Microwave pasteurisation facility incorporating a ventilation cooling system

Abstract

The invention relates to a microwave pasteurisation facility (1) for pasteurising food products contained in packages (2) that are hermetically sealed by an impermeable film, the facility comprising at least: - a microwave cavity (3); - a conveyor line (4) conveying the packages through the microwave cavity; - at least one microwave generator (5) designed to generate and propagate through the microwave cavity microwave radiation (W) that heats the food products on the conveyor line; - a ventilation cooling system that injects cold air (A) into the microwave cavity by means of at least one air distribution plenum (6) transparent to the microwaves which extends continuously inside the microwave cavity, along and above the conveyor line, and is provided with holes for distributing air (60) along and opposite the conveyor line.

Description

[0001] DESCRIPTION

[0002] TITLE: Microwave pasteurization installation integrating a ventilation cooling system

[0003] [Technical field]

[0004] The invention relates to a microwave pasteurization installation for the pasteurization of foodstuffs contained in hermetically sealed packaging.

[0005] It relates more particularly to a microwave pasteurization installation comprising a ventilation cooling system.

[0006] The invention also relates to a microwave pasteurization method implemented by such a pasteurization installation.

[0007] The invention finds application in the food industry.

[0008] [State of the art]

[0009] Pasteurization is a process used in the food industry, consisting of the heat treatment of food, which is first heated to a moderate temperature between 60°C and 100°C for a given period of time, then cooled quickly immediately afterwards.

[0010] Pasteurization is used to significantly reduce the number of microorganisms / bacteria present in food and which can be both beneficial and harmful (salmonella, Listeria, Staphylococcus aureus, etc.) for humans. Thus, the pasteurization of certain foods, such as dairy products (milk, eggs, or any preparation based on these ingredients such as cheeses, yogurts), makes it possible to drastically reduce the risks of food poisoning, and guarantee the health safety of people with fragile immune systems (such as children, pregnant women, the elderly) and for whom these risks could be particularly dangerous.

[0011] Pathogenic bacteria responsible for food spoilage are also destroyed, which in fact increases their shelf life, while preserving their taste and organoleptic qualities; a pasteurized product can sometimes even be considered fresh (pasteurized fresh milk, fresh cream, etc.).

[0012] The pasteurization temperature and the duration for which it is applied to a food depend on the thermal resistance of the harmful microorganisms it contains (usually they are established on the basis of the most resistant microorganism).

[0013] Pasteurized food must be hermetically packaged (with or without a protective atmosphere or vacuum) to prevent external microorganisms from contaminating the food, and preferably refrigerated to slow the development of residual microorganisms that have not been completely destroyed during pasteurization. This is why food is packaged with materials / packaging suitable for contact with it, so that said materials / packaging do not alter / contaminate it. These materials / packaging must also have a certain thermal resistance so as not to soften during the pasteurization process.

[0014] Microwave pasteurization is a recent and developing pasteurization process. Compared to the conventional pasteurization process which relies on heat transmission from the outside to the inside by thermal conduction on the surface of the food (for example by steam, hot air, or hot water), microwave pasteurization relies on spatially uniform absorption of microwave radiation by the food. The possibility of applying this microwave radiation to the interior of the food allows it to be heated more quickly, i.e. to significantly reduce the pasteurization time from several hours with the conventional process to just a few minutes. The speed of microwave treatment ensures better taste and organoleptic qualities, particularly for heat-sensitive foods.

[0015] Microwave pasteurization is applied to one or more foodstuffs contained in a package hermetically sealed by a waterproof film and which may be, for example, a bag made of waterproof film or a tray sealed with a peelable waterproof film; such a waterproof film being, for example, made of a synthetic plastic material or a plant-based plastic material, such as, for example, a starch-based one.

[0016] When the packaging is heated by microwaves, a rise in temperature occurs within it. This rise in temperature causes the water present in the packaged food(s) to evaporate and therefore an increase in pressure. If the pressure exerted by the heated packaged food(s) is too high, the plastic bag or film of the packaging may possibly rupture / explode (particularly at the sealing areas), making the packaging leaky and therefore unfit for sale and consumption as it no longer fulfils its preservation function over time.

