The method of the invention as hereinafter defined relates particularly to the processing of fish, where fluid penetration is associated with processing thereof, particularly for extending the effective shelf life of the fish by providing the fish with good preservative qualities, or for otherwise enhancing required properties or qualities of the fish. A fluid used for penetrating fish is referred to hereinafter as a treatment fluid, which may be a liquid or a gas.

According to the invention there is provided a method of processing fish, which includes the steps of: introducing the fish to be processed into a pressure chamber; inducing a negative pressure in the pressure chamber to a negative pressure level at which moisture containing cells of the fish are ruptured and maintaining this negative pressure for a predetermined time period; and following rupturing of moisture containing cells of the fish, pressurizing the pressure chamber with a treatment fluid to a predetermined pressure level, by displacing the treatment fluid under pressure into the pressure chamber, and maintaining the pressure for a predetermined time period, the pressure level and the time period being such that the fish is penetrated by the treatment fluid.

The method of the invention may include, prior to introducing the fish into the pressure chamber, cleaning the fish, washing the fish and cutting the fish into at least one of loins and steaks. Such cleaning, washing and cutting of the fish particularly are carried out by conventional means, utilizing conventional methods.

The method of the invention may include also introducing the fish into the pressure chamber by stacking units of fish onto one another on a support structure. More particularly, the method may include stacking the units of fish onto one another in layers and positioning a fluid permeable sheet element between adjacent layers.

The negative pressure induced in the pressure chamber may be induced at a level of approximately-1 bar for a period between 10 minutes and 30 minutes.

Still further, the pressure chamber may be pressurized by the treatment fluid to a pressure between 6 bar and 10 bar and the pressure may be maintained for a period between 3 hours and 6 hours. Clearly, the above pressures and time periods will be determined by the characteristics of the fish being processed in relation to the hardness of the fish, the thickness of the units of the fish being processed, and the like.

The method of the invention also may include maintaining the temperature in the pressure chamber during the process at a temperature between 0°C and 3°C.

In relation to fish to be processed and that is provided in a frozen state, the method of the invention may include defrosting the fish prior to introduction into the pressure chamber.

The treatment fluid used within the method of processing fish, in accordance with the invention, may be a treatment gas including carbon monoxide. The treatment gas may include also, in combination with the carbon monoxide, either one or both of nitrogen and carbon dioxide. Typically the treatment gas includes by volume 60% to 80% carbon monoxide, 10% to 30% nitrogen and 5% to 15% carbon dioxide.

The method of the invention also may include, after exposing the fish to pressurized treatment gas for a predetermined time period, extracting the treatment gas from the pressure chamber. The extracted treatment gas may be displaced to a storage chamber, permitting recycling thereof.

After the extraction of the treatment gas from the pressure chamber, the method may include introducing a flavouring agent into the pressure chamber at a sufficient pressure that will provide for penetration of the fish by the flavouring agent. After such penetration of the fish with a flavouring agent, the method of the invention may include displacing the remaining flavouring agent from the pressure chamber.

It will be appreciated in relation to the use of a treatment fluid for treating fish, the treatment fluid as used within the method may include any fluid, being a gas or a liquid, that, through penetration of the flesh of the fish, can enhance the quality of the fish in terms of colour and general freshness appearance and/or the preservative qualities of the fish, or any other desired characteristics or qualities of the fish. It is envisaged in this regard that various different treatment fluids can fulfil different purposes and, as such, it is envisaged also that the fish being processed may be exposed to different treatment fluids, one after the other.

The method of the invention also may include vacuum packing the fish in respect of which the processing has been completed.

The invention extends also to apparatus for use in the processing of fish, which includes a pressure chamber; a treatment fluid storage chamber; fluid displacement means; and an arrangement of connecting pipes and valves which permit, by operation of the fluid displacement means, inducing a negative pressure in the pressure chamber and then pressurizing the pressure chamber by introduction of a treatment fluid from the storage chamber into the pressure chamber, to provide for penetration of the flesh of the fish with the treatment fluid.

The arrangement of connecting pipes and valves may permit also displacement of the treatment fluid back to the storage chamber.

The apparatus of the invention may include also cooling means for maintaining the temperature in the chamber within a predetermined temperature range.

The apparatus also may include a vent arrangement and air displacement means for displacing air through the pressure chamber.

