WO1994000022A1

WO1994000022A1 - Method and apparatus for shucking shellfish

Info

Publication number: WO1994000022A1
Application number: PCT/NZ1993/000052
Authority: WO
Inventors: Robert Malcolm Falconer; Arun Nanu
Original assignee: Industrial Research Ltd
Current assignee: Callaghan Innovation Research Ltd
Priority date: 1992-06-25
Filing date: 1993-06-23
Publication date: 1994-01-06
Anticipated expiration: 1994-12-25
Also published as: AU4361593A

Abstract

A method of opening uni-valve and bi-valve shellfish by exposing the region of the shell of a shellfish adjacent the adductor muscle to a stream of hot air for a period sufficient to detach the adductor muscle and facilitate opening of the shellfish. The method involves supplying between 25 to 450 kilojoules of energy to the shell of a shellfish within a period of between 5 to 60 seconds. The temperature of the stream of hot air is preferably between 300 to 600 °C at a flow rate of between 100 to 700 litres per minute or a surface flow rate over the shellfish of between 2 to 15 metres per second. There is also disclosed an apparatus for performing the method of the invention comprising a conveyor (74) which conveys a plurality of rows of shellfish underneath nozzles (75) which supply streams of hot air to the desired region of the mussels. The mussels may be subsequently cooked in a steam cooker (83) if required. The apparatus may also include means for aligning the shellfish in the desired orientation (62, 65).

Description

METHOD AND APPARATUS FOR SHUCKING SHELLFISH
Technical Field
This invention relates to a method and apparatus for shucking molluscan bi-valve and uni-valve shellfish.

Particularly, although not exclusively the method and apparatus of the present invention are particularly suitable for the shucking of greenshell and blue mussels and abalone.

Background of the invention
To date a number of methods have been used to shuck she: wish. Mechanical methods have been used to break or fce open the shellfish. Mechanical methods tend to damage the flesh and shell of the shellfish which lowers the visual appeal of either the extracted meat product or the half shell product, whether subsequently cooked or not. Other methods have included steam heating, which does not provide sufficient consistency in opening the shellfish and tends to cook the flesh, thus making the method unsuitable where uncooked meat from the shellfish is required. Microwave heating methods have also been used and have suffered similar problems to those experienced using steam heating methods.

Another method of opening shellfish has involved focusing infra-red heat on a shellfish. Difficulty has been experienced in focusing the heat. A further method used has been to direct a flame at the shell of a shellfish. This technique has generally led to damage to the flesh as well as the shell, making the technique unsuitable for both the shelled and half shell product.

Disclosure of the invention
It is an object of the present invention to provide a method and apparatus for shucking shellfish which is relatively inexpensive and mitigates at least some of the aforementioned disadvantages of the prior art, or to at least provide the public with a useful choice.

According to a first aspect of the invention there is provided a method of opening shellfish by impinging a stream of hot gas on an external region of a shell of a shellfish proximate the adductor muscle of the shellfish for a sufficient period to detach the adductor muscle and facilitate opening of the shellfish.

Preferably between 25 to 400 kilojoules of energy is applied to the shell of the shellfish within 5 to 60 seconds. The temperature of the stream of hot gas is preferably between 300 to 600"C at a flow rate of between 100 to 700 litres per minute. The surface velocity of the stream of hot air over the shell is preferably between 2 to 15 metres per second. For bivalve shellfish a stream of hot gas may be directed towards both plates of the shell. The shellfish may be subsequently cooked in a steam or other cooking process. The gas is preferably air.

According to a further aspect of the invention there is provided an apparatus for opening shellfish comprising heating means for supplying a stream of hot gas of a temperature between 300 to 600"C, preferably between 350 to 500 cm, most preferably between 400 to 450"C and a first conveyor for advancing shellfish through said stream of hot gas at such a rate that the adductor muscle is detached to facilitate opening of the shellfish.

The stream of hot gas is preferably normal to the surface of this shell. The first conveyor may be provided with a number of cups which accommodate the shellfish and orient them so that the region of the shell adjacent the adductor muscle is substantially normal to the stream of hot gas. An inclined in-feed conveyor may also be provided to sequentially supply single rows of shellfish to the first conveyor. A second conveyor may be provided in between the in-feed and first conveyor which conveys the shellfish through wedge shaped guides to longitudinally align the shellfish. Rotary alignment means may be provided between the wedge shaped guides and the first conveyor to orient the shellfish so that the ventral side lies towards one side of the conveyor.