[0017] To address this issue, one of the known solutions, notably from document ITVI20130082, consists of cooling packaging in the form of trays during their pasteurization, with the aim of reducing the air temperature and therefore the local pressure exerted by the water vapor under their sealed films. In document ITVI20130082, the trays are conveyed on a conveyor line, which enters and leaves a microwave cavity used as a heating tunnel. In order to cool the tray films, ventilation devices are arranged along the microwave cavity, opening onto its upper face and being interposed between microwave generators. The ventilation devices consist of fans injecting air through injection ducts opening punctually above the conveyor line.The proposed solution nevertheless has the following disadvantage: the films of the trays are only cooled intermittently during their passage under the injection ducts, especially since the speed of the air injected onto the sealed films is insufficient to promote significant heat dissipation due to the large diameters used for such injection ducts. Thus, the heat exchange time for the reduction of the pressure exerted under the sealed film is too short, implying that the risk of rupture of the sealed film remains and therefore that the sealing properties of the trays are not guaranteed.

[0018] [Summary of the invention]

[0019] The proposed invention is presented as a pasteurization installation for microwave pasteurization of foodstuffs contained in packages hermetically sealed by a waterproof film, the pasteurization installation comprising at least:

[0020] - a microwave cavity;

[0021] - a conveyor line passing through said microwave cavity to convey the packaging;

[0022] - at least one microwave generator coupled to at least one microwave guide opening into the microwave cavity, to generate and propagate microwave radiation inside the latter and heat the foodstuffs on the conveyor line;

[0023] - a ventilation cooling system designed to inject air into the microwave cavity; said pasteurization installation being remarkable in that the ventilation cooling system comprises at least one air distribution plenum formed of a tubular body which extends continuously inside the microwave cavity, along and above the conveying line, said at least one air distribution plenum being made of a material transparent to microwave radiation and being provided with air distribution orifices distributed along and opposite the conveying line.

[0024] A ventilation cooling system such as that provided in the proposed invention has the following advantages:

[0025] - the at least one air distribution plenum being arranged along and above the conveyor line, and being provided with air distribution orifices equally distributed along and opposite the conveyor line, it continuously cools the sealed films of the packaging throughout the time during which they are conveyed by the conveyor line inside the microwave cavity,

[0026] - at least one air distribution plenum is arranged in the microwave cavity such that it is interposed between an upper face of the cavity and the conveyor line.

[0027] Being made from a material transparent to microwave radiation, it does not interfere with the heating of food by microwave radiation when it is propagated inside the microwave cavity.

[0028] “Material transparent to microwave radiation” means that said material does not absorb microwave radiation.

[0029] The conveyor line is advantageously made from a microwave-transparent material, such as polypropylene or polyethylene.

[0030] Thus, throughout the pasteurization heat treatment, a thermal balance is maintained at the level of the sealed films of the packaging. The heat exchange between the projected cold air and the sealed films reduces the air temperature and induces a counterpressure which reduces the pressure difference between the outside and the inside of the packaging. The risk of rupture of the sealed films or the welds is then eliminated. The proposed pasteurization installation, through its at least one air distribution plenum, therefore responds favorably to the problem of heating foodstuffs by microwaves while preserving their sealing properties.

[0031] According to two alternative embodiments of the invention, the ventilation cooling system is configured so that the at least one air distribution plenum injects air constantly / continuously, or pulsed air at higher pressure, intermittently or by pulse, inside the microwave cavity.

[0032] According to another variant embodiment of the invention, an intelligent cooling system could also be implemented, which would project air, at more or less high pressure onto the sealed film of the packages, as soon as they pass under each of the air distribution orifices of the at least one air distribution plenum, on the condition that the distance between two air distribution orifices is at least equal to the distance separating two packages on the conveyor line.

[0033] According to a characteristic of the invention, the at least one microwave generator comprises one or more microwave generators coupled to several microwave guides opening into the microwave cavity and distributed along the conveyor line, and the at least one air distribution plenum extends at least between two microwave guides among the several microwave guides.

[0034] Depending on the length of the conveyor line, which depends on the desire to apply the pasteurization process simultaneously to foodstuffs contained in several packages, the at least one microwave generator may comprise one or more microwave generators coupled to as many microwave guides opening into the microwave cavity and distributed along the conveyor line. When several microwave generators are present along the conveyor line and therefore the microwave cavity, the electromagnetic fields induced by the microwave radiation emitted by each of the microwave generators form an electromagnetic field having a uniform intensity. Advantageously, the packages are thus subjected, continuously throughout the duration of their conveyance in the microwave cavity, to the same electromagnetic field intensity and therefore heated to a stabilized pasteurization temperature.

