FR2807955A1 - Preserving wood or vegetables, salting and/or dehydrating fish or meat, or dehydrating fruit or vegetables, comprises immersing and subjection to progressive depressurizing and/or repressurizing - Google Patents

Abstract

Impregnating a porous animal or vegetable based material comprises immersion in a liquid at atmospheric pressure and progressively lowering the pressure to a minimal pressure and then progressively returning the pressure to atmospheric. Independent claims are included for: (a) an apparatus comprising device controlling the speed of depressurizing and/or pressurizing applied to animal or vegetable materials immersed in a bath; and (b) animal or vegetable product treated as above.

Description

The present invention relates to a method and to a device for impregnation by variable pressure immersion of porous products of animal origin.

The invention applies to the impregnation of porous products, in particular of vegetable or animal origin. The term “porous product” is understood here to mean any product comprising pores but also products capable of being infiltrated by a liquid phase from the presence in particular of a capillary network.

The invention applies in particular to the impregnation of porous products, such as wood or plants, with preserving substances, to the salting and / or dehydration of meat products (meat and fish) as well as to the dehydration with fruit formulation. and vegetables.

EP 625,314 discloses a process for salting cheese which is immersed in an osmotic solution consisting of a brine containing 20 sodium chloride, in which the container receiving the solution is subjected to several cycles each comprising the following stages - lowering the pressure to 50 mbar, and maintaining this pressure for minutes, then - return to atmospheric pressure (1030 mbar), then - circulation of the brine for one hour.

This process is implemented using a liquid ring pump intended to put the container under vacuum.

According to this document, the lowering of the pressure causes partial degassing of the pores of the cheese which are open (in contact with the treatment solution), and return to atmospheric pressure causes the penetration of the solution into part of the open pore left free.

There are many other methods of impregnating such porous materials by immersion. A disadvantage of the known methods and devices results from the large amount of energy that they require.

another drawback lies in long treatment times for treating materials in depth, and / or in the shallow treatment depth.

An object of the invention is to provide an improved method for impregnating such porous materials, and devices for covering it.

objective of the invention is to at least partially remedy the drawbacks of known methods and devices.

According to a first aspect, the invention consists of such a process in which achieves a gradual and controlled decrease in the pressure of the material previously immersed in a liquid phase of treatment at atmospheric pressure, up to a minimum pressure, followed by a progressive (and controlled) increase in pressure to atmospheric pressure.

More particularly, a controlled volume expansion of the gas phase occluded in the material is caused by a gradual reduction and control of the pressure of the material previously immersed in a liquid phase treatment at atmospheric pressure, up to a minimum pressure (Pv), followed progressive and controlled infiltration of the liquid treatment phase into the material by a gradual and controlled increase in pressure to atmospheric pressure.

In one embodiment, said minimum pressure is low enough to cause a portion of the water contained in said material to boil at treatment temperature. This causes the creation of a water vapor phase generated by the boiling of part of the water.

The invention is based on the surprising observation that, unlike the process in document EP 625 314 in which a vacuum pulse is produced, a process according to the invention causes the appearance, within the treated material, of cavities, some of which communicate with the treatment solution; thus, the increased material porosity and its impregnation with the treatment solution is facilitated; another surprising effect consists in that the process increases the gain of the material in solute, without appreciable modification of the water loss of the material. In addition, the progressive and controlled nature of the pressure variation makes it possible to modulate in a controlled manner the quantity of solution infiltrated into the product, as well as the level of destructuring of the product as a function of the desired result.

particularly satisfactory results have been observed in the processing of meat products (of animal origin) by maintaining said controlled variations (decrease then increase) in pressure in a range from pascal / second to 106 pascal / second; preferably the temperature of the liquid phase and of the material is simultaneously maintained in a range from 0 ° C. to 15 ° C., said minimum pressure being situated in a range ranging from 600 Pa 1,700 For the treatment of fruits, vegetables and aromatic herbs, the pressure is preferably varied according to an average progression whose value is situated in a range going from 250 Pascal / second to 106 Pascal / second; depending on the type of liquid phase treatment material, and depending on the value of the minimum pressure, the temperature is maintained in a range from 0 C to 90 C.

For the treatment of wood and similar woody materials, the rate of variation of the pressure can be situated in a range going from 10 Pascal / second 106 Pascal / second, the temperature being preferably maintained at a value located between and 100 C.

