The combination set forth in claim 11 in which said second plastic film is polyethylene.