EP1874632B1 - Method for heat treating a product contained in a package such as a tray - Google Patents

Abstract

Disclosed is a tray including at least one deformable wall. The product contained in the tray is heated, the vapour produced by the heating being allowed to escape through an opening in the pack. The product is heated, being taken to a desired temperature, a temperature-holding stage is carried out, the vapour being allowed to escape, a gaseous fluid is introduced into the pack at the end of this temperature-holding stage and the pack is closed totally.

Description

The present invention relates to a method of heat treatment of a product, in particular a food product, contained in a packaging such as a container having at least one deformable wall, in which the product contained in the packaging is heated by carrying it at a desired temperature, a temperature holding step is carried out by allowing the steam produced by the heating to escape through an opening in the package.

A process of this type is already known from the French patent application no. 2,852,921 .

Heating the product serves to promote its conservation. It can be a simple cooking, complete or partial, or a pasteurization or sterilization.

As is known, pasteurization and sterilization are used to destroy certain bacteria by heating, to push back the deadline for consumption of the product.

The consumable product is in particular a food product, such as vegetables, fruits or other fresh foods, blanched or pre-cooked, or frozen. It can also be cooked dishes, including for example meat or fish, or any food preparation.

It is known that when heating a product of this type, steam is produced. These include water vapor, produced by water evaporating from the heated product under the effect of temperature. In addition, the gas initially contained in the package is dilated due to the rise in temperature, the excess gas volume forming part of the vapor that is allowed to escape from the opening of the package during heating to prevent it from occurring in the latter an overpressure that could lead to bursting or in any case to a deterioration of the packaging, and a failure of the heating process.

The aforementioned French patent application applies in particular to a package consisting of a tray or a flexible bag. According to this patent application, the opening of the package through which the steam can escape is formed by a zone provisionally not welded between two walls of this package, and this opening is closed at the end of the heating by welding.

After heating, the packaging is closed while its content is still hot. During cooling, be it sudden or gradual, the volume of gas contained inside the package decreases which, the wall of the package being deformable, causes deformation thereof. When the package is formed by a flexible bag, this retraction can be a desired effect.

This is not the case when the packaging is formed by a tray, which should normally have a substantially parallelepiped shape. Indeed, the consumer would be disturbed by the deformation of such a package.

In an attempt to avoid such distortions, the European patent no. 1,265,793 recommends that the package be closed only once the temperature of the product it contains has reached a precise value and that the inside of the package is still under pressure so that the package is not deformed after cooling. In fact, the volume of gas in excess pressure during the closure is found after cooling; a volume that correctly fills the normal interior volume of the package.

This method is of some interest, but it requires on the one hand to monitor very precisely the temperature of the product inside the package, which is extremely difficult on an industrial scale and, on the other hand, of ensure that the opening of the packaging initially has a dimension such that controlled overpressure will be ensured inside the packaging at the time when it is closed.

Thus, this method presents practical difficulties of implementation.

The object of the present invention is to propose a different solution to allow a release of steam during heating and to avoid excessive permanent deformation of the deformable wall of the packaging resulting from the heating.

This goal is achieved thanks to the fact that we introduce a fluid in the package at the end of this temperature maintenance step, and the packaging is completely closed.

According to the invention, the heating comprises a step of holding at temperature or "chambering" to obtain the value cooker (that is to say a value for cooking desired), pasteurizer or sterilizer desired, and during which let the steam escape. At the end of this step, a gaseous fluid is introduced into the package to cause an increase in its internal volume by a temporary deformation of its deformable wall and / or cause increased pressure. The packaging can then be closed and, when the gas contained inside this package has regained its "normal" volume at room temperature, the packaging will have found a shape close to its initial shape, without excessive deformation. As will be seen in the following, it is possible to determine the volume of gas introduced at the end of the temperature holding step such that the final shape of the package is substantially its initial shape, without significant deformation with respect to she. This volume can also be determined so that the final shape is intentionally slightly different from the initial shape. For example, the package may be a semi-rigid tray closed with a flexible film and it is possible to choose to inject a slightly insufficient volume of gas so that after cooling, the outer surface of the film is slightly concave, thereby testifying that the product has actually undergone a heat treatment, while the walls of the tray retain their original shape.

