WO2007132014A2 - Séchage sous vide assisté par haute fréquence - Google Patents

Séchage sous vide assisté par haute fréquence Download PDF

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Publication number
WO2007132014A2
WO2007132014A2 PCT/EP2007/054757 EP2007054757W WO2007132014A2 WO 2007132014 A2 WO2007132014 A2 WO 2007132014A2 EP 2007054757 W EP2007054757 W EP 2007054757W WO 2007132014 A2 WO2007132014 A2 WO 2007132014A2
Authority
WO
WIPO (PCT)
Prior art keywords
product
drying
vacuum
pieces
frequency
Prior art date
Application number
PCT/EP2007/054757
Other languages
German (de)
English (en)
Other versions
WO2007132014A3 (fr
Inventor
Horst Kriszio
Horst-Martin Mayer
Gerd Ahrens
Andreas KÜHNEL
Original Assignee
Becker Technologies Gmbh
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
Application filed by Becker Technologies Gmbh filed Critical Becker Technologies Gmbh
Publication of WO2007132014A2 publication Critical patent/WO2007132014A2/fr
Publication of WO2007132014A3 publication Critical patent/WO2007132014A3/fr

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B5/00—Drying solid materials or objects by processes not involving the application of heat
    • F26B5/04—Drying solid materials or objects by processes not involving the application of heat by evaporation or sublimation of moisture under reduced pressure, e.g. in a vacuum
    • F26B5/048—Drying solid materials or objects by processes not involving the application of heat by evaporation or sublimation of moisture under reduced pressure, e.g. in a vacuum in combination with heat developed by electro-magnetic means, e.g. microwave energy
    • A—HUMAN NECESSITIES
    • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
    • A23L19/00—Products from fruits or vegetables; Preparation or treatment thereof
    • A23L19/01—Instant products; Powders; Flakes; Granules
    • A—HUMAN NECESSITIES
    • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
    • A23L19/00—Products from fruits or vegetables; Preparation or treatment thereof
    • A23L19/03—Products from fruits or vegetables; Preparation or treatment thereof consisting of whole pieces or fragments without mashing the original pieces
    • A—HUMAN NECESSITIES
    • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
    • A23L5/00—Preparation or treatment of foods or foodstuffs, in general; Food or foodstuffs obtained thereby; Materials therefor
    • A23L5/30—Physical treatment, e.g. electrical or magnetic means, wave energy or irradiation
    • A—HUMAN NECESSITIES
    • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23P—SHAPING OR WORKING OF FOODSTUFFS, NOT FULLY COVERED BY A SINGLE OTHER SUBCLASS
    • A23P30/00—Shaping or working of foodstuffs characterised by the process or apparatus
    • A23P30/30—Puffing or expanding
    • A23P30/32—Puffing or expanding by pressure release, e.g. explosion puffing; by vacuum treatment
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/6432—Aspects relating to testing or detecting leakage in a microwave heating apparatus
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/647—Aspects related to microwave heating combined with other heating techniques
    • H05B6/6473—Aspects related to microwave heating combined with other heating techniques combined with convection heating
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/70—Feed lines
    • H05B6/704—Feed lines using microwave polarisers
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/70—Feed lines
    • H05B6/705—Feed lines using microwave tuning
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/74—Mode transformers or mode stirrers
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/78—Arrangements for continuous movement of material
    • H05B6/782—Arrangements for continuous movement of material wherein the material moved is food
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B2206/00—Aspects relating to heating by electric, magnetic, or electromagnetic fields covered by group H05B6/00
    • H05B2206/04—Heating using microwaves
    • H05B2206/046—Microwave drying of wood, ink, food, ceramic, sintering of ceramic, clothes, hair

Definitions

  • the invention generally relates to devices and methods for treating substances having electromagnetic radio frequency energy.
  • devices or methods it is for example possible to treat substances in the form of lumpy, free-flowing, sprayable or pumpable substances, wherein a change in the properties of the material can be caused.
  • a structural change, targeted warming, an acceleration / favoring of various chemical reactions, a gentle one can be achieved Drying, impregnation, etc. are in the foreground.
  • the invention in this context relates to a method and an apparatus for producing a product from fruits and / or vegetables with a certain special, desired property as well as the product itself.
  • the method in this case comprises a convective predrying of the starting products or product pieces to a water content about 20% to 40% of the total mass and subsequent treatment by means of electromagnetic high-frequency energy in a vacuum.
  • Another aspect relates to a device for feeding the high-frequency energy into the vacuum of the treatment chamber for puffing and drying the convectively predried products or product pieces (water content about 20% to 40% of the total mass) by means of electromagnetic high-frequency energy in a vacuum.
  • electromagnetic radio frequency energy in particular microwaves, thereby enables the simultaneous heating of the entire product volume, so that the drying process becomes more efficient and thus the duration of action of elevated temperatures on the product can be reduced.
  • the product to be dried is transported either with the aid of a continuous conveyor or with the aid of conveying containers which run continuously behind one another in the high-frequency treatment chamber and during this time are exposed to the high-frequency radiation and possibly to the vacuum.
  • the substances to be treated are introduced or removed via sluices on a belt circulating in the high-frequency treatment chamber under vacuum.
  • the high-frequency radiation is limited by suitably designed and provided with electromagnetically transparent coupling windows waveguide in the evacuated and electrically well conductive metallic walls Treatment room introduced. Due to the reduced electrical breakdown field strength in a vacuum, the high frequency power that can be supplied per injection point is comparatively low during vacuum drying, since glow discharges and flashovers must be avoided as much as possible for safety reasons as well as considerations of product quality.