Brief description of the drawings
The invention will now be described by way of example with reference to the accompanying drawings in which:
Figure 1: shows a plan view of a mussel; the
posterior adductor muscle being
indicated by hatching.

Figure 2: shows a view of a mussel along its
anterior-posterior axis.

Figure 3: shows schematically a proto-type
apparatus for performing the method of
the invention.

Figure 4: shows the configuration of the heating
means of the apparatus shown in figure
3.

Figure 5: shows a section of the conveyor belt
of the opening apparatus shown in
figure 3.

Figure 6: shows a cross-sectional view of the
cooking apparatus shown in figure 3.

Figure 7: is a graph showing the required gun
height and conveyor speed required to
achieve consistent opening of mussels
for flow rates of 250 litres per
minute and 500 litres per minute.

Figures 8 & 9: show schematically a possible
commercial apparatus for processing
shellfish according to the method of
the invention. The two halves of the
apparatus are split between figures 8
and 9.

Figure 10: shows the reciprocating selection gate
of figure 8 in perspective.

Figure 11: shows the paddle-wheel of figure 8 in
perspective.

Figure 12: shows in perspective the guides shown
in figure 8.

Figure 13: shows the rotary aligner shown in
figure 8.

Figure 14: shows a cup secured to the final
conveyor of figure 8.

Figure 15: shows in perspective the heating unit
shown in figure 9.

Figure 16: shows the steam cooker shown in figure
9.

Best mode for carrying out the invention
According to the method of the present invention a stream of hot gas is directed at the shell of a shellfish for sufficient time to destroy the bond between the adductor muscle and the shell, thus allowing the shell to open without restraint from the adductor muscle.

The method of the present invention is applicable both to bi-valve shellfish such as mussels, clams, pipis, tua tua, cockles etc as well as uni-valve shellfish such as abalone (which includes paua). Where reference is made to opening a uni-valve shellfish it will be appreciated that reference is being made to the separation of the meat from the shellfish, rather than to the separation of two shell halves (plates) as with bi-valve shellfish.

The method involves supplying sufficient energy to a region of the shell of a shellfish proximate the adductor muscle within such a period that the adductor muscle detaches from the shell. The adductor muscle of a mussel is indicated in figures 1 and 2 by the numeral 1.

Preferably between 25 to 400 kilojoules of energy is applied to the shell of the shellfish within a period of between 5 to 60 seconds. Preferably the energy supplied to the shell is between 25 to 230 kilojoules, most preferably between 25 to 95 kilojoules.

Preferably the shellfish is exposed to the stream of hot gas for between 5 to 35 seconds, most preferably for between 5 to 15 seconds. The temperature of the stream of hot gas is preferably between 300" to 600"C.

At temperatures below 300 a longer period of exposure to the hot gas stream is required and the meat tends to cook. For gas stream temperatures above 600"C the shell may be damaged and/or the meat may be singed.

The temperature of the stream of hot gas is preferably between 350 to 500"C, most preferably between 400 to 450"C. The flow rate of the stream of hot gas is between 100 to 700 litres per minute or the surface velocity of the stream of hot gas over the shell is between 2 to 15 metres per second. The flow rate of the stream of hot gas is preferably between 200 to 600 litres per minute, most preferably between 400 to 500 litres per minute. The surface velocity is preferably between 3 to 10 metres per second and most preferably between 6 to 8 metres per second.

The flow rate of the stream of hot gas is preferably greater than 300 litres per minute or preferably the surface velocity over the shellfish is greater than 5 metres per second. The period of exposure to the stream of hot gas is preferably less than 60 seconds, more preferably less than 35 seconds, and more preferably less than 25 seconds.

Referring now to figure 3 the method of the invention will be described with reference to a simple prototype machine shown in figures 3 to 6. The apparatus shown in figure 3 consists of an opening apparatus 4 and a cooking apparatus 5. Referring firstly to the opening apparatus 4, a conveyor 6 is provided between rails 9 and 10. The conveyor is driven by a suitably geared electric motor 7 and drive belt 8. The conveyor 6 will suitably be formed of wire mesh to withstand the temperatures of the process.