In other words, the invention makes it possible to avoid or control the deformations of the package. The final form is appreciated at room temperature and at "normal" atmospheric pressure.

For the purposes of the present invention, the ambient temperature is the normal storage temperature of the products contained in the package, ie, for frozen products, of the order of -18 ° C., for products stored in a cold room, order of 4 ° C and for products stored without cooling, of the order of 20 ° C.

Advantageously, the gaseous fluid introduced has a temperature at least close to the temperature of the vapor of the package during the temperature maintenance step.

This avoids a thermal shock between the contents of the packaging and the gaseous fluid introduced into the latter. In addition, it ensures that the gaseous fluid corresponds, from the point of view of its temperature, the desired cooking, pasteurization or sterilization criteria. The temperature of this fluid can even be used to promote pasteurization or sterilization.

Advantageously, the gaseous fluid is a neutral gas, such as nitrogen, a gas mixture nitrogen / oxygen dioxide or air, preferably filtered. This gaseous fluid is chosen according to the products treated.

The introduction of the gaseous fluid is managed so that when the package once closed will return to ambient temperature, the wall thereof is substantially undeformed or deformed in a controlled manner. It is possible to proceed empirically, by introducing, under the same conditions of introduction, different volumes of gaseous fluids in different packages, and then determining what is the volume of fluid introduced which leads to the desired final shape, so as to retain this volume as to be introduced industrially.

It is also possible to evaluate the volume of vapor that escapes from the packaging during heating and temperature maintenance and to introduce into this package a corresponding volume of gaseous fluid. The evaluation of the volume of vapor that escapes can be carried out by direct measurement or, indirectly, depending on the time during which the steam escapes, and taking into account the size of the opening of the package.

It is also possible, from tests, to determine the volume of fluid to be injected as a function of the deformation it causes on the wall of the package.

Having thus determined the best conditions for introducing the gaseous fluid, in particular relating to the duration during which this fluid is introduced or to the directly measured quantity of fluid that is introduced, the process can then be industrialized.

To obtain controlled deformation, of limited amplitude and affecting only certain zones (film) of the package, it is possible to inject a quantity of gas slightly different from that which would be necessary to avoid deformation and advantageously slightly less than the latter to obtain a controlled concave deformation. The difference measured in volume may for example be of the order of ± 5% to ± 10%.

• la figure 1 est une vue en coupe verticale d'une barquette contenant un produit, avant le traitement thermique ;
• les figures 2 et 3 sont des vues de dessus d'une telle barquette, pour deux variantes de réalisation de son ouverture ;
• la figure 4 illustre l'étape de chauffage du produit contenu dans l'emballage ;
• la figure 5 illustre l'introduction d'un fluide gazeux à l'intérieur de l'emballage ; et
• les figures 6 et 7 montrent la fermeture finale de l'emballage, pour les deux variantes des figures 2 et 3.

The invention will be better understood and its advantages will appear better on reading the detailed description which follows, of an embodiment shown by way of non-limiting example. The description refers to the accompanying drawings in which:

• the figure 1 is a vertical sectional view of a container containing a product, before the heat treatment;
• the Figures 2 and 3 are top views of such a tray, for two variants of its opening;
• the figure 4 illustrates the step of heating the product contained in the package;
• the figure 5 illustrates the introduction of a gaseous fluid inside the package; and
• the Figures 6 and 7 show the final closure of the packaging, for both variants of the Figures 2 and 3 .

The tray of the figure 1 comprises a receptacle portion 1 and a cover wall 2, such as a peelable film, disposed across the opening of this receptacle. Food products such as, for example, peeled potatoes 3 are arranged in this tray. Typically, this tray is made of plastic or aluminum, or a complex such as, for example, cardboard / plastic, cardboard / aluminum or aluminum / plastic and has a relatively thin wall, whose thickness is by example between 0.5 and 2 mm. The upper wall of this tray is formed by the film 2, which is sealed on the edge of the tray formed by the flange 1A of the receptacle. The materials chosen for the receptacle and the film are of all types known for this type of trays, for example based on aluminum or plastic, in particular polypropylene, possibly loaded as recommended by the patent application. EP No. 1,313,651 .

