AU2015401733A1

AU2015401733A1 - Dehydration apparatus and dehydration process

Info

Publication number: AU2015401733A1
Application number: AU2015401733A
Authority: AU
Inventors: Stephen Napier Beach
Original assignee: Australian Rural Dehydration Enterprise Pty Ltd
Current assignee: Starflow Holdings Pty Ltd
Priority date: 2015-07-03
Filing date: 2015-07-03
Publication date: 2018-02-08
Anticipated expiration: 2035-07-03
Also published as: WO2017004652A1; AU2015401733B2

Abstract

A dehydration apparatus (10) includes a continuous kiln (12) with two or more zones (14) in a kiln tunnel (16) and a conveyor assembly (18) for conveying food produce through the kiln tunnel (16). Each of one or more zones (14) is arranged to operate with a variable drying profile and atmosphere. Variations in drying profile and atmosphere are facilitated primarily by providing each zone (14) with varying levels of temperature, air velocity and microwave energy, which can each be determined primarily with reference to the type of food produce undergoing processing and/or the intended qualities of the resulting dehydrated food product. Operational parameters within each zone (14) can also be determined with reference to the hydroscopic state of the food produce as it progresses through the subsequent zones (14). The conveyor assembly (18) has conveyor belting (34), such as a mesh. Gauge of the conveyor belting (34) mesh diminishes from first zone (14a) to fourth zone (14d). Ventilation can be alternated between an air mode and an inert gas mode, such as using nitrogen. In a recycling mode, the apparatus can operate as a distillate still whilst also carrying out dehydration.

Description

FIELD OF THE INVENTION [0001] The present invention is directed to the dehydration of food products and relates to a dehydration apparatus and process for this purpose.

BACKGROUND TO THE INVENTION [0002] There is an increasing need for effective and efficient techniques to preserve food, including degraded food and prevent spoilage and wastage of foodstuffs. This is a need that arises at least in part to reduce the amount of food that is disposed of due to spoilage or due to food products being deemed sufficiently damaged and therefore not suitable for human presentation and consumption. There is also an increasing need to make greater use of existing food stocks, including producing viable food products from organic material that may otherwise be disposed of as waste.

[0003] There are a number of techniques available which act to prevent or inhibit microbiological growth that causes food spoilage. These techniques include use of temperature (heating or chilling), dehydration, preservatives, manipulation of pH, reduction of oxygen availability and radiation. One or more of these techniques can be used in order to inhibit microbiological activity sufficiently and ensure stability of the foodstuff.

[0004] Dehydration, where water content of the food product is removed, reduced or made unavailable, thereby making the food product unsuited to microbial activity that causes spoilage, is a technique that has several advantages. Firstly, dehydration only minimally affects the nutritional content of food if dehydration is carried out appropriately. Further, dehydration can provide significant economic benefits in storage and transport of the foodstuffs since the weight and bulk of the food can be significantly reduced and need for refrigeration

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PCT/AU2015/050377 and its associated energy requirements is largely, if not completely, dispensed with.

[0005] There are two general and established methods for drying food products:

a) heat applications to remove water; and

b) freeze-drying procedures.

Oven drying is presently the most widely used method of commercial dehydration and involves exposing the food product to dry heated air. Oven drying typically involves placing the food product into a chamber, whereupon heat is applied by gas, electricity, steam or ‘heat pump’. Water in the food product is heated until the water is vaporised, leaving the food product dry. This heating usually occurs at relatively high temperatures and is sensitive to both atmospheric humidity and ambient temperatures. It can also be desirable to subject the food product to one or more pre-treatments, such as hot water or preservatives, including infused preservatives, then decanting and desiccating before subjecting the food product to dehydration.

[0006] Freeze drying, also known as ‘lyophilisation’ involves first freezing the food product then reducing the surrounding pressure to allow the frozen water in the food product to sublimate directly from the solid phase to the gas phase. Using this process, flavour changes in the resulting product are minimal, product shrinkage is negligible and the dried material is porous and readily rehydrates.

[0007] Although these dehydration techniques offer many advantages, there are associated disadvantages, including high capital costs in setting up and operating dehydration plants. Further, these dehydration techniques typically operate as a batch process and the equipment is cumbersome and bulky. Freeze drying can rupture food tissue, resulting in a textural defect known as ‘woodiness’. Excessive heating can degrade the food product and its taste. Vitamin content, in particular, thiamine and ascorbic acid can be lost or significantly diminished. Similarly, beneficial bioactive food compounds such as anti-oxidants, anticarcinogens, anti-adiposity and natural antimicrobial compounds can also be

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PCT/AU2015/050377 degraded or destroyed by these existing techniques. Further, heated air dehydration inherently exposes the food product to oxidisation, thereby reducing nutritional value including anti-oxidants. Environmental waste problems are also typically created by use of known dehydration plants.

[0008] With the aforementioned in mind, it is therefore an object of the invention to provide a dehydration apparatus and process which overcomes at least one of the abovementioned difficulties or problems.

SUMMARY OF THE INVENTION [0009] According to a first aspect of the invention, there is provided a dehydration apparatus for dehydrating a food product including:

a kiln having two or more zones;

conveyor means for conveying food product through the kiln and sequentially through the two or more zones;

a circulation means for circulating warm and dehumidified air through the kiln; and a microwave emission source, wherein food products conveyed through the kiln are simultaneously exposed to microwave emissions and flow of warm air to dehydrate the food product, and whereby one or more of temperature, air velocity and/or microwave energy are variable between the two or more zones to create variable drying profiles and/or atmosphere within each zone.

[0010] Preferably, the kiln is a continuous kiln and has three zones, further preferably, four zones. Each zone can be provided with varying levels of temperature, air velocity and microwave energy, thereby providing zones having different drying profiles and atmospheres. Operational parameters of temperature, air velocity and microwave energy in each zone are each determined at least in part by the type of food product being conveyed through the kiln and/or intended qualities of the resulting dehydrated food product and at least in part with reference to the hydroscopic state of the food product.

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PCT/AU2015/050377 [0011] The kiln includes a kiln tunnel through which food products can be conveyed by the conveyor means. The conveyor means desirably includes a plurality of conveyor segments, each conveyor segment being positioned in an overlapping arrangement such that an end of a first conveyor segment is positioned above an adjacent end of an adjacent conveyor segment to define a vertical drop through which food products fall. An example of a suitable conveyor means is described in WO98/53711.

