WO2007039284A1

WO2007039284A1 - Processing frozen compositions

Info

Publication number: WO2007039284A1
Application number: PCT/EP2006/009591
Authority: WO
Inventors: Pieter Jozef Luypaert; Carlo Groffils; Johan De Schepper
Original assignee: Meac Nv
Priority date: 2005-10-04
Filing date: 2006-10-04
Publication date: 2007-04-12

Abstract

An industrial method for tempering or softening frozen organic materials, such as foodstuffs, in such a way that the temperature difference in the product due to handling, size or/and skin effect and microwave absorption is neutralised by initial application of a non polar non ionic cooling followed continuous microwave radiation. In order to keep the product penetration high for thick products, the surface of the organic material is frozen/cooled with non polar non ionic cooling media before the application of the microwave radiation. No cooling is applied during the microwave heating. The temperature at the surface goes down to up to -40°C and more to prevent not only local thawing, also to allow self correcting control of the heating rate. Microwave heating reduces the process time, energy needs and leads to quality improvements.

Description

PROCESSING FROZEN COMPOSITIONS

FIELD OF INVENTION

The present invention is broadly concerned with a new in line method of tempering frozen materials comprising the use of microwaves and non-polar or polar and/or non- ionic cooling composition such as a non-polar non-ionic snow, for instance a CO₂ snow, or liquid N₂ to put a body of a frozen composition, for instance a frozen aqueous composition, such as a frozen plant or animal tissue, in the optimum condition for processing (e.g. subdividing, for instance by cutting or slicing). This improved tempering method is particularly useful for tempering before cutting and processing and before slicing frozen organic materials like foodstuffs, such as frozen meat.

BACKGROUND OF THE INVENTION

A range of important raw materials are deep-frozen in order to preserve their quality during transportation and storage. They cannot be cut or sliced as such and have to be tempered first. Meat and fish are important examples and are widely used in the food processing. Factories have problems softening or tempering large bodies or blocks of frozen organic material, such as frozen aqueous compositions, prior to further processing. Various procedures are adopted, the most common being to place the blocks or bodies of the frozen organic in tempering rooms, where they may reside for several days while attaining the desired temperature. In order to accelerate the process, media such as warm air, steam or water have been used. Unfortunately, steps that speed up thawing rates tend to degrade the product, cause product loss and can induce a microbiological hazard. If the surface thaws too soon, then the outer layers may deteriorate before the bulk has thawed.

There currently is a need for fast and continuous methods, which does not induce deterioration, for homogenous tempering of blocks or bodies of frozen organic materials such as frozen foodstuff and other perishable goods to reach the - often varying in function of the type of processing - optimum condition for improved processing. The current techniques do not provide a technical and controlled solution for all these requirements. US Patent application US 2003-183623 discloses a technique of tempering which is fast but can't neutralise temperature differences leading to unequally tempered foodstuff due to the handling. This causes losses in the further processing. It involves a microwave oven with conveyor incorporating a shielding system mounted within an oven cavity of the microwave oven. The shielding system is provided to prevent selected portions of a food travelling through the microwave oven from overheating relative to the remainder other pieces of food items in the system. This document discloses a method that is particularly adapted for use in connection with the tempering, cooking or thawing of parallelepiped or rectangular-shaped food items and includes a frame structure fixedly mounted within and traversing substantially the entire length of the oven cavity, with the frame structure having a generally rectangular cross-section defined by both microwave impermeable portions and microwave transmissive portions on each side.

Rapid and controlled tempering could dramatically reduce the amount off drip loss that occurs during subsequent processing. Hence, the costs of microwave tempering are justified in terms of the yield savings made. This technique is fast but the foodstuff has to be in a conditioned room before entering the microwave oven.

In general the expected speed of a microwave approach is appreciated but leads to product quality decreases as the outer layer of the thick and irregular pieces of organic material tends to warm up too fast.

A need exists for a controlled and continuously processing microwave method, which has a considerable penetration depth into frozen organic material. In theory, by overcoming the heat transfer problem, operations taking 24 hours or more could be reduced to a few minutes. A major difficulty prevents the straightforward use of microwaves in this application. The problem is that water absorbs power much more rapidly than ice, on account of the relative dielectric properties. As soon as water is formed in any part of the product, then gross differential heating is initiated: the water absorbs energy rapidly and heats up to boiling point, while large parts of the block are still frozen. Thus the tempering in abovementioned way is not optimal for processing and causes losses too. In general, surface regions will thaw first, absorb an even increasing proportion of the available power and prevent effective power from reaching central regions.