  • the waveguide supplying the high-frequency power to larger round or rectangular cross-sections (for example, designed as horns) and an additional tapering of the waveguides, the feedable power can be increased to avoid undesired wave types, but the circumference is to which this is possible, unsatisfactory.
  • the product may be desirable for the product to behave in a somewhat opposite manner when in contact with water, i. remains in its dry state for a defined time and retains its crispy or crunchy character, i. crispy and when chewing quickly, possibly with a simultaneous crash noise, as e.g. when chewing dry rusk occurs, disintegrates.
  • the crispiness or crunchiness of a foodstuff can be assessed here by way of the noise occurring when chewing the piece of foodstuff as well as the nature of its deformation.
  • the invention is accordingly an object of the invention to provide a device and a method to from a suitable starting high moisture content (eg 75% to 95%), in particular using a high-frequency-based treatment, a product with "crispy” or “crunchy” properties produce.
  • a suitable starting high moisture content eg 75% to 95%)
  • Another object of the invention is to enable the introduction of a higher microwave power into a system for high frequency assisted drying.
  • a third object of the invention is to achieve the most uniform possible heating of the products to be dried, so that the high-frequency treatment can be carried out effectively.
  • this may be a food product consisting of individual product pieces or whole fruits
  • the method according to the invention comprises the following steps:
  • Predrying on a convection dryer reduces the high water content of many food products (usually between 75% and 95% of the product mass in fruit and vegetables) to levels appropriate to the microwave vacuum puffing process, with water fractions between 15% and 60%. , in particular between 20% and 40% of the product mass are advantageous.
  • the high water content can be removed in a cost effective manner.
  • the product After introduction into vacuum, the product is fed to the microwave vacuum puffing, where the residual water contained in the product (water content, for example, between 20% and 40% of the product mass) is vaporized by dielectric heating with the aid of high-frequency radiation.
  • water content for example, between 20% and 40% of the product mass
  • the product of the microwave vacuum drying is supplied. There, a portion of the remaining water is evaporated by the product is preferably finally dried in low vacuum at low and controlled by the product surface temperature high frequency power.
  • the product leaves this processing step after removal from the vacuum with a typical residual water content of up to 10%, preferably about 6% of the product mass, which allows its long-term storage.
  • a typical residual water content of up to 10%, preferably about 6% of the product mass, which allows its long-term storage.
  • the foam-like layer formed during their Puffung / drying can be broken before the discharge from the vacuum to a granulate.
  • a pre-treatment and / or, after drying, a post-treatment of the crude product or of the product produced can be carried out before predrying.
  • the product pretreatment may include the cleaning of the delivered raw product, the removal of unpalatable or unwanted portions of the raw product (eg dewatering, de-kerning, peeling), the cutting (eg cutting) of the raw product into product pieces and the preparation of the product for subsequent drying and include the consumption.
  • These include e.g. also the blanching of the raw product (s) and the addition of food grade excipients, e.g. for the preservation of the product color, for the improvement of the drying process or the consumption properties of the dried final product.
  • the additives used in this case may advantageously be obtained from the product itself (for example, home sugar).
  • drying of the e.g. make sense by a possibly pre-treated wet fruit surfaces can be achieved, for example, by circulating the pieces of fruit with moving air at room temperature or slightly above it, preferably at temperatures between 0 ° and 40 ° C. ("cold blowing"), for which an unheated or only with low power heated drying stage is sufficient. which precedes the actual predryer, which may also be suitable for thawing frozen fruits.
  • the product pieces are singulated, sorted or packaged, the packaging preferably being vapor-tight in order to prevent possible absorption of moisture.
  • the predrying of the product or the Arts Glachen begins by flowing around with air at temperatures between 60 0 C and 100 0 C.
  • the reduction of the air temperature as the drying progresses advantageously monotonically, but other temperature gradients, such as gradual discontinuous reduction are conceivable , Also, in the course of predrying the temperature could be briefly increased even again, if this should be necessary to achieve the desired product properties.
  • the electromagnetic high frequency irradiation in the process steps of Puffung and / or drying with frequencies in the range between 800 MHz and 8000 MHz, in particular in the range between 2000 MHz and 3000 MHz, preferably in the ISM band between 2400 MHz and 2500 MHz.
  • the power introduced into the product or the product particles by means of the electromagnetic high-frequency radiation is preferably controlled by measuring the surface temperature of the product or of the product particles.
  • the conventional methods of contactless temperature measurement such as radiation thermometers, are preferably used as measuring methods.
  • thermodynamic properties of the respective product or the product pieces are preferably determined experimentally.
  • the product or the pieces of product during puffing and / or drying by means of a continuous conveyor (eg a conveyor belt) or with the aid of preferably seamless consecutively running conveyor containers each for high frequency treatment transported used high-frequency treatment chamber.
  • a continuous conveyor eg a conveyor belt
  • preferably seamless consecutively running conveyor containers each for high frequency treatment transported used high-frequency treatment chamber.
  • the conveying speed and the layer thickness of the product or the product pieces are adjusted taking into account the constructively predetermined length of the respective high-frequency treatment chamber so that the product-dependent predetermined values for the exposure time of the high-frequency radiation to the product or the product pieces and the thereof when passing through the Treatment chamber absorbed by dissipation energy density can be maintained.