[0012] The arrangement of the conveyor segments, including the action of food product falling through the vertical drop, promotes exposure of the food product to warmed and dehumidified air within the kiln tunnel as well as simultaneously exposing the food product to microwave emissions.

[0013] The kiln tunnel includes microwave emission source for exposing the food products conveyed through the kiln tunnel with microwaves. The microwave emission source may include one or more microwave emitter horns or microwave applicators, appropriately positioned to provide varying levels of microwave energy into each zone. Microwave reflection means may be provided for each emitter horn/applicator.

[0014] Preferably, intensity of the microwave emissions diminishes from a first zone where food product is introduced into the kiln tunnel, to a terminal zone, immediately prior to the food product exiting the kiln tunnel. Intensity of microwave emissions is preferably successively reduced as the food product is conveyed from one zone to the next.

[0015] Microwave emissions are channelled to each zone to provide different microwave intensity to each zone. Microwave emissions are channelled by suitable means, such as via an appropriate waveguide conduit. Intensity of microwave emissions are varied to offset latent heat loss in the food produce.

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PCT/AU2015/050377 [0016] Flow and velocity of air within the kiln tunnel and within each zone is at least partly controlled by the circulation means. The circulation means may include an air circulation duct and a circulation fan located within the air duct for drawing air in. Flow and velocity of air is further controlled via the circulation means working in conjunction with plenum ducting and independent variable inlets located in individual ducts diverting off from the plenum ducting.

[0017] The circulation means further includes a variable air inlet, ideally upstream of the circulation fan, where an opening of the inlet can be adjusted between an open and closed position to modify flow path of air. The variable air inlet advantageously permits the apparatus to operate in a single pass or fresh air ventilation mode, suitable for processing of high protein food product such as meat; and a recycled air ventilation mode, suitable for processing of relatively low protein food product such as fruits and vegetables.

[0018] Air intake can be fresh to avoid contaminating the dehydration process, particularly if the apparatus is operating at temperatures below 65°C. Alternatively, air can be recycled as a closed or partially closed operation to improve thermal efficiencies. Closed or partially closed operation may be suitable when the apparatus is operating at temperatures above about 65°C.

[0019] Preferably, the circulation means also includes air ducting, for example, plenum ducting, progressively venting air into each zone of the kiln tunnel. In a preferred embodiment, air is directed into each zone via variable air inlets which operate in conjunction with the circulation means to control air flow and velocity into each zone.

[0020] Air velocity and flow is preferably successively reduced as the food product is conveyed from the first zone to the next. This advantageously avoids development of case hardening of the dehydrated food product. Preferably, air velocity in each zone is no more than about 4.0 m/sec, provided microwave emission source simultaneously delivers microwave energy to the kiln, to avoid

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PCT/AU2015/050377 the deleterious effect of case hardening of the food product. If no microwave energy is transmitted to the kiln, air velocity in each zone is ideally no more than about 2.0 m/sec.

[0021] A heating means provides heat to warm the air which is conveyed through the ducting and into each zone of the kiln tunnel. The heating means may be located within the air duct downstream of the circulation fan. The heating means preferably allows the apparatus to operate at different temperature settings, ranging from about 40°C up to about 90°C but preferably no more than about 80°C during production of dehydrated food product.

[0022] Operating temperature may be varied throughout zones of the kiln tunnel and is dependent largely on the type of food product being processed. Lower operating temperatures in the range of about 40 to 65°C, more typically about 40 to 50°C, are used for relatively high protein food product such as seafood and meat. Operating temperatures of about 60 to 80°C are more suitable for relatively low protein food product such as fruits, fungi, vegetables, and herbs/spices.

[0023] The apparatus preferably includes one or more sensors, preferably a plurality of sensors to monitor one or more operating parameters of temperature, air velocity, microwave intensity, humidity, conveyor speed and/or conveyor progression. Sensors preferably operate in a feedback loop with a control unit, whereby operating parameters can be modified within each zone during operation of the apparatus to achieve the desired food product dehydration effect.

[0024] Preferably, the apparatus includes refrigeration means, ideally including chilling coils and/or refrigeration compressors, which facilitates recovery of distillates, particularly extracts from fruit, flowers, berries, fungi, vegetables, herbs, spices and other plant based materials. Advantageously, the refrigeration means enables the apparatus to double as a commercial still, allowing collection of condensate of plant based material as it is processed in the apparatus.

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PCT/AU2015/050377 [0025] According to a further aspect of the present invention, there is provided a process for dehydrating food produce, the process including:

introducing a food product into a kiln tunnel, the kiln tunnel being arranged to receive microwave emissions from at least one microwave emission source;

dehumidifying and heating air and circulating the dehumidified heated air through the kiln tunnel;

whereby food produce is progressively conveyed through two or more zones of the kiln tunnel, simultaneously exposing the food produce to microwave emissions and flow of dehumidified warm air and whereby one or more of temperature, air velocity and/or microwave energy are varied between the two or more zones to create variable drying profiles and/or atmosphere within each zone.

[0026] Preferably, intensity of microwave emissions is diminished as the food produce is progressively conveyed through the two or more zones.

[0027] It is further preferred that air velocity is reduced as the food produce is progressively conveyed through the two or more zones.

[0028] Advantageously, the apparatus and process of the present invention provides savings on both weight and bulk of the resulting food product whilst also largely dispensing with need for refrigeration and minimising wastage factor by capturing bio-distillates and/or spoiled, reject or downgraded food produce that would routinely be lost or discarded during processing. Further, the apparatus and process is able to produce food products which although dried, retain superior levels of nutrients, colour, taste, texture, aroma and form.

[0029] Advantageously, the apparatus and process of the present invention enables production of useful and saleable food products from food that may otherwise have little or no value or be discarded as waste.

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BRIEF DESCRIPTION OF THE DRAWINGS [0030] It is convenient to further describe the present invention with respect to the accompanying drawings, which illustrate an embodiment of the invention and wherein:

[0031 ] Figure 1 is a schematic side view of an arrangement of a dehydration apparatus according to an embodiment of the present invention, illustrating operation of the apparatus in a single-pass ventilation mode; and [0032] Figure 2 is a schematic side view of the dehydration apparatus of Figure 1, illustrating operation of the apparatus in a recycled ventilation mode.