So any operation involving complete thawing has yielded problems. There is a need for microwave tempering, i.e. increasing the products temperature from the deep frozen state (say -15 °C to -30 °C) to a 'processable and/or cuttable' state (say -2 ⁰C to -8 °C) measured at all sides of product block. For slicing other temperatures apply depending on the type of frozen food that needs to be sliced. However the problem is to avoid any water formation so that the "thermal runaway" described above cannot occur and successful tempering is possible.

Various attempts have been made to solve this problem. GB 1 212 365 discloses an inert gas coolant in combination simultaneously with microwave heating. US 3 536 129 discloses subfreezing gases and liquids in combination with microwave energy.

WO 82/00403 proposes a stream of coolant air in combination with microwave energy.

All these methods propose a combination of a coolant, used simultaneously with microwave energy. The purpose of this combination is to try and increase the penetration depth by constantly and continuously cooling the outside and so to heat the middle. However, combining coolant and microwave heating has certain problems. By doing so, the outer surface layer of the object is kept at temperatures just below 0°C in order to avoid water formation. At O⁰C, the penetration depth is about 1 cm while in many cases the smallest dimension of the object is 10 cm and more. This means that the energy due to the low penetration depth has a difficulty to reach the inside of the object to thereby raise the temperature. It is possible to burn layers below the cooled outer layer or, at least to still not achieve a uniform temperature after the heating step. Also monitoring the process is not easy. Providing cooling in a microwave oven increases the complexity of the system.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and apparatus for tempering frozen materials using microwaves and non-polar or polar and/or non-ionic cooling composition such as a non-polar non-ionic snow, for instance a CO₂ snow, or liquid N₂. An advantage of some of the embodiments of the present invention is that it puts a body of a frozen composition, for instance a frozen aqueous composition, such as a frozen plant or animal tissue, in an optimum condition for processing (e.g. subdividing, for instance by cutting or slicing) and hence can solve a problem exhibited by prior art methods and equipment.

It is an embodiment of present invention that the object to be thawed out is cooled on the outside with a non-polar or polar and/or non-ionic cooling composition before the microwave radiation step. During the initial cooling step, the temperature at the surface goes down to a temperature lower than the inside or middle temperature of the object to be tempered, e.g. down to at least 1O⁰C below the temperature in the middle of the object. The object may be cooled by any suitable method, e.g. dipped, sprayed or coated in a cooling medium. Shock freezing may be used. For example, a temperature of -4O⁰C may be achieved on the outside of the object to prevent not only local thawing, but also to control the heating rate during the microwaving step. Cooling the outside with respect to the inside before the microwave application step keeps the microwave penetration depth high initially until the middle portion of the object is heated up after which the outer layer is heated resulting in a final relatively controlled uniform temperature throughout. It is not necessary to apply coolant during the microwave step, in fact it is preferred if there is no application of coolant during the application of microwave energy. Due to the fact that no coolant is applied the microwave oven can be operated in a continuous manner, e.g. the object to be thawed can be conveyed through the oven continuously, e.g. on a conveyor belt. The microwave oven can be operated at room temperature, e.g. between 10 and 35°C.

The microwave tempering can be used to increase the product's temperature from the deep frozen state (say -15 ⁰C to -30 ⁰C) to a 'cuttable or processable' state (say -2 ⁰C to -8 ⁰C). For slicing or other processing steps, other temperatures may apply (ranging from - 18 ⁰C to 0 ⁰C).