According to another surprising aspect of the process according to the invention, it turned out that it was not necessary, contrary to known processes, to maintain minimum pressure, that is to say partial vacuum, for a significant period of time for obtain satisfactory treatment; it seems in fact to emerge from the tests carried out boiling and the increase in porosity are essentially favored by transient phases of the process, rather than by the duration of the stationary phase maintaining the minimum pressure which has proved to be unnecessary, although favorite.

value of this minimum pressure is preferably chosen in a range from 600 to 1,700 Pa for processes of animal origin, from 600 to 70,000 for processes of non-woody plant origin, and from 1,200 to 90,000 Pa for wood products such as wood, the reduction of this pressure increasing the quantity of solute impregnated in the pores of the material, and the depth of penetration. Preferably, in a method according to the invention, several successive cycles are carried out, each comprising the following successive steps - controlled and gradual reduction in pressure, from atmospheric pressure to said minimum pressure; the duration of this step is preferably between 0.1 sec and 120 sec; - maintains pressure at said minimum pressure (partial vacuum) for a period of between 0 sec and 360 sec; - controlled and gradual increase in pressure from minimum pressure to atmospheric pressure; the duration of this step is preferably between 0.1 sec and 120 sec; - maintaining the pressure at said atmospheric pressure for a period of between 0 and 360 sec.

Thus, the total duration of each cycle is preferably in a range from 0.2 sec to 10 minutes. The number of cycles depends on the size of the product. Thus, the treatment comprises for example, for a meat of small thickness of product, in particular 1 to 2 cm thick, from 2 to 20 cycles - in particular from 2 to 5 cycles, that is to say a total duration of treatment ranging from 0, 4 sec to 50 minutes. For a determined total treatment time, the solute gain increases and the water loss decreases when the number of cycles increases.

According to another aspect, a device according to the invention comprises means for measuring, controlling (that is to say controlling) the depressurization speed and / or the pressurization speed, so that the kinetics of these steps being under control, these speeds can be maintained within ranges of value allowing the creation, within tissues, of the material of cavities from which an increase in porosity results; when a non-volumetric suction device is used for suction by partially evacuating the container receiving the materials to be treated (and the solution in which these materials are immersed), in particular when using a liquid ring pump , the device according to the invention comprises a reservoir (vacuum) interposed between said container and the suction device, and comprises a regulating valve between the container and the reservoir as well as preferably a sectioning valve between the reservoir and the suction device; said tank is preferably designed and dimensioned to ensure, by placing it in communication with the container and by means of the adequate control of the control valve by a computer or similar equipment receiving a signal delivered by a pressure sensor, said progressive depressurization of the container as well as, if necessary, the bearing for maintaining the minimum pressure.

According to a particular embodiment illustrated in Figure 2, the device comprises two vacuum tanks connected in parallel and connected to said container and said suction device; this makes it possible to accelerate the rhythm of the cycles by operating the suction device in a substantially continuous manner; during a first cycle, a first tank, previously depressurized, is isolated from the suction device and is used to depressurize the container ; during this time, the second tank which is isolated container, is put in communication with the suction device to depressurize it; during a second cycle consecutive to the first cycle, the roles of the two reservoirs are reversed, the state of the inlet and outlet valves of these reservoirs also being reversed. According to a preferred embodiment, the depressurization of the container, the maintenance of the minimum pressure, the subsequent pressurization are ensured by means making it possible to increase the volume of a cavity which is in direct communication with the container; in particular these means are essentially constituted by piston movable in translation in a chamber communicating with the lower part of the container, which therefore constitutes a volumetric suction device; in this case, the control of the depressurization (up to the minimum pressure) and of the subsequent pressurization are ensured very simply by measuring the pressure in the container and by controlling the displacement of the piston to ensure the desired pressure variation.

According to a preferred embodiment, the device comprises a second container communicating with the first container (that is to say the main container receiving the material to be treated) in the lower part; this second container contains the same treatment solution as the first container; while the first container is completely filled with the solution, without containing gas in the upper part, the second container comprises in the upper part a gas buffer facilitating the obtaining of a progressive variation of the pressure in the first container during the piston movement ; this design also facilitates degassing of the solution contained in the first container, which degassing is preferably carried out prior to treatment.

In addition, the use of a piston actuator - a cylinder - allows, by choosing a sufficient diameter and a piston stroke, to use this actuator to empty (and conversely fill) the first container the solution that it contains, which facilitates the introduction (and conversely the extraction) materials to be treated in the first container.