In the prototype shellfish are placed on conveyor 6 by hand in the region indicated by numeral 11. The shellfish are manually placed on the conveyor in the desired orientation. The conveyor advances the shellfish through heating means 12. Referring now to figure 4 a cross-section of the heating means along the axis of the conveyor is shown. A hot air gun 23 is provided above the conveyor 6 and produces a stream of hot air 24 substantially normal to the region of shellfish 27 to be heated. An adjustable guide 25 is provided to laterally position the shellfish 27 with respect to the stream of hot air 24. The guide will be set for a particular species to ensure that the stream of hot air is directed to the area adjacent the adductor muscle of the shellfish 27. In fact a longitudinal strip of the shellfish including the area proximate the adductor muscle is heated.

The heating of this surrounding shell also assists in heating the region of shell adjacent the adductor muscle. The speed of motor 7 is adjusted so that the shellfish are exposed to the stream of hot air for the required period.

Opposite and parallel to guide 25 is provided a ramp 26. This ramp gradually inclines so that one side of an advancing shellfish is raised so as to ensure that the region of the shellfish to be heated is normal to the stream of hot air 24. The height of the hot air gun 23 may be raised or lowered depending on the operating conditions. A bracket 28 (see, figure 5) may be secured to conveyor 6 by fastening means 29 to ensure that a mussel 27 passes along ramp 26 without being obstructed thereby. Where the meat is to be extracted from bi-valve shellfish a stream of hot air may be applied to either side of the shellfish. Where a half shell product is required only one side need be heated.

After passing through heating means 12 the mussels slide down ramp 13 onto conveyor 15. Guides 14 are provided to ensure that the mussels are directed onto conveyor 15. Conveyor 15 is supported between rails 16 and 17 and is driven by a suitably geared electric motor 18 via belt 19. Conveyor 15 advances the mussels through the cooking apparatus 20.

The cooking apparatus 20 is shown in cross-section along the axis of the conveyor in figure 6. Steam is supplied to the cooking apparatus 20 via steam line 21. Steam is supplied within the enclosure by a steam distributor 30. The speed of the conveyor is set so that the shellfish are exposed to the steam for a sufficient period of time to cook them. The cooked product then leaves the conveyor at 22 to be collected and subsequently opened by hand.

A number of tests were conducted on greenshell mussels using an opening apparatus 4 as shown in figure 3.

Figure 7 illustrates the test results in graphical form. The vertical axis of the graph represents the height of hot air gun 23 above conveyor 6. The horizontal axis indicates the speed of conveyor 6 in millimetres per second. The hot air gun used in the test was a Bosch PHG600 CE hot air gun. This has two flow rates of 250 litres per minute (the low flow rate) and 500 litres per minute (the high flow rate).

The temperature of the hot air stream at the outlet of the gun was 525"C. The thick line indicates the required gun height and conveyor speed to achieve consistent opening at the high flow rate. The thin line represents the gun height and conveyor speed required to achieve consistent opening at the low flow rate. At the lower flow rate a lower gun height and slower conveyor speed were required to achieve consistent opening.

The tests also revealed that most consistent opening was achieved when the ventral side of the mussels was directed towards the guide. Best results were also achieved when the anterior end of the mussels passed through the stream of hot air first, although satisfactory results were also obtained when the posterior end passed through the stream of hot air first.

Referring now to figures 8 to 17 an apparatus which may be suitable for commercial use will now be described. A general schematic form of the apparatus is shown in figures 8 and 9. Shellfish 50 may be supplied to the apparatus via chute 51. A conveyor 52 is provided with a number of brackets 53 thereon.

These brackets push forward one row of shellfish at a time. Reciprocating selection gate 54 ensures that the shellfish lay flat on the conveyor. Referring to figure 10 the reciprocating selection gate 54 is shown in perspective. The gate is seen to be corrugated to deflect the shellfish. Gate 54 is secured to member 55 which reciprocates back and forth along axle 56 due to the reciprocating force applied by air cylinder 57.

The shellfish are transferred from conveyor 52 to conveyor 58 by a paddle wheel 59. Referring to figure 11 paddle wheel 59 is seen to consist of a central drum 60 having a number of stiff rubber paddles 61 projecting radially therefrom. The paddle wheel preferably rotates slightly faster than the preceding conveyor.

Conveyor 58 advances the shellfish through guides 62.