This non-polar or polar and/or non-ionic cooling composition preferably has a temperature below -2O⁰C, more preferably below -25°C, yet more preferably below - 30⁰C and most preferably below -35°C. The non-polar or polar and/or non-ionic cooling composition can be in the form of a fluid, e.g. gas or liquid, or a solid. If the non-polar or polar and/or non-ionic cooling composition is a solid it can be for instance be in the form of a snow, small granules such as micro-granules, or small particles such as micro-particles to cover the frozen organic material to be micro- waved. If the non-polar or polar and/or non-ionic cooling composition is a liquid it can be applied as a mist or droplets to cover the frozen organic material to be micro-waved or can be bulk liquid. The non-polar or polar and/or non-ionic cooling composition can be supplied to the bodies or blocks of frozen organic composition to be tempered in such an amount and/or during such a time that the surface temperature of the frozen organic material to be tempered stays optimal (e.g. under -3°C) during the subsequent microwaving step to obtain a optimal quality of the outer layer and also the bulk of the object.

A sensor may be used at the surface of the bodies or blocks of the frozen organic material to control the supply of the non-polar or polar and/or non-ionic cooling composition. The sensor can be a contact (e.g. thermometer, thermoresistor) or non- contact sensor, e.g. an infra-red sensor. The output of the sensor may be used to determine when the needed cooling of the outside of the object has been obtained. A sensor may be used at the surface of the bodies or blocks of the frozen organic material to control the microwave power applied or when the microwave heating step is to be terminated. The sensor can be a contact or non-contact sensor, e.g. an infra-red sensor.

An embodiment of present includes directly covering the bodies or blocks of frozen organic materials by the non-polar or polar and/or non-ionic cooling composition before, e.g. just before, the microwave treatment.

Another embodiment of present includes covering the bodies or blocks of frozen organic materials packed in a packing material suitable for microwave treatment by the non-polar or polar and/or non-ionic cooling composition before, e.g. just before the microwave treatment.

An advantage of present invention is that controlled tempering of thick (e.g. in the range 1 to 30 cm, preferably 1 to 20 cm and most preferably 10 to 15 cm) and non- conditioned boxed meat is obtainable in a very short time, for instance, less than 20 min. or even less than 10 min., e.g. going from bulk temperature of - 18 °C to -3 °C. Large scale equipment suitable for the method of present invention is commercially available (e.g. MEAC Oven TYPE MEACHEAT32) which produces microwave (MW) pasteurized food with sixteen 1.8 kW units or a total of 28.8 kW microwave power output at 2450 MHz. Typical throughputs are 1200 kg/hour, or more, depending on the temperature range to be covered and the product type/sizes.

An advantage of the rapid tempering regime according to the present invention is the dramatic reduction of drip loss that can occur during subsequent processing. The costs of microwave tempering are often justified in terms of time and throughput compared to classical methods as well as controlling better the sanitary conditions of these phases in the process. The method of present invention overcomes at least one of the the problems described above with prior art methods and achieves the requirement of rapid tempering linked with dramatic reduction of drip loss.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the propagation of a plane wave in a lossy medium. It shows the essential features of such propagation. The wave is attenuated as it traverses the medium and therefore the power dissipated, which is a function of E², reduces to an even larger extent.

Figure 2 demonstrates the penetration as a function of the temperature for various frequencies

Figure 3 demonstrates the dielectric properties data for various foodstuffs

Figure 4 demonstrates the temperature dependency of the dielectric constant

Figure 5 shows a schematic illustration of temperature behaviour throughout the beef during operation ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

The treatment process and apparatus of the present invention is applicable to many types of frozen organic materials. The present invention is in particular applicable to many types of foodstuffs, bodies of tissues or food mass or bodies comprising tissue pieces with or without a binder, in selected shapes. It may be applied to larger cuts of meat or cubed or sliced meats, but also comminute foodstuffs such as ground meats are suited for the method of present invention. Furthermore, the invention is applicable to vegetable and fruit material. These and other objects, advantages, and features of the invention will be apparent from the following description of the preferred embodiments, considered along with the accompanying drawings.

Theoretical background

Tempering or softening of foodstuff frozen foodstuff/tissues/meat is on the one hand based on propagation and penetration of microwave energy. On the other hand energy is transferred into heat according to thermodynamic laws.

However, for several products, the skin effect is limited by the thickness or irregularity of the products to be tempered. The present invention overcomes this problem by the use of none polar snow which allow the microwaves to pass and prevents the outer (skin) layer from heating up too fast.

