WO2005100890A1 - Method for the continuous production of a powdered product from the product in the liquid state - Google Patents

Method for the continuous production of a powdered product from the product in the liquid state Download PDF

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Publication number
WO2005100890A1
WO2005100890A1 PCT/FR2005/000735 FR2005000735W WO2005100890A1 WO 2005100890 A1 WO2005100890 A1 WO 2005100890A1 FR 2005000735 W FR2005000735 W FR 2005000735W WO 2005100890 A1 WO2005100890 A1 WO 2005100890A1
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WO
WIPO (PCT)
Prior art keywords
product
milk
powdered
thermomechanical treatment
liquid state
Prior art date
Application number
PCT/FR2005/000735
Other languages
French (fr)
Inventor
Jean-Marie Bouvier
Daniel Durand
Maxwell Scott
Stewart Stevenson
Stevens Robert
Original Assignee
Clextral
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from FR0410025A external-priority patent/FR2875589B1/en
Application filed by Clextral filed Critical Clextral
Publication of WO2005100890A1 publication Critical patent/WO2005100890A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B1/00—Preliminary treatment of solid materials or objects to facilitate drying, e.g. mixing or backmixing the materials to be dried with predominantly dry solids
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B17/00—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement
    • F26B17/18—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by rotating helical blades or other rotary conveyors which may be heated moving materials in stationary chambers, e.g. troughs
    • F26B17/20—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by rotating helical blades or other rotary conveyors which may be heated moving materials in stationary chambers, e.g. troughs the axis of rotation being horizontal or slightly inclined
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B7/00—Drying solid materials or objects by processes using a combination of processes not covered by a single one of groups F26B3/00 and F26B5/00

Definitions

  • the present invention relates to a process for the continuous preparation of a powdered product from the product in the liquid state, in the form of a mixture of the solution, suspension or emulsion type in aqueous media.
  • the invention relates in particular to a process for the continuous preparation of powdered milk from liquid milk and a powdered milk obtained by such a method.
  • powdered milk is obtained industrially by carrying out various operations which make it possible, from liquid milk generally having a dry matter concentration of approximately 12%, to obtain a powdered milk having a dry matter concentration of 1 '' from 96 to 97% without degrading the nutritional and functional properties of milk.
  • the operation requires specific drying conditions which include the application of a low temperature in the evaporation and concentration operations of the liquid milk and the use of short residence times. during the transition from the liquid state to the solid state.
  • the resulting milk powder must be quickly and completely rehydratable.
  • the drying of the milk comprises several successive operations, namely: - an operation of evaporation under vacuum of the milk in the liquid state having an initial dry matter concentration of approximately 12% to obtain a concentration of between 50 and 60% dry matter; - A spray drying operation of the milk from the previous operation and in which the milk is sprayed into very fine droplets which are brought into direct contact with hot air.
  • This operation makes it possible to obtain milk powder whose dry matter content is of the order of 82%; - a final drying operation in a fluidized bed to reach the final dry matter content of approximately 96 to 97%; and - grinding and sieving to calibrate the milk powder before packaging.
  • This milk powder manufacturing technique used until now has drawbacks.
  • spray drying has a high cost, particularly in terms of investment and energy consumption.
  • the energy consumption is in the range of 2.6 to 2.8 kg of steam and 0.8 kW per kg of milk powder produced so that this operation is by far the largest consumer of energy for the whole process , with approximately 70% of thermal energy and approximately 40% of electrical energy.
  • the object of the invention is to provide a process for the continuous production of a powdered product from the product in the liquid state, in the form of a mixture of the solution, suspension or emulsion type in aqueous media, in which: - at least one step of vacuum evaporation of the mixture in the liquid state is carried out to obtain the product in the viscous state, - at least one step of drying the product in the viscous state is carried out to obtain the product in solid form, characterized in that said drying step comprises at least a first step of thermomechanical treatment by means of a thermomechanical treatment machine into which one injects simultaneously the product in the viscous state: coming from the evaporation step under vacuum and a determined proportion of powdered product of the same family as the product in the liquid state, the treatment machine being configured to mix the product in the viscous state and the product in powder form to obtain pellets of product solidified in contact with ambient air.
  • the method comprises one or more of the following characteristics, taken alone or according to any technically possible combination: - after said drying step, a step of shaping the solid product is carried out to obtain the powdered product; -
  • the powdered product injected into the thermomechanical treatment machine is entirely of the powdered product recycled after the shaping step or is partly of the powdered product recycled after the shaping step;
  • the product in the viscous state has a dry matter concentration of between 55 and 75%, preferably between 65 and 75%;
  • the evaporation step comprises a first evaporation step at the end of which the dry matter concentration is between approximately 50 and 55%, and a second evaporation step at the end of which the concentration in dry matter is between about 70 and 75% and preferably between 65 and 75%;
  • the product in solid form has a dry matter concentration of about 96 to 97%;
  • the drying step comprises a
  • FIG. 1 is a flowchart showing the different stages of a process for producing powdered milk in accordance with the invention
  • FIG. 2 is a schematic sectional view in a vertical plane passing through the tax of a screw of an extrusion machine used in an embodiment of the production process according to the invention
  • - FIG. 3 is a sectional view along line 3-3 of FIG. 2
  • - Fig. 4 is a sectional view of a thermomechanical treatment machine of the mixer, kneader or kneader type
  • liquid milk generally having a dry matter concentration of between 7 and 20% is firstly treated during a first step E1 of evaporation under vacuum to obtain a milk in the viscous state having a concentration of dry matter between 55 and 75% and preferably between 65 and 75%.
  • first step E1 the liquid milk is for example brought to a boil at a high temperature, below 100 ° C., and at a pressure below atmospheric pressure. This evaporation under vacuum makes it possible not to degrade the milk.
  • the milk in the viscous state undergoes at least one drying step and preferably in the process according to the invention two successive drying steps E2 and E3, in order to obtain a milk in solid form. with a dry matter concentration of around 96 to 97%, then a step E4 of shaping the solid milk to obtain the powdered milk.
  • a drying step which comprises a first step E2 of plasticizing-concentrating the milk in an extrusion machine with two co-rotating screws and generally designated by the reference 10.
  • the extrusion machine 10 is of the type with two co-rotating and co-penetrating screws and comprises two screws 11 and 12 driven in rotation about their axes by a motor and a reduction gear, not shown, inside an elongated enclosure forming a sheath 13 which envelops them.
  • the screws 11 and 12 are provided in particular with helical threads or elements for processing the material introduced into the sheath 13 and which mesh with one another.
  • the internal wall of said sheath 13 forms two intersecting cylindrical lobes of diameter slightly greater than the external diameter of the threads and of the treatment elements.
  • the two screws 11 and 12 are driven at the same speed of rotation and in the same direction so that the two screws are identical, the threads and the treatment elements being simply offset from each other. As shown in Fig.
  • the screws 11 and 12 advantageously consist of splined shafts, respectively 14 and 15, on which the screw sections are stacked.
  • the internal bore of these sections of screw is provided with grooves corresponding to those of the shaft and the external part is provided with helical threads or with elements for processing the material, the pitch and configuration of which differ according to the section considered for the processing and transportation of this material. It is thus possible to have in the sheath 13 a fairly large number of screw sections having different configurations depending on the type of treatment to be performed on the material.
  • the extrusion machine 10 comprises a zone A for continuously introducing into the barrel 13, simultaneously, on the one hand, milk in the viscous state coming from step E1 of evaporation under vacuum and, on the other hand share, a determined proportion of milk powder to about 96 to 97% of dry matter.
  • the milk powder injected into zone A of the extrusion machine 10 is wholly or in part milk powder recycled after the shaping step.
  • the rate of powdered milk injected that is to say the ratio between the mass flow rate of milk powder recycled to approximately 96 to 97% of dry matter and the mass flow rate of milk in the viscous state is between 0.25 and 2.5 and preferably between 0.70 and 1.30.
  • the sheath 13 is pierced, at its upstream end relative to the direction of flow of the material, with a feed orifice 16 into which the recycled powdered milk is continuously poured.
  • the screws 11 and 12 are provided with threads 18 with a wide pitch in order to transport the milk introduced through the orifice 16.
  • the milk is transported downstream from the extrusion machine 10 in zone B which comprises a first section B1 in which the screws 11 and 12 are provided with threads 19 with a wide pitch and a second section B2 in which the screws 11 and 12 are provided with threads 20 with tight pitch.
  • the milk in the viscous state is fed at the start of the first section B1 of the zone B.
  • the whole injected powdered milk and milk in the viscous state are transported in the second section B2.
  • the milk is then transported by the screws 11 and 12 into a first zone C in which it is subjected to intense mixing under pressure.
  • the screws 11 and 12 in this zone C are formed, in a known manner, by kneading elements, for example tri-lobe elements 24 juxtaposed and which have the shape of an isosceles triangle whose vertices are truncated to provide a passage controlled mixing downstream of the extrusion machine 10.
  • the kneading elements 24 of each screw 11 and 12 are also offset from one another and are offset from one screw to the other so that they overlap with each other in order to achieve kneading and an intense mixing of the pasty milk and the powdered milk. Due to this intense mixing, there is a rise in the temperature of the milk.
  • the milk is introduced into the extrusion machine 10 at ambient temperature of approximately 20 ° C. and at the outlet of the kneading zone C, it is at a temperature of approximately 80 ° C.
  • the milk in the pasty state is transferred into a zone D in which the screws 11 and 12 are provided with threads 25 with a wide pitch towards a second mixing zone E provided for example with 'screw elements constituted by threads 26 with inverted pitch whose peripheral edges are provided with openings regularly distributed around the charge of the corresponding screw making it possible to control the passage of the flow of milk downstream which determines braking in this zone E and a compression force at Tamont. It therefore follows a shear which homogenizes the milk in order to obtain a very viscous paste. The shear intensity is controlled by the length of the reverse pitch screw elements and by the passage section of the openings at the edges of the threads, so as to control the resulting increase in temperature.
  • zone E the mixing operation in zone E causes the mixture to heat up, a significant part of the mechanical work being converted into thermal energy.
  • the temperature of the milk leaving zone E varies from about 90 ° C to 125 ° C.
  • the temperature of the milk at the exit from zone E is all the more important as the viscosity of the milk paste is high, which depends on the injection rate of the milk powder at about 96 to 97% of dry matter in l feed port 16 of the extrusion machine 10. The higher the injection rate of powdered milk, the higher the dry matter content of the milk paste, and the higher the viscosity of the milk paste is high and, consequently, the higher the temperature of the milk paste leaving the zone E.
  • the screws 11 and 12 of the extrusion machine determine a zone F for transporting and cooling the milk paste.
  • the cooling of the milk paste is done in two different ways according to the temperature level at the entry of zone F.