Referring to figure 12 it will be seen that the guides are wedge shaped to channel the shellfish into a plurality of rows. The number of guides provided will depend upon the width of the conveyor. Upon passing through guides 62 the shellfish will be oriented substantially longitudinally. At the end of conveyor 58 each shellfish is gripped between fingers 63 and 64 of rotary aligner 65. Fingers 63 and 64 may be slightly curved to facilitate easy gripping of the shellfish. The interior surfaces of fingers 63 and 64 may be provided with a resilient material on the interior thereof to further facilitate gripping of the shellfish. Once a shellfish is located between fingers 63 and 64 they are drawn together to grip the shellfish. An air cylinder 66 may then move rotary aligner 65 along shaft 67 until the shellfish is held above the plate 68.

A camera 69 may then send data to processing unit 70 regarding the orientation of the shellfish. Processing unit 70 may then rotate portion 71 of rotary aligner 65 relative to portion 72 so that the shellfish has the desired alignment. In this way each mussel can be aligned so that its ventral side lies in the same direction.

Air cylinder 66 then moves rotating means 65 above a support cup 73. Fingers 63 and 64 are then moved apart and the shellfish drops into cup 73 in the desired orientation. Cup 73 is profiled to ensure that the shellfish is held in the correct orientation with regard to the stream of hot air (i.e.: the region of the shell adjacent the adductor muscle is approximately normal to the stream of hot air).

Referring now to figure 9 the other half of the apparatus is shown. The continuation of conveyor 74 of figure 8 is shown to the left of figure 9. The shellfish are conveyed under a number of streams of hot air. Each line of mussels is advanced by conveyor 74 under a hot air outlet nozzle 75. The arrangement of the heating means alone is shown in perspective in figure 16. An individual outlet nozzle 75 is provided for each line of shellfish. An extractor 76 collects the hot air supplied from the outlets 75 and recycles it through the system. The hot air collected at extractor 76 is forced through duct 77 by fan 79 and heated by heater 78. Preferably heater 78 consists of an electric heating element. Heater 78 may however consist of a gas or steam heater. The heated air from heater 78 is then forced via fans 80 through outlets 75.

From conveyor 74 the open mussels are forced by paddle wheel 81 onto conveyor 82. The conveyor conveys the mussels through a steam cooking unit 83 where the mussels are cooked. Steam is supplied via inlet pipe 84 and is distributed via distribution pipes 85. At the end of conveyor belt 82 the top shell of each mussel is removed manually and the mussels stacked in suitable containers.

It is to be appreciated in particular that the section for aligning the shellfish including rotary aligner 65 is merely an illustration of a possible way of orienting the shellfish. It will be appreciated that there are a number of ways in which the shellfish may be oriented to ensure that one side always faces a given direction. Although it is preferred that the shellfish are aligned it will be appreciated that satisfactory results may be obtained if the alignment section between conveyors 58 and 74 is omitted.

Alternatively, this alignment may be performed manually.

The method of the present invention allows rapid opening of shellfish without damage to the flesh.

Opening times as short as five seconds can be achieved in comparison to the prior art steam heating methods which took more than two minutes. The method of the present invention also provides consistent opening of shellfish with either no or minimal cooking of the meat as desired. The heat applied to the shell of the shellfish may be easily controlled using the method of the invention, thus resulting in little or no shell damage.

It is to be appreciated that the operating parameters may be varied for different species due to shell thickness and the size and location of the adductor muscle. The method of the present invention has produced particularly good results for greenshell and blue mussels and paua (abalone) which have a relatively thin shell. Satisfactory results have also been achieved for tua tua. However, due to the thicker shell, longer opening times and partial cooking of the meat results.

Industrial Applicability
The method and apparatus of the invention may find wide application in the opening of shellfish, particularly greenshell and blue mussels and abalone.

The method and apparatus have particular advantage where a raw or half shell product is required.

Claims

CLAIMS:

1. A method of opening shellfish by impinging a stream of hot gas on an external region of a shell of a shellfish proximate the adductor muscle of the shellfish for a sufficient period to detach the adductor muscle and to facilitate opening of the shellfish.

2. A method as claimed in claim 1 wherein between 25 to 400 kilojoules of energy is applied to the shell of the shellfish, preferably between 25 to 230 kilojoules, most preferably between 25 to 95 kilojoules, for a period of between 5 to 60 seconds, preferably between 5 to 35 seconds and most preferably between 5 to 15 seconds.