DESCRIPTION OF PREFERRED EMBODIMENT [0033] Referring to Figures 1 and 2, there is shown a dehydration apparatus 10 according to an embodiment of the invention. The dehydration apparatus 10 includes a continuous kiln 12 having two or more zones 14 in a kiln tunnel 16 and a conveyor assembly 18 for conveying food produce through the kiln tunnel 16.

[0034] In the embodiment shown in Figure 1, the apparatus 10 includes four zones 14a-d, though it should be understood that the apparatus 10 may have more or less zones 14 as required without departing from the scope of the present invention. Each zone 14 is arranged to operate with a variable drying profile and atmosphere. Variations in drying profile and atmosphere are facilitated primarily by providing each zone 14 with varying levels of temperature, air velocity and microwave energy. These operational parameters of temperature, air velocity and microwave energy in each zone 14 are each determined primarily with reference to the type of food produce undergoing processing and/or the intended qualities of the resulting dehydrated food product. Operational parameters within each zone 14 are also determined with reference

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PCT/AU2015/050377 to the hydroscopic state of the food produce as it progresses through the subsequent zones 14.

[0035] In the embodiment shown, the apparatus has four zones, 14a-d. Food produce is introduced into a first zone 14a via intake conveyor 30. Food produce is moved progressively through each zone 14 by conveyor assembly 18 to a terminal zone, which in the embodiment shown is a fourth zone 14d, whereupon the dehydrated food product exits the kiln tunnel 16 via outlet conveyor 32.

[0036] The conveyor assembly 18 includes a plurality of conveyor segments 28. The conveyor segments 28 are positioned on an incline and in an overlapping arrangement wherein a downstream end of each conveyor segment is located above the upstream end of the adjacent conveyor segment 28. This arrangement of conveyor segments 28 allows for cascading of the food produce from one conveyor segment 28 to the next as the food produce is conveyed through the kiln tunnel 16. This cascading effect facilitates more uniform exposure of the food produce to warm air and/or microwave emissions and amplifies fluidising effect of back ventilation of air throughout the kiln tunnel 16.

[0037] In the embodiment shown in Figures 1 and 2, the conveyor assembly 18 includes eight individual and inclined conveyor segments 28. In this embodiment, size of each zone 14 is effectively determined by size of conveyor segments 28. In the embodiment shown in Figures 1 and 2, each zone 14 includes two conveyor segments 28, though this number can be varied as required.

[0038] The conveyor assembly 18 is operated by appropriate drive means. Drive means may include drive drums and conveyor belts, operating in conjunction with drive pulley and belt drive assembly. Other means of driving the conveyor are also envisaged. Desirably, the conveyor assembly 18 is operable at varying speeds. Varying speed of the conveyor assembly 18 enables variation of dwell period of the food produce in each zone 14. Dwell period can thus be

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PCT/AU2015/050377 varied as required and generally ranges from about 5 to 20 minutes per zone 14, equating to a total dwell time in the kiln tunnel 16 of about 20 to 80 minutes.

[0039] The conveyor assembly 18 further includes conveyor belting 34. Conveyor belting 34 may comprise a mesh, ranging from a coarse ‘chain mesh’ through to a fine gauge ‘chain-mail’ and ultra-fine gauge ‘woven-belt mesh’, depending on food produce being processed and the degree of dehydration required for that food product. Gauge of the conveyor belting 34 mesh diminishes from first zone 14a to fourth zone 14d. Conveyor belting 34 in each zone 14 may have a different gauge mesh to accommodate capture of the different size of particulate matter that may fall away from the food product.

[0040] The design of mesh belting to conveyor segments 28 provides a continuous self-cleaning mechanism to remove particulate food matter which may lodge in crevices. In a preferred embodiment, teeth of drive drums of each conveyor segment 28 are accommodated in the changing mesh apertures between chain links of the conveyor belt 34 to push out food particles that may have accumulated therein.

[0041] The conveyor assembly 18 may be provided with an agitation mechanism, operating in one or more of the zones 14. Typically, agitation is considered necessary only in the final zones 14 of the kiln tunnel 18 which in the embodiment shown, is fourth zone 14d and optionally, third zone 14c. The agitation mechanism operates to inflict underside beating of the conveyor belting 34 and so agitate food product thereon. The agitation mechanism may take suitable form, such as a mechanical arm that is arranged to beat an underside of the conveyor belt 34.

[0042] The air duct 20 supports a refrigerated dehumidification means for dehumidifying the air entering the air duct 20 via air intake pipe 24 and heater means. Heater means is arranged to heat the air entering the duct 20 before it is channelled to the kiln tunnel 16. As food produce is moved through the kiln

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PCT/AU2015/050377 tunnel 16, dehumidified and warmed air is supplied to the kiln tunnel 16 by a circulation means which includes an air duct 20 and a circulation fan 22 for supplying air to the air duct 20. The fan 22, dehumidification means and heater means may collectively operate as a ‘heat-pump’ arrangement.

[0043] Heater means warms the air which is circulated through the air duct 20 and kiln tunnel 16. The heater means is located within the air duct 20 downstream of circulation fan 22. The heater means, which can include one or more heating coils 52, preferably a bank of coils 52, operates in conjunction with microwave emission source 42 to facilitate operation of the apparatus 10 at different temperature settings, ranging from about 40°C up to about 90°C. Heater means, in conjunction with emission of microwave energy from microwave emission source 42, may increase the dry bulb temperature within zones 14 of the kiln tunnel 16 up to about 80°C during operation of the apparatus 10.

[0044] In the embodiment shown in Figures 1 and 2, heater means includes a series of heater coils 52 and heat booster 54. The heater coils 52 are capable of heating the air up to about 65°C. The heat booster 54 is arranged to provide any further heating of the air prior to circulation of the air into the kiln tunnel 16. The heat booster 54 may be operated with externally sourced heat source, such as hot water, to achieve dry air heating of up to about 80°C or 90°C.