  • a uniform dissipation of the radiated power to the product to be treated or in the entire product volume and thus uniform heating thereof is achieved according to a preferred embodiment of the method according to the invention by the treatment in the process steps Puffung and / or drying not as usual using is made of high frequency radiation of a constant frequency, but rather a high frequency radiation of different frequencies, which are used simultaneously or in rapid change, is used.
  • a frequency modulation or a frequency spread of the radiated electromagnetic high-frequency radiation is preferably performed around an average value.
  • the system for coupling the radiation into the high-frequency treatment chamber comprising coupling waveguide, wave filter and coupling window can then be tuned to the center frequency of the frequency band used and used in combination with a variable frequency high frequency wave generator.
  • the bandwidth of the frequency modulation or the frequency spread should in this case preferably have a maximum value of ⁇ 10% about a center frequency.
  • the electromagnetic radio-frequency radiation is preferably generated with the aid of a source from the group traveling-wave tubes, klystrons, cross-field amplifiers, gyrotrons, frequency-constant or frequency-agile coaxial magnetrons or Twystrons.
  • FM Frequency modulation
  • DSSS direct sequence spread spectrum
  • the device according to the invention for the drying treatment of products in particular in the context of the previously described method, has two on treatment chambers, which are each shielded from the electromagnetic environment and each comprising systems for coupling electromagnetic high frequency radiation to introduce by dielectric dissipation in the product to be treated energy for heating the same.
  • the treatment chambers are housed in a common, acted upon with vacuum space, the products to be treated in this space via locks on or be discharged from this.
  • the sluices for the introduction and discharge of the products to be treated in or out of the space acted upon with vacuum are designed as flap valves fed in the vertical direction.
  • the locks are designed here as a rotary flap locks.
  • the locks are each equipped with up to two additional product retention flaps. These prevent direct contact of the product with the lock flaps. In this way, the product pieces are kept away from the vacuum flaps so that no product pieces adhere to them and can be trapped between the flap and the lock wall when closing the respective vacuum flap. Without the use of product retention flaps, damage to the product and the lock mechanism could result,
  • the product retaining flaps can be designed, for example, as butterfly flaps and in the closed state have a sufficiently narrow gap between the flap edge and the lock wall.
  • the closed product retention flap effectively retains product chips without interfering with the gas exchange in the vacuum lock.
  • the lock takes place in such a way that the respective product retaining flap is always opened only when the associated vacuum flap is also open, so that no product piece passes directly to the vacuum flap.
  • every vacuum flap thus requires exactly one product retention flap.
  • a product retaining flap is dispensable if the conveying device feeding the product from the pre-dryer according to the invention can be controlled in such a way that no product is supplied when the upper vacuum flap is closed. Consequently, in one embodiment of the device according to the invention, the lock for the product entry via a product retaining flap only above the lower vacuum flap, while the lock for the product discharge each has a product retaining flap above the upper and lower lock flap.
  • the process step of the puffing takes place in the first treatment chamber and the drying process step in the second treatment chamber.
  • the high-frequency power required for drying is generally much smaller than the power required for the previously occurring puffing, it must be ensured that the drying area in the second treatment chamber is sufficient with respect to the puffing area in the first treatment chamber is well shielded to prevent the product supplied to the drying from overheating due to irradiation from the puffing area.
  • the two treatment chambers are sufficiently shielded from each other with regard to the introduced electromagnetic high-frequency radiation.
  • the products to be dried are each guided by a conveyor belt through the respective treatment chamber.
  • the conveying speeds of the conveyor belts of the two treatment chambers can advantageously be adjusted independently of one another.
  • the two treatment chambers are preferably separated from each other by a transfer area, in which the high-frequency radiation passes through known shielding only in attenuated form. In this are then advantageously the band position control and / or the deflection rollers of the products transporting conveyor belts are arranged.
  • the second problem to be solved according to the invention relates to the achievement of higher coupled powers to high-frequency radiation without disturbing glow discharges occurring.
  • the coupling system consisting of the coupling waveguide, the electromagnetically transparent but pressure-tight coupling window and the socket of the coupling window is designed with respect to its geometry so that the standing wave ratio occurring therein causes a minimum of the electric field strength on the vacuum-side surface of the coupling window, so that the electric field strength values in the treatment chamber are below a predetermined maximum value for a given power. This maximum value lies in particular below the breakthrough value resulting from the applied vacuum.
  • This configuration can preferably be effected as a function of the geometry of the vacuum treatment chamber.
  • One possibility for lowering the electric field strength values occurring on the vacuum side of the coupling window according to the invention is to use a convexly curved window in the treatment chamber, which is transparent to high-frequency radiation and has as low a loss as possible dielectric material as a coupling window. Due to the divergence of the radiation, smaller field strengths are obtained at the convex surface of the window exposed to the vacuum than when a plane window were still arranged within the coupling waveguide.
  • the coupling-in window can preferably have the shape of a hemisphere projecting into the treatment chamber, in which case the coupling-in waveguide preferably has an approximately circular cross-section, at least in the region adjoining the coupling window.
  • the coupling window in particular in another cross section of the coupling waveguide, also have a different geometric shape, as long as the reduction of the field strength according to the invention on the treatment chamber side of the window is ensured due to a divergence of the coupled radiation due to the specific shape of the window.