Propagation factor and penetration depth

Many problems in microwave engineering involve the use of Maxwell's equations through which one can derive the following wave equations of the electromagnetic field (E electric field and H magnetic field) in the z direction (von Hippel, 1954): b*E _ _t , d²E dz^{2 " e}°^{ε μ}°^μ J?

and 3²// B²H _dzf = _fo e'^^» —

where ε is the dielectric constant and μ the permeability. The solution to be considered here is that of a plane wave, which for the electric field E attains the form

(equation 1)

This is a periodic field travelling in the z direction with a complex propagating factor γ, given by

(equation 2) where ω is the circle frequency α is the attenuation factor and β is the phase factor. Figure 1 shows the essential features of such propagation. The wave is attenuated as it traverses the medium and therefore the power dissipated, which is a function of E¹, reduces to an even larger extent.

To derive an expression for the attenuation of the incident power, we equate the real and imaginary part of equation 2, yielding after solving for α and β and assuming μ * = μ ^'

(equation 3) and

β [(I + (eyeγ)^»2 + I] ¹'² rad/m

The expression for the attenuation factor can be simplified as follows: (a) For a highly lossy medium, where (e_eff / € ) > 1 , equation 3 reduces to

(equation 4) which is the case for conducting materials, since from equation

^~^j [(I + (fe'φΥY'² - 1] ⁱⁿ Np/m with e^"= 0 , σ = ωε_Qε_e ^" _ff . Therefore equation 4 yields α = l/δ_s where δ_s is the skin depth.

(b) For a low loss medium, where [e_eff / e ) < 1 , equation 3 after substitution of TD = 2 πf- 2 πc / λ _o reduces to

where λ ₀ is the free space wavelength and the free space velocity c has been equated to

Substitution of equation 2 into equation 1 yields p ~ p - az j (ωt - βz)

'mαx

The first exponential term gives the attenuation of the electric field and therefore the dissipated power follows the form

P <^χ _e-^{20ι z}

The penetration depth is defined as the distance from the surface of the material at which the power drops to ε^"1 from its value at the surface, that is

_1_

D_p = —

^{2 a} (equation 5) Substitution of equation 3 into equation 5 yields the general expression for the penetration depth

(equation 6) In terms of the free space wavelength equation 6 reduces with μ ' = 1 to

- 1/2

(equation 7)

For low loss dielectrics [e_eff / e ) < 1 and the penetration depth approximates to

A₀ (^β ) 2 πe_e ^κ/ _f '_f (equation 8)

Equations 7 and 8 shows that the power of the penetration depth increases with larger wavelengths or in other words with decreasing frequencies. In general the penetration depths at frequencies below 100 MHz are of the order of metres and presents little problem as far as power penetration unless the loss factors are exceedingly high. At frequencies near the microwave heating regime the penetration depths are correspondingly smaller and often the size of the material to be treated, particularly when it is very wet, is many times larger than Dp and microwave heating could result in unacceptable non-uniformities in the temperature distribution. Ohlsson et al. (1974) have calculated the variation of the penetration depths of foodstuffs with temperature near the three industrially allocated frequency bands. Their results are shown in figure 2. The general trends, as could be expected, are that we see higher penetration depths at lower temperatures and frequencies, since we have seen the effective losses for ice are much less than those for liquid water. For raw (frozen) beef, depths of penetration of about 150 mm at sub-zero temperatures reduce to about 20 mm at room temperature, whereas in gravy the penetration depths are correspondingly smaller since the effective losses are primarily conductive and larger.

Perhaps, surprisingly, gravy would be more uniformly heated to temperatures above 40 ⁰C at 2,45 GHz than at the other two lower g-frequencies. In contrast, in pure water the penetration depths increase with increasing temperatures highlighting the differences in the dielectric properties of foodstuffs with large salt content. More depth of penetration data have been published by Bengtsson and Risman (1971) on a variety of foodstuffs at 2,8 GHz and in cod various temperatures from -20 °C to +60 °C at 2.45 GHz, as shown in figure 3. It transpires that there could be limitations in the treatment of lossy dielectrics if the dimensions are comparable with, or exceed, the penetration depth. Web materials on the other hand do not usually suffer from such limitations, as their thickness is small.

Figure 4 shows the dielectric constant temperature dependency of various foodstuffs.