The methods and devices according to the invention therefore make it possible to accelerate the treatment and to reduce the energy cost thereof.

Other advantages and characteristics of the invention will be understood through the following description which refers to the accompanying drawings, which illustrate without any limiting character the preferred embodiments of the invention.

Figures 1 and 5 are two timing diagrams each illustrating the variations of the pressure as a function of time during successive cycles according to two embodiments of a treatment method according to the invention.

FIG. 2 schematically illustrates the main components of an embodiment of a device according to the invention.

FIG. 3 schematically illustrates the main components of another embodiment of a device according to the invention.

FIG. 4 illustrates in perspective view the device of FIG. 3.

As illustrated in FIG. 1, each pressure variation cycle prevailing in the sealed container containing the products to be treated immersed in a treatment solution, comprises four steps a) a first step of duration ta, during which pressure prevailing in the container varies from pressure atmospheric (Pa) up to the vacuum pressure (Pv), ie said minimum pressure; b) a second step of duration t1, during which the pressure in the container is maintained at the vacuum pressure (Pv); c) a third step of duration t2, during which the pressure in the container varies from the vacuum pressure (Pv) to atmospheric pressure (Pa); d) a fourth step of duration t3, during which the pressure in the container is maintained at atmospheric pressure Pa.

As illustrated in these figures, the variation of the treatment pressure can vary linearly during steps a) of depressurization and c) of pressurization; however, it is possible to make non-linear variations in pressure during these phases, while preferably remaining within the preferred ranges of variation speed defined above; moreover, as mentioned above, it is not critical to maintain an absolutely constant pressure during phases b) and d) above: it is possible, as a variant, to cause pressure variations as illustrated diagrammatically in FIG. 5.

These parameters can be optimized on a case-by-case basis, based on the following considerations, resulting from the observations made - for a determined treatment duration, when the number of cycles increases, the solute gain increases and the water loss decreases; - the more the duty cycle t1 / t3 increases, the more the solute gain increases and the more the water loss decreases; - the choice of Pv and the temperature allows the control of the boiling of the water included in the material.

In the embodiment illustrated in FIG. 2, the device 1 comprises an enclosure 2 for processing products 3; this treatment enclosure contains the treatment liquid 4 and has the lowest possible dead volume of noncondensable gas, preferably at the start of the treatment; the products are immersed during the entire treatment period by means of racks and / or grids; two vacuum tanks 5, 6 are proposed here in order to limit the power of the vacuum pump 7; nevertheless a second tank 6 is not essential if the vacuum pump makes it possible to reduce the pressure of the tank 5 from Pa to at least Pv in less than (t, + t2 + t3).

The device illustrated in FIGS. 3 and 4 comprises three main sub-assemblies - a treatment enclosure 17 (constituting said first container) containing product to be treated and the immersion solution, a coil 18 for controlling the temperature inside this enclosure, a piezoresistive sensor 20 for measuring the absolute pressure prevailing in the enclosure, a thermocouple 26 for measuring the interior temperature, and a system of two successive valves 11, 12 in the upper part 14 of the enclosure 17, for close it; a safety valve can be connected to the duct 19 to avoid any overpressure in the enclosure 17, risking in particular damage to the sensor 20; - A reserve flask 15 (constituting said second container) for the immersion solution, provided with a valve 13 in the upper part for filling the flask and keeping the internal volumes of the device under pressure; the flask is connected by tubing 16 in the lower part of the treatment enclosure 17; this flask also allows the introduction of a volume of gas (ambient air) to facilitate control of the expansion of the gases during the process; - A jack 22 allowing the enclosure 17 and the vial 15 to be placed under vacuum, the control and maintenance of this depressurization, as well as of the pressurization up to atmospheric pressure; this jack comprises a piston 23 movable in chamber 24 connected in the lower part of the enclosure 17; the piston is set in translational movement along the axis 25 inclined relative to the vertical, by a slide cylinder controlled by a controlled electric motor which rotates an endless (whose speed of rotation is controlled by the applied motor voltage electric).

The entire device is controlled by a computer which controls the piston stroke 23 for setting under vacuum, the pressure level, the opening and closing of the solenoid valves of the treatment chamber, and the parameters (duration) of a cycle. treatment.

The assembly is mounted on a support 30 in FIG. 4.

To this equipment is added means (not shown) for circulating and temperature the heat transfer fluid circulating in the coil 18 to maintain a set temperature in the treatment enclosure, as well as device for recycling the treatment solution; in order to optimize the expansion of the material to be treated and to increase its effective porosity during the vacuum phase, a second piston and / or an ultrasonic generator in the solution can be provided.