  • the electric field intensity values occurring on the vacuum side of the coupling-in window can be lowered according to the invention by selecting the propagation modes and the geometry of the coupling waveguide, in particular its length and cross section, and the coupling window so that the vacuum-facing surface of the coupling window is at a minimum the electric field strength coincides.
  • the next maximum field strength occurring in the vacuum chamber is already so far weakened by the divergence of the radiation that it does not or only insignificantly exceeds the value occurring at the window surface.
  • the two alternatives above are combined, ie the propagation modes and the geometry of the coupling waveguide and of the coupling chamber arched into the treatment chamber are selected such that the vacuum-facing, convex surface of the coupling window coincides with a minimum of the electric field strength.
  • the dimensioning of the system consisting of coupling window and coupling waveguide depending on the geometry of the vacuum treatment chamber leading to the standing wave ratio according to the invention and distribution of the minima and maxima of the electric field strength can hereby be estimated with the aid of the analytical calculation methods known from high-frequency technology. Examples of corresponding calculation methods can be found e.g. in Meinke / Gundlach, "Taschenbuch der Hochfrequenztechnik” or David Pozar: "Microwave Engineering”. In order to refine the geometries calculated using these methods, corresponding numerical methods of electromagnetic field simulation known to the person skilled in the art can be used by means of finite element methods.
  • the coupling-in waveguide is preferably designed in such a way that only a certain mode can propagate in it. In this way it can be achieved that in the region of the coupling window, a desired field distribution according to the invention is achieved.
  • the coupling-in waveguide is constructed as an axially symmetrical circular waveguide.
  • the coupling-in waveguide has the mode TM O i, which is selected for coupling, while the here also capable of spreading but unwanted mode TEn is largely suppressed by suitable Wellentypfilter, for example in the form of a ⁇ / 2-locking pot.
  • suitable Wellentypfilter for example in the form of a ⁇ / 2-locking pot.
  • the flange required for mechanical reasons for clamping the radio-frequency-transparent dielectric coupling window is dimensioned in particular as a function of the geometry of the coupling window and the coupling waveguide so that the electric field strength at the clamping point becomes minimal.
  • the depth of the window flange engaging into a groove of the metallic socket of the coupling-in window has an electrical length of approximately ⁇ / 2, where ⁇ is the wavelength of the high-frequency radiation used in the respective medium.
  • the manufacturing tolerances of the flange are set so that its treatment chamber facing and thus exposed to the vacuum surfaces can have no air gap to the chamber wall.
  • the risk of glow discharges, especially in the present low-level vacuum, due to the higher electric field strengths can be avoided, which are to be expected in the air gap than the dielectrically thinner medium.
  • the means described in DE 196 43 989 A1 can be used to achieve a substantial homogenization of the MW energy absorbed by the product during the passage of the puffing or drying region over the product layer width.
  • regions of higher dissipation density act on the product only during a product-specific maximum period of time. This can be achieved, for example, by avoiding areas that are too extensive and thus triggering overheating due to the long cycle time with the aid of the shutters described in DE 196 43 989 A1 and suitably arranged.
  • the process steps puffing and drying are carried out using the described device according to the invention for the drying treatment of products.
  • the treatment chambers in this case may be injection systems using the above described NEN device for coupling high frequency radiation high power have.
  • 1 is a flow chart illustrating one embodiment of the process of the invention for producing "crispy” or “crunchy” products using high frequency assisted drying;
  • FIG. 2 shows an exemplary embodiment of the construction of a coupling according to the invention in which the electric field intensity values occurring on the vacuum side of the coupling-in window remain as small as possible;
  • FIG. 3 shows a detail of the flange of the coupling-in window from FIG. 2;
  • FIG. 4a shows a geometric overview sketch for the arrangement of the coupling with respect to the treatment chamber and the product layer conveyed through it in an embodiment of the device according to the invention for the drying treatment of products in cross-section with respect to the transport direction;
  • 4b shows a geometric overview sketch for the arrangement of the coupling with respect to the treatment chamber and the product layer conveyed through it in an embodiment of the device according to the invention for the drying treatment of products in longitudinal section with respect to the transport direction;
  • FIG. 5 shows a schematic representation of an embodiment of the device according to the invention for the high frequency-assisted drying treatment of products with medium and low water content for use in the method according to the invention for producing a product piece or whole fruit.
  • food product with a crispy or crunchy character
  • FIG. 1 shows the process sequence according to an embodiment of the inventive method for producing a "crispy” or “crunchy” product with the aid of high-frequency-based vacuum drying as a flow chart.
  • a crude product in the form of fruits and vegetables usually has humicities in the range between 75% and 95% of the product mass.
  • the crude product is first subjected to product preparation, which can be divided into mechanical and chemical-chemical preparation.
  • the mechanical preparation includes the cleaning and sorting of the delivered products as well as the removal of inedible or unwanted parts. These include stalks, woody parts, cores or stones, core casings, shells and under-maturity, rotten or otherwise unsuitable for eating fruits and vegetables or parts thereof, overripe.
  • the mass flow supplied to the drying process is reduced relative to the raw mass flow, and waste is formed which can possibly be otherwise recycled.
  • the mechanical preparation is also the division of the product to assign, for example, cutting into cubes, slices or segments whose size depends on the desired use of the final product.
  • the chemical-thermal product preparation may comprise thermal processes for breaking up the product, for example blanching, cooking or other processes customary in the food preparation.
  • Chemical product preparation refers to the addition of excipients approved for food production in order to improve the taste, eg by adding sugar, acid or spices and / or to maintain the color of the product beyond drying or, for example, adhesions or changes in shape during the subsequent drying process (especially pre-drying) to avoid.