[0045] Operating temperature may be adjustable within each zone 14 and throughout the kiln tunnel 16 and is varied dependent on the type of food being processed. Operating temperature may be varied between one zone 14 to the next during operation, though it is typical for temperature to be held relatively constant for any food type during any single treatment process. Processing of high protein food produce such as meat and/or seafood necessitates dehydration at relatively lower temperature, typically below 65°C, whereas processing of relatively low protein and high fibre foods, such as fruit and vegetables, can be conducted at relatively higher temperatures, typically above 65°C and generally up to a maximum of about 80°C.

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PCT/AU2015/050377 [0046] To maximise energy efficiency of the dehydration apparatus 10, at least a portion of the heated dehumidified air can be recycled through the air duct 20 and into the kiln tunnel 16. Processing of food produce using recycled air is appropriate when the food produce has relatively low protein content, such as fruit and vegetables. When the apparatus 10 is used for dehydration of relatively high protein food produce such as meat and/or seafood, it is important that there be hygienic full venting of ‘single passed’ air. That is, the air is not recirculated back into the kiln tunnel 16 once it has passed through the kiln tunnel 16 and come into contact with the food produce.

[0047] Fresh air is drawn up by the fan 22 through the intake pipe 24 and into the air duct 20. Air is passed through first filtration means 26, which is disposed downstream of air intake pipe 24 and upstream of circulation fan 22, to filter out fine particulate matter and other potential contaminants. First filtration means 26 operates to filter out approximately 90% of potentially contaminating particulate matter. The first filtration means 26 may include one or more cyclone arresters comprising a plurality of precipitating tubes, which act to capture dust or food fines circulating in the air duct 20. Alternatively, first filtration means 26 may include any type of filter capable of trapping fine particulate matter. A dust hopper or storage bin 50 is ideally located below and in communication with the first filtration means 26 to collect the trapped dust and/or food fines.

[0048] Preferably, air is channelled through the air duct 20 and through a secondary filtration means 27, located downstream of circulation fan 22 before air is introduced into the kiln tunnel 16. Secondary filtration means 27 is desirably a micro filter, adapted to filter particulate matter of approximately 5 m or less from the air. Secondary filtration means 27 is useful in removing potential contaminants from the kiln tunnel 16. It also assists to maximise quality of condensates extracted during operation of the apparatus 10, ensuring that condensate is substantially free of contaminants and particulate matter and is of a quality sufficient for use as high value products such as nutraceuticals or essential oils.

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PCT/AU2015/050377 [0049] Air circulation through the air duct 20 and kiln tunnel 16 can be alternated between ‘single pass’ and recycling/recirculating ventilation modes via operation of a variable air inlet 36 located in the air duct 20 upstream of circulation fan 22 and first filtration means 26. An opening of the variable air inlet 36 can be adjusted between an open and closed position with a bi-vane or other suitable means to switch air circulation mode between ‘single pass’ and recycled air flow of ventilation modes.

[0050] The variable air inlet 36 is in a closed position when it is required that air be circulated through the kiln tunnel 16 once only, as is required when high protein food produce is treated and hygienic full venting of the air is required. In this single-pass mode of operation, air is introduced into the air duct 20 via intake pipe 24 and through first filtration means 26, whereby it is channelled via fan 22 through secondary filtration means 27 and into each zone 14 of the kiln tunnel 16 via plenum ducting 56. Air exits the kiln tunnel 16 at first zone 14a and returns into air duct 20 before exiting via exhaust pipe 38 as assisted by fan 40. A heat sink 66 located adjacent or in exhaust pipe 38 assists to disperse heat. Single pass ventilation mode is illustrated in Figure 1.

[0051] Lower temperature dehydration of high protein food produce necessitates hygienic full venting of air once it has passed through the kiln tunnel 16 and been exhausted therefrom. Once air has passed through the kiln tunnel 16 and contacted high protein food produce therein, it exits the apparatus via exhaust pipe 38, assisted by exhaust fan 40.

[0052] Heat is inevitably lost during single pass ventilation mode since air is expelled from the apparatus 10 after passing through the kiln tunnel 16. To minimise heat loss during operation of the apparatus 10, heat is collected by a heat recovery coil 58. Heat recovery coil 58 is located in the air exhaust stream exiting from the kiln tunnel 16 and operates to recover heat from the air that would otherwise be lost from venting air through exhaust pipe 38. The heat recovery coil 58 improves the overall efficiency of the apparatus 10 and about 50% of heat can typically be recovered from the air in this manner.

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PCT/AU2015/050377 [0053] Higher temperature dehydration for fibre or plant-based food produce allows for full recirculation or recycling of the air and the apparatus 10 can be set to operate in recycling/recirculating ventilation mode. This mode is illustrated in Figure 2.

[0054] In recycle ventilation mode, where air is recirculated or recycled through the kiln tunnel 16 for any number of cycles, the variable air inlet 36 is in an open position. Variable air inlet 36 is opened by opening a bi-vane. In this mode of operation, air is partially introduced into the air duct 20 via air intake pipe 24, channelled into and throughout the kiln tunnel 16 and once exhausted therefrom, recirculated back into the air duct 20 and through the variable air inlet 36. Air is returned or recycled back into the kiln tunnel 16 for as many cycles as necessary. This recycling of air is only permitted during operation when ambient kiln temperatures exceed about 65°C, which constitutes the threshold hygiene temperature for dehydrating perishables.

[0055] During recycling ventilation mode, whilst the majority of the air is recycled, it is desirable to introduce at least a portion of fresh air to ensure that the air in the kiln tunnel 16 does not become stale. Replenishing air is pulled into the air duct 20 via air intake pipe 24. This intake of fresh air is conducted in concert with a bleed-off valve 37, whereby a portion of recycled air exits through the bleed-off valve 37 and substantially the same volume of air is introduced into air duct 20 via the air intake pipe 24.

[0056] Recycling ventilation mode allows full recirculation of the air and at least a two-thirds heat recovery by the apparatus 10. However, some heat loss is inevitable. In order to maintain the temperature required for dehydration of the low-protein, plant-based food product, which is typically in the range of about 65 to 80°C, additional heat can be added to the air via heat booster 54. Heat booster 54 operates to provide heat in addition to heat provided by heating coils 52.