The film constituting the upper wall 2 forms a wall which is easily deformable. However, insofar as the wall of the receptacle 1 is relatively thin, in fact all the walls of the tray are deformable, but the film 2 is more.

Before subjecting the product 3 contained in the tray to the heat treatment, this tray is closed incompletely, leaving an opening. On the figure 2 this opening is formed by an interruption 4A of the sealing bead 4 between two walls of the package, in this case between the rim 1A of the receptacle and the film 2.

On the figure 3 ; the opening 5 is formed by a hole in a wall of the package, in this case in the film 2, while the sealing bead 4 between the film 2 and the rim of the receptacle is continuous.

In general, the opening through which the vapor can escape during sealing has relatively small dimensions so that the inside of the packaging is put under overpressure during heating, because this overpressure favors the heart heating of the products. food.

As indicated above, the vapor that emerges comes from, on the one hand, the vaporization of the water initially contained in the package, in particular in the products which are arranged inside, and on the other hand the expansion of the gas initially contained in the package. For the purpose of the present invention, these two sources of off-gas are designated by "steam".

On the figure 4 , the tray of Figures 1 and 2 is placed in a heating chamber 6. It is in particular a microwave oven or tunnel inside which microwaves are emitted by a generator. The tray is carried by a support 8. In the case where the enclosure is formed by the interior space of a microwave tunnel, the support 8 may be a conveyor whose path passes through the interior of this tunnel which has an inlet and an outlet for the tray which are not shown. Of course, several trays can be simultaneously in the tunnel, the length of the latter and the advancement of the conveyor can be adjusted so that the parking time of a tray in the enclosure is sufficient to allow the desired heating .

The tray and its contents are subjected to heating to, on the one hand, allow a rise in temperature of the product contained in the tray and, on the other hand, perform a temperature maintenance step. Conventionally, for a pasteurization, the temperature maintenance stage is conducted in such a way that the food product remains maintained at a temperature of the order of 80 ° C. to 100 ° C. for a period of given time, for example of the order of 3 to 5 minutes. For sterilization, the product is brought to a temperature of the order of 120 ° C to 130 ° C for the necessary time, for example of the order of 3 to 5 minutes. The steps of heating and temperature maintenance can be performed in the same microwave chamber. Alternatively, two microwave tunnels arranged end to end may be used, the first using a larger power to perform the temperature rise step, while the second only carries out the temperature holding step, with less power.

Of course, heating by microwaves is only one example, knowing that other heating modes can be used, in particular heating by other electromagnetic waves such as high frequency waves, or else steam heating.

The temperature maintenance step can be carried out as shown in FIG. figure 4 . On the one hand, it can be seen that under the effect of the overpressure generated inside the packaging by the steam produced during heating, its most deformable wall, in this case the film 2, is is deformed to increase the volume of the package. The excess steam V escapes through the opening 4A.

At the end of the temperature maintenance step, a gaseous fluid is introduced into the package as shown in FIG. figure 5 . This introduction can be carried out in the heating chamber as shown in FIG. figure 5 . It should be noted, however, that it can also be performed after the temperature maintenance step at the outlet of the heating chamber. -

In the example of the figure 5 this introduction of the fluid F is carried out by an injection cannula 9 which is engaged in the opening 4A. This cannula is connected to a gaseous fluid supply system represented symbolically by a square 10. It should be noted that the introduction of the cannula into the opening 4A is easy since, under the effect of the vapor evolution V, this opening is at least ajar, that is to say that the film 2 is kept locally at a distance from the flange 1A.

The introduction of a cannula is also easy, from an opening formed on one of the walls of the container, as the opening 5 of the figure 3 . It should be noted that, because of the overpressure in the package, the film 2 is then remote products contained in the package, so that the introduction of the cannula does not damage these products.

