Method for drying food products

Abstract

A method for drying a food product includes the step of: a) inserting the food product in an enclosure, the enclosure being defined by the vessel of a mixer; and b) drying the food product in the enclosure by applying a vacuum to the enclosure. The supplying of heat to the product located inside the enclosure is carried out when the vacuum is applied to the enclosure during step b) such as to maintain and/or increase the temperature of the product during all or part of the process of drying by applying a vacuum to the enclosure. The supplying of heat is carried out by heat transfer between at least one heat-transfer fluid and the product and/or by irradiating the product with electromagnetic radiation.

Claims

1. A method for drying a food product, the food product having a core surrounded by an outer surface, the method comprising: a) introducing the food product into an enclosure, the enclosure being defined by a tank of a mixer with a double jacket in which at least one heat transfer fluid circulates; b) heating the food product in the enclosure by application of heat transfer between the at least one heat transfer fluid circulating within the double jacket of the enclosure and the food product; c) stabilizing the temperature of the food product; d) cooling the outer surface of the food product upon completion of the step c) to create a temperature differential between the outer surface of the food product and the core of the food product in which an outer surface temperature of the food product is less than a core temperature of the food product; and e) drying the food product present in the enclosure by applying a vacuum to the enclosure with a pressure less than or equal to 200 mbar and applying heat at a temperature chosen so as to obtain the range of the phase diagram of pure water where the pure water is in the gaseous state, the applying of the vacuum to the enclosure during step e) being initiated at a first time point and concluded at a second time point, wherein the heat is applied to the food product present in the enclosure when the vacuum is applied to the enclosure during the step e) so as to keep the temperature of the food product constant or increase it during all or part of the step e), and wherein the heat is applied to the food product present in the enclosure when the vacuum is applied to the enclosure during the step e) such that the temperature of the food product at the second time point is greater than or equal to the temperature of the food product at the first time point, and wherein the heat applied in the step e) is applied by further heat transfer between the at least one heat transfer fluid circulating within the double jacket of the enclosure and the food product, in which the duration of step e) is chosen so that the food product has lost, at completion of the step e), a weight equal to at least 4% of its weight taken before the implementation of the step e).

2. The method as claimed in claim 1, wherein the pressure in the enclosure during all or part of the step e) is less than 100 mbar.

3. The method as claimed in claim 1, further comprising salting the food product, the salting taking place before the step e) and/or during all or part of the step e).

4. The method as claimed in claim 3, wherein the salting is performed by wet means, the food product being in contact with a brine during the salting.

5. The method as claimed in claim 1, further comprising a step f) of baking, in which the enclosure is raised to a temperature greater than or equal to 20 C., and to a pressure greater than or equal to 24 mbar.

6. The method as claimed in claim 5, wherein the step f) is initiated after the step e) at the second time point.

7. The method as claimed in claim 1, wherein the food product undergoing the step e) exhibits one or more cut-outs.

8. The method as claimed in claim 1, wherein the food product undergoes, after a step b a step e), of shaping, by means of a press.

9. The method as claimed in claim 1, wherein the food product is set in motion within the enclosure during all or part of the step e).

10. The method of claim 2, wherein pressure is less than 75 mbar.

11. The method of claim 2, wherein pressure is less than 40 mbar.

12. The method of claim 5, wherein at the step f), the temperature within the enclosure is raised between 22 C. and 55 C. and to a pressure within the enclosure is raised between 200 mbar and 1020 mbar.

13. The method of claim 1, wherein the food product has lost, at completion of the step e) a weight equal to at least 10% of its weight taken before the implementation of the step b).

14. The method of claim 1, wherein the steps b), c) and d) are repeated at least once prior to proceeding to step e.

15. The method of claim 7, wherein the cut-outs are formed before implementation of the step e).

16. The method of claim 1, wherein the pressure in the enclosure during all or part of the step e) is from 2 to 20 mbar.

17. The method of claim 1, wherein the temperature differential between the outer surface of temperature of the food product and the core temperature of the food product is at least 0.3 C.

18. The method of claim 1, wherein the temperature differential between the outer surface of temperature of the food product and the core temperature of the food product is approximately 5 C.