  • the temperature at the entry of zone E is higher than 100 ° C
  • cooling is preferably done by atmospheric degassing or under vacuum, because it is more efficient.
  • the screws 11 and 12 are formed by several sections of different pitch, a first section F1 of threads 28 with narrow pitch, a second section F2 provided with threads 29 with wide pitch, a third section F3 provided with threads 30 with tight pitch and a fourth section F4 provided with threads 31 with wide pitch.
  • the sheath 13 of the extrusion machine 10 has a degassing orifice 32 which opens into the intersecting bores of said sheath 13.
  • the dough undergoes in sections F1 and F2 of zone F a decompression so that the water contained in said paste evaporates and escapes through the orifice 32.
  • This degassing has the effect of instantly reducing the temperature of the milk paste, to a temperature level at most equal to 100 ° C.
  • zone E When the temperature at the entrance of zone E is less than 100 ° C., cooling by indirect heat exchange, that is to say by heat exchange by convection and by conduction, between the milk paste and the wall of the sheath 13 of the extrusion machine 10 is sufficient.
  • the screws 11 and 12 are, as mentioned previously, formed of several sections of different pitches F1, F2, F3 and F4.
  • the three sections F1, F2 and F3 are provided with narrow pitch threads 28 and the fourth section F4 is provided with wide pitch threads 31.
  • This cooling has the effect of reducing the temperature of the milk paste to a temperature level at most equal to 100 ° C.
  • the dough is cooled to maintain it at a temperature between 90 and 100 ° C.
  • the sheath 13 of the extrusion machine 10 is provided with an orifice 21 for introducing additives, such as, for example, flavorings, vitamins or minerals.
  • additives such as, for example, flavorings, vitamins or minerals.
  • the dough passes through a third zone G of kneading and heat exchange with cooling to maintain it at a temperature in the region of 95 ° C.
  • the screws 11 and 12 are, in known manner, constituted by kneading elements, for example bi-lobe elements 33 identical to the bi-lobe elements in zone C. These kneading elements contribute to intimately mixing the milk paste and the additives introduced in zone F4.
  • the dough is then transferred by a zone H of transport and heat exchange towards the outlet of the extrusion machine 10 and in this zone H, the screws 11 and 12 are provided with threads 34 with tight pitch.
  • the milk paste is cooled so as to maintain it at a temperature of between 75 and 95 ° C.
  • the cooling of this paste during its transfer into the extrusion machine 10 is carried out in a known manner, by a circuit for circulating a cooling fluid which is formed in the wall of the sleeve 13.
  • the extrusion machine 10 is equipped at its downstream end with respect to the direction of flow of the material, an extrusion zone I formed by a die 35 equipped with a granulating knife, not shown and of known type, which continuously produces pellets which solidify on contact with ambient air.
  • the granulator knife is ventilated to avoid sticking of the product during cutting.
  • the pellets thus obtained having a dry matter concentration of the order of 60 to 85%, undergo during stage E3 a final drying so as to obtain a product having a concentration of dry matter of the order of 96 to 97%.
  • the drying step E3 is carried out for example by drying in a fluidized bed.
  • the extrusion machine 10 makes it possible to carry out thermomechanical plasticization-mixing work on the milk dough allowing in particular the mixing, kneading, shearing and heating of the milk dough in order to achieve a homogeneous milk dough in the end.
  • the extrusion machine has the advantage of allowing continuous processing.
  • other machines allowing thermomechanical treatment of the milk paste are used during the first drying step E2.
  • Such machines are for example a mixer, a kneader, or a kneader. In general, and as illustrated in FIG.
  • these machines comprise a tank 36 intended to receive the milk dough, movable members 37 for mixing adapted to move in the tank 36, and means for driving these movable members 37 comprising a motor 41 and an axis 42 carrying the movable members 37.
  • the movable members 37 can have a simple rotational movement around an axis, or more complicated kinematic movements combining rotations along several axes and possibly axial displacements.
  • paddle mixers comprising paddles driven in rotation about the same axis, screw mixers in which several screws are driven in rotation in the tank, viscous fluid mixers such as mixers scraped surface, and mixers.
  • an extrusion machine comprising a single screw, preferably provided with separate sections, is used to carry out the thermomechanical treatment step, each section being provided with material processing elements whose pitch and configuration differ depending on the section considered for the treatment and transport of this material
  • One or more additional treatments can be implemented during the first stage of drying by thermomechanical treatment, in the thermomechanical treatment machine.
  • a degassing step is carried out in the thermomechanical treatment machine. Degassing is an almost instantaneous evaporation of water contained in the product, this evaporation being caused by a sudden drop in pressure, and allowing a change of state from the liquid phase to the vapor phase of water.
  • the tank 36 of a thermomechanical treatment machine is for example provided with a cover 43 allowing the tank 36 to be sealed, and means for forming a vacuum comprising a pipe 45 connected to the tank and a pump vacuum 47 arranged on the pipe.
  • the degassing step can be carried out in a section where the screw or screws have a suitable profile, that is to say a profile allowing rapid decompression of the milk paste.
  • thermomechanical working machine This corresponds to the sections F1 and F2 of decompression of the twin screw extrusion machine of FIG. 2.
  • a gas is injected in a terminal phase of the thermomechanical treatment step, for example an inert gas, into the thermomechanical working machine. Injecting the gas during a stage in which the milk paste is stirred makes it possible to obtain a milk paste having a porous structure in the end.
  • Such a structure facilitates the subsequent drying of the milk paste by substantially increasing the surface area for exchange of the milk paste with the ambient medium, and thus facilitating the transfer of water vapor.
  • thermomechanical treatment machine when the thermomechanical treatment machine is an extruder with two co-rotating screws, the injection of inert gas will take place, for example, through orifice 21, in zone 4 (Fig. 2).
  • the thermomechanical treatment machine is a kneader, or a mixer, as illustrated in FIG. 4, the gas is injected via a pipe 49 opening into the tank 36 and a pump 51 for supplying inert gas.
  • a coating step E6 consisting in coating the milk powder with a coating.
  • the coating step E6 is for example implemented between the step of shaping the milk powder E4 and the packaging step E5.
  • the coating step E6 is carried out for example by spraying a coating product onto the powdered milk.
  • a possible coating product is lecithin, which facilitates the subsequent grinding operation of the powdered milk.
  • the milk in the liquid state generally having a dry matter concentration of the order of 12% is treated to obtain a milk in the viscous state having a dry matter concentration of between about 50% and 55%.
  • the viscous milk from the first evaporation step E'1 is treated to obtain a viscous milk having a concentration in dry matter between about 70% and 75%.
  • the first vacuum evaporation step E'1 is for example carried out in a falling film evaporator. It is an evaporator comprising at least one vertical heating body and of tubular type. In operation, the liquid to be evaporated flows into the tubular heating body and a heat transfer fluid circulates outside the tubular heating body to heat the latter. The liquid to be evaporated enters from above and flows by gravity, forming a film along the internal walls of the tubular heating body of the evaporator.
  • the second vacuum evaporation step E "1 is for example carried out in a scraped surface exchanger.
  • a scraped surface exchanger comprises a heated tubular enclosure into which the viscous milk is conveyed from a first end of the enclosure to the second end. Pales scrape the internal walls of the enclosure to prevent milk in the viscous state from sticking to these internal walls.
  • the product obtained after the drying step E3 is directly packaged.
  • the method according to the invention is applicable to different compositions of liquid milk having variable fat contents and to powdered substitute products.
  • thermomechanical treatment machine extruder, kneader, mixer ...), which allows the development and production of milk powder of different types and therefore with higher added value.
  • the method according to the invention allows, in the case of the production of milk powder, significant energy savings of the order of 40% compared to the conventional method as well as a significant reduction in the investment cost.
  • the consumption of water vapor per 100 kg of treated liquid milk is of the order of 33 kg with the process according to the prior art while it is around 19 kg with the process according to the invention, for substantially identical power consumption.
  • the process of the invention can be used, with similar advantages, for the production of powdered products other than powdered milk, from all types of solutions, suspensions, emulsions of different compositions comprising a dry matter. in aqueous media.
  • the process is for example applicable for the production of powdered products of the type: - starchy products: cereal flours (wheat, oats, corn, barley), potato flours, potato granules and flakes, tapioca flour .
  • These products can be native, i.e. without modifications chemical and / or physical, and simply dried and ground.
  • These products can be physically modified, for example by modification of the crystal structure of starches, inter alia by gelatinization and fusion processes; they can also be chemically modified, for example by hydrolysis, esterification, or etherification; - protein products: milk casein, wheat gluten, corn zein, soy protein, legume proteins (peas, for example), oleoprotein proteins (sunflower, rapeseed, for example).
  • - protein products milk casein, wheat gluten, corn zein, soy protein, legume proteins (peas, for example), oleoprotein proteins (sunflower, rapeseed, for example).
  • These products can be native, that is to say without chemical and / or physical modifications and simply dried and ground.
  • These products can be physically modified, for example by modification of the quaternary, tertiary and secondary structures of proteins (denaturation process); they can also be modified chemically, for example by hydrolysis, amidation, succinylation, or condensation, that is to say by reaction with functional organic groups: amine, carboxyl, for example.
  • the process is also applicable to co-products / by-products of milk fractionation, i.e. liquid fractions obtained when the milk is fractionated by means of processes such as centrifugation, filtration, nanofiltration, ultrafiltration, reverse osmosis ... these operations are intended to separate the different components of milk (fat, proteins, sugars ).
  • the process is also applicable for the production of powdered products, which allow re-hydration to obtain baby food: reconstituted milks according to different ages, various porridge, jar mixes, etc.

Abstract

The invention relates to a method for the continuous production of a powdered product, such as powdered milk, from the product in the liquid state. The inventive method comprises the following steps, namely: at least step one comprising the vacuum evaporation (E1) of a mixture in the liquid state in order to obtain a product in the viscous state; and at least one step comprising the drying (E2, E3) of the viscous state product in order to obtain the product in the solid form thereof. According to one aspect of the invention, the aforementioned drying step (E2, E3) comprises at least one first thermomechanical treatment step (E2) which is performed using a thermomechanical treatment machine into which the viscous state product from the vacuum evaporation step and a determined proportion of powdered product from the same family as the liquid state product are injected simultaneously.