Specific heat

The internal energy of a system U in terms of its pressure p, volume V and external heat supplied to it is given in differential form by (Tabor, 1969)

dU = dQ_h -pd V

(equation 9) Moreover, the system enthalpy is given by

H_h = U + ^pV (equation 10)

Differentiating equation 10 and using equation 9 yields

^{dHh = dQh + Vdp} (equation 11)

The specific heat of a material in SI units, c, is the amount of heat required to raise a Kg by 1 °C. We can observe two definitions of specific heat, which follow from the above equation. First, differentiating equation 9 with respect to temperature at constant volume gives

which defines the specific heat at constant volume. Also, differentiating equation 11 with respect t temperature T at constant pressure gives

( SH_h \ dQ_h ^V '" (equation 12) which defines the specific heat at constant pressure. In gases there is a significant difference between C_p and C_v which does not apply to liquids and solids. In fact, in the latter, the difference is extremely small and can be neglected. Furthermore, the specific heat of most materials can be taken as constant with temperature down to well below the freezing point and starts to decrease at significantly lower temperatures. Measurements of the specific heat in solids are normally made at constant pressure. Table 1 shows the values of C_p for some common industrial materials.

Table 1 Specific heat of some common industrial materials

Specific heat c_B

Material Cal/(g°C) kJ/(kg°C)

Acetone 0 51 2 13

Alcoholethyl 0 55 2 31

Asbestos 0 2 0 84

Asphalt 04 1 67

Bakehte 0 3-04 1 26 -1 67

Beeswax 0 82 3 43

Brick common 0 22 0 92 hard 0 24 1 0 Cellulose 0 32 1 34 Charcoal, wood 0 24 IO Clay 0 23 096

Coal anthracite 03 1 26 Coal bituminous 0 33 1 38 Coal tar oils 0 34 1 42 Coke 027 1 13

Concrete (stone) 0 17 0 71 Cork board 045 1 88 granulated rolled 049 2 05 Earth (dry) 03 1 26 Fibre board (light) 0 6 2 51 Fibre hard board O S 209 Glass crown 0 16-0 2 0 67-0 84 flint 0 12 0 5 pyrex 0 2 0 84 silicate 0 19 0 79 wool 0 J6 0 67

Graphite powder 0 16 0 67 Gypsum board 0 26 1 O9 Ice (0°C) 049 2 05 India rubber 0 48 2 0 Leather (dry) 0 36 1 5 Limestone 0 22 092

Specific heat c_D

Material Cal/(g °O w/0cR°α

Marble 0-21 0-88

Mica 0-11 0-46

Mineral wool blanket 0-2 0-84

Oils caster 0-44 1 -84 olive 0-47 1-97

Paper 0-33 1 -38

Paraffin wax 0-7 2-89

Plaster light 0-24 1 -0 sand 0-22 0-92

Porcelain 0-22 0-92

Plastics foamed 0-3 1 -25 solid 0-4 1-67

Sand 0 19 0-79

Sandstone 0-22 0-92

Sawdust 0-21 0-88

Silica aerogel 0-2 0-84

Sodium chloride brine + 10 part H₂O 0-8 3-34

+ 200 part H₂O 0-98 4-00

Turpentine 0-411 1 -72

Water 1 00 4-18

Wood fir 0-65 2-12 oak 0-5 2 09

Pine 0-67 2-8

Wool felt 0-33 1 -38 loose 0-3 1-26

Rate of rise of temperature

As the microwave energy is absorbed in the material its temperature increases at a rate depending upon a number of distinct parameters. The power required to raise the temperature of a mass M_a kg of material from T₀ °C to T °C in t seconds is given by extending equation 12.

(equation 13)

Substituting P using equation ^P°^{υ ωe}° ^{eeff Brms V} , equation 13 yields

where p is the density of the material in kg/m³ and the specific heat is given in J/kg °C. For a given material heated by high frequency energy at a given/ the rate of rise of T depends on (e_eff" erms²), which is usually a function of the temperature (due to the variation of e_eff" with T).

