The present invention relates to the removal of the shells from crustaceans such as shrimps and even the so-called krill, i.e. small crustaceans forming an immense source of protein especially in the antarctic oceans.

Conventionally, crustaceans have been peeled or - - shelled by means of mechanical pressure rollers serving to crack the shells, but as well known this kind of peeling is highly inefficient and requires a lot of manual afterpeeling.

There is known several proposals for improved peeling methods and systems, but so far seemingly without practical results. Thus, according to US-PS 2,798,334 and f 3,812,271, it has been proposed to peel crabs by freezing ^' the crabs and thereafter either a) expose them to a pressure drop at a very high vacuum, b) store them at a high pressure for building up a high pressure inside the crabs, whereafter the pressure is suddenly relieved for causing the shell to explode, or c) store then in a pressurized explosive gass mixture, which diffuses into the crab portions inside of the shell, whereafter the gas is ignited upon the pressure being relieved, whereby the shells are sought to be removed by a combustion explosion. These methods are intricate, a.o. already because of the said freezing, and just like the said mechanical roller method they show the disadvantage that a considerable and unavoidable portion of the product as processed, viz. all the crustaceans which have been only partly shelled, shall have to be manually shelled, because a repeated treatment of partly shelled crustaceans will be practically fruitless.

Another proposal is disclosed in US-PS 4,251,902

and DE-OS 3,000,072. Here the crustaceans are subjected to a jet of a working liquid as injected into a moving stream of crustaceans, whereby the high velocity of the liquid jet along the crustaceans, prior to these being fully accelerated, shall account for a sub pressure to be created immediately about the crustaceans and hereby for a shell loosening effect. The accelerated crustaceans are caused to pass through a pipe section having a corrugated wall, which may engage the crustaceans frictionally and thus show some peeling effect on the- - - already loosened shell portions. However, this will apply only to the outermost crustaceans in the flow, and the efficiency of the method must be deemed low. Again, manual afterpeeling would be necessary, because a repeated treatment of the only partially peeled crustaceans would probably be still less efficient, and the known proposal itself is silent- in this respect. It is the purpose of the invention to provide an improved method of peeling crustaceans with a generally high efficiency and simplicity, based on a pressure difference treatment and. a following mechanical treatment for separating the loosend shell portions from the body portions of the crustaceans, all in such a manner that the entire process is effective not only for whole crustaceans, but even for only partly shelled crustaceans, i.e-. such that it may be really possible to further process the partly-shelled crustaceans simply by a repeated treatment.

According to the invention the crustaceans, in preboiled condition, are exposed to a pressure drop from a pressure level, at which the body liquid adjacent the surface of the bodies and just inside the shells exists in a liquid phase, to a lower pressure level, which is low enough to cause a boiling up of the said body liquid just inside the shells, whereafter the crustaceans for said mechanical treatment are caused to be rapidly moved

against or into a brake liquid serving to frictionally engage the outside of the moved crustaceans and thus to peel or draw off the already loosened shell portions thereof. The said pressure drop boiling of the liquid just inside the shells is a very simple expedient for loosening the shells reasonably effectively, and the rapid motion of the crustaceans into the brake liquid is not only a simple expedient, but a manner of ensuring that all the crustaceans are subjected to a rather effective, yet - - - gentle surface friction resulting in a peeling action. The two expedients together, however, account for the very important possibility of repeating the treatment for crustaceans having been only partly peeled or shelled in the first instance. Thus, the said pressure drop boiling is effective for shell loosening even if a major portion of the shell has already been removed, and once the remaining shell has thus been repeatedly loosened it almost cannot avoid getting in frictional contact with the brake liquid, whereby in the second treatment it will be removed with a very high degree of probability. Therefore, because both of the method steps are well suited for renewed treatment of partly-shelled crustace¬ ans, none of them need show any extreme efficiency, and they may thus be correspondingly simple.

Experiments have shown that already by one treatment a considerable yield of totally shelled crustaceans is achievable and that by only one repeated treatment of the partly-shelled crustaceans the total yield is so close to 100% that a further repeated treatment may hardly be profitable.

In the two method steps, as mentioned, the crustaceans are handled in a gentle manner, and it has been observed as a surprising fact that the bodies of the ready processed crustaceans may be infact such various fine details which are otherwise inevitably

removed from the bodies in connection with conventional mechanical peeling.

Especially for enabling the said repeated treatment of the only partly peeled crustraceans it will be import- ant in practice that these crustaceans are separated from the entirely peeled crustaceans and from the loose shells as already peeled off. It has been found that an efficient separation is achievable already in the said brake liquid, when under subpressure, but even external separation may be utilized, as known per se in the art-. - However, it is still an aspect of the invention that the relevant separation may be effected in a very simple manner in a liquid under subpressure.

The invention also comprises a system for carrying out the discussed method, as more specifically defined in the appended claims.

In the following the invention is described in more detail with reference to the drawings, in which:-

Fig. 1 is a schematic, view of a system according to the invention.