Description

Procédé de production en continu d'un produit en poudre à partir du produit à l'état liquide. La présente invention concerne un procédé de préparation en continu d'un produit en poudre à partir du produit à l'état liquide se présentant sous la forme d'un mélange du type solution, suspension ou émulsion en milieux aqueux. L'invention concerne en particulier un procédé de préparation en continu de lait en poudre à partir de lait liquide et un lait en poudre obtenu par un tel procédé. De manière classique, le lait en poudre est obtenu industriellement en effectuant diverses opérations qui permettent à partir de lait liquide ayant généralement une concentration en matière sèche d'environ 12%, d'obtenir un lait en poudre ayant une concentration en matière sèche de l'ordre de 96 à 97% sans dégrader les propriétés nutritionnelles et fonctionnelles du lait. Compte tenu de la thermo-sensibilité du lait, l'opération exige des conditions de séchage particulières qui sont notamment l'application d'une température faible dans les opérations d'évaporation et concentration du lait liquide et le recours à des temps de séjours courts lors du passage de l'état liquide à l'état solide. De plus, le lait en poudre qui en résulte doit être rapidement et totalement réhydratable. Jusqu'à présent, le séchage du lait comporte plusieurs opérations successives, à savoir : - une opération d'évaporation sous vide du lait à l'état liquide ayant une concentration initiale en matière sèche d'environ 12% pour obtenir une concentration comprise entre 50 et 60% de matière sèche ; - une opération de séchage par atomisation du lait issu de l'opération précédente et dans laquelle le lait est pulvérisé en très fines gouttelettes qui sont mises en contact direct avec de l'air chaud. Cette opération permet d'obtenir du lait en poudre dont la teneur en matière sèche est de l'ordre de 82% ; - une opération de séchage terminal en lit fluidisé pour atteindre la teneur finale en matière sèche d'environ 96 à 97% ; et - un broyage et un tamisage pour calibrer la poudre de lait avant son conditionnement. Cette technique de fabrication de lait en poudre utilisée jusqu'à présent comporte des inconvénients. En effet, le séchage par atomisation a un coût élevé notamment en investissement et en consommation énergétique. La consommation énergétique est de Tordre de 2,6 à 2,8 kg de vapeur et 0,8 kW par kg de lait en poudre produit si bien que cette opération est de loin la plus grande consommatrice d'énergie pour l'ensemble du procédé, avec environ 70% de l'énergie thermique et environ 40% de l'énergie électrique. De plus, même si le séchage par atomisation peut être appliqué à différentes compositions de lait, y compris les produits succédanés du lait en poudre, cette technique n'autorise pas le traitement de lait liquide enrichi en ingrédients vaporisables tels que des arômes par exemple qui seraient éliminés lors du séchage si bien que le développement et la production de produits nouveaux comme par exemple du lait vitaminé ou du lait aromatisé n'est pas envisageable par le séchage par atomisation. L'invention a pour but de proposer un procédé de production en continu d'un produit en poudre à partir du produit à l'état liquide se présentant sous la forme d'un mélange du type solution, suspension ou émulsion en milieux aqueu , dans lequel : - on effectue au moins une étape d'évaporation sous vide du mélange à l'état liquide pour obtenir le produit à l'état visqueux, - on réalise au moins une étape de séchage du produit à l'état visqueux pour obtenir le produit sous forme solide, caractérisé en ce que ladite étape de séchage comprend au moins une première étape de traitement thermomécanique au moyen d'une machine de traitement thermomécanique dans laquelle on injecte simultanément le produit à l'état visqueux: provenant de l'étape d'évaporation sous vide et une proportion déterminée de produit en poudre de la même famille que le produit à l'état liquide, la machine de traitement étant configurée pour mélanger le produit à l'état visqueux et le produit en poudre pour obtenir des pellets de produit solidifiés au contact de l'air ambiant. Selon des modes de mise en œuvre particuliers, le procédé comprend une ou plusieurs des caractéristiques suivantes, prise(s) isolément ou selon toutes les combinaisons techniquement possibles : - après ladite étape de séchage, on effectue une étape de mise en forme du produit solide pour obtenir le produit en poudre ; - le produit en poudre injecté dans la machine de traitement thermomécanique est en totalité du prod uit en poudre recyclé après l'étape de mise en forme ou est en partie du produit en poudre recyclé après l'étape en forme ; - à l'issue de l'étape d'évaporation sous vide, le produit à l'état visqueux présente une concentration en matière sèche comprise entre 55 et 75%, de préférence entre 65 et 75% ; - l'étape d'évaporation comprend une première étape d'évaporation à l'issue de laquelle la concentration en matière sèche est comprise entre environ 50 et 55%, et une seconde étape d'évaporation à l'issue de laquelle la concentration en matière sèche est comprise entre environ 70 et 75% et de préférence entre 65 et 75% ; - à l'issue de l'étape de séchage, le produit sous forme solide présente une concentration en matière sèche d'environ 96 à 97% ; - outre la première étape de traitement thermomécanique, l'étape de séchage comprend une deuxième étape de séchage des pellets obtenus à l'issue de l'étape de traitement thermomécanique ; - la deuxième étape de séchage des pellets est une étape de séchage en lit fluidisé de ces pellets ; - après ou pendant cette deuxième étape de séchage, on enrobe les particules de produit en poudre d'un revêtement extérieur, par exemple à l'aide de lécithine ; - les pellets présentent à l'issue de l'étape de traitement thermomécanique une concentration en matière sèche variant entre 60 et 85% et de préférence compris entre 80 et 85 % ; - le rapport entre le débit massique de prod uit en poudre injecté dans la machine de traitement thermomécanique et le débit massique de produit à l'état visqueux introduit dans la machine de traitement thermomécanique est compris entre 0,25 et 2,50 et de préférence entre 0 ,70 et 1 ,30 ; - au cours de l'étape de traitement thermomécanique, on réalise un dégazage sous pression atmosphérique ou sous vide ; - au cours de l'étape de traitement thermomécanique, on injecte un gaz dans la machine de traitement thermomécanique ; - on réalise l'étape de traitement thermomécanique du produit à l'état visqueux en introduisant le produit à l'état visqueux et le produit en poudre dans une machine d'extrusion à deux vis co-rotatives ; - on réalise l'étape de traitement thermomecanique en introduisant le produit à l'état visqueux et le produit en poudre dans un malaxeur, ou un pétrisseur, ou un mélangeur et/ou une machine d'extrusion à une vis ; - le produit à l'état liquide présente initialement une concentration en matière sèche comprise entre 7 et 20%; - le produit à l'état liquide est du lait liquide, ce par quoi on obtient à l'issue du procédé du lait en poudre ; - le produit à l'état liquide est un produit amylacé, natif ou modifié (physiquement et/ou chimiquement) à base de farines de céréales (blé, avoine, maïs, orge, etc.), de farine de pomme de terre, de granules de pomme de terre, de flocons de pomme de terre, et/ou de farine de tapioca, le produit étant initialement sous la forme d'un mélange du type solution, suspension ou émulsion en milieux aqueux, ce par quoi on obtient à Tissue du procédé le produit sous forme pulvérulente ; - le produit à l'état liquide est un produit protéinique, natif ou modifié (physiquement et/ou chimiquement), choisi parmi la caséine du lait, le gluten du blé, la zéine du maïs, les protéines de soja, les protéines de légumineuses, en particulier de pois, et/ou les protéines d'oléoprotéagineux, en particulier de tournesol ou de colza, le produit étant initialement sous la forme d'un mélange du type solution, suspension ou émulsion en milieux aqueux, ce par quoi on obtient à Tissue du procédé le produit sous forme pulvérulente ; - le produit à l'état liquide est un co-produit/sous-produit de fractionnement du lait, obtenu par fractionnement du lait par centrifugation, filtration, nanofiltration, ultrafiltration, et/ou osmose inverse ; et - le produit en poudre injecté dans la machine de traitement thermomécanique est à environ 90-96% de matière sèche pour les produits d'origine amylacée et protéinique et à environ 97% pour les produits d'origine lactée. L'invention concerne également du lait en poudre obtenu par un procédé tel que défini ci-dessus. D'autres caractéristiques et avantages de l'invention apparaîtront au cours de la description qui va suivre, faite en référence aux dessins annexés, sur lesquels : - la Fig. 1 est un organigramme montrant les différentes étapes d'un procédé de production de lait en poudre conforme à l'invention, - la Fig. 2 est une vue schématique en coupe dans un plan vertical passant par Taxe d'une vis d'une machine d'extrusion utilisée dans un mode de mise en œuvre du procédé de production conforme à l'invention, - la Fig. 3 est une vue en coupe selon la ligne 3-3 de la Fig. 2, - la Fig. 4 est une vue en coupe d'une machine de traitement thermomécanique du type mélangeur, malaxeur ou pétrisseur, et - la Fig. 5 est un organigramme analogue à celui de la Fig. 1 , montrant les étapes d'un procédé selon une variante de mise en œuvre. Ainsi que montré sur l'organigramme de la Fig. 1 , du lait liquide ayant généralement une concentration en matière sèche comprise entre 7 et 20% est tout d'abord traité au cours d'une première étape E1 d'évaporation sous vide pour obtenir un lait à l'état visqueux ayant une concentration en matière sèche comprise entre 55 et 75% et de préférence entre 65 et 75%. De manière classique, au cours de cette étape E1 , le lait liquide est par exemple porté à ébullition à une température élevée, inférieure à 100°C, et à une pression inférieure à la pression atmosphérique. Cette evaporation sous vide permet de ne pas dégrader le lait. A la suite de cette première étape de traitement, le lait à l'état visqueux subit au moins une étape de séchage et de préférence dans le procédé selon l'invention deux étapes de séchage E2 et E3 successives, pour obtenir un lait sous forme solide avec une concentration en matière sèche d'environ 96 à 97%, puis une étape E4 de mise en forme du lait solide pour obtenir le lait en poudre. En se reportant maintenant à la Fig. 2 on va décrire l'étape de séchage qui comprend une première étape E2 de plastification-concentration du lait dans une machine d'extrusion à deux vis co-rotatives et désignée dans son ensemble par la référence 10. La machine d'extrusion 10 est du type à deux vis co-rotatives et co- pénétrantes et comprend deux vis 11 et 12 entraînées en rotation autour de leurs axes par un moteur et un réducteur, non représentés, à l'intérieur d'une enceinte allongée formant un fourreau 13 qui les enveloppe. Les vis 11 et 12 sont munies notamment de filets hélicoïdaux ou d'éléments de traitement de la matière introduite dans le fourreau 13 et qui engrènent les uns dans les autres. La paroi interne dudit fourreau 13 forme deux lobes cylindriques sécants de diamètre légèrement supérieur au diamètre extérieur des filets et des éléments de traitement. Les deux vis 11 et 12 sont entraînées à la même vitesse de rotation et dans le même sens de telle sorte que les deux vis sont identiques, les filets et les éléments de traitement étant simplement décalés les uns par rapport aux autres. Comme montrées à la Fig. 3, les vis 11 et 12 sont avantageusement constituées d'arbres cannelés, respectivement 14 et 15, sur lesquels sont empilés les tronçons de vis. L'alésage intérieur de ces tronçons de vis est muni de cannelures correspondant à celles de l'arbre et la partie extérieure est munie de filets hélicoïdaux ou d'éléments de traitement de la matière dont le pas et la configuration diffèrent selon le tronçon considéré pour le traitement et le transport de cette matière. On peut ainsi disposer dans le fourreau 13 d'un assez grand nombre de tronçons de vis ayant des configurations différentes selon le type de traitement à réaliser sur la matière. La machine d'extrusion 10 comprend une zone A d'introduction en continu dans le fourreau 13, simultanément, d'une part, du lait à l'état visqueux provenant de l'étape E1 d'évaporation sous vide et, d'autre part, une proportion déterminée