[0035] When the pasteurization installation comprises several microwave guides distributed along the conveyor line for continuous heating of the foodstuffs during their conveyance, the at least one air distribution plenum extends at least between two microwave guides in order to be able to continuously cool the sealed films of the packaging during their conveyance between said two microwave guides.

[0036] According to one embodiment of the invention, the at least one microwave guide comprises at least one upper microwave guide, opening above and opposite the conveyor line, the at least one air distribution plenum being interposed between said at least one upper microwave guide and said conveyor line. According to one embodiment of the invention, the at least one upper microwave guide comprises at least two upper microwave guides, and the at least one air distribution plenum extends at least between said two upper microwave guides.

[0037] According to one embodiment of the invention, the at least one microwave guide comprises at least one lower microwave guide, opening below and opposite the conveyor line, said conveyor line then being interposed between the at least one air distribution plenum and said at least one lower microwave guide.

[0038] As previously indicated, according to different embodiments of the invention, the pasteurization installation may comprise, for heating the foodstuffs, one or more microwave generators, as well as one or more waveguides shaped to propagate in the microwave cavity the microwave radiation emitted by the microwave generator(s). The one or more microwave guides may be arranged so as to propagate the microwave radiation above the conveyor line and / or below, meaning then that the microwave guides open into the microwave cavity via its upper face and / or its lower face, hence respectively the designations upper microwave guide and lower microwave guide.

[0039] The at least one air distribution plenum being shaped to cool the sealed films of the packages while they are simultaneously heated by the microwave radiation, if the at least one microwave guide comprises one or more upper microwave guides, then the latter is interposed in the microwave cavity between the conveyor line and the upper microwave guide(s). It is understood that to continuously cool the packages during their conveyance in the microwave cavity, if the at least one microwave guide comprises at least two upper microwave guides, the at least one air distribution plenum extends at least between the at least two upper microwave guides.

[0040] It is also possible to heat food by integrating a single microwave generator into the pasteurization installation, which is connected to several upper microwave guides which are power divider waveguides.

[0041] According to various embodiments, it is also possible to integrate into the pasteurization installation at least one microwave generator coupled to at least one lower microwave guide, provided that the conveyor line is also made from a material transparent to microwaves, the at least one lower microwave guide then propagating microwave radiation under the conveyor line and therefore under the packaging.

[0042] In this case, this means that the conveyor line is interposed between the at least one air distribution plenum and the at least one lower microwave guide.

[0043] Advantageously, placing microwave generators and microwave guides above and below the conveyor line allows for more uniform and homogeneous heating of the surface and also the core of the food, and therefore reduces the duration of the pasteurization treatment as well as the pasteurization temperature.

[0044] According to a characteristic of the invention, the ventilation cooling system comprises at least one ventilation unit, of the blower or fan or pump type, connected to the at least one air distribution plenum and designed to suck air from outside the microwave cavity in order to inject it into the at least one air distribution plenum.

[0045] According to a characteristic of the invention, the at least one ventilation unit has an air flow rate of between 100 and 1000 m 3 / h.

[0046] In other words, in addition to the at least one air distribution plenum, the ventilation cooling system comprises at least one ventilation unit which may be a fan, or a pump, or even a blower as in the case of the preferred embodiment of the invention. The ventilation unit is shaped to suck air from outside the microwave cavity and inject cold air into the at least one air distribution plenum. The ventilation unit has an air flow rate of between 100 and 1000 m 3 / h (typically 280 m 3 / h) in order to inject into the at least one air distribution plenum air at different cooling temperatures and for several injection speeds, with a view to making the ventilation cooling advantageously suitable for all types of foodstuffs to be treated by the pasteurization installation, more precisely at the temperature to which they are heated by microwave radiation.

[0047] According to a characteristic of the invention, the at least one air distribution plenum has a tubular section in which the air distribution orifices are provided.

[0048] According to a characteristic of the invention, the tubular section of the at least one air distribution plenum has a transverse dimension of between 50 mm and 100 mm, for example 75 mm.

[0049] The at least one air distribution plenum is in the form of a tubular body which may have different geometric shapes (round, square, etc.) having a transverse dimension of between 50 mm and 100 mm, for example 75 mm, to advantageously adapt as best as possible to the dimensions of the microwave cavity and the products to be pasteurized. The tubular body is provided, as previously mentioned, with air distribution orifices distributed along and opposite the conveyor line in order to project air onto the packaging.

