FIELD OF INVENTION

[0001 ] The present invention relates to the field of food science, particularly reheating processed food.

[0002] In one form, the invention relates to reheating packaged food for extended periods of time.

BACKGROUND ART

[0003] It is to be appreciated that any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the present invention. Further, the discussion throughout this specification comes about due to the realisation of the inventor and/or the identification of certain related art problems by the inventor. Moreover, any discussion of material such as documents, devices, acts or knowledge in this specification is included to explain the context of the invention in terms of the inventor’s knowledge and experience and, accordingly, any such discussion should not be taken as an admission that any of the material forms part of the prior art base or the common general knowledge in the relevant art in Australia, or elsewhere, on or before the priority date of the disclosure and claims herein.

[0004] Food packaging performs five basic functions (i) protection, (ii) containment, (iii) information, (iv) handling/storage and (v) promotion. The correct selection of processing and packaging material is fundamental to maintaining product quality and freshness during distribution and storage.

[0005] Packaged foods intended to stored and presented to consumers while hot present significant challenges. Commercial outlets such as convenience stores and motorway refuelling stations that do not have kitchens or cooking areas and are limited to selling cold packaged products such as sandwiches, iced doughnuts and cakes. [0006] However, there is significant demand for hot food for immediate consumption 'on the go'. Accordingly, some commercial outlets use glass-fronted heated cabinets that hold food at a pre-set temperature for extended periods. The desired temperature for holding the food is 62 to 65°C so the heated cabinets typically have a temperature setting of 75 to 80°C in order to compensate for heat leakage such as when the door is opened to insert or remove servings of the food. The warm cabinet reduces the shelf life of food because it quickly dries out, or alternatively components of the food become flaccid, unattractive and unpalatable and the food product ultimately becomes unsuitable for sale. Lowering the heat in the cabinet to reduce these effects is not an option because dangerous microorganisms can grow at lower temperatures.

[0007] Some pastry products such as pies, pasties and sausage rolls are often stored in heated cabinets for about 4 hours before they become dry and inedible, but other foodstuffs such as burgers or egg and bacon muffins are more quickly ruined.

[0008] The prior art packaging used for reheatable foods does little to extend their shelf life at elevated temperatures. In one particularly popular method of packaging of the prior art foods are sealed within thermoformable polymer film from which most of the air has been removed by application of a vacuum. Thermoforming is a manufacturing process where a polymer sheet is heated to a temperature at which it is pliable, formed to a desired shape in a mold, sealed (if necessary) and trimmed to from a neat package. Vacuum forming is a type of thermoforming and uses reduced pressure to conform the polymer film to the mold during forming.

[0009] Thermoforming vacuum packaging machines such as those marketed under the trade marks Variovac™ or Multivac™ are well known in the food industry.

[0010] If necessary, the package is heated to cook the food. The sous vide technique is often used in the food industry and involves placing the vacuum packaged food in a water bath or steam environment for extended periods at a temperature that is much lower than normal cooking temperatures. The packaged food is then chilled or frozen for storage and transport prior to reheating.

[001 1 ] In the past, attempts have been made to create packaging that facilitates storage in a heated cabinet. However, these attempts have not generally been successful. For example, attempts to provide packages with vents, or that open by themselves during heating have permitted excessive moisture loss from the food, particularly bread based products.

[0012] However, similar hermetically sealed packaging (without vents) have resulted in internal water condensation and caused the food to go soggy. Food elements such as bread and pastry are particularly susceptible to becoming soggy. Some hermetically sealed packaging also tends to puff up, which consumers find to be unattractive.

SUMMARY OF INVENTION

[0013] An object of the present invention is to provide a packaging that keeps re-heated food in good condition for extended periods.

[0014] A further object of the present invention is to alleviate at least one disadvantage associated with the related art.

[0015] It is an object of the embodiments described herein to overcome or alleviate at least one of the above noted drawbacks of related art systems or to at least provide a useful alternative to related art systems.

[0016] The present invention relates generally to a method of packaging food in a controlled anaerobic atmosphere within a food grade film, and wherein the moisture content is optimised upon re-heating the packaged food.