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PCT/AU2015/050377 [0057] During recycled ventilation mode, it is desirable to discourage formation of condensate in the apparatus 10 and in particular within the air duct 20, until the air reaches chill coils 48, whereupon deliberate cooling of the air encourages condensate formation and it can be appropriately separated, potentially fractionated and collected. To discourage inappropriate condensate formation, a heat discharge coil 60 is in operation during recycled ventilation mode. Heat discharge coil 60 is located in the air stream exhausted from kiln tunnel 16. Heat discharge coil 60 warms air exiting the kiln tunnel 16 sufficiently to avoid formation of condensate within the portion of air duct 20 between exhaust of the kiln tunnel 16 and second filtration means 27.

[0058] In one embodiment, the apparatus 10 also includes an oxygen-purging module 62 which operates to substantially purge oxygen from the kiln tunnel 16 and create an atmosphere within the kiln tunnel 16 that is comprised largely of an inert gas. The oxygen purging module 62 is desirably located at the air intake pipe 24 and operates as a continuous flow module to ensure that air intake into the kiln tunnel 16 is gradually purged of oxygen and recycled to produce an inert gas environment. The oxygen purging module 62 intakes a portion of air, which is substantially stripped of oxygen by the oxygen purging module 62 prior to entering the air duct 20. A substantially similar flow of air exits via bleed-off valve 37. The bleed-off valve 37 is desirably located between chill coils 48 and heating coils 52, located downstream of the circulation fan 22, so that condensate is removed from the air before it is gradually exhausted from the air duct 20 via bleed-off valve 37.

[0059] The oxygen purging module 62 is preferably a gas splitter module which operates to strip oxygen from air introduced into the air duct 20 and simultaneously introduce inert gas into the air duct 20. Preferably, the inert gas is a nitrogen gas. The oxygen purging module 62 is operative during operation of the apparatus in recycling ventilation mode. Table 1 below provides a summary of temperature and ventilation settings during operation of the apparatus 10 in dehydrating (i) high protein food produce; and (ii) relatively low protein food produce.

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Food Category	High Protein (fish, meat, offal)	Low protein (fruit, fungi, vegetable)
Temperature	40 - 65°C	65 - 80°C
Heat boost (54)	off	on
Ventilation mode	single-pass	recycled
Variable air inlet (36)	closed	open
Bleed-off valve (37)	closed	open
Heat recovery coil (58)	on	off
Heat discharge coil (60)	off	on
Oxygen purging module (62)	off	on
Ambient atmosphere in kiln tunnel (16)	air	inert gas (nitrogen)
Distillate recovery (52)	atmospheric condensate (distilled water)	specific moisture condensate

Table 1: Apparatus temperature and ventilation operating settings [0060] Substantially replacing air within the kiln tunnel 16 with inert gas and thereby greatly reducing oxygen content within the kiln tunnel 16 air space ensures greater retention of total antioxidant activity of dried food products and reduces browning of the food product by minimising exposure of the food product to oxidation. Further, purging of air space within the kiln tunnel 16 also advantageously contributes to higher retention rates of nutritional content, in particular of vitamin C, antioxidants and other beneficial bioactive compounds, thereby ensuring dried fruit, berries and vegetables of highest possible nutritional quality.

[0061] The heat-pump component of the apparatus 10 also enables the apparatus 10 to function as a still, allowing separation of condensates from recycled kiln air. Recycling of the air to the air duct 20 upstream of the heat pump allows the apparatus 10 to also function as a still upon dehydration of organic materials, particularly plant-based material such as flowers, fruit, berries, vegetables and other plant material. Chill coils 48 of the heat pump cools the air after it has passed through the kiln tunnel 16 during processing of the food product, enabling extraction of condensates. Condensates are collected in collection vessel 52 and can be further processed as required. In the embodiment shown in Figures 1 and 2, the apparatus 10 includes a plurality of chill coils 48, enabling collection of fractionated condensate.

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PCT/AU2015/050377 [0062] As food produce progresses through the zones 14 of the kiln tunnel 16 and becomes increasingly dehydrated, it can sustain different air velocities for optimum drying. Consequently, diminishing air velocity is required from first zone 14a to fourth zone 14d to avoid development of ‘case hardening’ of the final dehydrated food product. Velocity of ventilation is controlled throughout the kiln tunnel 16 and within each zone 14 at least partially by providing a variable drive to circulation fan 22. The fan 22, in conjunction with plenum ducting 56 and individual variable inlets 46 allows adjustable volumes of air to be provided through the kiln tunnel 16, ranging in velocities from mild, typically about 0.5 to 1.0 m/sec, through to medium (1.0 to 2.0 m/sec); to strong (2.0 to 3.0 m/sec) and blast (3.0 to 4.0 m/sec). Table 2 below provides a summary of air velocity rates in the various zones 14. It should be noted that the air velocity rates recited in Table 2 reflect operating parameters when microwave emissions are directed into the kiln tunnel 16. Air velocities are reduced to no more than a maximum of 2.0m/sec if microwave emission source 42 is switched off.

Kiln exhaust out 4-4Food produce in

Zone	Zone 1	Zone 2	Zone 3	Zone 4
Air velocity (m/sec)	4.0 - 2.0	3.0-1.5	2.0 - 1.0	1.0-0.5
T reatment phase	Primary	Intermediate	Final
% moisture content of food product (available water)	-90% to 60%	-55% to 35%	-30% to 20%	-15% to 5%

Table 2: Summary of variable air velocity in kiln zones

Air in 4-4Dehydrated food product out [0063] Control of air velocity is enhanced by use of overhead plenum ducting 56 having ducts channelling air to each zone 14, progressively back-venting the kiln tunnel 16 through a number of variable air inlets 46. The number of variable air inlets 46 corresponds to the number of zones 14, there being one variable air inlet 46 for each zone 14. Each variable inlet 46 can be adjusted between an open and closed position by suitable means, including appropriate adjustable valve or vane such as a bi-vane, to vary air velocity into each zone 14.

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PCT/AU2015/050377 [0064] The apparatus 10 is further provided with at least one microwave energy source 42. In the embodiment shown in the Figures, the apparatus 10 is provided with a microwave energy source 42 for each zone 14. Microwave energy emitted from each microwave energy source 42 is channelled to corresponding zone 14 by suitable means, such as by appropriate waveguide conduit 70.