[0050] According to one embodiment of the invention, the at least one air distribution plenum comprises one or more air distribution plenums extending over at least 90% of the length of the microwave cavity measured along the conveyor line.

[0051] Advantageously, by extending over at least 90% of the length of the microwave cavity, the at least one air distribution plenum makes it possible to continuously cool the sealed films of the packaging, and therefore maintain a thermal equilibrium at their level, throughout the duration of the pasteurization and their transport on the conveyor line from the inlet of the microwave cavity to its outlet. The at least one air distribution plenum, according to the embodiment of the invention, may comprise: either a single air distribution plenum extending over at least 90% of the length of the microwave cavity; or several air distribution plenums of identical or different lengths which, when placed end to end along and above the conveyor line, extend over at least 90% of the length of the microwave cavity.

[0052] According to a feature of the invention, the ventilation cooling system is designed to inject air at a cooling temperature between 4°C and 65°C.

[0053] According to a characteristic of the invention, the ventilation cooling system is designed to inject air, at the outlet of the air distribution orifices, at a propagation speed of between 10 m / s and 15 m / s.

[0054] In other words, the ventilation cooling system is configured so that the cold air is projected onto the packages at the outlet of the distribution orifices of the at least one air distribution orifice at a propagation speed of between 10 m / s and 15 m / s and that it is characterized by a cooling temperature of between 4°C and 65°C, the propagation speed and the cooling temperature being adapted: to the pasteurization temperature applied to all types of foodstuffs to heat treat them, and to dissipate the heat and reduce the pressure exerted locally on the sealed film inside the packages during their heating in order to avoid rupture of said sealed film or of the seal. According to a characteristic of the invention, the air distribution orifices are located at a separation height above the conveyor line, said separation height being between 10 cm and 15 cm.

[0055] In order for the cold air to effectively cool the sealed films of the packaging, it must be projected above and as close as possible to them. This is why it is planned that the distribution orifices be arranged above the conveyor line at a separation height of between 10 cm and 15 cm, this height being chosen in particular according to the height of the microwave cavity.

[0056] According to a characteristic of the invention, the air distribution orifices have an orifice dimension of between 3 mm and 10 mm, for example 5 mm.

[0057] In order to accelerate and advantageously project the air onto the packaging at a propagation speed suitable for maintaining thermal equilibrium at the level of their sealed film, the distribution orifices are designed to have an orifice dimension which can be between 3 mm and 10 mm, for example 5 mm.

[0058] According to a characteristic of the invention, the air distribution orifices are spaced from each other by a given minimum spacing distance, said minimum spacing distance being between 40 mm and 50 mm.

[0059] In order to advantageously continuously cool the packages throughout the pasteurization period while they are being conveyed inside the microwave cavity, the distribution orifices are more or less uniformly distributed over the at least one air distribution plenum according to a minimum spacing distance of between 40 mm and 50 mm, this minimum spacing distance being chosen according to the length of the microwave cavity.

[0060] According to one embodiment of the invention, the material transparent to microwave radiation is chosen from polypropylene, polyethylene and polytetrafluoroethylene.

[0061] The air distribution plenum being arranged in the microwave cavity, and for example between the conveyor line and one or more microwave generators shaped to emit microwave radiation above the packaging, it is manufactured from a material transparent to microwaves so as not to disturb the microwave radiation(s) and thus the heating of the foodstuffs. According to different embodiments, the plenum can be manufactured with polypropylene, polyethylene, or even polytetrafluoroethylene (i.e. Teflon).

[0062] The invention also relates to a pasteurization process for microwave pasteurization of foodstuffs contained in packages hermetically sealed by a waterproof film, said pasteurization process being implemented within a pasteurization installation such as that described above, and which comprises at least:

[0063] - a conveying stage during which the packaging is conveyed on the conveyor line,

[0064] - a heating step, taking place simultaneously with the conveying step, during which the at least one microwave generator generates and propagates via the at least one microwave guide microwave radiation to heat the foodstuffs on the conveying line,

[0065] - a ventilation cooling step, taking place simultaneously with the conveying step and the heating step, during which air is injected along and above the conveying line through the air distribution orifices provided in the at least one air distribution plenum.