de lait en poudre à environ 96 à 97% de matière sèche. Le lait en poudre injecté dans la zone A de la machine d'extrusion 10 est en totalité ou en partie du lait en poudre recyclé après l'étape de mise en forme. Le taux de lait en poudre injecté, c'est à dire le rapport entre le débit massique de lait en poudre recyclé à environ 96 à 97% de matière sèche et le débit massique de lait à l'état visqueux est compris entre 0,25 et 2,5 et de préférence compris entre 0,70 et 1 ,30. Dans cette zone A, le fourreau 13 est percé, à son extrémité amont par rapport au sens d'écoulement de la matière, d'un orifice d'alimentation 16 dans lequel se déverse en continu le lait en poudre recyclé. Dans la zone d'introduction A, les vis 11 et 12 sont munies de filets 18 à pas large afin d'assurer le transport du lait introduit par l'orifice 16. Ainsi, le lait est transporté vers l'aval de la machine d'extrusion 10 dans la zone B qui comporte un premier tronçon B1 dans lequel les vis 11 et 12 sont munies de filets 19 à pas large et un second tronçon B2 dans lequel les vis 11 et 12 sont munies de filets 20 à pas resserré. Le lait à l'état visqueux est alimenté au début du premier tronçon B1 de la zone B. L'ensemble lait en poudre injecté et lait à l'état visqueux est transporté dans le second tronçon B2. Le lait est ensuite transporté par les vis 11 et 12 dans une première zone C dans laquelle il est soumis à un malaxage intense sous pression. Pour cela, les vis 11 et 12 dans cette zone C sont formées, de manière connue, par des éléments malaxeurs, par exemple des éléments tri-lobes 24 juxtaposés et qui présentent une forme de triangle isocèle dont les sommets sont tronqués pour réaliser un passage contrôlé du mélange vers l'aval de la machine d'extrusion 10. Les éléments malaxeurs 24 de chaque vis 11 et 12 sont également décalés les uns par rapport aux autres et sont décalés d'une vis à l'autre de manière qu'ils s'imbriquent les uns dans les autres afin de réaliser un malaxage et un mélange intense du lait à l'état pâteux et du lait en poudre. Du fait de ce malaxage intense, il se produit une élévation de la température du lait. A titre d'exemple, le lait est introduit dans la machine d'extrusion 10 à la température ambiante d'environ 20°C et à la sortie de la zone C de malaxage, il est à une température d'environ 80°C. A la sortie de la première zone de malaxage C, le lait à l'état pâteux est transféré dans une zone D dans laquelle les vis 11 et 12 sont munies de filets 25 à pas large vers une deuxième zone E de malaxage pourvue par exemple d'éléments de vis constitués par des filets 26 à pas inversé dont les bords périphériques sont munis d'ouvertures régulièrement réparties autour de Taxe de la vis correspondante permettant de contrôler le passage du débit du lait vers l'aval ce qui détermine un freinage dans cette zone E et un effort de compression à Tamont. Il s'ensuit donc un cisaillement qui homogénéise le lait afin d'obtenir une pâte très visqueuse. L'intensité du cisaillement est contrôlée par la longueur des éléments de vis à pas inversé et par la section de passage des ouvertures des bords des filets, de manière à contrôler l'augmentation de la température qui en résulte. En effet, l'opération de malaxage dans la zone E entraîne un échauffement du mélange, une partie importante du travail mécanique étant convertie en une énergie thermique. La température du lait à la sortie de la zone E varie de Tordre de 90°C à 125°C. La température du lait à la sortie de la zone E est d'autant plus importante que la viscosité de la pâte de lait est élevée, laquelle dépend du taux d'injection du lait en poudre à environ 96 à 97% de matière sèche dans l'orifice d'alimentation 16 de la machine d'extrusion 10. Plus le taux d'injection de lait en poudre est élevé, plus la teneur en matière sèche de la pâte de lait est élevée, et plus la viscosité de la pâte de lait est élevée et, par voie de conséquence, plus la température de la pâte de lait à la sortie de la zone E est élevée. A la suite de la deuxième zone E de malaxage et de cisaillement, les vis 11 et 12 de la machine d'extrusion déterminent une zone F de transport et de refroidissement de la pâte de lait. Dans cette zone F, le refroidissement de la pâte de lait se fait de deux façons différentes selon le niveau de température à l'entrée de la zone F. Lorsque la température à l'entrée de la zone E est supérieure à 100°C, le refroidissement se fait de préférence par dégazage atmosphérique ou sous vide, car il est plus efficace. Dans la zone F, les vis 11 et 12 sont formées de plusieurs tronçons de pas différents, un premier tronçon F1 de filets 28 à pas resserré, un deuxième tronçon F2 muni de filets 29 à pas large, un troisième tronçon F3 muni de filets 30 à pas resserré et un quatrième tronçon F4 muni de filets 31 à pas large. Au début de la zone F, le fourreau 13 de la machine d'extrusion 10 comporte un orifice de dégazage 32 qui débouche dans les alésages sécants dudit fourreau 13. Après le passage de la pâte de lait dans la zone E où cette pâte a été soumise à un malaxage, la pâte subit dans les tronçons F1 et F2 de la zone F une décompression de telle sorte que l'eau contenue dans ladite pâte se vaporise et s'échappe par l'orifice 32. Ce dégazage a pour effet de réduire instantanément la température de la pâte de lait, à un niveau de température au plus égal à 100°C. Lorsque la température à l'entrée de la zone E est inférieure à 100°C, le refroidissement par échange de chaleur indirect, c'est à dire par échange de chaleur par convection et par conduction, entre la pâte de lait et la paroi du fourreau 13 de la machine d'extrusion 10 est suffisant. Dans cette zone F, les vis 11 et 12 sont, comme mentionné précédemment, formées de plusieurs tronçons de pas différents F1, F2, F3 et F4. Les trois tronçons F1, F2 et F3 sont munis de filets 28 à pas resséré et le quatrième tronçon F4 est muni de filets 31 à pas large. Ce refroidissement a pour effet de réduire la température de la pâte de lait à un niveau de température au plus égal à 100°C. Au cours de son transfert dans la zone F, la pâte est refroidie pour la maintenir à une température comprise entre 90 et 100°C ce qui permet également d'ajuster la viscosité. En fin de la zone F, le fourreau 13 de la machine d'extrusion 10 est pourvu d'un orifice 21 d'introduction d'additifs, comme par exemple des arômes, des vitamines ou des minéraux. A la sortie de la zone de transport F, la pâte traverse une troisième zone G de malaxage et d'échange thermique avec un refroidissement pour la maintenir à une température voisine de 95°C. Dans cette zone G, les vis 11 et 12 sont, de façon connue, constituées par des éléments de malaxage, par exemple des éléments bi-lobes 33 identiques aux éléments bi-lobes de la zone C. Ces éléments de malaxage contribuent à mélanger intimement la pâte de lait et les additifs introduits dans la zone F4. La pâte est ensuite transférée par une zone H de transport et d'échange thermique vers la sortie de la machine d'extrusion 10 et dans cette zone H, les vis 11 et 12 sont munies de filets 34 à pas resserré. Au cours de son passage dans les zones G et H, la pâte de lait est refroidie de façon à la maintenir à une température comprise entre 75 et 95°C. Le refroidissement de cette pâte au cours de son transfert dans la machine d'extrusion 10 est réalisé de manière connue, par un circuit de circulation d'un fluide de refroidissement qui est ménagé dans la paroi du fourreau 13. La machine d'extrusion 10 est équipée à son extrémité avale par rapport au sens d'écoulement de la matière, d'une zone I d'extrusion formée par une filière 35 équipée d'un couteau granulateur, non représenté et de type connu, qui produit en continu des pellets qui se solidifient au contact de l'air ambiant. De préférence, le couteau granulateur est ventilé pour éviter le collage du produit lors de la coupe. A la sortie de la machine d'extrusion 10, les pellets ainsi obtenus ayant une concentration en matière sèche de Tordre de 60 à 85%, subissent au cours de l'étape E3 un séchage terminal de façon à obtenir un produit ayant une concentration en matière sèche de Tordre de 96 à 97%. L'étape de séchage E3 est réalisée par exemple par séchage en lit fluidisé. Les pellets ainsi séchés sont ensuite broyés et tamisés au cours de l'étape E4 afin d'obtenir un lait en poudre qui est conditionné lors de l'étape finale E5. La machine d'extrusion 10 permet de réaliser sur la pâte de lait un travail thermomécanique de plastification-mélange permettant notamment le mélange, le malaxage, le cisaillement et Téchauffement de la pâte de lait pour parvenir au final à une pâte de lait homogène. La machine d'extrusion présente l'avantage de permettre un traitement en continu. En variante, d'autres machines permettant un traitement thermomécanique de la pâte de lait sont utilisées lors de la première étape de séchage E2. De telles machines sont par exemple un mélangeur, un malaxeur, ou un pétrisseur. De façon générale, et comme illustrées sur la Fig. 4, ces machines comprennent une cuve 36 destinée à recevoir la pâte de lait, des organes mobiles 37 de mélange adaptés pour se déplacer dans la cuve 36, et des moyens d'entraînement de ces organes mobiles 37 comprenant un moteur 41 et un axe 42 portant les organes mobiles 37. Les organes mobiles 37 peuvent avoir un simple mouvement de rotation autour d'un axe, ou des mouvements cinématiques plus compliqués combinant des rotations suivant plusieurs axes et éventuellement des déplacements axiaux. A titre d'exemple, on peut citer les mélangeurs à pâles comprenant des pâles entraînées en rotation autour d'un même axe, les mélangeurs à vis dans lesquels plusieurs vis sont entraînées en rotation dans la cuve, les mélangeurs à fluides visqueux tels que mélangeurs à surface raclée, et les malaxeurs. Dans une autre variante, on utilise pour réaliser l'étape de traitement thermomécanique une machine d'extrusion comprenant une unique vis, muni de préférence de tronçons distincts, chaque tronçon étant muni d'éléments de traitement de la matière dont le pas et la configuration diffèrent selon le tronçon considéré pour le traitement et le transport de cette matière Un ou plusieurs traitements supplémentaires peuvent être mis en œuvre pendant la première étape de séchage par traitement thermomécanique, dans la machine de traitement thermomécanique. Selon un premier traitement, on réalise dans la machine de traitement thermomécanique une étape de dégazage. Le dégazage est une evaporation quasi-instantanée d'eau contenue dans le produit, cette evaporation étant provoquée par une chute brutale de pression, et permettant un changement d'état de la phase liquide à la phase vapeur de l'eau. La baisse rapide de pression du produit ou du lait est obtenue, selon la pression initiale du produit ou du lait, par mise rapide à l'atmosphère, si le produit ou le lait est à une pression supérieure à la pression atmosphérique, ou par formation d'une dépression A cet effet, dans le mode de réalisation représenté sur la Fig. 4, la cuve 36 d'une machine de traitement thermomécanique est par exemple munie d'un couvercle 43 permettant de fermer la cuve 36 de façon étanche, et de moyens pour former un vide comprenant une conduite 45 raccordée à la cuve et une pompe à vide 47 disposée sur la conduite. On notera que dans une extrudeuse à vis, du type à une vis ou à deux vis, l'étape de dégazage peut être réalisée dans un tronçon où la ou les vis présentent un profil adapté, c'est-à-dire un profil permettant une décompression rapide de la pâte de lait. Ceci correspond aux tronçons F1 et F2 de décompression de la machine d'extrusion à deux vis de la Fig. 2. Lors du dégazage, la partie de la pâte de lait restant sous forme liquide dans la machine de travail thermomécanique voit sa température baisser. Selon un deuxième traitement alternatif ou complémentaire du premier, on injecte dans une phase terminale de l'étape de traitement thermomécanique un gaz comme par exemple un gaz inerte dans la machine de travail thermomécanique. L'injection du gaz pendant une étape où la pâte de lait est brassée permet d'obtenir au final une pâte de lait présentant une structure poreuse. Une telle structure facilite le séchage ultérieur de la pâte de lait en augmentant sensiblement la surface d'échange de la pâte de lait avec le milieu ambiant, et en facilitant ainsi le transfert de vapeur d'eau. A cet effet, lorsque la machine de traitement thermomécanique est un extrudeur à deux vis co-rotatives, l'injection