However, instead of introducing a cannula into the opening, it is possible to have a gas injection system in the immediate vicinity of this opening, whether it be the opening 4A or the opening 5, ensuring that the pressure and the flow of gaseous fluid are sufficient for it to enter the package.

As can be seen by comparing the Figures 4 and 5 during the introduction of the gaseous fluid F into the package, the film 2 is further deformed, further increasing the interior volume of the package.

After the introduction of the gaseous fluid, the package is completely closed. On the figure 6 this closing is performed by completing the weld bead 4, as indicated by the hatched area 4B. The opening 4A can in particular be made and closed as recommended by the French patent application no. 2,852,921 .

On the figure 7 this closure is achieved by closing the piercing 5 with a pellet 5 '.

Advantageously, as indicated above, the gaseous fluid is introduced through the opening through which the steam is allowed to escape during holding at temperature. Alternatively, another port may be used. In particular, the steam can be introduced by a cannula forming a needle which, for the introduction of the gaseous fluid, pierces a wall of the package. The pierce thus formed is then closed, for example by placing a pellet across this piercing; the opening through which the vapor V has escaped is also closed, for example by sealing or by affixing a pellet.

Advantageously, the gaseous fluid which is introduced into the package at the end of the temperature maintenance stage has a temperature which is between 80% and 130%, preferably between 90% and 110%, of the temperature of the steam during the temperature holding step. As indicated above, the choice of a gaseous fluid temperature at least close to the temperature of the steam is advantageous. When even a higher temperature is chosen for this gaseous fluid, especially when it is close to 130% of the temperature of the vapor, one can use the gaseous fluid and heated to promote cooking, pasteurization or sterilization.

Tests carried out under different conditions of introduction of vapor packaging at the end of the temperature maintenance stage make it possible to determine what are the optimal conditions for introducing the gaseous fluid so that, once the package is closed, and after the cooling of its contents, the pressure balance between the inside and the outside of the package is such that the walls of this package remain substantially undeformed with respect to the figure 1 or that they are only slightly deformed in the desired manner, only the film 2, for example, being slightly concave.

The conditions for introducing the gaseous fluid are defined by parameters such as: the temperature of the gaseous fluid introduced, its composition, the volume of the introduced fluid or, to indirectly determine this volume, the duration of the introduction step, the flow of fluid at the outlet of the injection system and entering the packaging, ....

Tests may also be performed for different types of openings of the package, knowing that the size of the opening obviously influences the volume of vapor escaping from the package during the temperature maintenance step. This volume of vapor can be indirectly determined by knowing the time during which the evolution of gas takes place, and the dimensions of the opening, knowing that the pressure of this vapor is generally known elsewhere.

Thus, advantageously, a volume of gaseous fluid corresponding at least approximately to the volume of vapor that escapes from the packaging during heating and temperature maintenance is introduced.

As indicated previously, these volumes of vapor and gaseous fluid can be determined by tests, empirically and by comparison between different tests.

For example, one can evaluate the volume that escapes and then introduce a corresponding volume. It is also possible to test under the same conditions by introducing different volumes of gaseous fluid and by comparing the initial mass of the package with its content and mass after closure and cooling which, by calculation gives the difference between the volume of vapor that escaped and the volume of gas introduced.

Advantageously, the volume of gaseous fluid introduced is determined such that this volume is substantially equal to the volume of vapor that escapes from the packaging during heating and temperature maintenance, preferably being less than this volume. For example, the volume of gaseous fluid introduced into the package may be less than 5 to 10% of the volume of vapor that escaped from the latter. This makes it possible to ensure that, after the cooling of the contents of the package, the most deformable wall of the latter, in particular the film 2 which forms the upper wall, has a slight concavity, which favors the handling steps. subsequent packaging, in particular the stacking of several such packages. This wall which is slightly concave can also be the bottom of the container. This concavity is then light enough not to constitute a troublesome deformation for the consumer but, as indicated above, it has certain advantages. For the purposes of the present invention, this concavity is light enough for the package to be considered "substantially undeformed" after cooling.