[0066] [Brief description of the figures]

[0067] Other characteristics and advantages of the present invention will appear on reading the detailed description below, of a non-limiting example of implementation, made with reference to the appended figures in which:

[0068] [Fig 1] is a schematic view illustrating the operating principle of the pasteurization plant;

[0069] [Fig 2] is a schematic view illustrating the pasteurization installation in an example of the invention, which comprises two microwave cavities placed end to end and crossed by the conveyor line, each of the two microwave cavities comprising an air distribution plenum supplied with air by its own ventilation unit;

[0070] [Fig 3] is a schematic and partial view of the pasteurization installation of Figure 2, showing the interior of the two microwave cavities;

[0071] [Fig 4] is a schematic partial bottom perspective view of the pasteurization plant of Figure 2.

[0072] [Detailed description of one or more embodiments of the invention]

[0073] The pasteurization installation 1 of the invention comprises at least:

[0074] - at least one microwave cavity 3;

[0075] - a conveyor line 4 passing through the at least one microwave cavity 3 through openings located at its two side walls, and which is used to convey packaging 2;

[0076] - at least one microwave generator 5 coupled to at least one microwave guide 51, 52 opening into the at least one microwave cavity 3, to generate and propagate inside the latter microwave radiation W heating the foodstuffs contained in the packages 2 transported on the conveyor line 4;

[0077] - a ventilation cooling system designed to inject air A into the at least one microwave cavity 3 and onto the packages 2, with the aim of reducing the air temperature and the pressure difference between the inside and the outside of the packages 2 during their heating, and eliminating the risk of rupture / explosion of their waterproof film and / or their welds.

[0078] The at least one microwave generator 5 is configured to generate microwave radiation W for a frequency band between 300 MHz and 10 GHz, the pasteurization installation 1 thus covering the frequencies authorized / allocated normatively in the ISM (Industrial, Scientific and Medical) band for heating / pasteurizing foodstuffs in different regions of the world (for example: 915 MHz and 2.45 GHz in Europe and the United States, 896 MHz in the United Kingdom, 922 MHz in Australia, etc.); as well as other frequencies currently under study in the agri-food research environment and potentially promising, such as the 433 MHz frequency.

[0079] The conveyor line 4 is made from a microwave-transparent material, for example polypropylene or polyethylene, so that it does not absorb the microwave radiation W emitted by the at least one microwave generator 5, causing them not to heat the packages 2 as expected.

[0080] With reference to Figure 1 to Figure 3, several embodiments of the invention are possible.

[0081] The pasteurization installation 1 may comprise a single microwave cavity 3, as illustrated in Figure 1, or several microwave cavities 3 placed end to end and all crossed by the conveyor line 4, as illustrated in Figures 2 to 4, which correspond to an illustrative and non-limiting embodiment of the invention for which two microwave cavities 3 of the same length are used, for example each 1.5 m long.

[0082] Also, the pasteurization installation 1 may comprise, depending on the length of the at least one microwave cavity 3 and depending on whether the pasteurization installation 1 is designed to simultaneously and uniformly pasteurize several foodstuffs during their conveyance in the at least one microwave cavity 3, several microwave guides 51, 52 opening into the at least one microwave cavity 3 and distributed along the conveyor line 4 and propagating the microwave radiation W. In the case where the pasteurization installation 1 comprises several microwave guides, these may each be coupled to a different microwave generator 5; or else be connected to the same microwave generator 5, the microwave guides then being associated with power distributors / dividers.

[0083] According to different embodiments of the invention, the at least one microwave guide may be an upper microwave guide 51, respectively a lower microwave guide 52, opening into the at least one microwave cavity 3 via an upper face of the microwave cavity 3, respectively via a lower face of the microwave cavity 3, and exposing the top, respectively the bottom, of the conveyor line 4 and therefore the packages 2 conveyed on it to microwave radiation W.

[0084] In the example illustrated in Figure 1, the pasteurization installation comprises four upper microwave guides 51 distributed along the conveyor line 4 and each coupled to a microwave generator 5. In the embodiment illustrated in Figures 2 to 4, each of the microwave cavities 3 is connected to two upper microwave guides 51 and two lower microwave guides 52, arranged interleaved so that the packages 2 during their conveyance along the conveyor line 4 are alternately heated from above and then from below; the two upper microwave guides 51 and the two lower microwave guides 52 each being coupled to a microwave generator 5.As previously indicated, arranging the microwave generators 5 and the microwave guides above and below the conveyor line 4 makes it possible to propagate the microwave radiation W volumetrically in the at least one microwave cavity 3, and thus to heat in a more uniform and homogeneous manner the surface but also the core of the foodstuffs contained in the packages 2.