de gaz inerte se fera par exemple par l'orifice 21 , en zone 4 (Fig. 2). Lorsque la machine de traitement thermomécanique est un malaxeur, ou un mélangeur, telle que illustrée sur la Fig. 4, le gaz est injecté via une conduite 49 débouchant dans la cuve 36 et une pompe 51 d'alimentation en gaz inerte. Il est également possible, pour améliorer les propriétés du produit final, d'opérer une étape d'enrobage E6 consistant à revêtir le lait en poudre d'un revêtement. Comme illustrée sur la figure 5, l'étape d'enrobage E6 est par exemple mise en œuvre entre l'étape de mise en forme du lait en poudre E4 et l'étape de conditionnement E5. L'étape d'enrobage E6 est effectuée par exemple par pulvérisation d'un produit de revêtement sur le lait en poudre. Un produit de revêtement possible est de la lécithine, qui permet de faciliter l'opération de broyage ultérieur du lait en poudre. En outre, en variante, et comme illustré sur la figure 5, il est possible de réaliser l'étape d'évaporation sous vide en deux étapes successives d'évaporation sous vide, E'1 et E"1. Lors de la première étape d'évaporation sous vide E'1 , le lait à l'état liquide ayant généralement une concentration en matière sèche de Tordre de 12% est traité pour obtenir un lait à l'état visqueux ayant une concentration en matière sèche comprise entre environ 50% et 55%. Lors de la seconde étape d'évaporation sous vide E"1 , le lait à l'état visqueux issu de la première étape d'évaporation E'1 est traité pour obtenir un lait à l'état visqueux ayant une concentration en matière sèche comprise entre environ 70% et 75%. La première étape d'évaporation sous vide E'1 est par exemple réalisée dans un évaporateur à film tombant. Il s'agit d'un évaporateur comportant au moins un corps de chauffe vertical et de type tubulaire. En fonctionnement, le liquide à évaporer s'écoule dans le corps tubulaire de chauffe et un fluide caloporteur circule à l'extérieur du corps tubulaire de chauffe pour chauffer celui-ci. Le liquide à évaporer entre par le haut et s'écoule par gravité en formant un film le long des parois internes du corps tubulaire de chauffe de Tévaporateur. La seconde étape d'évaporation sous vide E"1 est par exemple réalisée dans un échangeur à surface raclée. Un tel échangeur comprend une enceinte tubulaire chauffée dans laquelle le lait à état visqueux est convoyé d'une première extrémité de l'enceinte à la seconde extrémité. Des pâles viennent racler les parois internes de l'enceinte pour éviter que du lait à l'état visqueux ne reste collé sur ces parois internes. Selon une variante illustrée à la Fig. 5, le produit obtenu après l'étape de séchage E3 est directement conditionné. Le procédé selon l'invention est applicable à différentes compositions de lait liquide ayant des teneurs en matière grasse variables et à des produits succédanés en poudre. De plus, il permet le traitement de lait liquide complémenté avec divers ingrédients tels que arômes, vitamines, minéraux, grâce à l'excellente capacité de mélange de la machine de traitement thermomécanique (extrudeuse, malaxeur, mélangeur...), ce qui autorise le développement et la production de lait en poudre de différentes natures et donc à plus forte valeur ajoutée. Le procédé selon l'invention permet, dans le cas de la production de lait en poudre, des économies d'énergie importantes de Tordre de 40% par rapport au procédé conventionnel ainsi qu'une diminution importante du coût d'investissement. A titre de comparaison, la consommation de vapeur d'eau pour 100 kg de lait liquide traité est de Tordre de 33 kg avec le procédé selon l'état de la technique alors qu'il est d'environ 19 kg avec le procédé selon l'invention, pour une consommation électrique sensiblement identique. De manière générale, le procédé de l'invention est utilisable, avec des avantages analogues, pour la production de produits en poudre autres que le lait en poudre, à partir de tous types de solutions, suspensions, émulsions de différentes compositions comprenant une matière sèche en milieux aqueux. Le procédé est par exemple applicable pour la production de produits en poudre du type : - produits amylacés : farines de céréales (blé, avoine, maïs, orge), farines de pomme de terre, granules et flocons de pomme de terre, farine de tapioca. Ces produits peuvent être natifs, c'est-à-dire sans modifications chimiques et/ou physiques, et simplement séchés et broyés. Ces produits peuvent être modifiés physiquement, par exemple par modification de la structure cristalline des amidons, entre autres par des processus de gélatinisation et de fusion ; ils peuvent aussi être modifiés chimiquement, par exemple par hydrolyse, estérification, ou éthérification ; - produits protéiniques : caséine du lait, gluten du blé, zéine du maïs, protéines de soja, protéines de légumineuses (pois, par exemple), protéines d'oléoprotéagineux (tournesol, colza, par exemple). Ces produits peuvent être natifs, c'est-à-dire sans modifications chimiques et/ou physiques et simplement séchés et broyés. Ces produits peuvent être modifiés physiquement, par exemple par modification des structures quaternaire, tertiaire et secondaire des protéines (processus de denaturation) ; ils peuvent aussi être modifiés chimiquement, par exemple par hydrolyse, amidation, succinylation, ou condensation, c'est-à-dire par réaction avec les groupes organiques fonctionnels : aminé, carboxyle, par exemple. Le procédé est aussi applicable aux co-produits/sous-produits de fractionnement du lait, c'est-à-dire des fractions liquides obtenues lorsque le lait est fractionné au moyen de procédés tels que centrifugation, filtration, nanofiltration, ultrafiltration, osmose inverse... ces opérations étant destinées à séparer les différents composants du lait (matière grasse, protéines, sucres...). Le procédé est également applicable pour la production de produits en poudre permettant par la suite, par réhydratation, d'obtenir des aliments pour bébé : laits reconstitués selon les différents âges, bouillies diverses, mélanges en pots... Process for the continuous production of a powdered product from the product in the liquid state. The present invention relates to a process for the continuous preparation of a powdered product from the product in the liquid state, in the form of a mixture of the solution, suspension or emulsion type in aqueous media. The invention relates in particular to a process for the continuous preparation of powdered milk from liquid milk and a powdered milk obtained by such a method. Conventionally, powdered milk is obtained industrially by carrying out various operations which make it possible, from liquid milk generally having a dry matter concentration of approximately 12%, to obtain a powdered milk having a dry matter concentration of 1 '' from 96 to 97% without degrading the nutritional and functional properties of milk. Given the thermosensitivity of the milk, the operation requires specific drying conditions which include the application of a low temperature in the evaporation and concentration operations of the liquid milk and the use of short residence times. during the transition from the liquid state to the solid state. In addition, the resulting milk powder must be quickly and completely rehydratable. Up to now, the drying of the milk comprises several successive operations, namely: - an operation of evaporation under vacuum of the milk in the liquid state having an initial dry matter concentration of approximately 12% to obtain a concentration of between 50 and 60% dry matter; - A spray drying operation of the milk from the previous operation and in which the milk is sprayed into very fine droplets which are brought into direct contact with hot air. This operation makes it possible to obtain milk powder whose dry matter content is of the order of 82%;  - a final drying operation in a fluidized bed to reach the final dry matter content of approximately 96 to 97%; and - grinding and sieving to calibrate the milk powder before packaging. This milk powder manufacturing technique used until now has drawbacks. In fact, spray drying has a high cost, particularly in terms of investment and energy consumption. The energy consumption is in the range of 2.6 to 2.8 kg of steam and 0.8 kW per kg of milk powder produced so that this operation is by far the largest consumer of energy for the whole process , with approximately 70% of thermal energy and approximately 40% of electrical energy. In addition, even if spray drying can be applied to different milk compositions, including milk powder substitutes, this technique does not allow the processing of liquid milk enriched with vaporizable ingredients such as flavorings, for example. would be eliminated during drying so that the development and production of new products such as vitamin milk or flavored milk is not possible by spray drying. The object of the invention is to provide a process for the continuous production of a powdered product from the product in the liquid state, in the form of a mixture of the solution, suspension or emulsion type in aqueous media, in which: - at least one step of vacuum evaporation of the mixture in the liquid state is carried out to obtain the product in the viscous state, - at least one step of drying the product in the viscous state is carried out to obtain the product in solid form, characterized in that said drying step comprises at least a first step of thermomechanical treatment by means of a thermomechanical treatment machine into which one injects simultaneously the product in the viscous state: coming from the evaporation step under vacuum and a determined proportion of powdered product of the same family as the product in the liquid state, the treatment machine being configured to mix the product in the viscous state and the product in powder form to obtain pellets of product solidified in contact with ambient air. According to particular modes of implementation, the method comprises one or more of the following characteristics, taken alone or according to any technically possible combination: - after said drying step, a step of shaping the solid product is carried out to obtain the powdered product; - The powdered product injected into the thermomechanical treatment machine is entirely of the powdered product recycled after the shaping step or is partly of the powdered product recycled after the shaping step; - At the end of the vacuum evaporation step, the product in the viscous state has a dry matter concentration of between 55 and 75%, preferably between 65 and 75%; the evaporation step comprises a first evaporation step at the end of which the dry matter concentration is between approximately 50 and 55%, and a second evaporation step at the end of which the concentration in dry matter is between about 70 and 75% and preferably between 65 and 75%; - At the end of the drying step, the product in solid form has a dry matter concentration of about 96 to 97%; - In addition to the first step of thermomechanical treatment, the drying step comprises a second step of drying the pellets obtained at the end of the step of thermomechanical treatment; - The second stage of drying the pellets is a stage of drying in a fluidized bed of these pellets;  - After or during this second drying step, the powdered product particles are coated with an external coating, for example using lecithin; - The pellets present at the end of the thermomechanical treatment step a dry matter concentration varying between 60 and 85% and preferably between 80 and 85%; the ratio between the mass flow rate of powdered product injected into the thermomechanical treatment machine and the mass flow rate of product in the viscous state introduced into the thermomechanical treatment machine is between 0.25 and 2.50 and preferably between 0.70 and 1.30; - During the thermomechanical treatment step, degassing is carried out at atmospheric pressure or under vacuum; - During the thermomechanical treatment step, a gas is injected into the thermomechanical treatment machine; - The step of thermomechanical treatment of the product in the viscous state is carried out by introducing the product in the viscous state and the powdered product into an extrusion machine with two co-rotating screws; - the thermomechanical treatment step is carried out by introducing the product in the viscous state and the powdered product into a kneader, or a kneader, or a mixer and / or a single screw extrusion machine; - the product in the liquid state initially has a