  • the product auxiliary substances (possibly also as additives to Blanchierbad) are supplied, which may be obtained wholly or partly from the same fruits and vegetables as the food to be processed.
  • the product leaves the process step of product preparation with almost the same water content, with which it is fed.
  • the mechanical and in whole or in part the chemical-thermal preparation may be separated in time and space from the remaining process steps.
  • frozen fruits and vegetables are prepared immediately after harvest in a manner similar to that described and then frozen.
  • the correspondingly pretreated product is fed to the predrying, where it is removed by far the greater part of the water content.
  • the product is placed on the convective pre-dryer (eg air belt dryer) with the aid of a suitable product distributor.
  • a method suitable for the treatment of most fruits is described in document EP 1 092 353 A3.
  • the water content of the treated product decreases on average to about 20% to 40% of the product mass, wherein the moisture concentrates on the inside of the product pieces in the case of lumpy products, while the surface is stronger due to the relatively dry warm air passing over it dries out and hardens more or less strongly.
  • the withdrawn water content is released into the atmosphere in the form of vapor or precipitated in a condenser in liquid form.
  • the operating parameters of the convective predrying and the subsequent microwave vacuum puffing further determine whether the product will assume the characteristic "crispy" or "crunchy” after passing through the entire puffing and drying process according to the invention.
  • the residual moisture in the interior of the product must be adjusted by predrying so that on the one hand there is sufficient moisture to generate the steam needed for puffing during the microwave vacuum puffing; on the other hand, it must be reduced to such an extent that the product is sufficiently viscous that the vapor produced by the volumetric absorption of high frequency radiation throughout the product interior can form a multitude of small voids during its release.
  • the product pieces here recover largely their original shape and obtain a porous structure, which during the subsequent micro- stabilized wave vacuum drying and thus causes the "crispy" character of the dried end product.
  • the microwave vacuum puffing station must be able to produce in the product to be treated by high-frequency irradiation a sufficiently high dissipated power density that the resulting vapor volume flow is able to inflate the product pieces in the desired manner (Puffung) and in the interior to create the porous bubble structure and finally break up the keratinized surface.
  • the pre-drying may possibly be omitted completely.
  • the product is then immediately subjected to the following treatment step, the high-frequency treatment in the microwave vacuum processor fed.
  • This treatment can be subdivided into the two steps of microwave vacuum puffing and microwave vacuum drying.
  • the product After being introduced into the vacuum, the product is distributed in a suitable manner on a conveyor belt and fed to the microwave vacuum puffing, in which the product shreds shrunk during the predrying by the dehydration by the short-term (about 4 to 8 minutes) application particularly high dissipated power densities and therefore rapid release of large amounts of steam are again approximately expanded to their original volume.
  • the product feed can be fed via a tube which can be pivoted for the purpose of more uniform product distribution.
  • the product arrives at a residual moisture content of about 10% to 20% of the product mass for microwave vacuum drying as the second step supported by the use of high-frequency radiation.
  • the remaining water contained in the product is largely discharged up to a residual water content of about 6% of the product mass, for which only small dissipated power densities are used in comparison to Puffung, in order to avoid a quality overheating of the product.
  • Puffing and drying are advantageously combined with each other, so that a discharge and re-entrainment in the vacuum between these process steps can be omitted. Since water vapor escapes during the microwave vacuum treatment, the product mass flow is also reduced here, albeit to a much lesser extent than during pre-drying. Finally, the product is discharged and subjected to aftertreatment. Viscous or pasty applied products are usually present after the microwave vacuum treatment as a continuous layer with frothy structure (such as meringue). For this purpose, a crusher can be connected upstream of the discharge lock, which granulates this layer and thus enables further treatment similar to a lumpy product.
  • the product After the product has cooled and thereby lost its possibly existing thermoplastic properties, it becomes, e.g. with the help of a cluster crusher, isolated, sorted and finally vapor-tight packed, so that the finished product is moisture-proof and thus storable for a long time.
  • the ejection from the microwave vacuum drying and the aftertreatment are advantageously carried out in a room with a dry climate (low air humidity) in order to exclude rewetting as far as possible.
  • drying parameters for obtaining a "crispy" end product are explained below using the example of the treatment of fresh strawberry cubes with an edge length of about 10 mm, as well as deviating parameters for producing a "crunchy" end product.
  • convective pre-drying is treated with a monotonically decreasing temperature profile during drying, which starts at 85 ° C air temperature and ends at 75 ° C ,
  • the treatment time is adjusted so that the product reaches a high-frequency treatment with a residual water content of 30% to 35% of the product mass.
  • the supplied high-frequency power is adjusted such that the dissipated power density in the product chips is at least about 4 W / g and the desired puffing occurs.
  • the high-frequency power is reduced to such an extent that the product surface temperature does not exceed about 60 ° C.
  • the duration of the product passage through the microwave vacuum drying is adjusted so that the desired final moisture of present 6% of the product mass is maintained and the product has "crispy" properties.
  • the predrying is further extended to fall below the above residual water content of 30% to 35% of the product mass.
  • FIGS. 2 and 3 show an embodiment of the device according to the invention for coupling in high-frequency radiation of high power.
  • the radiant energy generated in a high-frequency generator such as, for example, a magnetron or a frequency-variable microwave source passes through the feed waveguide 1 designed in the form of a rectangle in the present embodiment into the device according to the invention.