[0085] The ventilation cooling system includes:

[0086] - at least one cooling unit 7, such as a fan, a blower or a pump, which sucks air A out of the at least one microwave cavity 3;

[0087] - at least one air distribution plenum 6 connected to the outlet of the cooling unit 7 by a connecting pipe 71, receiving the air A, and which extends inside the at least one microwave cavity 3, along and above the conveyor line 4.

[0088] Optionally, a refrigeration unit is integrated into the cooling system to cool the air A which is taken at ambient temperature from outside the microwave cavity 3.

[0089] In the case where the at least one microwave cavity 3 is connected to at least one upper microwave guide 51, the at least one air distribution plenum 6 is interposed between the at least one upper microwave guide 51 and the conveyor line 4.

[0090] In the case where the at least one microwave cavity 3 is connected to at least one lower microwave guide 52, this means that it is the conveyor line 4 which is interposed between the at least one air distribution plenum 6 and the at least one lower microwave guide 52.

[0091] In the case where the at least one microwave cavity 3 is connected to at least two microwave guides (whether upper microwave guides 51 or lower microwave guides 52), the at least one air distribution plenum 6 extends at least between these at least two microwave guides to cool the packages 2 during the time interval when they are conveyed by the conveyor line 4 between the at least two microwave guides.

[0092] In the case where the pasteurization installation 1 comprises a single microwave cavity 3, only a ventilation system, comprising a cooling unit 7 and an air distribution plenum 6, is necessary for cooling the packaging 2. In the case where it comprises several microwave cavities 3, different implementation solutions are possible:

[0093] - each of the several microwave cavities 3 is associated with a cooling system comprising at least one cooling unit 7 and at least one air distribution plenum 6.

[0094] - the cooling system comprises a single ventilation unit 7 and the side walls of the several microwave cavities 3 are shaped to have openings allowing a single air distribution plenum 6 to pass through the assembly.

[0095] - the cooling system comprises two ventilation units 7 and two air distribution plenums 6 such that, if the pasteurization installation has n microwave cavities: the first cooling unit 7 injects air A in a first direction into a first air distribution plenum 6 which extends longitudinally in x microwave cavities; the second cooling unit 7 injects air A in a second direction, opposite to the first direction, into a second air distribution plenum 6 which extends longitudinally in the (nx) other microwave cavities 3.

[0096] In the embodiment of Figures 2 to 4, the cooling system comprises two ventilation units 7 each injecting air A, in opposite directions, into two air distribution plenums 6 each associated with one of the two microwave cavities 3. The at least one air distribution plenum 6 is in the form of a tubular body which may have different geometric shapes (round, square, etc.) having a transverse dimension D of between 50 mm and 100 mm to best adapt to the dimensions of the at least one microwave cavity 3 and the products to be pasteurized. Thus, the or each air distribution plenum 6 is formed of a tubular body which extends continuously along and above the conveyor line 4; this tubular body extends continuously in the sense that it extends continuously over its entire length, from one of its two ends to the other of its two ends.For the purposes of the invention, it is clear that the or each air distribution plenum 6 does not necessarily extend over the entire length of the conveyor line 4, depending on whether the pasteurization installation 1 comprises a single air distribution plenum 6 or comprises several air distribution plenums 6 aligned along the conveyor line 4.

[0097] In order not to absorb W microwave radiation and not to disturb the pasteurization of foodstuffs, the at least one air distribution plenum 6 is made from a material transparent to microwaves, such as polypropylene, polyethylene or polytetrafluoroethylene (Teflon).

[0098] In order to continuously cool the packages 2 during their conveyance along the at least one microwave cavity 3, the at least one air distribution plenum 6:

[0099] - extends over at least 90% of the length of the at least one microwave cavity 3; and

[0100] - is provided with air distribution orifices 60 distributed along and opposite the conveyor line 4, and which project the air A onto the packages 2.

[0101] For the purposes of the invention, if the pasteurization installation 1 comprises a single air distribution plenum 6, then the latter has a length which is at least equal to 90% of the length of the at least one microwave cavity 3; and if the pasteurization installation 1 comprises several aligned air distribution plenums 6, then the sum of the lengths of these several air distribution plenums is at least equal to 90% of the length of the at least one microwave cavity 3. In other words, the at least one air distribution plenum 6 may comprise one or more air distribution plenums 6 extending over at least 90% of the length of the microwave cavity 3 measured along the conveyor line 4.