In addition to controlling the various parameters of vacuum immersion at variable pressure, this device makes it possible to identify the gases released in the partial vacuum phase of the material immersed in the solution and to quantify their volume; it is indeed possible to choose a pressure setpoint level above degassing or boiling phenomena of the material and to control the opening of the solenoid valve until eliminating the gases in the internal volumes 14, 17 treatment. The volume of gas is then trapped between the solenoid valve 12 and the valve 11; a syringe can be used for the extraction of these released gases for their identification.

The use of the piston easily makes it possible to reach in a controlled manner the boiling pressure of the internal solvent in the material at surrounding temperature, in particular in a duration to less than a second.

For the preliminary degassing step of the treatment solution, the device presented above is used to expel in gaseous form the gases dissolved in the treatment solution; for this, the solution is introduced through the reserve bottle 15, the valve 13 the conduit 16, in the treatment chamber 14, 17; the set temperature for the upcoming treatment is maintained by the exchanger 18.

This solution is then placed under vacuum to the level of the vacuum pressure setpoint to be reached, and maintained at this setpoint for the time necessary for complete degassing of the dissolved gases.

The solution is then brought back to atmospheric pressure; the volume of gas thus created trapped in the flared upper part 14 of the enclosure 17 and is then purged from the enclosure; the level of the solution is readjusted by introducing non-degassed solution; other depressurization and repressurization cycles can be carried out until there is no boiling of the solution in the pressure range sought during the treatment to come.

The material to be treated is then immersed in the degassed treatment solution. The set temperature is maintained. The assembly is then placed under vacuum until the solvent contained in the material is boiled with prior or simultaneous degassing of the gases occluded and / or dissolved in this same solvent.

The bubbles thus obtained within the material by vacuum, thanks to a sufficiently low pressure setpoint, seek to escape under the effect of the volume forces of gravity towards the upper part of the product; a product expansion is created according to its structural characteristics; the bubbles generated take either the conduits of the existing pores or generate a destructuring product with creation of porosity; in addition to the pressure set point which overcomes the activation barrier of these bubbles internal to the materials, the duration of the plateau at this set point makes it possible to control this phenomenon of material destructuring; Gas bubbles thus generated leave the pores as long as the internal pressure of the material remains higher than the external pressure. The whole product / solution is then gradually brought back to the initial atmospheric pressure. During this ascent, the internal boiling is stopped as well as the degassing of occluded and / or dissolved gases in the material; the compression of the residual gases obtained in pores as described above creates a free volume which is filled with the treatment solution: thus has obtained an infiltration of exogenous solution in the material structure.

This volume of solution is then partly trapped in the material during maintenance at atmospheric pressure (this is then called occluded solution), giving way in particular to the diffusive phenomenon allowing impregnation of the solutes the occluded solution towards the core of the material; the gain in volume of infiltrated solution of the surface for the exchange of diffusive phenomena is an essential point brought by this process by boiling of the internal solvent in the product.

Another notable advantage brought about is due to the control of the transport of materials across the internal surface of the pores created during boiling; in fact, as a function of the initial solute concentration of the infiltrated solution, of the solute concentration of the product, of the diameter of the pores, the holding time at minimum pressure can be optimally determined to fix the loss or gain in solvent. exogenous solution and the gain in solute in the product. We are in the presence of a diffusion mechanism in a condition of decreasing concentration between the infiltrated solution and the internal surface of the pores of the product. Simultaneously, the conventional diffusion of impregnation by immersion between the external solution and the external surface of the product continues, a priori essentially in the atmospheric pressure phase; it is to be thought that the boiling obtained under partial vacuum limits this mechanism.

new cycle can then be implemented; the multiplication of the cycles makes it possible, from a hydrodynamic point of view, to increase the volume of the pores created or even the formation of new pores causing a progressive destructuring of the material, thus increasing the volume of solution infiltrated at each return to atmospheric pressure.

can then control the level of diffusion of solutes through the internal surface of the pores and the mass yield of the process (gains in solute and in material solvent).

each cycle, a new quantity of exogenous solution of given concentration infiltrated during re-atmospheric pressure, leaving room for the diffusive mechanism.

 After a series of cycles, the infiltrated solution is trapped in the material.