3. A method as claimed in claim 2 wherein the temperature of the stream of hot gas is between 300 to 600"C, preferably between 350 to 500"C, most preferably between 400 to 450"C.

4. A method as claimed in claim 1 wherein the temperature of the stream of hot gas is between 300 to 600"C, preferably between 350 to 5000C, most preferably between 400 to 4500C; the flow rate of the stream of hot gas is between 100 to 700 litres per minute, preferably between 20 to 600 litres per minute, most preferably between 400 to 500 litre per minute, and the period of exposure to the stream of hot gas is between 5 to 60 seconds, preferably 5 to 35 seconds, most preferably 5 to 15 seconds.

5. A method as claimed in claim 1 wherein the temperature of the stream of hot gas is between 300 to 600"C, preferably between 350C to 500"C, most preferably between 400" to 450"C; the surface velocity of the stream of hot gas over the surface of the shellfish is between 2 and 15 metres per second, preferably between 3 and 10 metres per second, most preferably between 6 and 8 metres per second, and the period of exposure to the stream of hot gas is between 5 to 60 seconds, preferably between 5 to 35 seconds, most preferably between 5 to 15 seconds.

6. A method as claimed in claim 1 wherein the temperature of the stream of hot gas is between 300 to 600"C, preferably between 350 to 5000C, most preferably between 400 to 450"C; and the rate of flow of the stream of hot gas is greater than 300 litres per minute or the surface velocity over the surface of the shell is greater than 5 metres per second and the period of exposure to the stream of hot gas is less than 60 seconds, preferably less than 35 seconds, most preferably less than 25 seconds.

7. A method as claimed in any one of the preceding claims wherein the stream of hot gas is substantially normal to the region of the shell of the shellfish adjacent the adductor muscle.

8. An apparatus for opening shellfish comprising heating means for supplying a stream of hot gas of a temperature between 300 to 600"C, preferably between 350 to 500"C, most preferably between 400 to 450"C and a first conveyor for advancing shellfish through said stream of hot gas at such a rate that the adductor muscle detaches to facilitate opening of the shellfish.

9. An apparatus as claimed in claim 8 wherein the shellfish is exposed to the stream of hot gas for less than 35 seconds, preferably less than 25 seconds, and the flow rate of hot gas is greater than 300 litres per minute or the surface velocity over the shellfish is greater than 5 metres per second.

10. An apparatus as claimed in claim 8 wherein the shellfish is exposed to the stream of hot gas for between 5 to 60 seconds, preferably 5 to 35 seconds, most preferably 5 to 15 seconds, and the flow rate is between 100 to 700 litres per minute, preferably between 200 to 600 litres per minute, most preferably between 400 to 500 litres per minute or the surface velocity over the shell of the shellfish is between 2 to 15 metres per second, preferably 3 to 10 metres per second, most preferably 6 to 8 metres per second.

11. An apparatus as claimed in any one of claims 8 to 10 wherein said first conveyor is provided with a plurality of cups therealong adapted to accommodate the shellfish so that the region of the shell of each shellfish adjacent the adductor muscle is substantially normal to the stream of hot air.

12. An apparatus as claimed in any of claims 8 to 11 including an in-feed conveyor, prior to said first conveyor, said in-feed conveyor being inclined and having a plurality of transverse brackets secured at intervals therealong to supply a single layer of shellfish to the next stage of the apparatus.

13. An apparatus as claimed in claim 12 including a longitudinal aligner between said in-feed conveyor and said first conveyor, said longitudinal aligner including a second conveyor for conveying shellfish through a plurality of longitudinally oriented wedge shaped guides to align said shellfish so that their longitudinal axes are generally parallel with the conveyor.

14. An apparatus as claimed in claim 13 including rotary alignment means to align the shellfish so that the ventral side of the shellfish lies towards one side of the first conveyor.

15. An apparatus as claimed in claim 14 wherein said heating means includes a plurality of spaced apart nozzles which blow a plurality of streams of hot gas onto a plurality of lines of shellfish, said heating means including extractor means which collects hot gas from said nozzles and recirculates the hot gas through a heater back to said nozzles.

16. An apparatus as claimed in claim 14 wherein the heater is an electrical element.