Microwave tempering

In accordance with an embodiment of the present invention use is made of the change of penetration depth with temperature and the change of absorption of microwave energy with temperature. For frozen organic materials which contain water the penetration depth increases rapidly below freezing point of water O⁰C, e.g. particularly below -20°C. This means that when the outside or frozen organic material is cooled to temperatures below -20°C, the penetration depth is high and the centre of the material will be heated by microwave energy. During the microwave heating step no additional coolant need be added. The microwave oven can be at room temperature, e.g. between 10°C and 35⁰C. The initial temperature and depth of the freezing before microwaving is selected and cooling applied so that on application of the microwave the inner parts start to heat up first. This will reduce the penetration depth which means that parts closer to the outside will begin to be heated up. However, this will lower the penetration depth even more meaning that only an outer layer is heated up. It can be seen that the use of microwave energy, e.g. without adding additional coolant has a self-limiting effect. This is shown schematically in Fig. 5.

Three parameters are set in accordance will an embodiment of the present invention:

1. Degree of lowering of the initial temperature of an outside region of the frozen organic material, e.g. achieved by setting the duration time of initial cooling, e.g. (partial) dipping, (partial) spraying, (partial) coating, or layer thickness of snow or frozen particles and the temperature of the cooling medium.

2. Density of the microwave energy

3. Duration of application of the microwave energy

The above parameters may also depend upon the shape and orientation of the frozen organic material. For example, the frozen organic material can be in a block, in slices, conglomerations of particulate products, e.g. peas.

The present invention also includes a method and apparatus for tempering or softening bodies of a frozen organic material, wherein the bodies are cooled by a non-polar or polar and/or non-ionic cooling material before being subjected to a microwave radiation until an optimal temperature has been reached to further process the organic material. No additional coolant need be added during the microwave step. The cooling material can be a non-polar or polar and/or non-ionic snow. The cooling material can be CO₂, e.g. in the form of dry ice or snow. The cooling liquid can be a snow comprising N₂. The cooling material can be a snow comprising Argon. The cooling material can be a non-polar or polar and/or non-ionic granulate material. The granulate material can be CO₂ N_2, or Argon. The cooling material can be a non-polar or polar and/or non-ionic particulate material. Examples of the particulate material are CO₂, N₂, or Argon. The cooling material can be mist of a non-polar or polar and/or non-ionic particulate liquid. A mist of liquid N₂ or Argon can be used.

Preferably, the cooling material has a temperature of less than -20°C, less than -25°C, less than -30°C, less than -40°C.

The frozen organic material to be tempered can be selected from the group comprising aqueous organic material, foodstuff, tissue, bodies comprising tissue pieces with or without a binder, cuts of meat or cubed meats, foodstuffs, vegetable material and fruit material, for example.

If the organic material has large difference in dielectric absorbing properties and/or heat capacity, differences in local initial degree of cooling may used to even these out.

If the organic material has large difference in dielectric absorbing properties and/or heat capacity, interrupting the microwave energy for periods of time can be used to allow conduction to even out temperature differences.

The microwave radiation can be submitted to one side of the organic material, or two sides or three sides or four sides or five sides, or six sides. The microwave radiation and the initial application of cooling material to the frozen organic material to be tempered is linked in such way that the temperature difference in the product due to handling, size or/and skin effect is neutralised and controlled.

The organic material may be turned over or turned around or rotated or dipped and sprayed completely or partially during the cooling before the microwave processing. The organic material may be turned over or turned around or rotated microwave step.

The above method allows control of the operation because a non-contact, e.g. infra-red sensor or a contact sensor measuring the temperature of the outside can signal when this outside temperature has reached the desired temperature for the subsequent application, e.g. cutting, slicing, sawing, mincing, etc. As no additional coolant is added during the microwave step, the outside of the organic material is freely available for temperature measurement.

Microwave tempering ensures consistently controlled temperatures throughout the block of product. This improved temperature uniformity eliminates most drip loss and therefore will enhance flavour, aroma and juiciness of the finished product.

Because drip loss is virtually eliminated, an operation can expect up to a 6 or more % increase in finished yield.

Precise temperature control will assure consistency of particle size in all ground meat products. This enables a high degree of quality control concerning visual uniformity and consistency of bite.