[0102] The air distribution ports 60 are provided for:

[0103] - be distributed uniformly over the entire length of the at least one air distribution plenum 6, being spaced apart from each other by a minimum spacing distance S of between 40 mm and 50 mm depending on the length of the at least one microwave cavity 3; - have an orifice dimension of between 3 mm and 10 mm to propagate the air A at a suitable speed over the packages 2 to reduce the pressure difference at the level of their sealed film;

[0104] - Be positioned at a separation height H of the packages 2 of between 10 cm and 15 cm so that the projection of air A can effectively reduce the pressure difference, the separation height H being chosen according to the height of the at least one microwave cavity 3.

[0105] In the embodiment of Figures 2 to 4, for which each of the two microwave cavities 3 is for example 1.5 m long, the two air distribution plenums 6 are cylinders having a transverse dimension D of 75 mm and being 1.4 m long. They both comprise thirty-two air distribution orifices 60 having an orifice dimension of 5 mm, spaced from each other by 40 mm and placed opposite the packages 2 at a separation height H of between 10 cm and 15 cm, so that the air is projected as close as possible to the packages 2 for the best possible efficiency.

[0106] The at least one ventilation unit 7 is shaped to have an air flow rate of between 100 and 1000 m 3 / h, typically 280 m 3 / h, in order to inject into the at least one air distribution plenum 6 air A at different cooling temperatures, which may be between 4°C and 65°C, and for several injection speeds, with the aim that the ventilation cooling is suitable for all types of foodstuffs to be treated by the pasteurization installation, and for the heating temperature and the internal pressure of the packages 2 when subjected to microwave radiation W. Depending on the characteristics of the at least one ventilation unit 7 and the at least one air distribution plenum 6, the air A leaving the air distribution orifices 60 of the at least one air distribution plenum 6 is projected onto the packages 2 at a propagation speed of between 10 m / s and 15 m / s.

[0107] Pasteurization plant 1 implements a microwave pasteurization process comprising at least three stages taking place simultaneously:

[0108] - a conveying step during which the packages 2 are conveyed on the conveying line 4 inside the at least one microwave cavity 3, this for a predetermined conveying speed;

[0109] - a heating step during which the at least one microwave generator 5 generates, at an emission frequency, and propagates inside the at least one microwave cavity 3, via the at least one microwave guide, microwave radiation W to heat the foodstuffs on the conveyor line 4;

[0110] - a ventilation cooling step during which the at least one ventilation unit 7 of the ventilation cooling system injects air A into the at least one air distribution plenum 6 passing through the interior of the at least one microwave cavity 3, along and above the conveyor line 4, which projects the air A onto the packages 2, by means of its air distribution orifices 60, to cool them and reduce the pressure difference at the level of their sealed film.

[0111] Pasteurization plant 1 is controlled by means of a control unit U from which an operator:

[0112] - defines all or part of a set of parameters involved in the steps of the pasteurization process, comprising at least: the duration of the pasteurization treatment, the frequency of emission of the microwave radiation W generated by the at least one microwave generator 5, the speed of the conveyor line, the air flow rate of the at least one ventilation unit 7 and the temperature to which the air A external to the pasteurization installation must optionally be cooled;

[0113] - and monitors the proper progress of the pasteurization treatment, the pasteurization installation 1 being able, for example, to include sensors returning the conveying speed, the air flow rate, the temperature inside the at least one microwave cavity 3.

[0114] In the embodiment of the invention, each of the two microwave cavities 3 has a window 6 allowing the operator to examine the interior of the microwave cavity 3 and to carry out a visual check to verify whether the pasteurization process is proceeding as expected, for example by verifying whether the packages 2 have not suffered a rupture / explosion of the sealed film.

[0115] During the ventilation cooling step, the operator can choose whether the at least one ventilation unit 7, for the duration of the pasteurization treatment, injects air A into the at least one air distribution plenum 6 continuously or intermittently (in the second case the operator can set the time interval separating two injections).

Claims

DEMANDS 1. Pasteurization installation (1) for microwave pasteurization of foodstuffs contained in packages (2) hermetically sealed with a waterproof film, the pasteurization installation (1) comprising at least: - a microwave cavity (3); - a conveyor line (4) passing through said microwave cavity (3) to convey the packages (2); - at least one microwave generator (5) coupled to at least one microwave guide (51, 52) opening into the microwave cavity (3), to generate and propagate microwave radiation (W) inside the cavity and heat the foodstuffs on the conveyor line (4); - a ventilation cooling system designed to inject air (A) into the microwave cavity (3); said pasteurization installation (1) being characterized in that the ventilation cooling system comprises at least one air distribution plenum (6) formed of a tubular body which extends continuously inside the microwave cavity (3), along and above the conveyor line (4), said at least one air distribution plenum (6) being made of a material transparent to microwave radiation (W) and being provided with air distribution orifices (60) distributed along and opposite the conveyor line (4).