[0017] In a first aspect of embodiments described herein there is provided a method of preserving food within a package, the method characterised by maintaining an atmosphere within the package comprising:

• a partial oxygen pressure of less than 10 kPa, a moisture content of 40 to 56 wt%, preferably 44 to 48 wt% a pressure of 0.9 to 1 .1 atm, and a temperature of 57 to 83°C, preferably 62 to 65°C.

[0018] In a particularly preferred embodiment, there is provided a method of preserving food within a package the method characterised by the steps of:

(i) applying heat to cook at least a part of the food,

(ii) forming a package around the food, the package comprising a food grade film, and

(iii) maintaining an atmosphere within the package comprising:

• a partial oxygen pressure of less than 10 kPa,

• a moisture content of 40 to 56 wt%, preferably 44 to 48 wt%,

• a pressure of 0.9 to 1.1 atm, and

• a temperature of 57 to 83°C, preferably 62 to 65°C.

[0019] The present invention further provides a packaged food preserved according to the method of the present invention as disclosed herein.

[0020] Typically, the atmosphere within the package and according to the present invention is maintained for at least 12 mins, more preferably at least 6 hours, even more preferably at least 24 hours.

[0021] In one preferred embodiment of the present invention, the food has a single element. An example of a single element food would be a dumpling consisting solely of a grain, rice or potato based dough. In another preferred embodiment, the food will have at least two, possibly three or more elements. An example of a two component food would be a meat ball sub comprising meat ball (first element) and bread bun (second element). Another example, would be a dumpling that includes a small portion of meat, fish, vegetable or fruit. An example of a three component food would be an egg and bacon muffin. At least part of the food may be cooked before being packaged. For example two elements (the egg and bacon) may be cooked before being placed on the muffin.

[0022] In one preferred embodiment the cooking (step (i)) is a pasteurisation step.

[0023] Some foods have a high volume of water, and are referred to as 'wet' foods so that the moisture is principally within the food. These foods are often closely surrounded by their packaging so that the volume of surrounding atmosphere is quite small.

[0024] In a second aspect of embodiments described herein there is provided a method of preserving food within a package, the method characterised by:

• maintaining an average moisture content within the food of 40 to 56 wt%, preferably 44 to 48 wt%, and maintaining an atmosphere within the package comprising;

• a partial oxygen pressure of less than 10 kPa,

• a pressure of 0.9 to 1.1 atm, and

• a temperature of 57 to 83°C.

[0025] In a particularly preferred embodiment, there is provided a method of preserving food within a package the method characterised by the steps of:

(i) applying heat to cook at least a part of the food,

(ii) forming a package around the food, the package comprising a food grade film, and

(iii) maintaining an average moisture content within the food of 40 to 56 wt%, preferably 44 to 48 wt%, and maintaining an atmosphere within the package comprising: a partial oxygen pressure of less than 10 kPa,

• a pressure of 0.9 to 1 .1 atm, and

• a temperature of 57 to 83°C.

[0026] In this case step (i) may occur before and/or after forming the package around the food.

[0027] For example, products such as dim-sims are often packaged by thermoforming with a relatively small volume of surrounding atmosphere. According to the present invention a dim-sim, comprising a meat and cabbage mixture wrapped in dough would be formulated with an appropriate moisture content. Alternatively, or in addition, ice may be added just prior to the dim sim being thermoform packaged to provide the appropriate level of moisture at 57 to 83°C. Solid water (ice) is used rather than liquid water because the application of reduced pressure during thermoforming would draw off liquid water.

[0028] The film suitable for use in the present invention must be a foodgrade, ovenable film. For example, for low temperature re-heating, up to 83°C the person skilled in the art will appreciate that a nylon based film may be appropriate. For high temperature re-heating film with a heat resistance rating of at least 218°C may be appropriate. The latter would include laminate PET films such as the Mylar™ range of films from DuPont Teijin Films, which satisfy the US Food & Drug Administration regulations 21 CFR177.1630 or 21 CFR177.1390 such as CKP5-200 and CKFP-400/600.