  • the feed hollow conductor 1 opens into the cylindrical coupling 3 to the treatment chamber 12.
  • the coupling 3 in this case consists of the cylindrical coupling waveguide 4, in which the waveguide mode TM O i is to propagate in the present example.
  • a Wellentypfilter 5 is provided.
  • this is a ⁇ / 2-Sperrtopf for suppressing the TE 11 -WeIIe, which is always also able to propagate because of their compared to the desired TM 01 -WeIIe lower cutoff frequency in the circular waveguide 4 of the coupling 3.
  • both the circular cross section and the length of the coupling waveguide 4 and the geometry of the coupling window 6 have been selected according to the invention such that the electric field strength at the window surface 6a on the treatment chamber 12 side passes through a minimum.
  • the product 16 to be treated passes through the cylindrical treatment chamber 12 on a conveyor 15 running centrally in the axial direction, which is a conveyor belt or conveyor containers running continuously one behind the other.
  • the treatment chamber 12 is hereby divided by intermediate and end panels 13 in a number of segments having openings 14 to allow the conveyor 15, the transport of the product 16. Due to the higher high-frequency power density required there, the length 17 of the segments in the area of the microwave vacuum puffing is smaller, for example, half as long as the segment length in the area of microwave vacuum drying.
  • the conveying means 15 is supported if necessary by bilateral metallic Aufschadorelonne 18, by the lower edges of the apertures 14 and by additional traverses between the Aufschdorflache 18.
  • the couplings 19 for coupling the high-frequency electromagnetic radiation are mounted in pairs radially on suitable container flanges 19 a of the cylindrical treatment chamber 12 flanged.
  • the axes of the couplings are each in the median plane between adjacent intermediate or end caps 13.
  • the container flanges 19a are as close as possible structurally approximated to the cylindrical surface of the wall of the treatment chamber 12.
  • the coupling window 6 has been designed to project convexly into the treatment chamber 12.
  • the coupling window 6 in the present case has a shape which substantially corresponds to the shape of a hemisphere projecting into the treatment chamber.
  • the coupling-in window 6 consists essentially of a half-sphere, which initially continues at its edge in a hollow cylinder 8 and is closed off by a brim 7 formed as a circular ring.
  • the coupling window 6 consists of PTFE (trade name: Teflon). At its brim 7, the coupling-in window 6 is clamped between the flange 4a of the waveguide 4 and the flange 9a of the metallic chamber wall 9, which is in electrical contact therewith, and is thereby held stationary in its position.
  • PTFE trade name: Teflon
  • the cylindrical continuation 8 makes it possible here to design the chamber flange 9a such that it bears tightly along its contact surface 8a with respect to the coupling window 6 and thus has no air gap on the surface 6a of the window 6 facing the vacuum.
  • the electrical length of the 10 surrounded by the metal of the flanges 4a and 9a brim 7 of the dielectric window 6 and the material thickness 11 of the spherical part of the window 6 have been optimized in the present case with respect to the used frequency of 2450 MHz with the methods mentioned in the general description part.
  • the mean electrical length 10 in the present case is approximately ⁇ ⁇ / 2
  • the material thickness of the flange is approximately 0.12 ⁇ ⁇
  • the material thickness 11 of the spherical window 6 is approximately 0.18 ⁇ ⁇
  • the wavelength ⁇ ⁇ itself at the frequency used of 2450 MHz in the material PTFE to 0.085 m results.
  • the design of the flange construction thus fulfills the criterion of the lowest possible electric field strength in the area of the contact point between the spherical window and the edge of the window flange facing the vacuum. The exact design was further refined by simulation calculations.
  • the thickness of the spherical window 6 differs in the illustrated embodiment from the required for reflection freedom material thickness of ⁇ ⁇ / 4. As a result of this and due to the transition between the cylindrical coupling hollow conductor 4 into the chamber volume 12 bounded by the chamber wall 9, standing waves are formed in the region of the coupling-in waveguide 4.
  • its length is chosen according to the invention so that an electric field maximum of the standing wave is established within the semispherical dome of the spherical window 6, while at its vacuum-facing surface 6a minimum electric field strengths are established for a given power input.
  • FIG. 5 there is shown a schematic representation of one embodiment of the apparatus of the present invention for high frequency assisted drying treatment of medium and low water content products for use in the process of the present invention to produce a food consisting of individual product pieces or whole fruits. tel.s, which has a crispy or crunchy character.
  • the device according to the invention comprises a microwave vacuum processor 20, which consists of a combination of microwave vacuum puffing station 21, microwave vacuum drier 23 and an intermediate transfer region 22 and serves to treat lumpy products.
  • the microwave vacuum booster station 21 and the microwave vacuum drier 23 are each provided with a conveyor belt 25 and 25a, respectively.
  • the conveyor belts 25 and 25a are hereby independently adjustable.
  • the product to be dried passes through an entry lock 24 in the vacuum applied vacuum vacuum processor 20, more precisely in the microwave vacuum puffing station 21. From the lock 24 falls the product to be dried on the first conveyor belt 25 and is using an adjustable product distributor 26 distributed to a continuous and uniformly thick layer.
  • the product passes through an aperture device 27 and enters the microwave treatment chamber 28 which is acted upon with a high dissipated power density.
  • the aperture device 27 serves to shield the high-frequency radiation within the microwave treatment chamber 28 to the outside.