Fig. 2 is a perspective view of a modified, preferred system.

Fig. 3 is a schematic side view of this system, Fig. 4 is a perspective view of an external separator belonging to the system shown in Figs. 2 and 3,

Fig. 5 is a schematic side view of this separator, and

Fig. 6 is a schematic side view of a further modified system according to the invention.

In Fig. 1 is shown a waterfilled half cylindrical vat 2, in which a rotor cylinder 4 with protruding shovels 6 rotates so as to scrape the shovels along the vat bottom from the left towards the right side thereof. Preboiled crustaceans are supplied to the vat of the left side thereof, as shown by an arrow a, and by

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the action of the shovels 6 the crustaceans are moved through the vat 2 and are lifted off the vat at the right hand side thereof for delivery to a downwardly directed channel 8, in which there is mounted a stop valve 10 actuated by a hydraulic or pneumatic cylinder 12.

The channel 8 merges into a vertical cylinder 14, the top end of which is closed by a valve 16, and the bottom of which is closed by a valve 18, while the bottom portion of the cylinder 14 is otherwise connected to a tank 20 holding a bath of water 22 partly confined - by a low overflow end wall 24. Adjacent the wall 24 is arranged a downlet 26 from the bottom of the bath 22, this downlet continuing in a sluice system 28 with associated sluice valves and with an outlet 30 just above an inclined screen chute 32. Adjacent the other side of the wall 24 is arranged a downlet 34, which is upwardly open upwardly open towards the closed tank 20 and continues downwardly through a sluice system 36 to an outlet 38 just above another screen chute 40. The tank 20 has a water inlet valve 42 and a pipe

44 connected to a vacuuπi source (not shown) . In the water bath is arranged a reciprocating scraper conveyor 46, which is reciprocated by means of a working cylinder 48 and has an upper portion 50 located so as to be operable to move goods floating on the bath surface towards the left and over the top edge of the wall 24 by means of monolaterally pivotable lamellas 52, and a bottom wise arranged conveyor portion 54 correspondingly operable to move bottom settled goods towards the left and into the downlet 26.

In operation, e.g. for peeling shrimps, the shrimps are supplied to the vat 2 along the inlet arrow a., and are moved through the vat by rotation of the cylinder . The vat is heated, either for boiling the shrimps or preferably for reheating preboiled shrimps during such short time that they are heated surfacewise only. The

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shrimps thus heated are delivered to the channel 8, and a predetermined charge of shrimps is filled into the cylinder 14 through the open valve 10, which is then closed, the top and bottom valves 16 and 18 hereby remaining closed. The top valve 16 is arranged between the cylinder 14 and the atmosphere or a source of com¬ pressed air (not shown) .

Thereafter the valves 16 and 18 are opened, and with a vacuum existing in the tank 20 the charge of shrimps will hereby be "fired" downwardly into this vacuum and- - - get rapidly accelerated towards the water bath underneath the cylinder 14. The temperature and pressure conditions are adjusted such that a first result of the heated shrimps being exposed to the lower pressure in the tank 20 is that a vivid boiling of the shrimp body liquid just inside the shrimp shells will occur, whereby the shells are effectively loosened from the bodies. A further result is that the shrimps as conveyed by a powerful air flow from above will get thrown into the water bath 22, and the water will hereby act as a braking liquid frictionally decelerating the shrimps and thus peeling off the previously loosened shell portions due to the inertia of the moved shrimps.

By this treatment many of the shrimps will be totally peeled, while the remaining shrimps will only be partly peeled. In the water bath 22, therefore, will be collected totally peeled shrimps, partly peeled shrimps and loose shell portions, and it is of course necessary to there¬ after carry out some relevant separation of these products in order to first of all recover the totally peeled shrimps, while it is even relevant processing. It has been noticed as a remarkable fact that in the bath 22 as under vacuum the shrimp products separate naturally, as the totally peeled shrimps sink to the bottom of the bath, while both the loose shell portions and the partly peeled shrimps are collected in the surface

of the bath. Therefore, as the conveyor 46 operates, the lower conveyor portion 54 will move the totally peeled shrimps into the downlet 26, while the upper conveyor portion 50 will move both the free whell portions and the partly peeled shrimps over the wall 24 and thereby into the downlet 34.

Thus, through the sluice system 28 the totally peeled shrimps will be delivered to the screen chute 32, and with the associated water drained off through the screen the ready peeled shrimps will be delivered from - - the chute 32 as shown by an outlet arrow A.