[0029] The film used in the packaging of the present invention is typically used in sheet form. When the packaging is carried out by thermoforming, the thermoforming device draws the film against a shaped mould or forming tool. Depending on the type of packaging required one film may be used as a forming web, and the other used as release film, such as the release films disclosed in US patent 5,795,649.

[0030] Inert anaerobic gases suitable for use in the atmosphere around the food in present invention include food grade nitrogen (E941 ), carbon dioxide (E290), helium (E939) or argon (E938) which do not chemically alter the food they protect. In a preferred embodiment, the atmosphere around the enclosed food is up to 100% N2, or up to 90% CO2. In a particularly preferred embodiment, the atmosphere is a combination of 60 to 80% N2 with 20 to 40% CO2. These gasses are usually dry, or substantially dry when used in food packaging. Accordingly, moisture in the atmosphere within the packaging is typically derived from the food.

[0031] In the field of food science, the amount of water in food is often measured as (i) water activity (aw), or (ii) moisture content. The term 'water activity' (aw) or equilibrium relative humidity (ERH) is the partial vapour pressure of water in a food substance divided by the partial vapour pressure of pure water at the same pressure. In other words aw = p/ ps where p is the water vapour pressure above the product surface and ps is the water vapour pressure above the surface of pure water at the water temperature. (ERH = 100 x aw). It is based on a scale from 0 to 1. Water tends to migrate from areas of high water activity to areas of lower activity and must remain within a specified range for food quality and safety.

[0032] By contrast, moisture content of food is usually defined as the percent weight of water content in relation to the dry weight of the sample.

[0033] Packaged food products are often designed to have components of similar moisture content to minimise moisture migration. The moisture content of a product will always tend towards an equilibrium with the surrounding atmosphere. In the case of the present invention, any moisture migration within the package contributes to stabilising the water activity.

[0034] Food packaged according to the method of the present invention can be re- heated by any convenient method, such as a heated cabinet or oven. In a particularly preferred embodiment the food is re-heated in a so-called 'hot fridge' such as those marketed under Evereo™. In another example, the food may be re-heated and kept in a preserving chamber according to the method described in WO 2015/018682.

[0035] In another aspect of embodiments described herein there is provided a food product manufactured according to the method and process of the present invention. [0036] Other aspects and preferred forms are disclosed in the specification and/or defined in the appended claims, forming a part of the description of the invention.

[0037] In essence, embodiments of the present invention stem from the realization that controlling the atmosphere immediately surrounding a food product by a combination of processing and film choice can significantly improve the reheating shelf life of a packaged product.

[0038] Advantages provided by the present invention comprise the following:

• increased shelf life of a reheated product,

• improved palatability of reheated product for extended periods, and

• reduced food spoilage and waste.

[0039] Further scope of applicability of embodiments of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure herein will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Further disclosures, objects, advantages and aspects of preferred and other embodiments of the present application may be better understood by those skilled in the relevant art by reference to the following description of embodiments which are given by way of illustration only, and thus are not limitative of the disclosure herein.

[0041 ] Figure 1 is a flow chart that illustrates a non-limiting example of steps involved in the method of the present invention. DETAILED DESCRIPTION

Example 1 - Egg, cheese and bacon muffin

[0042] The present invention is further illustrated with reference to packaging and reheating an egg, cheese and bacon muffin. This is an example of a food that is typically at least partially cooked prior to packaging, and chilled or frozen after packaging.

[0043] As a first step, an egg is cracked into each of a series of recesses in an egg tray. Each recess is of a size that allows the albumin to spread to a diameter that is slightly greater than the diameter of the muffins to be used in the product. A bacon rasher - preferably not too fatty - is placed on top of each egg. The tray of egg/bacon fillings is cooked (for example 8 mins at 185°C) until the egg yolk has formed a thin 'skin' and the bacon has curled slightly which provides a visual indication that the desired moisture content has been achieved. After this step, the moisture content of the egg/bacon filling approximately matches the moisture content of the muffin.