In addition to the composition characteristics of the treatment solution with a view to obtaining a given final product, it is of course necessary to ensure that the boiling pressure of the solution is lower than that of the solvent (water) bound to the core. material ; for a solvent identical to the core of the material and of the treatment solution, this is reflected, according to Raoult's law, by a minimum level of concentration of solutes in the treatment solution to comply with this condition; the higher the level, the lower the boiling pressure; otherwise, the effect of the process would be zero, treatment solution not sufficiently concentrated, starting to boil without the boiling of the solvent bound to the material being obtained.

The tables below summarize the main experimental data treatments carried out with the device of Figures 3 and 4, by varying the pressure substantially linear manner.

Claims (1)

CLAIMS 1 - Method of impregnation by immersion under variable pressure of porous products (3) of animal or vegetable origin, characterized in that a progressive and controlled reduction in the pressure of the material previously immersed in the liquid treatment phase is achieved at atmospheric pressure, to a minimum pressure (Pv), followed by a gradual and controlled increase in pressure to atmospheric pressure. - Method according to claim 1, characterized in that more particularly causes a controlled volume expansion of the gas phase occluded in the material by a gradual and controlled decrease in the pressure of the material previously immersed in a liquid phase of treatment at atmospheric pressure, up to 'at a minimum pressure (Pv), followed by a gradual and controlled infiltration of the liquid treatment phase into the material by a gradual and controlled increase in pressure up to atmospheric pressure. - Method according to claim 1 or 2, characterized in that said minimum pressure is low enough to cause the boiling of part of the water contained in said material at the treatment temperature. 4 - Process for impregnating meat products according to any one of claims 1 to 3, in which the pressure variations are maintained in a range going from 103 pascal / second to 106 pascal / second, and in which the temperature of said liquid phase in a range from 0 C '15 C. 5 - A method of impregnating fruits, vegetables or aromatic herbs according to any one of claims 1 to 3, wherein variations in pressure are maintained in a range from 250 pascal / second to 106 pascal / second, and in which the temperature of said liquid phase is maintained in the range from 0 C '90 C. - Method for impregnating wood products according to any one of claims 1 to 3, in which the pressure variations are maintained in a range from 10 pascal / second to 106 pascal / second, and in which the temperature of said liquid phase is maintained in a range from 10 C to 00 C. 7 - Process according to any one of Claims 1 to 6, in which several successive cycles are carried out, each comprising the following successive steps - controlled and progressive reduction in pressure, from atmospheric pressure to said pressure minimum, the duration of this step being between 0.1 sec and 120 sec; - if necessary maintains the pressure at said minimum pressure for a period of between 0 sec and 360 sec; - controlled and gradual increase in pressure from minimum pressure to atmospheric pressure, the duration of this step being between 0.1 120 sec; - if necessary, maintain the pressure at said atmospheric pressure for a period of between 0 sec and 360 sec. 8 - Process according to any one of claims 1 to 7, in which degassing of the liquid treatment phase is carried out before subjecting the products to pressure variations. 9 - Method according to any one of claims 1 to, in which a device according to any one of claims 10 to 1 is used. 10 - Device (1) for impregnation by immersion in a container (2,14,17), under variable pressure, of products (3) of animal or vegetable origin, characterized in that it comprises means for measuring and controlling the depressurization speed and / or the pressurization speed of the products immersed in a solution (4 ) treatment. 11 - Device according to claim 10 which comprises a reservoir (5,6) interposed between said container (2,14,17) and an apparatus (7) for suction, and comprises a valve (V2, V5) for regulation between the container and the tank, as well as a shut-off valve (V3, V4) between the tank and the suction device, and a computer receiving a signal delivered by a pressure sensor (20) to control said progressive depressurization of the container as well as, if necessary, a bearing for maintaining the minimum pressure. 12 - Device according to claim 11 which comprises two vacuum tanks (5,6) connected in parallel and connected to said container and to said suction device. - Device according to claim 10 which comprises means (22,23) for increasing and decreasing the volume of a cavity (24) which is in direct communication with the container (14,17). 14 - Device according to claim 13 wherein said means (22,23) are essentially constituted by a piston (23) movable in translation in a chamber (24) communicating with the lower part (17) of the container. - Device according to claim 13 or 14 which comprises a second container (15) reserve communicating with the first container (14,17) by a conduit 6) connecting them at the bottom, this second container containing said treatment solution and a gas buffer . 16 - Porous product (3) of animal or vegetable origin obtained by a process according to any one of Claims 1 to 9.