dry matter concentration of between 7 and 20%; - The product in the liquid state is liquid milk, whereby we obtain milk powder after the process; - the product in the liquid state is a starchy product, native or modified (physically and / or chemically) based on cereal flours (wheat, oats, corn, barley, etc.), potato flour, granules of potato, potato flakes, and / or tapioca flour, the product initially being in the form of a mixture of the solution type, suspension or emulsion in aqueous media, whereby the product is obtained in powder form; - the product in the liquid state is a protein product, native or modified (physically and / or chemically), chosen from milk casein, wheat gluten, corn zein, soy proteins, legume proteins , in particular peas, and / or oleoproteinous proteins, in particular sunflower or rapeseed, the product being initially in the form of a mixture of the solution, suspension or emulsion type in aqueous media, which is obtained the fabric of the process the product in powder form; - the product in the liquid state is a co-product / by-product of milk fractionation, obtained by fractionation of milk by centrifugation, filtration, nanofiltration, ultrafiltration, and / or reverse osmosis; and - the powdered product injected into the thermomechanical treatment machine is approximately 90-96% dry matter for products of starch and protein origin and approximately 97% for products of milk origin. The invention also relates to milk powder obtained by a process as defined above. Other characteristics and advantages of the invention will appear during the description which follows, given with reference to the appended drawings, in which: - FIG. 1 is a flowchart showing the different stages of a process for producing powdered milk in accordance with the invention, - FIG. 2 is a schematic sectional view in a vertical plane passing through the tax of a screw of an extrusion machine used in an embodiment of the production process according to the invention, - FIG. 3 is a sectional view along line 3-3 of FIG. 2, - Fig. 4 is a sectional view of a thermomechanical treatment machine of the mixer, kneader or kneader type, and  - Fig. 5 is a flow diagram similar to that of FIG. 1, showing the steps of a method according to an alternative implementation. As shown in the flow diagram of FIG. 1, liquid milk generally having a dry matter concentration of between 7 and 20% is firstly treated during a first step E1 of evaporation under vacuum to obtain a milk in the viscous state having a concentration of dry matter between 55 and 75% and preferably between 65 and 75%. Conventionally, during this step E1, the liquid milk is for example brought to a boil at a high temperature, below 100 ° C., and at a pressure below atmospheric pressure. This evaporation under vacuum makes it possible not to degrade the milk. Following this first processing step, the milk in the viscous state undergoes at least one drying step and preferably in the process according to the invention two successive drying steps E2 and E3, in order to obtain a milk in solid form. with a dry matter concentration of around 96 to 97%, then a step E4 of shaping the solid milk to obtain the powdered milk. Referring now to FIG. 2 we will describe the drying step which comprises a first step E2 of plasticizing-concentrating the milk in an extrusion machine with two co-rotating screws and generally designated by the reference 10. The extrusion machine 10 is of the type with two co-rotating and co-penetrating screws and comprises two screws 11 and 12 driven in rotation about their axes by a motor and a reduction gear, not shown, inside an elongated enclosure forming a sheath 13 which envelops them. The screws 11 and 12 are provided in particular with helical threads or elements for processing the material introduced into the sheath 13 and which mesh with one another. The internal wall of said sheath 13 forms two intersecting cylindrical lobes of diameter slightly greater than the external diameter of the threads and of the treatment elements.  The two screws 11 and 12 are driven at the same speed of rotation and in the same direction so that the two screws are identical, the threads and the treatment elements being simply offset from each other. As shown in Fig. 3, the screws 11 and 12 advantageously consist of splined shafts, respectively 14 and 15, on which the screw sections are stacked. The internal bore of these sections of screw is provided with grooves corresponding to those of the shaft and the external part is provided with helical threads or with elements for processing the material, the pitch and configuration of which differ according to the section considered for the processing and transportation of this material. It is thus possible to have in the sheath 13 a fairly large number of screw sections having different configurations depending on the type of treatment to be performed on the material. The extrusion machine 10 comprises a zone A for continuously introducing into the barrel 13, simultaneously, on the one hand, milk in the viscous state coming from step E1 of evaporation under vacuum and, on the other hand share, a determined proportion of milk powder to about 96 to 97% of dry matter. The milk powder injected into zone A of the extrusion machine 10 is wholly or in part milk powder recycled after the shaping step. The rate of powdered milk injected, that is to say the ratio between the mass flow rate of milk powder recycled to approximately 96 to 97% of dry matter and the mass flow rate of milk in the viscous state is between 0.25 and 2.5 and preferably between 0.70 and 1.30. In this zone A, the sheath 13 is pierced, at its upstream end relative to the direction of flow of the material, with a feed orifice 16 into which the recycled powdered milk is continuously poured. In the introduction zone A, the screws 11 and 12 are provided with threads 18 with a wide pitch in order to transport the milk introduced through the orifice 16. Thus, the milk is transported downstream from the extrusion machine 10 in zone B which comprises a first section B1 in which the screws 11 and 12 are provided with threads 19 with a wide pitch and a second section B2 in which the screws 11 and 12 are provided with threads 20 with tight pitch. The milk in the viscous state is fed at the start of the first section B1 of the zone B. The whole injected powdered milk and milk in the viscous state are transported in the second section B2. The milk is then transported by the screws 11 and 12 into a first zone C in which it is subjected to intense mixing under pressure. For this, the screws 11 and 12 in this zone C are formed, in a known manner, by kneading elements, for example tri-lobe elements 24 juxtaposed and which have the shape of an isosceles triangle whose vertices are truncated to provide a passage controlled mixing downstream of the extrusion machine 10. The kneading elements 24 of each screw 11 and 12 are also offset from one another and are offset from one screw to the other so that they overlap with each other in order to achieve kneading and an intense mixing of the pasty milk and the powdered milk. Due to this intense mixing, there is a rise in the temperature of the milk. By way of example, the milk is introduced into the extrusion machine 10 at ambient temperature of approximately 20 ° C. and at the outlet of the kneading zone C, it is at a temperature of approximately 80 ° C. At the exit from the first mixing zone C, the milk in the pasty state is transferred into a zone D in which the screws 11 and 12 are provided with threads 25 with a wide pitch towards a second mixing zone E provided for example with 'screw elements constituted by threads 26 with inverted pitch whose peripheral edges are provided with openings regularly distributed around the charge of the corresponding screw making it possible to control the passage of the flow of milk downstream which determines braking in this zone E and a compression force at Tamont. It therefore follows a shear which homogenizes the milk in order to obtain a very viscous paste. The shear intensity is controlled by the length of the reverse pitch screw elements and by the passage section of the openings at the edges of the threads, so as to control the resulting increase in temperature. Indeed, the mixing operation in zone E causes the mixture to heat up, a significant part of the mechanical work being converted into thermal energy. The temperature of the milk leaving zone E varies from about 90 ° C to 125 ° C. The temperature of the milk at the exit from zone E is all the more important as the viscosity of the milk paste is high, which depends on the injection rate of the milk powder at about 96 to 97% of dry matter in l feed port 16 of the extrusion machine 10. The higher the injection rate of powdered milk, the higher the dry matter content of the milk paste, and the higher the viscosity of the milk paste is high and, consequently, the higher the temperature of the milk paste leaving the zone E. Following the second zone E of kneading and shearing, the screws 11 and 12 of the extrusion machine determine a zone F for transporting and cooling the milk paste. In this zone F, the cooling of the milk paste is done in two different ways according to the temperature level at the entry of zone F. When the temperature at the entry of zone E is higher than 100 ° C, cooling is preferably done by atmospheric degassing or under vacuum, because it is more efficient. In zone F, the screws 11 and 12 are formed by several sections of different pitch, a first section F1 of threads 28 with narrow pitch, a second section F2 provided with threads 29 with wide pitch, a third section F3 provided with threads 30 with tight pitch and a fourth section F4 provided with threads 31 with wide pitch. At the start of zone F, the sheath 13 of the extrusion machine 10 has a degassing orifice 32 which opens into the intersecting bores of said sheath 13. After the milk paste has passed through zone E where this paste has been subjected to kneading, the dough undergoes in sections F1 and F2 of zone F a decompression so that the water contained in said paste evaporates and escapes through the orifice 32. This degassing has the effect of instantly reducing the temperature of the milk paste, to a temperature level at most equal to 100 ° C. When the temperature at the entrance of zone E is less than 100 ° C., cooling by indirect heat exchange, that is to say by heat exchange by convection and by conduction, between the milk paste and the wall of the sheath 13 of the extrusion machine 10 is sufficient. In this area F, the screws 11 and 12 are, as mentioned previously, formed of several sections of different pitches F1, F2, F3 and F4. The three sections F1, F2 and F3 are provided with narrow pitch threads 28 and the fourth section F4 is provided with wide pitch threads 31. This cooling has the effect of reducing the temperature of the milk paste to a temperature level at most equal to 100 ° C. During its transfer to zone F, the dough is cooled to maintain it at a temperature between 90 and 100 ° C. which also makes it possible to adjust the viscosity. At the end of zone F, the sheath 13 of the extrusion machine 10 is provided with an orifice 21 for introducing additives, such as, for example, flavorings, vitamins or minerals. At the exit from the transport zone F, the dough passes through a third zone G of kneading and heat exchange with cooling to maintain it at a temperature in the region of 95 ° C. In this zone G, the screws 11 and 12 are, in known manner, constituted by kneading elements, for example bi-lobe elements 33 identical to the bi-lobe elements in zone C. These kneading elements contribute to intimately mixing the milk paste and the additives introduced in zone F4. The dough is then transferred by a zone H of transport and heat exchange towards the outlet of the extrusion machine 10 and in this zone H, the screws 11 and 12 are provided with threads 34 with tight pitch.  