  • the high-frequency power in the present case adjustable up to max. 48 kW at 2450 MHz, the treatment chamber 28 is supplied via a number of couplings 29.
  • the high power density causes the supplied high frequency power rapid evaporation of a Part of the moisture contained in the product and thus an expansion (puffing) of the product pieces (eg fruit or vegetable cubes).
  • the couplings 29 are formed in this case according to the embodiment shown in FIG. 2, i. that due to the adaptation according to the invention of the treatment chamber side, electric field strength immediately after the coupling 29, a higher performance compared to the prior art in the vacuum of the treatment chamber 28 can be introduced.
  • the treatment chamber 28 is, as described for example in the publication DE 196 43 989 A1, provided with a system of transversely and longitudinally to the product flow direction arranged apertures 30, of which only the intermediate and end panels are shown in Figure 5 for reasons of clarity.
  • the geometry of this diaphragm system 30 is chosen so that a distribution of the dissipated power density is achieved.
  • the puffing station 21 is equipped with radiation thermometers (pyrometers) 31.
  • Glow detectors 32 monitor the chamber 28 in order to extinguish immediately despite the possibly used special couplings 29 from FIGS. 2 and 3 due to the process-related high electric field strengths possibly occurring glow discharges.
  • the product exits the treatment chamber 28 through the aperture 33 attenuating the high frequency radiation introduced in the chamber 28, which may be a simplified version of the substantially microwave-tight aperture device 27.
  • the product is in a transfer region 22, which is characterized by a low exposure to high-frequency radiation.
  • the weak application of area 22 is based on the range 28 and 28a acting microwave attenuating aperture 33 and 33a.
  • the product already having a low water content of 10% to 20% of the product mass but still to be dried passes into the treatment chamber 28a of the microwave vacuum dryer 23.
  • the individual segments separated from one another by intermediate and end shutters of the diaphragm system 34 are twice as long as in the microwave puffing station 21, while the maximum power that can be introduced per segment is halved.
  • the high-frequency power in the present case adjustable up to max. 36 kW at 2450 MHz, the treatment chamber 28a via a number of couplings 37, in the present case six Einkopplungsploe, of which in Figure 5, however, only schematically four are shown, fed and causes the substantial evaporation of the residual moisture contained in the product.
  • the product is transferred to a second belt 25a before drying, so that the product residence times in the microwave puffing station 21 and in the microwave vacuum drier 23 can be set independently of one another within certain limits.
  • thermometers 35 are also present in the area of the treatment chamber 28a of the microwave vacuum dryer 23 for temperature monitoring.
  • a process control (not shown), in particular based on the values determined by radiation thermometers 31 and 35, calculates essential process parameters, e.g. the maximum product surface temperature during puffing and drying, and adjusts the power of the RF generators (not shown) feeding the couplers 29 and 37 accordingly.
  • Tasks of the process control are further compliance with the predetermined residual pressure in the vacuum chamber 20 and the triggering of countermeasures when glow discharges occur.
  • the inventively by means of high frequency in the microwave vacuum dryer 23 finished dried product leaves the treatment chamber 28a through the largely microwave-tight aperture device 38 and reaches the product discharge lock 39, through which it leaves the combined microwave vacuum processor 20 again.
  • the vacuum locks 24 and 39 are designed for the introduction and discharge of the product as vertically operating rotary flap locks with the flaps 24a and 39a.
  • the locks 24 and 39 have additional product retention flaps 24b and 39b, respectively.
  • the product retaining flaps 24b and 39b have the task, as described above, of keeping the product pieces away from the vacuum flaps 24a and 39a, respectively.
  • the product retaining flaps 24b and 39b are designed as butterfly flaps and designed so that they have a sufficiently narrow gap between the flap edge and the lock wall in the closed state, so that the closed product retaining flap effectively retains product pieces without the gas exchange in the vacuum lock 24 or 39 to hinder.
  • each vacuum flap 24a or 39a thus requires a product retention flap.
  • microwave vacuum processor 20 in both the puffing station 21 and in the dryer 23 high frequency radiation of different frequencies or a center frequency modulated high frequency radiation fed in order to achieve even more even distribution of power and better avoidance of hot spots.
  • FM Frequency Modulation
  • DSSS direct sequence spread spectrum
  • the respective dwell times in the individual treatment chambers 28 and 28a and the resulting power consumption by the respective product can be achieved in the present case by adjusting the running speed of the treadmills 25, 25a.
  • the substantially independent treadmills 25, 25a allow greater flexibility.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Polymers & Plastics (AREA)
  • Chemical & Material Sciences (AREA)
  • Food Science & Technology (AREA)
  • Health & Medical Sciences (AREA)
  • Nutrition Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Molecular Biology (AREA)
  • Power Engineering (AREA)
  • Drying Of Solid Materials (AREA)
  • Freezing, Cooling And Drying Of Foods (AREA)

Abstract

La présente invention concerne un procédé permettant de produire un produit alimentaire constitué de morceaux de produit individuels ou de fruits entiers qui présente un caractère croustillant ou croquant, ainsi qu'un dispositif qui peut notamment être aussi utilisé pour mettre en oeuvre ledit procédé et qui permet de soumettre des produits à un traitement de séchage et un dispositif qui est conçu pour injecter dans une chambre de traitement au moins partiellement vidée, à travers une fenêtre d'injection qui laisse passer les rayonnements électromagnétiques, mais qui est étanche à la pression, un rayonnement haute fréquence à puissance élevée, en particulier des micro-ondes, provenant d'un guide d'ondes d'injection. Le procédé selon cette invention consiste à sécher préalablement le produit ou les morceaux de produit au moyen d'un séchoir à convection, puis à soumettre à une expansion et à sécher le produit ou les morceaux de produit sous vide à l'aide d'une dissipation d'énergie diélectrique dans le produit ou les morceaux de produit par exposition à un rayonnement haute fréquence.