[0065] At least one microwave energy source 42 emits microwave energy into a chamber of each zone 14, the chamber having at least two substantially parallel and opposing inner surfaces separated from each other by a predetermined distance. This configuration promotes cross coupling of microwave energy to produce a processing zone smaller in size than the zone 14. The microwave energy source 42 may include any commercially available source of magnetrons and be operated at required frequency settings.

[0066] During passage of food produce through the kiln tunnel 16 of the apparatus, the excitement of polarity of water molecules by microwaves creates a pressure differential which effectively progressively drives residual moisture to the surface of the food product. Upon moisture being driven to the surface, the moisture can be evaporated by warm air. The use of microwave energy stimulates porosity in the food product by encouraging moisture to move towards the surface of the food product as it is treated, thereby minimising shrivelling, hardening or oxidation. Volume of the food product is typically reduced to about 2/3 of the pre-dehydration size, compared to reduction to about 1/3 of size using traditional dehydration techniques. This advantageously leads to production of a superior dehydrated food product in terms of at least texture and capacity for rehydration, whilst simultaneously reducing drying time and hence operating expense.

[0067] Each microwave energy source 42 is operable to emit variable intensity of microwave energy and allow variation of intensity of microwaves in each zone 14 of the kiln 16. Microwave intensity is progressively reduced as the food product passes from first zone 14a and through subsequent zones, since

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PCT/AU2015/050377 moisture content of the food product diminishes as it progresses through the kiln tunnel 16. Microwave intensity is high and differential in primary zones 14, namely in the first zone 14a; medium and graduated in intermediate zones, i.e. second and third zones 14b, 14c; and is low and intermittent in final zone, i.e. fourth zone 14d. That is, microwave intensity is progressively reduced as the food product is conveyed through the kiln tunnel 16 in response to changes in the hydroscopic state of the food product. Microwave intensities in each zone 14 during operation of the apparatus 10 are summarised in Table 3.

Food Produce Feed-in	Zone 1	Zone 2	Zone 3	Zone 4	Food Product Feed-out
Inherent Water State	Surface water	Intermediate water	Bound water
% moisture content (available water)	-90% to 60%	-55% to 35%	-30% to 20%	-15% to 5%
Product Phase	Primary	Intermediate	Final
Dielectric Loss Factor (Er)	13.0 ~ 9.0	5.0 - 3.0	1.0 - 0.5
Microwave Intensity	High and differential microwaves	Medium, graduated & diminishing microwave intensity	Low and intermittent microwaves

Table 3: Microwave Intensities for operation of dehydration apparatus [0068] The variations in microwave intensity can be achieved by operating the magnetrons to achieve desired intensity. Magnetron cathode tube heating elements should be capable of variable settings to facilitate variation of the intensity of microwave emissions into each zone 14. As an example, a first magnetron providing microwave energy to the first zone 14 can operate at 20kw at 2450MHz; a second magnetron providing microwave energy to the second zone 14b can operate at 20 Kw at 2410 MHz; a third magnetron providing microwave energy to the third zone 14c can operate at 15 Kw at 2440 MHz; and a fourth magnetron can supply microwave energy to the fourth zone 14d at 15Kw at 2430 MHz. Each magnetron is desirably operated at a different setting to others in the apparatus 10 primarily to avoid microwave resonance effect.

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PCT/AU2015/050377 [0069] Differing microwave settings between each microwave emission source 42 additionally assists in eradication of microorganisms, including pathogenic microbes and spores. Desirably, at least the first zone 14a and optionally the second zone 14b, is subjected to intense applications of different microwave frequencies. Use of dual frequencies produces a differential frequency, ideally around 40MHz, which is effective at eliminating both surface microbial and spore activity as well as undesirable microbes which may be located within the food product. The application of differential microwaves operates to disable protective enzymes in primarily anaerobic bacteria, allowing the bacteria to be oxidised and be attenuated at least and more likely destroyed.

[0070] The apparatus 10 further includes one or more sensors 68, including sensors 68 to detect one or more of heat temperature, air humidity, air velocity, microwave intensity, conveyor progression and/or conveyor speed within the air duct 20 and/or each zone 14.

[0071] Each sensor 68 is in communication with a central processing unit (CPU). The CPU has an associated control panel with direct connections to at least the heat pump, circulation means and microwave emission source. Sensors 68 in each zone 14 and/or the air duct 20 provide feedback communication to the CPU, whereby operational parameters of the apparatus 10 can be varied to ensure that each zone 14 is functioning with an appropriate drying profile and atmosphere. For example, feedback from heat sensors 68 allows for temperature to be controlled by variations of microwave energy input, volume of heat of dehumidified air and/or food product feed rates, i.e. conveyor speed. Electrical functions and controls are computer coordinated via the CPU and are programmable to provide a substantially automated system.

[0072] The apparatus 10 of the present invention has capacity to reduce power consumption by about half, compared to standard plants utilising standard dehydration techniques. This is due to a combination of the reduced processing time, facilitated by combined use of warm, dry air and simultaneous application of microwave emissions, each diminishing as the food produce is conveyed through

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PCT/AU2015/050377 subsequent zones 14; and capacity for the apparatus to capture and recycle heat. The apparatus 10 further facilitates overall size to be substantially reduced relative to traditional dehydration plants, greatly reducing the footprint of the apparatus 10. The reduced size of the apparatus 10 uniquely allows it to operate as a stand-alone and self contained apparatus, which can be conveniently transported and operated where required. For example, the apparatus 10 can be conveniently added to or integrated with existing operations, such as existing food processing plants, including abattoirs, plantations and farms.

[0073] In use, food produce enters the dehydration apparatus 10 via intake conveyor 30 and progresses into the first zone 14a of the kiln tunnel 16 where it is progressed through the length of the first zone 14a by action of the conveyor assembly 18. Dwell period in the first zone 14a is set to a desired time by varying speed of the conveyor segments 28 in the first zone 14a. Heater means, dehumidification means, circulation fan 22 and microwave energy source 42 are activated to simultaneously expose the food product to microwave emissions and flow of warm, dehumidified air as it progresses through the first zone 14a.