19. A method for drying a food product, the food product having a core surrounded by an outer surface, the method comprising: a) introducing the food product into an enclosure, the enclosure being defined by a tank of a mixer with a double jacket in which at least one heat transfer fluid circulates; b) heating the food product in the enclosure by irradiation of the food product by electromagnetic radiation; c) stabilizing the temperature of the food product; d) cooling the outer surface of the food product upon completion of the step c) to create a temperature differential between the outer surface of the food product and the core of the food product in which an outer surface temperature of the food product is less than a core temperature of the food product; and e) drying the food product present in the enclosure by applying a vacuum to the enclosure with a pressure less than or equal to 200 mbar and applying heat at a temperature chosen so as to obtain the range of the phase diagram of pure water where the pure water is in the gaseous state, the applying of the vacuum to the enclosure during step e) being initiated at a first time point and concluded at a second time point, wherein the heat is applied to the food product present in the enclosure when the vacuum is applied to the enclosure during the step e) so as to keep the temperature of the food product constant or increase it during all or part of the step e), and wherein the heat is applied to the food product present in the enclosure when the vacuum is applied to the enclosure during the step e) such that the temperature of the food product at the second time point is greater than or equal to the temperature of said food product at the first time point, wherein the heat applied in the step e) is applied by further irradiation of the food product by the electromagnetic radiation.

Description

(1) In order to enable a better understanding of the invention, there now follows a description of exemplary embodiments of the method according to the invention with reference to the attached drawing in which:

(2) FIG. 1 represents the trend of the boiling point of water as a function of pressure,

(3) FIG. 2 represents a longitudinal schematic view of a first exemplary mixer that may be used in the method according to the invention,

(4) FIG. 3 represents a longitudinal schematic view of a second exemplary mixer that may be used in the method according to the invention,

(5) FIG. 4 represents a view of a mixer that may be used in the context of the methods according to the invention, and

(6) FIGS. 5 to 9 represent experimental conditions and experimental results relating to methods according to the invention.

(7) FIG. 2 shows a mixer comprising a tank 1 mounted on a frame 2 about a substantially horizontal axis of rotation 3. A stirring means such as a straight or helical paddle (not represented) is provided inside the tank.

(8) To drive the tank 1 in rotation, the frame 2 comprises a motor 4 rotationally secured to a driving member 5.

(9) The tank comprises a peripheral friction area 6 which cooperates with a friction wheel 7 of the driving member 5.

(10) The front part of the tank, situated on the right in the drawing, has a convergent tapered form, at the end of which there is a leak-tight door 8 which makes it possible to load and unload the food products to be treated into and from the tank 1.

(11) A pipeline 9 linking the interior of the tank 1 to a vacuum pump 10 penetrates into the central part of the leak-tight door making it possible to apply the primary vacuum in the tank, the pipeline 9 being provided with a valve 12.

(12) A pipeline 20 is connected to the pipeline 9 and provided with a valve 22 linking the interior of the tank to a powerful vacuum generator 21.

(13) The vacuum implemented for the step b) may be obtained using a powerful vacuum pump (for example: vane pump, liquid ring pump, screw pump, etc.) that may be coupled to a low vacuum booster (roots), an ejector if necessary being able to be added to this setup. The throughput of the vacuum pump may be approximately: 0.1 to 5.0 m.sup.3/h per kg of food product treated.

(14) There may also be a pipeline 14, linked to a vapor generator 19 and provided with a valve 18, penetrating into the central part of the tank.

(15) The pipelines 9 and 17, in the example of FIG. 1, are provided with a revolving coupling 11 which allows the rotation of the tank 1 about its axis 3 without damage to the pipelines. The pipeline 17 is linked directly to the interior of the tank 1 through the door 8 and the rotating coupling 11.

(16) A pipeline 14, linked to a vapor generator 19 and provided with a valve 18, may also penetrate into the rear of the tank 1 (on the left in the drawing). The pipeline 19 penetrates into the tank 1 through a rotating coupling 13 situated at the rear of the tank 1.

(17) A heated/refrigerated unit 32 is linked to the double jacket 40 of the tank 1 via pipelines 30 and 31 provided with a valve 33. This heated/refrigerated unit 32 makes it possible to apply heat to the food product when the vacuum is applied to the enclosure.