PCT/EP2007/054757 2006-05-17 2007-05-16 Séchage sous vide assisté par haute fréquence WO2007132014A2 (fr)

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DE102006023198.8 2006-05-17
DE102006023198A DE102006023198A1 (de) 2006-05-17 2006-05-17 Hochfrequenzgestützte Vakuumtrocknung

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WO2011002321A3 (fr) * 2009-06-29 2011-02-24 Firma Produkcyjno-Handlowa "Paula" Sp. Z O.O. Spółka Komandytowa Chips d'artichaut de jérusalem (topinambour) et leur procédé de production
CN113017059A (zh) * 2021-04-20 2021-06-25 中国农业科学院农产品加工研究所 可常温保存的复水核桃仁的制备方法
CN114292680A (zh) * 2021-11-18 2022-04-08 霍山丰乐生物能源科技有限公司 一种利用农林废弃物制备生物质颗粒的方法
US11484050B2 (en) 2016-02-11 2022-11-01 The Hershey Company Crispy pulse products and processes of making the same

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US8756826B2 (en) * 2010-11-30 2014-06-24 Mei, Llc Liquid coalescence and vacuum dryer system and method
EP2762013A1 (fr) * 2013-01-30 2014-08-06 Intersnack Group GmbH & Co. KG Procédé de fabrication d'une collation de type chips en pommes de terre et/ou légumes et collation ainsi fabriquée
DE102015210890A1 (de) * 2014-10-02 2016-04-07 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Trockenprodukt aus Obst und/oder Gemüse sowie Verfahren zur Herstellung
CA2988666C (fr) * 2015-06-15 2023-03-21 Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E.V. Produit sec a base de fruits et/ou de legumes et procede de production
DE102020105340B3 (de) * 2020-02-28 2021-04-08 Zahoransky Automation & Molds GmbH Vorrichtung und Verfahren zum Trocknen von Dialysefiltern
DE102022131025B3 (de) * 2022-11-23 2024-03-07 SAJA GmbH Vorrichtung und Verfahren zur Trocknung und Puffung

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DE3538899A1 (de) * 1985-11-02 1987-05-07 Hauni Werke Koerber & Co Kg Anlage zur mikrowellenbehandlung eines gutes
US4640020A (en) * 1985-11-27 1987-02-03 Mcdonnell Douglas Corporation Zoned microwave drying apparatus and process
JPS63304941A (ja) * 1987-06-03 1988-12-13 Suntory Ltd 野菜又は果実スナック食品の製造方法
EP0338626A2 (fr) * 1988-04-21 1989-10-25 Pannevis B.V. Procédé et dispositif pour enlever des liquides d'un mélange de solides et de liquides
US5020237A (en) * 1989-01-03 1991-06-04 The J. M. Smucker Company Method and apparatus for dehydrating fruit
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WO1993025090A1 (fr) * 1992-06-18 1993-12-23 General Mills, Inc. Procede permettant de griller aux micro-ondes des cereales soufflees pretes a consommer
WO1994015481A2 (fr) * 1993-01-06 1994-07-21 Tgtbt, Ltd. Procede et appareil pour preparer des chips d'aperitif sans matieres grasses
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DE19804386A1 (de) * 1998-02-04 1999-09-09 Ttp Ingenieurbuero Verfahren und Vorrichtung zur Trocknung oder Wärmebehandlung von Produkten, insbesondere mit Hilfe von Mikrowellenstrahlung, und damit hergestellte Bananenchips und Bananenpulver
US5962057A (en) * 1998-06-30 1999-10-05 The University Of Bristish Columbia Process for drying mango and pineapples
EP1092353A2 (fr) * 1999-10-05 2001-04-18 Santrade Ltd. Procédé de séchage des fruits ou des légumes et installation pour la mise en oeuvre d'un tel procédé. Séchoir pour bandes
WO2005004542A1 (fr) * 2003-07-01 2005-01-13 Forschungszentrum Karlsruhe Gmbh Resonateur micro-ondes, chaine de processus constituee selon le principe modulaire a partir d'un resonateur micro-ondes, procede de fonctionnement et objets/pieces traites thermiquement par micro-onde selon ce procede

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WO2011002321A3 (fr) * 2009-06-29 2011-02-24 Firma Produkcyjno-Handlowa "Paula" Sp. Z O.O. Spółka Komandytowa Chips d'artichaut de jérusalem (topinambour) et leur procédé de production
US11484050B2 (en) 2016-02-11 2022-11-01 The Hershey Company Crispy pulse products and processes of making the same
CN113017059A (zh) * 2021-04-20 2021-06-25 中国农业科学院农产品加工研究所 可常温保存的复水核桃仁的制备方法
CN113017059B (zh) * 2021-04-20 2022-04-26 中国农业科学院农产品加工研究所 可常温保存的复水核桃仁的制备方法
CN114292680A (zh) * 2021-11-18 2022-04-08 霍山丰乐生物能源科技有限公司 一种利用农林废弃物制备生物质颗粒的方法

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