2. Pasteurization installation (1) according to claim 1, wherein at least one microwave generator (5) comprises one or more microwave generators (5) coupled to several microwave guides opening into the microwave cavity (3) and distributed along the conveyor line (4), and at least one air distribution plenum (6) extends at least between two microwave guides among the several microwave guides.

3. Pasteurization installation (1) according to claim 1 or 2, wherein at least one microwave guide comprises at least one upper microwave guide (51), opening above and opposite the conveyor line (4), at least one air distribution plenum (6) being interposed between said at least one upper microwave guide (51) and said conveyor line (4).

4. Pasteurization installation (1) according to claims 2 and 3, wherein at least one upper microwave guide (51) comprises at least two upper microwave guides (51), and at least one air distribution plenum (6) extends at least between said two upper microwave guides (51).

5. Pasteurization installation (1) according to any one of the preceding claims, wherein the at least one microwave guide comprises at least one lower microwave guide (52), opening below and opposite the conveyor line (4), said conveyor line (4) being interposed between the at least one air distribution plenum (6) and said at least one lower microwave guide (52).

6. Pasteurization installation (1) according to any one of the preceding claims, wherein the ventilation cooling system comprises at least one ventilation unit (7), of the blower or fan or pump type, connected to at least one air distribution plenum (6) and designed to draw air (A) from outside the microwave cavity (3) in order to inject it into at least one air distribution plenum (6).

7. Pasteurization installation (1) according to claim 6, wherein at least one ventilation unit (7) has an air flow rate of between 100 and 1000 m 3 / h.

8. Pasteurization installation (1) according to any one of the preceding claims, wherein at least one air distribution plenum (6) has a tubular section (61) in which the air distribution orifices (60) are provided.

9. Pasteurization installation (1) claim 8, wherein the tubular section (61) of at least one air distribution plenum (6) has a transverse dimension (D) between 50 mm and 100 mm, for example 75 mm.

10. Pasteurization installation (1) according to any one of the preceding claims, wherein at least one air distribution plenum (6) comprises one or more air distribution plenums (6) extending over at least 90% of the length of the microwave cavity (3) measured along the conveyor line (4).

11. Pasteurization installation (1) according to any one of the preceding claims, wherein the ventilation cooling system is designed to inject air (A) at a cooling temperature between 4°C and 65°C.

12. Pasteurization installation (1) according to any one of the preceding claims, wherein the ventilation cooling system is designed to inject air (A), at the outlet of the air distribution orifices (60), at a propagation speed between 10 m / s and 15 m / s.

13. Pasteurization installation (1) according to any one of the preceding claims, wherein the air distribution orifices (60) are located at a separation height (H) above the conveying line (4), said separation height (H) being between 10 cm and 15 cm.

14. Pasteurization installation (1) according to any one of the preceding claims, wherein the air distribution orifices (60) have an orifice dimension between 3 mm and 10 mm, for example 5 mm.

15. Pasteurization installation (1) according to any one of the preceding claims, wherein the air distribution orifices (60) are spaced from each other by a given minimum spacing distance (S), said minimum spacing distance (S) being between 40 mm and 50 mm.

16. Pasteurization installation (1) according to any one of the preceding claims, wherein the microwave (W) radiation transparent material is selected from polypropylene, polyethylene and polytetrafluoroethylene.

17. A pasteurization process for microwave pasteurization of foodstuffs contained in hermetically sealed packaging (2) made with a waterproof film, said pasteurization process being carried out in a pasteurization installation (1) according to any one of the preceding claims, and comprising at least: - a conveying stage during which the packages (2) are conveyed on the conveying line (4), - a heating stage, taking place simultaneously with the conveying stage, during which at least one microwave generator (5) generates and propagates via at least one microwave guide a microwave radiation (W) to heat the foodstuffs on the conveyor line (4), - a ventilation cooling stage, taking place simultaneously with the conveying and heating stages, during which air (A) is injected along and above the conveying line (4) through the air distribution ports (60) provided in at least one air distribution plenum (6).

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