During its passage through zones G and H, the milk paste is cooled so as to maintain it at a temperature of between 75 and 95 ° C. The cooling of this paste during its transfer into the extrusion machine 10 is carried out in a known manner, by a circuit for circulating a cooling fluid which is formed in the wall of the sleeve 13. The extrusion machine 10 is equipped at its downstream end with respect to the direction of flow of the material, an extrusion zone I formed by a die 35 equipped with a granulating knife, not shown and of known type, which continuously produces pellets which solidify on contact with ambient air. Preferably, the granulator knife is ventilated to avoid sticking of the product during cutting. On leaving the extrusion machine 10, the pellets thus obtained having a dry matter concentration of the order of 60 to 85%, undergo during stage E3 a final drying so as to obtain a product having a concentration of dry matter of the order of 96 to 97%. The drying step E3 is carried out for example by drying in a fluidized bed. The pellets thus dried are then ground and sieved during step E4 in order to obtain a milk powder which is conditioned during the final step E5. The extrusion machine 10 makes it possible to carry out thermomechanical plasticization-mixing work on the milk dough allowing in particular the mixing, kneading, shearing and heating of the milk dough in order to achieve a homogeneous milk dough in the end. The extrusion machine has the advantage of allowing continuous processing. As a variant, other machines allowing thermomechanical treatment of the milk paste are used during the first drying step E2.  Such machines are for example a mixer, a kneader, or a kneader. In general, and as illustrated in FIG. 4, these machines comprise a tank 36 intended to receive the milk dough, movable members 37 for mixing adapted to move in the tank 36, and means for driving these movable members 37 comprising a motor 41 and an axis 42 carrying the movable members 37. The movable members 37 can have a simple rotational movement around an axis, or more complicated kinematic movements combining rotations along several axes and possibly axial displacements. By way of example, there may be mentioned paddle mixers comprising paddles driven in rotation about the same axis, screw mixers in which several screws are driven in rotation in the tank, viscous fluid mixers such as mixers scraped surface, and mixers. In another variant, an extrusion machine comprising a single screw, preferably provided with separate sections, is used to carry out the thermomechanical treatment step, each section being provided with material processing elements whose pitch and configuration differ depending on the section considered for the treatment and transport of this material One or more additional treatments can be implemented during the first stage of drying by thermomechanical treatment, in the thermomechanical treatment machine. According to a first treatment, a degassing step is carried out in the thermomechanical treatment machine. Degassing is an almost instantaneous evaporation of water contained in the product, this evaporation being caused by a sudden drop in pressure, and allowing a change of state from the liquid phase to the vapor phase of water. The rapid drop in product or milk pressure is obtained, depending on the initial pressure of the product or milk, by rapid venting, if the product or milk is at a pressure greater than atmospheric pressure, or by forming a depression For this purpose, in the embodiment shown in FIG. 4, the tank 36 of a thermomechanical treatment machine is for example provided with a cover 43 allowing the tank 36 to be sealed, and means for forming a vacuum comprising a pipe 45 connected to the tank and a pump vacuum 47 arranged on the pipe. It will be noted that in a screw extruder, of the one screw or two screw type, the degassing step can be carried out in a section where the screw or screws have a suitable profile, that is to say a profile allowing rapid decompression of the milk paste. This corresponds to the sections F1 and F2 of decompression of the twin screw extrusion machine of FIG. 2. During degassing, the part of the milk paste remaining in liquid form in the thermomechanical working machine sees its temperature drop. According to a second alternative or complementary treatment to the first, a gas is injected in a terminal phase of the thermomechanical treatment step, for example an inert gas, into the thermomechanical working machine. Injecting the gas during a stage in which the milk paste is stirred makes it possible to obtain a milk paste having a porous structure in the end. Such a structure facilitates the subsequent drying of the milk paste by substantially increasing the surface area for exchange of the milk paste with the ambient medium, and thus facilitating the transfer of water vapor. To this end, when the thermomechanical treatment machine is an extruder with two co-rotating screws, the injection of inert gas will take place, for example, through orifice 21, in zone 4 (Fig. 2). When the thermomechanical treatment machine is a kneader, or a mixer, as illustrated in FIG. 4, the gas is injected via a pipe 49 opening into the tank 36 and a pump 51 for supplying inert gas.  It is also possible, to improve the properties of the final product, to carry out a coating step E6 consisting in coating the milk powder with a coating. As illustrated in FIG. 5, the coating step E6 is for example implemented between the step of shaping the milk powder E4 and the packaging step E5. The coating step E6 is carried out for example by spraying a coating product onto the powdered milk. A possible coating product is lecithin, which facilitates the subsequent grinding operation of the powdered milk. In addition, as a variant, and as illustrated in FIG. 5, it is possible to carry out the evaporation step under vacuum in two successive steps of evaporation under vacuum, E'1 and E "1. During the first step evaporation under vacuum E'1, the milk in the liquid state generally having a dry matter concentration of the order of 12% is treated to obtain a milk in the viscous state having a dry matter concentration of between about 50% and 55%. During the second vacuum evaporation step E "1, the viscous milk from the first evaporation step E'1 is treated to obtain a viscous milk having a concentration in dry matter between about 70% and 75%. The first vacuum evaporation step E'1 is for example carried out in a falling film evaporator. It is an evaporator comprising at least one vertical heating body and of tubular type. In operation, the liquid to be evaporated flows into the tubular heating body and a heat transfer fluid circulates outside the tubular heating body to heat the latter. The liquid to be evaporated enters from above and flows by gravity, forming a film along the internal walls of the tubular heating body of the evaporator. The second vacuum evaporation step E "1 is for example carried out in a scraped surface exchanger. Such an exchanger comprises a heated tubular enclosure into which the viscous milk is conveyed from a first end of the enclosure to the second end. Pales scrape the internal walls of the enclosure to prevent milk in the viscous state from sticking to these internal walls. According to a variant illustrated in FIG. 5, the product obtained after the drying step E3 is directly packaged. The method according to the invention is applicable to different compositions of liquid milk having variable fat contents and to powdered substitute products. In addition, it allows the treatment of liquid milk supplemented with various ingredients such as flavorings, vitamins, minerals, thanks to the excellent mixing capacity of the thermomechanical treatment machine (extruder, kneader, mixer ...), which allows the development and production of milk powder of different types and therefore with higher added value. The method according to the invention allows, in the case of the production of milk powder, significant energy savings of the order of 40% compared to the conventional method as well as a significant reduction in the investment cost. By way of comparison, the consumption of water vapor per 100 kg of treated liquid milk is of the order of 33 kg with the process according to the prior art while it is around 19 kg with the process according to the invention, for substantially identical power consumption. In general, the process of the invention can be used, with similar advantages, for the production of powdered products other than powdered milk, from all types of solutions, suspensions, emulsions of different compositions comprising a dry matter. in aqueous media. The process is for example applicable for the production of powdered products of the type: - starchy products: cereal flours (wheat, oats, corn, barley), potato flours, potato granules and flakes, tapioca flour . These products can be native, i.e. without modifications chemical and / or physical, and simply dried and ground. These products can be physically modified, for example by modification of the crystal structure of starches, inter alia by gelatinization and fusion processes; they can also be chemically modified, for example by hydrolysis, esterification, or etherification; - protein products: milk casein, wheat gluten, corn zein, soy protein, legume proteins (peas, for example), oleoprotein proteins (sunflower, rapeseed, for example). These products can be native, that is to say without chemical and / or physical modifications and simply dried and ground. These products can be physically modified, for example by modification of the quaternary, tertiary and secondary structures of proteins (denaturation process); they can also be modified chemically, for example by hydrolysis, amidation, succinylation, or condensation, that is to say by reaction with functional organic groups: amine, carboxyl, for example. The process is also applicable to co-products / by-products of milk fractionation, i.e. liquid fractions obtained when the milk is fractionated by means of processes such as centrifugation, filtration, nanofiltration, ultrafiltration, reverse osmosis ... these operations are intended to separate the different components of milk (fat, proteins, sugars ...). The process is also applicable for the production of powdered products, which allow re-hydration to obtain baby food: reconstituted milks according to different ages, various porridge, jar mixes, etc.

Claims

REVENDICATIONS
1. Procédé de production en continu d'un produit en poudre, à partir du produit à l'état liquide se présentant sous la forme d'un mélange du type solution, suspension ou émulsion en milieux aqueux, dans lequel : - on effectue au moins une étape d'évaporation sous vide (E1 ) du produit à l'état liquide pour obtenir le produit à l'état visqueux, - on réalise au moins une étape de séchage (E2, E3) du produit à l'état visqueux pour obtenir le produit sous forme solide, caractérisé en ce que ladite étape de séchage (E2, E3) comprend au moins une première étape de traitement thermomécanique (E2) au moyen d'une machine de traitement thermomécanique (10 ; 36-51) dans laquelle on injecte simultanément le produit à l'état visqueux provenant de l'étape d'évaporation sous vide et une proportion déterminée de produit en poudre de la même famille que le produit à l'état liquide, la machine de traitement (10 ; 36-51 ) étant configurée pour mélanger le produit à l'état visqueux et le produit en poudre pour obtenir des pellets de produit solidifiés au contact de l'air ambiant. 1. Process for the continuous production of a powdered product, starting from the product in the liquid state, in the form of a mixture of the solution, suspension or emulsion type in aqueous media, in which: at least one step of evaporation under vacuum (E1) of the product in the liquid state to obtain the product in the viscous state, - at least one drying step (E2, E3) of the product in the viscous state is carried out to obtaining the product in solid form, characterized in that said drying step (E2, E3) comprises at least a first thermomechanical treatment step (E2) by means of a thermomechanical treatment machine (10; 36-51) in which the product in the viscous state originating from the vacuum evaporation step is simultaneously injected with a determined proportion of powdered product of the same family as the product in the liquid state, the treatment machine (10; 36- 51) being configured to mix the product the viscous state and the powdered product to obtain pellets of product solidified in contact with the ambient air.
2. Procédé selon la revendication 1 , caractérisé en ce que, après ladite étape de séchage (E2, E3), on effectue une étape de mise en forme du produit solide pour obtenir le produit en poudre. 2. Method according to claim 1, characterized in that, after said drying step (E2, E3), a step of shaping the solid product is carried out to obtain the powdered product.