(18) FIG. 3 shows another mixer comprising a tank 1.

(19) In this example, a network of glycol water replaces the heated/refrigerated unit 32 described in FIG. 2. In the example of FIG. 3, the glycol water makes it possible to apply heat to the food product when the vacuum is applied to the enclosure.

(20) The network of glycol water comprises a glycol water generator 34 and an exchanger (for example plate exchanger or tubular exchanger) 35. As a variant, the exchanger 35 could be replaced by an electric preheater.

(21) The glycol water network also comprises a system of valves 36, 37, 38 and 39, notably valves of three-way type, the valves 37 and 38 being situated on either side of the exchanger 35.

(22) Two pipelines 41 and 42 make it possible to also link the glycol water network to the double jacket 40 of the tank 1.

(23) FIG. 4 shows a mixer in which the leak-tight door 8 is in the open position. As represented, a stirring member 50, which may be a paddle as represented or an arm or an articulated mixer axis, is present in the enclosure 60 in which the food product is intended to be introduced. The mixer may be vertical or else horizontal, of dough mixer type. One or more containers 100 are present outside the tank so as to be able to receive the dried food product after the implementation of the method according to the invention.

(24) The invention is not limited to the exemplary embodiments which have just been described.

(25) FIG. 5 shows the conditions of a method according to the invention in which a salting is initiated before an evaporative vacuum isothermal drying. The salting performed has a duration of 4 days and was performed at 4 C. and the temperature of the product is maintained at 8 C. during the evaporative vacuum isothermal drying. The food products implemented are open pork hams.

(26) The pressure imposed during at least a part of the salting step may be greater than or equal to 20 mbar, preferably 25 mbar, preferably 30 mbar.

(27) In the conditions of FIG. 5, water losses higher than 6% in vacuum drying in isothermal conditions at 8 C. were obtained.

(28) In order to further speed up the process, it is possible to conduct the vacuum evaporation by gradually increasing the temperature of the product so as to maintain a good evaporative potential as the activity of the water of the product decreases (FIG. 6). The conditions of FIG. 6 are as follows: salting for 4 days at 4 C., drying at a temperature increasing from 8 to 18 C. in evaporative vacuum, and baking of open pork hams at 35 C.

(29) A high-temperature baking may be conducted at atmospheric pressure or in a very weak vacuum to promote the contact with oxygen, or even in a stronger vacuumpossibly with pulsed vacuum or lung vacuum cyclesfor the food to remain in contact with the oxygen (FIG. 6).

(30) FIG. 7 compares the relative efficiencies of drying in evaporative vacuum in isothermal conditions and in increasing temperature conditions.

(31) From a health point of view, the progressive rise in temperature of the meat is made possible by the rapid and simultaneous lowering of the activity of the water of the product. The implementation of a drying in variable temperature conditions leads to more significant drying (FIG. 7).

(32) FIG. 8 shows an exemplary cycle making it possible to produce a more uniform drying between the core and the outer skin when the product is subjected to an evaporative vacuum.

(33) The product first undergoes a heating step in order to heat the product as uniformly as possible.

(34) This heating step (step i)) may have a duration of between 10 minutes and 24 hours, preferably between 30 minutes and 8 hours, preferably between 1 hour and 4 hours.

(35) Once the product is heated as uniformly as possible, it undergoes a step of balancing of its temperature (step ii)).

(36) A step of surface cooling is then conducted so as to cool the outer skin of the product more than its core before the implementation of the evaporative drying.

(37) The surface cooling step may be performed using a double jacket fed with cooled heat-transfer fluid, by direct injection of a cryogenic fluid or simply by increasing the vacuum of the medium in which the food product is placed.

(38) FIG. 9 shows the trend of the salinometry value on the surface and at the core of a ham deboned according to the so-called tunnel boning method, salted and dried in evaporative vacuum in a mixer.

(39) The speed of the drying produced in evaporative vacuum in the mixer makes it possible to consider formulating products intended for drying by wet means (brine) in order to further speed up the salting.

(40) The expression comprising a should be understood to mean comprising at least one.

(41) The expression lying between . . . and . . . or ranging from . . . to . . . should be understood to include the bounds.