The present invention relates to a method and a device for pasteurizing, sterilizing or more generally for reducing or eliminating the microbial flora present in active or latent form in a medium formed by solid particles whose particle size is extended (from a few microns to a few centimeters).

 There are many foodstuffs in the solid state divided into bulk which, because they contain or capture moisture, are likely to develop microbial flora. This development is all the more rapid as the solid offers a greater contact surface. This is the case in particular for spices or aromatics in whole or ground state or flours or semolina and also grains and seeds, almonds, hazelnuts, and divided dietary fiber ...

 Several techniques are known for sterilizing or pasteurizing food products. Certain products such as drinks or food are sterilized in their packaging.

 These are, to cite only a few examples, the appertisation which consists in autoclaving the contents and the closed container, or pasteurization processes in tunnel ovens in which the packaged products pass successively through showers. increasingly hot water. Mention will also be made, for the record, of the techniques for applying microwaves or infrared for very specific applications such as the pasteurization of pastries or of packaging and of certain cooked dishes but the use of which is currently limited by the still high cost of their implementation.

 With regard to solids divided in bulk, the sterilization techniques for packaged products are ill-suited due to the poor heat transmission coefficients within the products.

 A steam sterilization is mainly used which consists in bringing the product into contact with a flow of steam in an autoclave. More precisely, the product is placed in horizontal beds on openwork supports in an enclosure and the passage of steam from top to bottom is forced through these beds. However, this process encounters several implementation difficulties.

 It is first of all necessary to seek a compromise between the speed of the processing and the quantity of loading of the device. In fact, the more the device is loaded and in particular with products of fine particle size, the larger the total external surface of the products. It therefore takes a long residence time so that this external surface is actually in contact with the heat source that is steam. Conversely, to obtain a rapid treatment, the quantity of product to be treated should be reduced, resulting in a low flow rate and a reduced yield in favor of the quality of the treatment.

 In addition, there is a heterogeneity of the heat exchange between the upper layers and the lower layers of the product. Especially since there is a condensation of the vapor which, trickling on the lower beds, decreases the heat exchange coefficients between the steam and the products located on the lower beds.

 Finally, the products are cooled by brutal depression which brings into play the latent heat of evaporation of the water contained in the products to obtain a lowering of temperature, but to the detriment of the structure of the bursting tissues.

 Infrared or microwave techniques have so far been little used in this field because, in addition to their high cost, which is prohibitive for products with low added value, they generate a drying effect for products with a high content of water and leave the cooling problem unresolved.

Finally, we will indicate the pasteurization and sterilization by ionization processes which consist in exposing the products to electromagnetic radiation (gamma ray) or to a particular bombardment (accelerated electrons) using Cobalt 60 as irradiation source or
Cesium 197. Depending on the irradiation dose, one obtains either a radiopasteurisation (105 to 106 rad) (destruction of the germs with the exception of the sporulated) or a radiosterilization (106 a
7 10 rad) (destruction of all all the microorganisms and all the enzymes), ie a less intense treatment which reduces the microbial load without damaging the product The installations necessary for the implementation of these techniques are extremely heavy (protective infrastructure) for delicate driving (protection of radiation sources in the event of plant shutdown) and require significant exposure times (therefore significant capacities if high flow rates are desired) taking into account the limited flow of sources of radiation. The costs are of course very high and the installations must be versatile to be profitable in the short term.

 There is therefore an unmet need in the field of pasteurization and / or sterilization of sprayed products of a process which is simple to implement and highly efficient.

The object of the invention is to meet this need by means of a method and a device which make it possible to bring the product to be treated to the desired temperature, in a homogeneous manner despite the intrinsic heterogeneity of this product and for an adjustable and controllable time of precisely without using heat transfer fluid in contact with the product to eliminate the "pollution" of the product by this fluid and thus be exempt from any reprocessing after sterilization
To this end, the pasteurization or sterilization process according to the invention for divided solid products having a wide particle size spectrum consists in gradually introducing the product at the base of an elongated and rising hot sole, the inner cross section of which is concave curvilinear. and to animate this sole with a vibration having a horizontal component and a vertical component, the length of the sole, its temperature, the frequency and the amplitude of the vibrations being determined by the temperature to which the product is to be worn and the time desired treatment.

 In addition, in the device of the invention, to implement the method, the sole is formed by a helical tubular element integral with a vibrating table, driven in vibration according to orthogonal translation and rotation movements. This geometry allows the constitution of a compact device which at the same time forms transporter - elevator of the treated product.

 In one embodiment, the tubular element is made of an electrically resistant material heated by the Joule effect.

 In another embodiment, the tubular element is arranged in a heat exchange enclosure.