3. Procédé selon la revendication 1 ou 2, caractérisé en ce que le produit en poudre injecté dans la machine de traitement thermomécanique (10 ; 36 -51 ) est en totalité du produit en poudre recyclé après l'étape de mise en forme. 3. Method according to claim 1 or 2, characterized in that the powdered product injected into the thermomechanical treatment machine (10; 36 -51) is entirely of the powdered product recycled after the shaping step.
4. Procédé selon la revendication 1 ou 2, caractérisé en ce que le produit en poudre injecté dans la machine de traitement thermomécanique (10 ; 36-51 ) est en partie du produit en poudre recyclé après l'étape de mise en forme. 4. Method according to claim 1 or 2, characterized in that the powdered product injected into the thermomechanical treatment machine (10; 36-51) is partly of the powdered product recycled after the shaping step.
5. Procédé selon Tune quelconque des revendications 1 à 4, caractérisé en ce que, à Tissue de l'étape d'évaporation sous vide (E1), le produit à l'état visqueux présente une concentration en matière sèche comprise entre 55 et 75%, de préférence entre 65 et 75%. 5. Method according to any one of claims 1 to 4, characterized in that, at the end of the vacuum evaporation step (E1), the product in the viscous state has a dry matter concentration of between 55 and 75 %, preferably between 65 and 75%.
6. Procédé selon Tune quelconque des revendications 1 ou 5, caractérisé en ce que l'étape d'évaporation sous vide (E1) comprend une première étape (E'1 ) à Tissue de laquelle la concentration en matière sèche est comprise entre environ 50 et 55%, et une seconde étape (E1") à Tissue de laquelle la concentration en matière sèche est comprise entre environ 70 et 75%, et de préférence entre 65 et 75%. 6. Method according to any of claims 1 or 5, characterized in that the vacuum evaporation step (E1) comprises a first tissue step (E'1) of which the dry matter concentration is between approximately 50 and 55%, and a second stage (E1 ″) in which the dry matter concentration is between approximately 70 and 75%, and preferably between 65 and 75%.
7. Procédé selon Tune quelconque des revendications précédentes, caractérisé en ce qu'à Tissue de l'étape de séchage (E2, E3) du produit à l'état visqueux, le produit sous forme solide présente une concentration en matière sèche d'environ 96 à 97%. 7. Method according to any one of the preceding claims, characterized in that, in the drying step (E2, E3) of the product in the viscous state, the product in solid form has a dry matter concentration of approximately 96 to 97%.
8. Procédé selon Tune quelconque des revendications précédentes, caractérisé en ce que, outre la première étape de traitement thermomécanique (E2), l'étape de séchage (E2, E3) comprend une deuxième étape de séchage (E3) des pellets obtenus à Tissue de l'étape de traitement thermomécanique (E2). 8. Method according to any one of the preceding claims, characterized in that, in addition to the first thermomechanical treatment step (E2), the drying step (E2, E3) comprises a second drying step (E3) of the pellets obtained at Tissue of the thermomechanical treatment stage (E2).
9. Procédé selon la revendication 8, caractérisé en ce que la deuxième étape de séchage (E3) des pellets est une étape de séchage en lit fluidisé. 9. Method according to claim 8, characterized in that the second drying step (E3) of the pellets is a drying step in a fluidized bed.
10. Procédé selon la revendication 8 ou 9, caractérisé en ce que, après ou pendant la deuxième étape de séchage (E3), on enrobe les particules de produit en poudre d'un revêtement extérieur, par exemple à l'aide de lécithine. 10. Method according to claim 8 or 9, characterized in that, after or during the second drying step (E3), the powdered product particles are coated with an external coating, for example using lecithin.
11 . Procédé selon Tune quelconque des revendications précédentes, caractérisé en ce que les pellets présentent à l'issue de l'étape de traitement thermomécanique (E2) une concentration en matière sèche variant entre 60 et 85% et de préférence comprise entre 80 et 85%. 11. Process according to any one of the preceding claims, characterized in that the pellets have, at the end of the thermomechanical treatment step (E2), a concentration of dry matter varying between 60 and 85% and preferably between 80 and 85%.
12. Procédé selon Tune quelconque des revendications précédentes, caractérisé en ce que le rapport entre le débit massique de produit en poudre injecté dans la machine de traitement thermomécanique (10 ; 36-51) et le débit massique de produit à l'état visqueux introduit dans la machine de traitement thermomécanique est compris entre 0,25 et 2,50 et de préférence entre 0,70 et 1 ,30. 12. Method according to any one of the preceding claims, characterized in that the ratio between the mass flow rate of powdered product injected into the thermomechanical treatment machine (10; 36-51) and the mass flow rate of product in the viscous state introduced in the thermomechanical treatment machine is between 0.25 and 2.50 and preferably between 0.70 and 1.30.
13. Procédé selon Tune quelconque des revendications précédentes, caractérisé en ce que, au cours de l'étape de traitement thermomécanique (E2), on réalise un dégazage sous pression atmosphérique ou sous vide. 13. Method according to any one of the preceding claims, characterized in that, during the thermomechanical treatment step (E2), degassing is carried out under atmospheric pressure or under vacuum.
14. Procédé selon Tune quelconque des revendications précédentes, caractérisé en ce que, au cours de l'étape de traitement thermomécanique (E2), on injecte un gaz dans la machine de travail thermomécanique (10 ; 36- 51). 14. Method according to any one of the preceding claims, characterized in that, during the thermomechanical treatment step (E2), a gas is injected into the thermomechanical working machine (10; 36-51).
15. Procédé selon Tune quelconque des revendications précédentes, caractérisé en ce que on réalise l'étape de traitement thermomécanique (E2) du produit à l'état visqueux en introduisant le produit à l'état visqueux et le produit en poudre dans une machine d'extrusion (10) à deux vis (11 , 12) co- rotatives. 15. Method according to any one of the preceding claims, characterized in that the step of thermomechanical treatment (E2) of the product in the viscous state is carried out by introducing the product in the viscous state and the powdered product into a machine d extrusion (10) with two co-rotating screws (11, 12).
16. Procédé selon Tune quelconque des revendications précédentes, caractérisé en ce que on réalise l'étape de traitement thermomécanique (E2) en introduisant le produit à l'état visqueux et le produit en poudre dans un malaxeur, ou un pétrisseur, ou un mélangeur et/ou une machine d'extrusion à une vis. 16. Method according to any one of the preceding claims, characterized in that the thermomechanical treatment step (E2) is carried out by introducing the product in the viscous state and the powdered product into a kneader, or a kneader, or a mixer. and / or a single screw extrusion machine.
17. Procédé selon Tune quelconque des revendications précédentes, caractérisé en ce que le produit à l'état liquide présente initialement une concentration en matière sèche comprise entre 7 et 20%. 17. Method according to any one of the preceding claims, characterized in that the product in the liquid state initially has a dry matter concentration of between 7 and 20%.
18. Procédé selon Tune quelconque des revendications précédentes, caractérisé en ce que le produit à l'état liquide est du lait liquide, ce par quoi on obtient du lait en poudre. 18. Method according to any one of the preceding claims, characterized in that the product in the liquid state is liquid milk, whereby powdered milk is obtained.
19. Procédé selon Tune quelconque des revendications 1 à 17, caractérisé en ce que le produit à l'état liquide est un produit amylacé, natif ou modifié (physiquement et/ou chimiquement) à base de farines de céréales (blé, avoine, maïs, orge, etc.), de farine de pomme de terre, de granules de pomme de terre, de flocons de pomme de terre, et/ou de farine de tapioca, le produit étant initialement sous la forme d'un mélange du type solution, suspension ou émulsion en milieux aqueux, ce par quoi on obtient à Tissue du procédé le produit sous forme pulvérulente. 19. Method according to any one of claims 1 to 17, characterized in that the product in the liquid state is a starchy product, native or modified (physically and / or chemically) based on cereal flours (wheat, oats, corn , barley, etc.), potato flour, potato granules, potato flakes, and / or tapioca flour, the product being initially in the form of a solution-type mixture , suspension or emulsion in aqueous media, whereby the product is obtained in powder form.
20. Procédé selon Tune quelconque des revendications 1 à 17, caractérisé en ce que le produit à l'état liquide est un produit protéinique, natif ou modifié (physiquement et/ou chimiquement), choisi parmi la caséine du lait, le gluten du blé, la zéine du maïs, les protéines de soja, les protéines de légumineuses, en particulier de pois, et/ou les protéines d'oleoproteagineux, en particulier de tournesol ou de colza, le produit étant initialement sous la forme d'un mélange du type solution, suspension ou émulsion en milieux aqueux, ce par quoi on obtient à Tissue du procédé le produit sous forme pulvérulente. 20. Method according to any one of claims 1 to 17, characterized in that the product in the liquid state is a protein product, native or modified (physically and / or chemically), chosen from milk casein, wheat gluten , corn zein, soy protein, legume protein, especially pea protein, and / or oil protein, especially sunflower or rapeseed protein, the product being initially in the form of a mixture of solution, suspension or emulsion type in aqueous media, whereby the product is obtained in powder form.
21. Procédé selon Tune quelconque des revendications 1 à 17, caractérisé en ce que le produit à l'état liquide est un co-produit/sous-produit de fractionnement du lait, obtenu par fractionnement du lait par centrifugation, filtration, nanofiltration, ultrafiltration, et/ou osmose inverse. 21. Method according to any one of claims 1 to 17, characterized in that the product in the liquid state is a co-product / by-product of milk fractionation, obtained by fractionation of milk by centrifugation, filtration, nanofiltration, ultrafiltration , and / or reverse osmosis.
22. Procédé selon Tune quelconque des revendications précédentes, caractérisé en ce que le produit en poudre injecté dans la machine de traitement thermomécanique (10 ; 36-51) est à environ 90-96% de matière sèche pour les produits d'origine amylacée et protéinique et à environ 97% pour les produits d'origine laitière. 22. Method according to any one of the preceding claims, characterized in that the powdered product injected into the thermomechanical treatment machine (10; 36-51) is approximately 90-96% dry matter for the products of starchy origin and protein and around 97% for dairy products.
23. Lait en poudre, caractérisé en ce qu'il est obtenu par le procédé selon l'une quelconque des revendications 1 à 18. 23. Milk powder, characterized in that it is obtained by the process according to any one of claims 1 to 18.
PCT/FR2005/000735 2004-03-30 2005-03-25 Method for the continuous production of a powdered product from the product in the liquid state WO2005100890A1 (en)

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FR0403288 2004-03-30
FR0403288 2004-03-30
FR0410025 2004-09-22
FR0410025A FR2875589B1 (en) 2004-09-22 2004-09-22 PROCESS FOR THE CONTINUOUS PRODUCTION OF A POWDER PRODUCT FROM THE LIQUID STATE PRODUCT

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US2979408A (en) * 1956-10-24 1961-04-11 Greenfield Charles Dehydration of fluid fatty mixtures
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AR048353A1 (en) 2006-04-19

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