Still further, the apparatus may include a flavouring agent storage chamber and liquid displacement means for displacing flavouring agent from the flavouring agent storage chamber to the pressure chamber and, after penetration of fish being treated with the flavouring agent, displacing the remaining flavouring agent from the pressure chamber back to the flavouring agent storage chamber. In order to facilitate penetration of fish with a flavouring agent, the apparatus may include a support vessel in which fish to be treated can be stacked for the support thereof during the treatment process and which permits charging of a liquid flavouring agent into the vessel to provide for the penetration of the fish being treated by the flavouring agent.

The invention extends also to apparatus that is particularly adapted for use in the method of processing fish, in accordance with the present invention.

It will be understood that the exact configuration of the apparatus is greatly variable while still permitting the implementation of the method of processing fish, in accordance with the present invention. In this regard it will be appreciated in particular that the treatment fluid for pressurising the pressure chamber may be provided from any source and, as such, the apparatus may not include a storage chamber as an actual part thereof. Also, in respect of the storage chamber, when forming part of the apparatus of the invention, the storage chamber may include one or more valve controlled inlet for feeding a required fluid or fluids into the storage chamber.

Further features of a method of processing fish, in accordance with the invention, and apparatus for use in this method, are described hereafter, by way of example, with reference to the accompanying diagrammatic drawings. In the drawings: Figure 1 illustrates schematically in cross-sectional view the configuration of apparatus for use in the method of processing fish, in accordance with the invention; Figure 2 illustrates schematically a mode of stacking units of fish, in accordance with the method of processing fish, in accordance with the invention; and Figure 3 illustrates schematically in cross-sectional end view the apparatus as shown in Figure 1, in relation to the penetration of fish being processed with a flavouring agent, in accordance with the method of processing fish, in accordance with the invention. Referring initially to Figure 1 of the drawings, apparatus for use in the method of processing fish, in accordance with the invention, is designated generally by the reference numeral 10. The apparatus 10 includes generally a pressure chamber 12, a gas storage chamber 14 and a gas displacement pump 16.

The pressure chamber 12 has a scaling hatch 22 which is displaceably securable onto the main container part 24 of the chamber 12, in a configuration in which it permits, through its displacement, introduction of fish to be processed into the container part of the pressure chamber 12.

The gas storage chamber 14 includes a valve controlled inlet 25 which permits any required gas, or any required combination of gases, to be introduced into the chamber 14, for the purpose described hereafter.

The pressure chamber 12 and the gas storage chamber 14 are connected in gas communication with the suction end 18 of the pump 16 via pipes 26, a valve 28 controlling communication with the pressure chamber 12 and a valve 30 controlling communication with the gas storage chamber 14. Pipes 32 similarly connect the two chambers in gas communication with the pressure end 20 of the pump 16, a valve 34 controlling communication with the pressure chamber 12 and a valve 36 controlling communication with the gas storage chamber 14.

The apparatus 10 includes also an air fan 38 which can displace air via a pipe 40 and a valve 42 into the pressure chamber 12, and from the pressure chamber 12, via a valve 44 and a vent pipe 46, to the atmosphere.

In accordance with the method of the invention, the removal of the hatch 22 of the pressure chamber 12 permits washed, cleaned and cut fish to be introduced into the container part 24 of the chamber 12, following which the hatch can again be sealingly applied to the container part 24. The washing, cleaning and cutting of the fish into loins and/or steaks, can be carried out by conventional means, using conventional methods and, therefore, is not described further herein.

Referring to the introduction of the units of fish, be it in the form of loins and/or steaks, or otherwise, as is illustrated in Figure 2 of the drawings, it is envisaged that the units of fish 50 will be stacked on one another on a support tray 52, the units of fish 50 particularly being stacked in layers and having a gas permeable sheet element 54 located between layers as indicated, each gas permeable sheet element 54 typically being in the form of conventional-type shade cloth, or the like. The sheet elements 54 ensure that during the introduction of a negative pressure in the pressure chamber 12, or a positive pressure, as hereinafter described, all the units of fish will be similarly exposed to these pressures, thereby ensuring that the fish processing, as described hereafter, is equivalently applied to all the units of fish.

Once the fish units have been located within the pressure chamber 12 and the scaling hatch 22 has been applied, the method of processing fish, in accordance with the invention, is continued by inducing a negative pressure within the pressure chamber 12, particularly by the operation of the pump 16. The negative pressure typically is in the order of-1 bar, which will result in rupturing of the moisture containing cells of the flesh of the fish. The fish typically is exposed to this negative pressure for a period between 10 minutes and 30 minutes, this time period and the particular negative pressure utilized being such that the fish will not be excessively dried out by this process step.