[0074] Temperature and air circulation mode are set in accordance with the food product being processed. Seafood, meats, maw and offal are processed at temperatures between about 40°C and generally not exceeding 65°C and air circulation mode is set to hygienic full venting of single passed air by closure of variable air inlet 36. Fruits, fungi, vegetables, herbs, spices and other generally plant or fungi based products are processed at temperatures between about 60°C and generally not exceeding 80°C. Air circulation mode is set to recycling mode by opening of the variable air inlet 36. Oxygen-purging module is also activated in this mode. Operating settings of the apparatus 10 are set depending on the category of food being dehydrated and on the basis of which ventilation mode is appropriate. These operating settings are as per those summarised in Table 1.

[0075] Intensity of microwave energy and air velocity are similarly set with reference to the type of food product and hydroscopic state of the food product

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PCT/AU2015/050377 and are varied in each zone 14 to accommodate the diminishing moisture content of the food product as it progresses through sequential treatment phases and zones 14 of the kiln 16.

[0076] Microwave intensity within the first zone 14 is set to deliver high and differential microwave emissions to the food product since the food product in this primary phase of treatment generally has moisture content of up to about 90% available water, though this can be reduced to about 70% by pre-processing, which typically includes desiccation. The food produce is thus able to withstand more aggressive microwave treatment during this primary stage of processing without diminishing the final food product. Relatively aggressive microwave treatment in the primary treatment phase is important to diminish or substantially eliminate microbial activity, as has been described above. Similarly, the food product is also able to withstand higher velocity of airflow, typically between about 4.0 to 2.0 m/sec (as long as microwave emissions are simultaneously applied), which is advantageous in the primary phase of dehydration, to remove a significant quantity of available water in the food product.

[0077] The food produce is progressed through the kiln tunnel 16 by the conveyor assembly 18 and into zones 14 representing an intermediate phase of dehydration treatment. In the embodiment of the apparatus 10 described above, the intermediate treatment phase is undertaken in the second and third zones 14b, 14c. In the intermediate treatment phase, both microwave intensity and air velocity is diminished relative to that applied in the first zone 14a as the percentage of available water in the food produce is reduced. Air velocity ranges from about 3.0 to 1.5m/sec in the second zone 14b and from about 2.0 to 1.0 m/sec in the third zone 14c when microwave energy is simultaneously applied. Microwave intensity in the intermediate treatment phase is delivered to the zones 14b, 14c at medium intensity.

[0078] A final treatment phase is undertaken in the terminal zone of the kiln tunnel 16, which in the embodiment described, is the fourth zone 14d. Since available water in the food product by this stage has been reduced to about 15WO 2017/004652

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5%, air velocity and microwave intensity can again be reduced. Microwaves are delivered intermittently and at low intensity to avoid thermal runaway effect and associated diminishing effect this can have on the food product. Air flow velocity is reduced to between about 1.0 to 0.5m/sec, again to avoid diminishing effect on the food product and also to avoid the now substantially lighter food product from being blown backwards in the kiln tunnel 16. The food product is optionally subjected to agitation by agitation mechanism to increase exposure of the food product to the low velocity circulating air and finish the dehydration process.

[0079] Operational parameters of the final treatment phase are set to ensure that the resulting food product exiting the kiln tunnel 16 via outlet conveyor 32 has the desired qualities for the intended use of the food product. Typically, the end food product will have moisture content of below about 12-13% in order to avoid spoilage. If the resulting food product is to have moisture content above this, some pre-processing is required, such as addition of preserving agents. For example, ‘chunked’ food product desirably has moisture content of around 2030%. In this case, the food produce must be appropriately contacted and/or infused with suitable preserving agent in pre-processing, prior to the food produce being introduced into the kiln tunnel 16 of the apparatus. This higher moisture content allows faster rehydration of the food product.

[0080] If the food product is intended for further processing such as grinding or powdering, it is more desirable that it has moisture content of about 7% or lower on exiting the final treatment phase and kiln tunnel 16. Table 4 provides a summary of operational parameters of the apparatus 10 during each treatment phase of the dehydration sequence.

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Operating Parameters	Primary Treatment Phase	Intermediate Treatment Phase	Final Treatment Phase
Zone	Zone 1	Zones 2 & 3	Zone 4
Microwave intensity	High and differential microwaves	Medium and diminishing microwaves	Low and intermittent microwaves
Air Exposure Rate	4.0 - 2.0 m/sec High velocity and turbulent	3.0 -1.0 m/sec Medium velocity	1.0 - 0.5 m/sec low velocity
Wet bulb depression	Deep depression	Severe depression	Extreme depression
Inherent Water State	Surface water	Internal water	Bound water
Moisture Content (Available water)	90 - 60%	55 - 20%	15 - 5%
Dielectric Loss Factor (Er)	~ 13.0-9.0	~ 5.0-3.0	~ 1.0-0.5
Conveyor Mesh	Coarse chain gauge	Chain mail mesh	Fine gauge and agitating mechanism activated

Table 4: Operating parameters during dehydration process [0081] During progression of the food product through the zones 14 and the respective dehydration treatment phases, sensors 68 in the zones 14 and/or air duct 20 provide feedback communication regarding temperature, air velocity, microwave intensity, air humidity, conveyor progression and/or conveyor speed to the CPU. This information is processed by the CPU and used to in turn vary operating parameters in one or more of the zones 14 by communicating and varying one or more of air circulation, heating, microwave emission intensity and/or conveyor speed to maintain a drying profile/atmosphere in each zone 14 that is appropriate for both the type of food product being treated and to achieve the desired qualities in the resulting dehydrated food product.

[0082] Dehydrated food product, having completed all treatment phases and passed through each of the zones 14 in the kiln tunnel 16, exits the apparatus 10 via outlet conveyor 32, whereupon the dehydrated food product can be appropriately packaged or undergo other suitable processing such as milling or combining with other products, for sale or transport.

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Claims

CLAIMS:

1. A dehydration apparatus for dehydrating a food product including: a kiln having two or more zones;

conveyor means for conveying food produce through the kiln and sequentially through the two or more zones;

a circulation means for circulating warm and dehumidified air through the kiln; and a microwave emission source, wherein food produce conveyed through the kiln is simultaneously exposed to microwave emissions and flow of warm, dehumidified air to dehydrate the food produce, and whereby one or more of temperature, air velocity and/or microwave energy are variable between the two or more zones to create variable drying profiles and/or atmosphere within each zone.
2. A dehydration apparatus according to claim 1, wherein the kiln is a continuous kiln.
3. A dehydration apparatus according to claim 1 or 2, wherein the kiln has three or more zones.
4. A dehydration apparatus according to any one of claims 1 to 3, wherein temperature, air velocity, microwave energy intensity and/or dwell time in each zone are determined at least in part with reference to hydroscopic state of the food produce.
5. A dehydration apparatus according to any one of the preceding claims, wherein temperature, air velocity, microwave energy intensity and/or dwell time in each zone are determined at least in part with reference to the type of food produce being conveyed through the kiln and/or intended qualities of the resulting food product following dehydration.