[0044] As a second step, the egg/bacon fillings in the egg tray are chilled and a slice of tasty cheese placed on top. Each egg/bacon/cheese filling is placed in an English muffin. The filled English muffin is then placed in the preformed pouch which has been pre- moulded to neatly follow the shape of the filled muffin.

[0045] The pouch is made from a pair of PET laminate films such as CKP5-200 and CKFP-400/600. One of the laminates forms a web and the other is an easy peel layer so that the consumer can easily rip open the pouch without the need for scissors or knives, yet the pouch is robust enough to avoid bursting when subjected to vacuum and heating.

[0046] As a third step the filled English muffin is placed in the vacuum chamber vacuum of a Thermovac™ packaging machine and the pressure inside the pouch is reduced to a pre-determined level to ensure that the film is pulled closely and neatly around the product but the product is not crushed. Vacuum forming the packaging film so that it almost touches the product results in a very small headspace is particularly preferred. [0047] The interior of the vacuum pouch is also back flushed with carbon dioxide or nitrogen to reduce aerobic bacterial growth. The egg, cheese and bacon muffin can then be snap frozen for storage or transport to retail outlets. The modified atmosphere in which the egg, cheese and bacon muffin is packaged permits defrosting in store and kept refrigerated for up to 9 days before heating.

[0048] The egg, cheese and bacon muffin can subsequently be held at a temperature of 62 to 65°C for at least 24 hours and remain soft, fresh and unspoiled from a microbiological point of view. Under these conditions, the moisture content of the ingredients equalises throughout the product. Usually, the moisture from elements of slightly higher water activity migrates to the elements of lower water activity and hinders them from drying out. This provides an egg and bacon muffin of excellent quality over an extended period.

[0049] The process described can be used for a wide range of products that include bread and meat, such as meatball subs, hotdogs, hamburgers and soforth. It is noted that the selection of the type of bread used is quite important as certain structured breads perform better than others.

Moisture Content

[0050] As mentioned above, during reheating the moisture content of the ingredients equalises throughout the product. As an illustration of this, two egg, bacon and cheese muffins were tested ('Sample T and 'Sample 2'). The moisture content of the entire muffin was then measured. Sample 3 lists the moisture content of individual elements measured separately.

Sample 1

[0051] The assembled egg, bacon and cheese muffin was packaged and frozen then defrosted and held under refrigeration for four days. [0052] The muffin (minus packaging) had a net weight of 135.8 g. The muffin was put in an oven to drive off all moisture. After drying, the muffin net weight was 71 .4 g. This reflects a moisture content of 64.4g or 47.5 wt%

Sample 2

[0053] The assembled egg, bacon and cheese muffin was packed and frozen then defrosted and held under refrigeration for four days. Finally, it was re-heated and held at 62°C for 24 hours.

[0054] The muffin (minus packaging) had a net weight of 151 .8 g. After drying, the muffin net weight was 77.3 g. This reflects a moisture content of 73.5 g or 47.7 wt%.

Sample 3

[0055] The following results reflect the moisture content of individual components of the egg, bacon and cheese muffin;

Example 2 - Dim Sims

[0056] This is an example of a food that is subjected to pasteurisation after packaging.

[0057] A dim sim is a dumpling comprising minced meat, cabbage and seasoning encased in a thick, dough wrapper similar to the wrapper of a Chinese shumai dumpling. They are often steamed, hence retaining them for sale in a retail outlet has provided difficult. Firstly, the retail outlet needs to have a steamer to keep the dim sims in hot steam. Secondly, unless they are purchased at exactly the right time they are either slightly chewy because the dough of the wrapper is not completely cooked or they are quite soggy because the dough has absorbed too much steam.

[0058] The present invention provides a useful alternative for producing dim sims and similar products such pot-stickers and other moist dumpling-style foods. The first step is to form a mould that holds three dim sims side-by-side, then provide the correct amount of moisture to optimise moisture absorption and palatability of the wrapper and its contents.

[0059] As a second step the dim sims are placed in the preformed pouch which has been pre-moulded to neatly follow the shape of each dim sim. The pouch is made from a pair of PET laminate films such as CKP5-200 and CKFP-400/600. One of the laminates forms a web and the other is an easy peel layer so that the consumer can easily rip open the pouch without the need for scissors or knives yet the pouch is robust enough to avoid bursting when subjected to vacuum and heating.