Atempering system according to the present invention requires relatively little floor space. This will afford a maximum level of throughput at a minimal allocation of valuable production space. In addition, the MEAC Heat 32 series is expandable. This will allow an immediate increase in throughput at a fraction of the cost for new construction. What's more, for overhead transmitter installations the expansion will require no more floor space. An examples of an apparatus according to an embodiment of the present invention comprises a cooling device or station along side a microwave oven. The organic material is first cooled using a controlled cooling device such as a CO₂ dosing machine and N₂ liquid bath. Once the outer temperature has reached the level required as explained above, i.e. lower than the middle temperature of the organic material, the organic material is placed in a microwave oven and heated, e.g. without addition of coolant.

Product handling is kept to a minimum. Each box or block is handled only once and in-line process design can be configured to reduce the tempering labour costs to the bare minimum.

Because microwave tempering takes only minutes, as compared to days for conventional tempering along the lines of best available technology, there is operational flexibility to instantaneously change production plans. In addition, the three day tempering requirement can be eliminated thereby reducing the in process inventory requirement to one day. This reduction in inventory frees valuable funds for other uses.

Controlled tempering also inhibits bacterial growth. This improves product quality and taste, increases shelf life, and reduce risk.

The elimination of bloody drippings such as water soluble proteins and vitamins on the floor upgrades the quality of the product and processing of the product as well as the overall sanitation in any plant. This contaminant will not be tracked throughout a facility.

Finishing cooked yield of many prepared foods can be improved because controlled microwave tempering does not allow valuable protein to leach from raw product.

The most frequent reason for processing equipment breakdown is improperly tempered meat. If meat is too cold, blades will break, parts will wear, and gears will be stripped. If meat is too warm, product will bind on blades, squeeze into crevices, and create undue stain. The resulting downtime can be dramatically reduced through microwave tempering techniques.

Portion control of the finished product is simplified because controlled tempering precludes overstuffing too warm product or under-filling too cold product. This eliminates product give-away, and reduces the risk of a fine due to short weighting.

Finally, the cleaned and controlled microwave tempering process will prevent the potential confrontation with Government Regulators over crowded and messy work areas, unsanitary handling procedures, blood on the floor, etc. This will save money in cleaning costs, downtime, and non-productive labour expense.

The present invention provides an industrial method for tempering or softening bodies of frozen components such as bodies of frozen tissue/food/meat in such a way that the temperature difference in the product due to handling, size or/and skin effect is neutralised and controlled by applying microwave energy after use of a non-polar or polar and/or non-ionic layer.

In order to keep the product penetration high for thick and bulky products; the surface is frozen/cooled with non-polar or polar and/or non-ionic coolant before the microwave radiation. The temperature at the surface goes down to at least 10⁰C below the bulk temperature, or below the middle temperature, e.g. to a temperature of -40⁰C, to prevent not only local thawing or warming up, but also to control the heating up rate in the microwave step.

Microwave (MW) heating reduces the process time and, energy consumption; additionally the use of MW after application of non-polar or polar and/or non-ionic coolant leads to better quality control of the tempering process. The use of a snow (e.g. CO₂) or cooling liquid (N₂) before application of microwave energy provides optimal control over the temperature profile of the products, leading to mastering of the end temperature that is needed to allow for good processing downstream. An embodiment of the present invention is an industrial tempering method that can be applied for different packing or containers Examples

Example 1: Two boxed beef of 50 by 40 by 15 cm³ are processed in a CO₂ dose- measuring device followed by application of microwave energy, e.g. using a MEACHEAT 32 system, e.g. as known from Patent application PCT/BE03/00214.

One boxed beef is without snow and one boxed beef is with snow. The difference between both methods is extraordinary. Differences at the surface of 18°C are measured between both qualities leading to not processable meat in the one not treated with non-polar snow.

Surface quality of beef treated with non-polar snow and MW tempered is high. The microwave field can be 0 to 30W/cm², preferably 0 to 20W/cm² and most preferably 1 to 2 W/cm² there is no cooking or overheating of the radiation side (Figure 5).

Claims

1. A continuous in line method for tempering or softening bodies of a frozen organic material, wherein a temperature at the surface of said bodies is first cooled by a non-polar or polar and/or non-ionic cooling material down to a temperature lower than the middle temperature of said bodies before being subjected to a continuous microwave radiation to raise the average temperature of the bodies.

2. The method of claim 1 wherein raising the average temperature is until an optimal temperature has been reached to further process the organic material.