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6. A dehydration apparatus according to any one of the preceding claims, wherein the kiln includes a kiln tunnel through which food produce is conveyed by the conveyor means.
7. A dehydration apparatus according to any one of the preceding claims, wherein the conveyor means includes a plurality of conveyor segments.
8. A dehydration apparatus according to claim 7, wherein each conveyor segment is positioned in an overlapping arrangement whereby an end of a first conveyor segment is positioned above an adjacent end of an adjacent conveyor segment to define a vertical drop through which food produce can fall.
9. A dehydration apparatus according to any one of the preceding claims, wherein microwave emission source includes one or more microwave emitter horns, microwave applicators and/or magnetrons.
10. A dehydration apparatus according to claim 9, wherein the apparatus further includes microwave reflection means for each microwave emitter horn/applicator.
11. A dehydration apparatus according to any one of the preceding claims, wherein microwave emissions are channelled from each microwave emission source to each zone by a waveguide conduit.
12. A dehydration apparatus according to any one of the preceding claims, wherein the circulation means includes an air duct and circulation fan located within the air duct and whereby air is drawn into the air duct by the circulation fan.
13. A dehydration apparatus according to any one of the preceding claims, wherein the apparatus further includes plenum ducting having individual ducts corresponding to and in communication with each zone.
14. A dehydration apparatus according to claim 13, wherein each individual duct of the plenum ducting has an independent variable inlet and whereby each

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PCT/AU2015/050377 independent variable inlet is adjustable between an open and closed position to vary air flow into each zone.
15. A dehydration apparatus according to claim 13 or 14, wherein flow and velocity of air into the kiln is controlled by the circulation means operating in conjunction with the plenum ducting and independent variable inlets.
16. A dehydration apparatus according to any one of the preceding claims, wherein the circulation means further includes a variable inlet which is adjustable between an open and closed position to modify flow path of air between a single pass ventilation mode and a recycled air ventilation mode.
17. A dehydration apparatus according to claim 16, wherein the variable inlet is in an open position when the apparatus is operating in the recycled air ventilation mode, whereby air exhausted from the kiln is conveyed through the air duct and subsequently returned into the kiln.
18. A dehydration apparatus according to claim 16, wherein the variable inlet is in a closed position when the apparatus is operating in single pass ventilation mode, whereby air exhausted from the kiln is exhausted from the apparatus by exhaust pipe.
19. A dehydration apparatus according to any one of the preceding claims, further including heater means arranged to warm the air conveyed into each zone of the kiln.
20. A dehydration apparatus according to claim 19, wherein the heating means includes one or more of heat exchanger and/or heat coil.
21. A dehydration apparatus according to any one of the preceding claims, further including one or more sensors to monitor one or more operating parameters of temperature, air velocity, air humidity, microwave intensity, conveyor progression or conveyor speed, whereby the one or more sensors

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PCT/AU2015/050377 operate in a feedback loop with a control unit to modify operating parameters within each zone during operation of the apparatus.
22. A dehydration apparatus according to any one of the preceding claims, further including refrigeration means, whereby refrigeration means cools air exhausted from the kiln to form a condensate.
23. A dehydration apparatus according to claim 22, wherein the condensate includes extract from the food produce undergoing dehydration in the kiln.
24. A dehydration apparatus according to any one of the preceding claims, further including an oxygen purging module, whereby the oxygen purging mode is arranged to strip oxygen from air introduced into the kiln, thereby reducing oxygen content within the kiln.
25. A dehydration apparatus according to claim 24, wherein the oxygen purging module is a gas splitter module which operates to strip oxygen from air introduced into the kiln and simultaneously introduce inert gas.
26. A dehydration apparatus according to claim 25, wherein the inert gas is nitrogen gas.
27. A process for dehydrating food produce, the process including: introducing a portion of food produce into a kiln tunnel, the kiln tunnel being arranged to receive microwave emissions from at least one microwave emission source;

dehumidifying and heating air and circulating the dehumidified heated air through the kiln tunnel;

whereby food produce is progressively conveyed through two or more zones of the kiln tunnel, simultaneously exposing the food produce to microwave emissions and flow of dehumidified warm air and whereby one or more of temperature, air velocity and/or microwave energy are varied between the two or more zones to create variable drying profiles and/or atmosphere within each zone.

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28. A process according to claim 27, wherein intensity of microwave emissions is diminished as the food produce is progressively conveyed through the two or more zones.
29. A process according to claim 27 or 28, wherein air velocity is reduced as the food produce is progressively conveyed through the two or more zones.
30. A process according to any one of claims 27 to 29, wherein one or more of temperature, air velocity and/or microwave energy are determined at least in part with reference to hydroscopic state of the food produce as it is conveyed through the kiln tunnel.
31. A process according to any one of claims 27 to 30, wherein air exhausted from the kiln tunnel following contact with the food produce is cooled to form a condensate.
32. A process according to any one of claims 27 to 31, wherein operating temperature within the kiln tunnel is varied with reference to the type of food produce being processed.
33. A process according to claim 32, wherein operating temperature is 65°C or less when the food produce has a high protein content.
34. A process according to claim 32, wherein operating temperature is between about 65°C and 80°C when the food produce has low protein content.
35. A process according to any one of claims 32 to 34, wherein operating temperature in the kiln tunnel is varied by operation of heater means in conjunction with adjustment of microwave emission intensity.
36. A process according to any one of claims 27 to 32, wherein air exhausted from the kiln tunnel is recycled back into the kiln tunnel.

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37. A process according to any one of claims 27 to 32, wherein air exhausted from the kiln tunnel is vented via an exhaust pipe.
38. A process according to claim 37, wherein heat is recovered from air exhausted from the kiln tunnel by a heat exchanger and the heat is used in maintaining operating temperature in the kiln tunnel.

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