The volume of gaseous fluid introduced into the packaging and the volume of vapor that escaped from it are compared under conditions allowing this comparison, in particular by computationally reducing these volumes to volumes equivalent to the same temperature, in particular the ambient temperature.

As a variant, the gaseous fluid is introduced into the package, causing deformation of the deformable wall, and the package is closed when it is found that this deformation has reached a given level.

As indicated previously, the introduction of the gaseous fluid can cause deformation of the film 2 (see figure 5 ). One can choose, by testing on several identical packages having the same content and heated under the same conditions, to close the packages for different deformations of their walls 2 and then determine which of these packages has the geometry most favorable to the from the cooling of its contents. We will then note the deformation found for this packaging as a criterion of industrialization of the process. The level of the deformation is in particular reflected by the amplitude thereof.

It has been indicated previously that, during heating, this wall also deforms, but to a lesser extent. During the temperature holding step, the flow of steam escaping through the opening 4A or 5 is stabilized, so that the deformation of the film 2 also stabilizes. It is possible to choose to measure the level of deformation at which the package is closed in a relative manner, by comparison between the stabilized deformation during temperature maintenance and the deformation obtained just before closing, after introduction of the gaseous fluid.

It is also possible to choose to introduce the gaseous fluid into the package for a determined period of time, after which the package is closed. Again, tests make it possible to check, taking into account the conditions of introduction (in particular pressure, flow and temperature) and determine which of these tests led to the best final geometry of the package. This makes it possible to retain a normal duration of introduction, which is used during industrialization of the process.

Claims (13)

1. Method for heat treatment of a product, in particular a food product, contained in a pack such as a tray (1, 2) having at least one deformable wall (2), in which the product (3) contained in the pack is heated by taking it to a desired temperature, a temperature-holding stage is carried out, vapour produced by the heating being allowed to escape through an opening (4A, 5) of the pack (1, 2), characterized in that a gaseous fluid (F) is introduced into the pack at the end of this temperature-holding stage, and the pack is totally closed.
2. Method according to claim 1, characterised in that the gaseous fluid introduced is at a temperature at least close to the temperature of the pack vapour during the temperature-holding stage.
3. Method according to claim 2, characterised in that the temperature of the gaseous fluid introduced is between 80% and 130%, preferably between 90% and 110%, of the vapour temperature during the temperature-holding stage.
4. Method according to any of claims 1 to 3, characterised in that a volume of gaseous fluid (F) is introduced, corresponding at least approximately to the volume of vapour (V) which escapes from the pack during heating and temperature holding.
5. Method according to claim 4, characterised in that the volume of gaseous fluid introduced is determined in such a way that this volume is substantially equal to the said volume of vapour, preferably slightly lower than this volume, when the said volumes are adjusted to the same temperature.
6. Method according to any of claims 1 to 3, characterised in that the gaseous fluid (F) is introduced into the pack (1, 2), causing deformation of the said deformable wall (2) and in that the pack is closed when it is found that the said deformation has reached a given level.
7. Method according to any of claims 1 to 3, characterised in that the gaseous fluid is introduced into the pack for a predetermined length of time, at the end of which the pack is closed.
8. Method according to any of claims 1 to 7, characterised in that the gaseous fluid (F) is a neutral gas.
9. Method according to any of claims 1 to 7, characterised in that the gaseous fluid (F) is air, advantageously filtered.
10. Method according to any of claims 1 to 9, characterised in that the gaseous fluid (F) is introduced through the said opening (4A) in the pack.
11. Method according to any of claims 1 to 10, characterised in that the opening is formed by at least one interruption (4A) in a sealing strip (4) between two walls of the pack and in that, at the end of the stage of introducing the gaseous fluid into the pack, the latter is closed by completion of this welding strip (4, 4B).
12. Method according to any of claims 1 to 10, characterised in that the opening is formed by at least one hole (5) in a pack wall and in that, at the end of the stage of introducing the gaseous fluid into the pack, this hole is closed by means of a cap (5').
13. Method according to any of claims 1 to 12, characterised in that the pack is a tray made of plastic (1, 2), the top wall (2) of which is formed by a film sealed at the tray edge (1A).

Images