Following the above step, by the operation of the pump and with the valves 28,36, 42 and 44 closed and the valves 30 and 34 open, a treatment gas contained in the storage chamber 14 can be displaced into the chamber 12. The treatment gas particularly includes a combination of carbon monoxide, nitrogen and carbon dioxide, the carbon monoxide typically making up 70% of the volume of the treatment gas, nitrogen 20% of the volume of the treatment gas and carbon dioxide 10% of the volume of the treatment gas. The pressure chamber particularly will be pressurized by the introduction of the treatment gas to a pressure in the order of 8 bar and the fish units within the pressure chamber will be exposed to the treatment gas at this pressure for a period between 3 and 6 hours, the apparatus of the invention providing also for means that can maintain the temperature of the fish within the chamber at approximately 3°C. By such exposure, the fish will be penetrated by the treatment gas, with the carbon monoxide serving to provide the fish with a fresh red colour, while the nitrogen gas will provide the gas with improved preservative qualities. The rupturing of the moisture containing cells of the flesh of the fish during the earlier step in the process particularly provides for more effective penetration of the flesh of the fish by the treatment gas introduced into the pressure chamber, as above described.

Following exposure of the fish units to the treatment gas as above described, by the closure of the valves 30 and 34, opening of the valves 20 and 36 and by the operation of the pump 16, the treatment gas can again be displaced from the chamber 12 into the chamber 14. This clearly renders the returned treatment gas re-usable. It is envisaged in this regard that the treatment gas that is returned to the storage chamber will also be passed through one or more filters (not shown) that will provide for the effective purification of the treatment gas and also the removal of any liquid or moisture simultaneously displaced from the pressure chamber.

Because of the use of carbon monoxide, prior to removing the gas penetrated fish from the pressure chamber 12 via the hatch 22, valves 42 and 44 can be opened while all the other valves are closed and the fan 38 can then be activated to provide for effective flushing of the chamber 12 with air and, thereby, the removal of carbon monoxide from the chamber and the discharge thereof to the atmosphere at a remote location, via the pipe 46. Following such flushing, the fish can be removed from the chamber, whereafter the fish can be frozen and/or vacuum packed for onward transport.

The above process can be applied to various different forms of fish, including sword fish and tuna and can be applied both to fresh fish and frozen fish. Where fish has been frozen, a defrosting step will precede introduction of the fish into the chamber.

Referring also to Figure 4 of the drawings, it is envisaged that the above fish treatment process can be associated also with a fish flavouring process and for this purpose the pressure chamber 12, shown here without the associated components and parts as shown in Figure 1, is associated also with a vessel-like fish support body 70 which permits stacking of fish units 72 therein, with or without gas permeable sheets, as illustrated. The vessel 70 is connected in liquid communication with a flavouring agent storage tank 74, effectively via a pump 76 and an inlet valve 78. The arrangement also provides for a return path for flavouring agent via a pipe section 80 and valve 82, which communicates also with the pump 76. As such, after the above described treatment gas processing of the fish units 72, and particularly also the removal of treatment gas from the chamber 12, a flavouring agent, e. g. a garlic flavoured olive oil, or the like, can be displaced by the pump 76 into the vessel 70. As a result of this introduction of the flavouring agent and consequent pressurisation of the vessel 12, the flavouring agent will penetrate the fish units, providing for flavouring thereof. It is envisaged that this process will occur over a period in the order of 3 to 10 hours and following this process the remaining flavouring agent can be discharged from the vessel via the pipe section 80 and the valve 82, permitting displacement back to the tank 74. The fish treatment process can then again be completed by effective vacuum packing of the fish units into packages that are suitable for transport and sale.

Insofar as the fish treatment process is associated with the use of carbon monoxide, which is dangerous, after venting of the pressure chamber as above described, a solution of water and chlorine dioxide optionally also can be sprayed into the chamber and onto the fish inside the chamber before removal thereof, providing for effective trapping of any remaining carbon monoxide. It will be understood that different treatment gases can be utilized in conjunction with the method of the invention in order to accommodate the same or different purposes in relation to the processing of fish. It will be understood also that the exact configuration of the apparatus is greatly variable, it being envisaged that the apparatus will comprise a plurality of state-of-the-art components and parts that can be linked with one another in order to accommodate the processing method of the invention.

The gas treatment as applied to fish will ensure that the fish maintains a fresh red colour over an extended time period, due to its exposure to the carbon monoxide, while the nitrogen enhances significantly the preservative qualities of the fish.