 Preferably, in order to gain bulk, the propeller formed by the tubular material has non-contiguous turns, the heat exchange enclosure being formed by the helical space between the turns closed by two side walls.

 Other characteristics and advantages of the invention will emerge from the description given below of several exemplary embodiments.

Reference will be made to the accompanying drawings in which
- Figure 1 is a diagram illustrating the method of the invention.

FIG. 2 is a view of a first embodiment of the device according to the invention,
- Figure 3 is a view of a second embodiment of the device of the invention.

 The diagram in Figure 1 is intended to illustrate the method of the invention. To this end, it represents a theoretical installation in which a sole 1 is in the form of a trough with a curvilinear and concave inner profile which extends upwardly from its left end in the figure. This chute is supported by a base 2 which rests on a vibrating table 3. A motor member 4, located under the vibrating table, is capable of communicating to the table 3 vibrations in a horizontal plane, for example a rotation, and vibrations vertical. To this end, it may comprise, in known manner, motors with unbalances or any other equivalent device.

 The chute I passes into a fixed enclosure 5 which makes it possible to supply calories and to raise the temperature of the chute. It will be noted in this regard that the chute can be closed inside the enclosure 5 to affect the shape of a tube. The enclosure will be supported by a structure (not shown) separate from the vibrating table. A hopper for supplying 6 with divided products (aggregates, powders, etc.) is placed directly above the lower end of the floor 1. The product from the upper end of the chute can also be collected by a hopper 7 which can be used to feed a second sole 8 if necessary.

 The divided product 9 therefore falls at the lower end of the chute which, vibrated, causes on the one hand a mixing of the product in the transverse direction and on the other hand advances the product along the rising ramp which it constitutes. . Thus the divided product is constantly stirred so that all its grains come successively in direct contact with the sole 1. This contact allows heat exchange and the product temperature gradually increases along its course. The length of this path as well as the intensity of the vibrations will make it possible to adjust the residence time of the product in the chute 1 as a function of the admitted flow rate. To do this, we can therefore provide lateral outlet openings to divert the product according to the conditions of the treatment it must undergo.

 It was found that by this device, there was no segregation between fine particles and large particles. Whatever their size, all the particles circulate on sole 1 at the same speed.

This arrangement is entirely advantageous for the sterilization treatment of ground products such as spices or flour where the particle size distribution of the particles extends over a wide spectrum. It is thus easy to control the operating parameters of the installation to obtain the desired treatment.

 FIG. 2 is a particular embodiment of a device for implementing the sterilization process of the invention. It is noted that the sole is here in the form of a helical tube 9 supported by a vibrating table 3 by means of internal uprights 10, the vibrating table itself being coupled to the vibrating group 4. The feed hopper 6 supplies the pulverulent product or divided at the base of the propeller 9 while the latter is collected at the top by a discharge tube 11. In this particular embodiment, the heat input and the temperature rise of the tube 9 are ensured by Joule effect by means of a source of electricity 12 connected at two points of the tube which is itself made of resistant material. electrically.

 It is entirely possible to act on the energy supply by varying the length which separates the connection rings 13 and 14 from the tube 9 to the energy source 12. The tube is used as d 'a rehostat. It is of course possible to provide intermediate product outlets which would derive the latter if the necessary residence time is to be varied. Of course in this embodiment, the uprights 10 and the table 3 will be made of insulating material.

Finally, provision will have been made to connect the hopper 6 which is fixed and the tube 11 which also is fixed to the vibrating tube 9, by means of flexible elements which absorb vibrations.

 In the embodiment of Figure 3, there are some of the elements already described with the same references.

The tube in helical turns, is here enclosed in an enclosure 15 in which, by means of the connecting ends 16, 17, it is possible to circulate a heat transfer medium.

If the two concentric walls 18 and 19 of the enclosure are spaced from the tube 9, the circulation of the heat transfer fluid will take place in an anarchic manner in this enclosure baffled by the tube 9. If on the other hand these two walls 18 and 19 are tangent internally and externally at each turn, and if along the lines of tangency these walls are integral with the walls of the tube, the circuit of the heat transfer fluid will be along a helical path between the turns of the tube 9. This circulation may be co or against the flow of product 7. The enclosure may include an external insulation 20.

 It will be noted that the advantage of using a hearth in the form of a tube rather than in the form of an open trough lies in the fact that this avoids any recontamination by the ambient medium of the treated product, which allows in addition to '' incorporate this technique into a completely aseptic process (pasteurization or sterilization preceding a packaging operation or sending to a mixing unit with at least one other product. On the other hand, we can note the possibility that a tube offers injecting a gaseous medium, of course sterile, into the circulation tube of the pulverulent or granular product to add to the sterilization a concomitant treatment, for example a coloring or a flavoring agent.