[0060] As it is difficult to reduce pressure in the presence of liquid water, the required amount of moisture was included in solid form (ice) in the packaged with each dim sim. The pouched dim sims are then move into the vacuum chamber and the pressure within each package is reduced.

[0061 ] As a third step, the packaged dim sims were placed in a steamer and Pasteurised. This was achieved by heating to a pre-determined temperature for a predetermined length of time. For example, the dim sim product may be boiled or steamed at 80° for 2.5 hours. Preferably the steaming is at 75 to 80°C to avoid bursting the pouch.

[0062] By doing the moisture and the environment or atmosphere is stable and constant as the moisture content equalises throughout the whole product.

[0063] This produces a safe, palatable, long life hot convenience food that is suitable for sale for up to 24 hours. Example 3 - Dumplings

[0064] Dumplings are cooked balls of dough, wherein the dough is based on a grain such as flour or matzah meal, rice or potatoes. The dough may be wrapped around, or stuffed with a small portion of meat, fish, vegetables or fruit. Typical fillings include sauerkraut, ground meat, cheese and fruits. Dumplings may be European in style such as pierogi, germknodel, knodel, gnocchi, kalduny, kibbeh, matzah balls, palt, kroppkaka, marillenknodel, Gondi dumplings or Silesian dumplings. Dumplings may be Asian in style, such as bao or baozi, idli, pempek, pundi, shumai, tangyuan, wonton and dim sum

[0065] This is an example of a combination of the processes of Example 1 and Example 2 as applied to the Asian dumpling known as bao or baozi and more generally applicable to other types of dumplings.

[0066] A yeast leavened dough was made using flour, water, sugar and yeast, although a chemical leavening agent such as baking powder can also be used instead of yeast. A shortening agent such as lard butter or margarine may be included in the dough if desired.

[0067] The dough was mixed and kneaded in the traditional way and left to rise. The risen dough was then divided into portions and each portion is filled with the desired filling, such as, for example, barbecue pork, Asian flavoured minced beef, minced chicken and oyster sauce,

[0068] The dumplings were then steamed until they rose and reached an internal temperature above 75°C. The dumplings were then removed from the steamers and blast chilled to less than 5°C within 90 minutes. Alternatively, the dumplings can be snap frozen.

[0069] The dumplings were placed in the vacuum chamber vacuum of a Thermovac™ packaging machine and the pressure inside the pouch was reduced to a pre-determined level to ensure that the film is pulled closely and neatly around the dumplings. The interior of the vacuum pouch is also back flushed with carbon dioxide or nitrogen to reduce aerobic bacterial growth. [0070] As an alternative, the dumplings can be vacuum packed prior to steaming to give an extended chilled shelf life.

[0071 ] During reheating to between 57 and 83°C the moisture content equalises throughout the dumplings to between 40 and 48wt%. The pressure inside each package is between 0.9 and 1 .1 atm with a partial oxygen pressure of less than 10 kPa.

[0072] While this invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification(s). This application is intended to cover any variations uses or adaptations of the invention following in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth.

[0073] As the present invention may be embodied in several forms without departing from the spirit of the essential characteristics of the invention, it should be understood that the above described embodiments are not to limit the present invention unless otherwise specified, but rather should be construed broadly within the spirit and scope of the invention as defined in the appended claims. The described embodiments are to be considered in all respects as illustrative only and not restrictive.

[0074] Various modifications and equivalent arrangements are intended to be included within the spirit and scope of the invention and appended claims. Therefore, the specific embodiments are to be understood to be illustrative of the many ways in which the principles of the present invention may be practiced. In the following claims, means-plus- function clauses are intended to cover structures as performing the defined function and not only structural equivalents, but also equivalent structures.

[0075] “Comprises/comprising” and“includes/including” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. Thus, unless the context clearly requires otherwise, throughout the description and the claims, the words‘comprise’,‘comprising’,‘includes’, ‘including’ and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to”.