3. The method of claim 1 or 2, wherein said temperature at the surface of said bodies is first cooled down to a temperature at least 10°C below said middle temperature of said bodies.

4. The method of any previous claim, wherein no additional cooling material is added during the microwave step.

5. The method of any previous claim, wherein the non-polar or polar and/or non- ionic cooling material is non-polar non-ionic snow.

6. The method of claim 5, wherein the non-polar non-ionic snow comprises CO₂.

7. The method of any of the previous claims, wherein the non-polar or polar and/or non-ionic cooling material is non-polar or polar and/or non-ionic snow N₂.

8. The method of any of the previous claims, wherein the non-polar or polar and/or non-ionic cooling material is non-polar or polar and/or non-ionic snow Argon.

9. The method of any of the claims 1 to 4, wherein the non-polar or polar and/or non-ionic cooling material is a non-polar or polar and/or non-ionic granulate material.

10. The method of claim 9, wherein the non-polar or polar and/or non-ionic granulate material comprising CO₂.

11. The method of claim 9, wherein the non-polar or polar and/or non-ionic granulate material comprises N₂.

12. The method of claim 9, wherein the non-polar or polar and/or non-ionic granulate material comprises Argon.

13. The method of any of the claims 1 to 4, wherein the non-polar or polar and/or non-ionic cooling material is a non-polar or polar and/or non-ionic particulate material.

14. The method of claim 13, wherein the non-polar or polar and/or non-ionic particulate material comprises CO₂.

15. The method of claim 13, wherein the non-polar or polar and/or non-ionic particulate material comprises N₂.

16. The method of claim 13, wherein the non-polar or polar and/or non-ionic particulate material comprises Argon.

17. The method of any of the claims 1 to 4, wherein the non-polar or polar and/or non-ionic cooling material is a mist of a non-polar or polar and/or non-ionic particulate liquid.

18. The method of claiml7, wherein the mist of non-polar or polar and/or non-ionic particulate liquid comprises CO₂.

19. The method of claim 17, wherein the mist of non-polar or polar and/or non-ionic particulate liquid N₂.

20. The method of claim 17, wherein the mist of non-polar or polar and/or non-ionic particulate liquid Argon.

21. The method of any of the claims 1 to 20, wherein the non-polar or polar and/or non-ionic cooling material has a temperature of less than -2O⁰C.

22. The method of ant of the claims 1 to 21, wherein the non-polar or polar and/or non-ionic cooling material has a temperature of less than -25⁰C.

23. The method of any of the claims 1 to 22, wherein the non-polar or polar and/or non-ionic cooling material has a temperature of less than -3O⁰C.

24. The method of any of the claims 1 to 23, wherein the non-polar or polar and/or non-ionic cooling material has a temperature of less than -4O⁰C.

25. The method of any of the claims 1 to 24, wherein the frozen organic material to be tempered is selected of the group consisting of aqueous organic material, foodstuff, tissue, bodies comprising tissue pieces with or without a binder, cuts of meat or cubed meats, comminuted foodstuffs, vegetable material and fruit material.

26. The method of any of the claims 1 or 25, wherein the microwave radiation is submitted to one side.

27. The method of any of the claims 1 or 26, wherein the microwave radiation is submitted to two sides.

28. The method of any of the claims 1 or 27, wherein the microwave radiation is submitted to three sides.

29. The method of any of the claims 1 or 28, wherein the microwave radiation is submitted to four sides.

30. The method of any of the claims 1 or 29, wherein the microwave radiation is submitted to five sides.

31. The method of the any of claims 1 or 30, wherein the microwave radiation is submitted to six sides.

32. The method of any of the claims 1 to 31, wherein the microwave radiation and the non-polar or polar and/or non-ionic cooling material to cover the frozen organic material to be tempered is linked in such way that the temperature difference in the product due to handling, size or/and skin effect is neutralised and controlled.

33. The product prepared by the methods 1 to 32.

34. An apparatus for tempering or softening bodies of a frozen organic material, comprising a cooling unit for dosing the cooling of the bodies with a non-polar or polar and/or non-ionic cooling material, a microwave radiation heating unit and means for transferring the organic material from the cooling unit to the heating unit.

35. The apparatus according to claim 34 wherein the heating unit is operated at between 5 and 35⁰C.