BACKGROUND TO THE INVENTION Various food products have been marketed which can be cooked in their packaging.

These include the well known pop-corn and a variety of ready-made meals that can be microwaved in a plastic tray. Other food products must be removed from any plastic packaging before placing the consumables in a microwave oven. The cooking process requires the food to be heated to such an extent that its contact with the surrounding packaging causes the plastic to melt or be otherwise degraded. The necessity of package removal serves as a significant impediment to the speed and overall convenience of microwave cooking.

There is a need to provide a food in the bag product which for the sake of convenience and cleanliness can be placed directly in a microwave without removing any surrounding packaging and without the need to provide a separate cooking container.

STATEMENTS OF INVENTION According to the present invention there is provided a food in bag product comprising a food which may be subjected to microwave heating in order to heat or cook the food and a bag, within which the food is located, the bag being formed of a plastics material which is formulated to withstand the heating or cooking conditions appropriate for the food.

Reference will be made hereinafter to potatoes but it should be understood that this invention has wider applicability.

Preferably the food in bag product includes gas exit means. The gas exit means may, by way of example, comprise a valve structure or a discontinuity in a seal of the bag.

In a preferred embodiment of the invention the gas exit means include one or more perforations extending through the plastics material.

Preferably the plastics material is polypropylene. The bag is preferably formed from a single sheet of perforated polypropylene material which is folded to provide a gusset feature at one end, preferably the bottom end, thus enabling the potato in bag product to stand upright, for instance on a shelf or other display unit.

The sides of the bag are preferably irreversibly heat sealed or welded. The polypropylene material may be transparent or coloured and may be printed with heat resistant designs.

The food in bag product has a rear and front face. The rear face of the bag extends beyond the length of the front face to provide a flap. The outward side of the front face of the bag is provided with an adhesive seal which is provided with a removable cover or strip.

When in use, and once the potatoes are located therewithin, the removable cover or strip which covers the adhesive seal on the outward side of the front face of the bag is removed to expose the adhesive seal. The flap is then folded along a foldline and overlies the adhesive seal, bonding thereto. The opening extending along the top of the bag is therefore closed.

In an alternative embodiment of the invention, the opening extending along the top of the bag is closed by means of a heat seal or welding.

The invention also provides for a bag for use in a food in bag product of the invention.

The food in bag product can be subjected to the full power of a conventional microwave oven which may vary, for instance, between 600 to 1000 watts. Although average cooking time may be approximately 10 minutes, it is appreciated that cooking times will vary according to the size and quantity of potatoes placed within the bag and to different taste preferences.

Accordingly the invention provides a method of heating or cooking a food product using a food in bag product which is closed by adhesion comprising any of the following steps: (1) removing the cover of the adhesive seal to expose the adhesive seal; (2) folding the flap along a foldline to overlie the adhesive seal and allow bonding thereto; (3) placing the bag in a microwave oven; (4) subjecting the food in bag product to heating or cooking conditions appropriate for the food which is located therewithin.

The invention also provides a method of heating or cooking a food product using a food in bag product which is closed by a heat seal or welding comprising: (1) placing the bag in a microwave oven; (2) subjecting the food in bag product to heating or cooking conditions appropriate for the food which is located therewithin; Either method of the invention may further comprise the step of piercing the bag prior to placing the bag in the oven.

The nature of the polypropylene material is such that as the cooking process continues the bag may become weaker or otherwise become degraded but it should not melt.

DETAILED DESCRIPTION OF THE INVENTION The invention will now be described by way of example only and with reference to the accompanying drawing which illustrates a side view of a bag for use with the invention.

A bag 1, which may be used in connection with the present invention, is formed by performing several folding operations on a single rectangular sheet of polypropylene material. The sheet is folded in half by bringing each opposing short side to meet with the other. One folded portion is then folded back on itself at a distance marked 'x'in the drawing which is positioned away from the central fold-line. The short side of this front portion is then folded upwardly towards the short side of the rear portion along another fold-line positioned at the same distance'x'from the first fold line.

This folding sequence gives rise to the formation of a gusset feature 10 at the bottom end of the bag and also upwardly extending rear portion 3 at the open uppermost end.

These operations may be carried out automatically using suitable bag-forming machinery.

The open uppermost end of the bag is provided with an adhesive seal 5 which is covered by a removable layer of film and upwardly extending rear portion or flap 3.

When in use, the removable layer of film is removed from adhesive seal 5 and flap 3 is folded down and sealed to adhesive seal 5. The two long sides 2 and 4 of the bag are irreversibly heat sealed or welded. In an alternative embodiment of the invention the open uppermost end of the bag is also heat sealed or welded after location of the product therein.

In one particular embodiment of the invention, the rectangular sheet of polypropylene material has a width approximating 18 cm. The rear face of the bag for use with the invention has a fully extended length which approximates 24 cm and extends approximately 4 cm beyond the length of the front face of the bag. The distance marked'x'in the diagram corresponds to a length of approximately 4 cm. It should be appreciated however that the bag for use with the invention may be of any shape

or size depending on the nature and quantity of the consumable items to be placed therewithin.

In production of the food in bag product. raw potatoes are placed within the bag through opening 6 which extends along the length of short side 8. The removable cover or strip which covers adhesive seal 5 located on the outward side of the front face of the bag is removed to expose the adhesive seal. Flap 3 is then folded along a foldline and overlies adhesive seal 5, bonding thereto. The opening extending along the top of the bag is therefore closed. In an alternative embodiment of the invention, the opening extending along the top of the bag is closed by means of a heat seal or welding. The food in bag product is now ready to be placed on sale.

After purchasing, the food in bag product may be stored until the consumer is ready to eat the foodstuff. The bag is then perforated or pieced and placed directly into the microwave oven for the cooking process.

Once cooking is completed, flap 3, which is adapted for ease of opening, is peeled back to provide easy access to food. The contents of the bag can be emptied into a dish or eaten straight from the bag.

Although reference has been made above to a potato in bag product, the invention has applicability to other foodstuffs, examples including other vegetables such as carrots, parsnips and turnips.

Materials other than polypropylene may form part or all of the material of a bag of use in the present invention. For instance, other plastics may be used, the main requirement being the ability of the material to withstand the cooking conditions for the product. In particular, the material should not melt or become vaporised during the cooking process, although it is acceptable if the material becomes somewhat weakened.