Through the sluice system 36 the loose shell portions and the partly peeled shrimps together with exess water will be supplied to the screen chute '40, and upon the water being drained off the combined product is delivered to a hopper 56, from which it proceeds to an area which is crosswise affected by an air flow as provided by a blower 58, whereby the loose shell portions are blown away through an outlet B, while the partly peeled shrimps pass the cross air flow into an outlet C, from which they are recirculated to the inlet side of the vat 2 through a pipe 60. This pipe, of cours'e, may be connected with suitable blower or other conveyor means for enabling the said recirculation. It will be understood that upon the said re¬ circulation of the partly peeled shrimps these shrimps will be subjected to a renewed heating in the vat 2 and a renewed pressure drop boiling of the body liquid inside the remaining shell portions; a surface liquid boiling will take place even on the already shelled portions of the body, but apparently this is of no negative effect, and the result is a renewed loosening effect on the remaining shell portions. When thereafter the shrimps hit the brake water the said remaining shell portions will be drawn off the bodies, again without any adverse effects on the already shelled body portions. Thus, the

treatment of the recirculated shrimps is gentle, yet still effective, and normally one or two recirculations will be sufficient to reduce the proportion of the not entirely shelled shrimps to an almost neglectible minimum. The said recirculation may take place in a continuous manner, i.e. concurrently with the treatment of the newly supplied, preboiled shrimps.

In Figs. 2 and 3 is shown a preferred embodiment of that part of a system according to the invention in which the crustaceans are subjected to pressure drop boiling" ^* " ^' and shelling. As in Fig. 1 the numeral 20 designates a vacuum tank, which is connected through a pipe 44 to a vacuum source tank 64 fitted with a vacuum pump 66. The crustaceans are supplied at arrow a. to a heater vat 2 and are moved through the vat by conveyor 4, which is speed adjustable to enable the preboiled and cooled crustaceans to be reheated at such short duration as required for raising the shell temperature to a desired level above the temperature of the interior body portions. The crustaceans thus heated are fed to a hopper 68 leading to a vacuum chamber 70 through a valve 72. The chamber 70 is located above the top plate of the vacuum tank 20 for communication with this tank through another valve 74. Furthermore the chamber 70 is connectable with a separate vacuum source (not shown) through a valve 76 and with a source of compressed air through a valve 78. With the valves 74,76 and 78 closed and the valve 72 open a charge of e.g. 1 kg crustaceans is filled into the chamber 70, whereafter the valve 72 is closed. Then the valve 76 is opened for subjecting the chamber 70 to a vacuum, which is somewhat smaller than the vacuum in the tank 20, but sufficient to cause the described rapid boiling up of warmed body liquid just inside the shells of the crustaceans. Very short time thereafter, e.g. after 10 seconds, the valve 76 is closed and the valves 74 and 78 are opened, whereby the charge of crustaceans

is "fired" down into a water bath 22, accelerated by the air flow as generated by the increased vacuum in the tank 20 and the supply of compressed air through the valve 78. Underneath the chamber 70, in or through the bottom of the tank 20, is arranged a certical, upwardly open cylinder 80, which is somewhat wider than the chamber 70 and is bottomwise provided with a water supply pipe 82 including a valve 84. The cylinder is completely filled with water 22, while the ta k 20 is otherwise kept empty - as described below. One purpose of the relatively narrow cylinder ^' 80 is to make sure that the crustaceans are "fired" down into a water surface which is as calm as possible, as such calmness seems to promote the shelling actio .

After the said firing a vacuum release valve 63 in the pipe 44 is actuated so as to vent the tank 20 to the atmosphere through a port 65, whereby all crustacean parts in the water seek downwardly. However, immediately after the said firing, the water supply valve 84 is opened so as to produce an upwardly directed water flow in the cylinder 80, whereby all crustacean parts in the water of the cylinder as well as the water itself will overflow the top edge of the cylinder 80 out into the surrounding tank 22. Hereby the various crustacean parts will fall to the bottom of the tank 20, while the water surface of the cylinder 80 will rapidly - in few seconds - be cleaned for such parts and thus be prepared for virgin- ally and calmly receiving a new "shot" of crustaceans from the chamber 70. The vacuum release valve 63 is switched over for the building up of a new vacuum in the tank 20.

The bottom of the tank 20 is sloping towards an outlet sluice system 86, and the water and the crustacean parts in the tank 20 will thus naturally seek towards this outlet sluice system 86 , which continues in an

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outlet pipe 88, through which both the loose shell parts and the fully and the partly shelled crustaceans are let away from the apparatus.

For a suitable operation of the outlet sluice 86 a pressure equalizing connection 90 is arranged between the outlet sluice and the vacuum tank 20, whereby the sluice may operate to keep the tank 20 empty even when there is vacuum in the tank.

All of the described valves, of course, may be controlled automatically by a non-illustrated control unit, and the process of "firing" a charge of shortly prewarmed ^" and pressure dro boiled crustaceans into the brake water of the cylinder 80 may be repeated over and over. The total outlet product as delivered through the pipe 88 may be separated according to any suitable technique, primarily for getting all loose shell parts sorted away and all fully shelled crustaceans sorted out to further handling and packaging, and secondarily - but important enough - for sorting out all partly shelled crustaceans for repeated processing. A relevant sorter arrangement has been described already in connection with Fig. 1, but in practice it is preferred to make use of a separate separator device as illustrated, by way of example, in Figs. 4 and 5. This device operates fully on the principles described already in connection with Fig. 1.

The separator device shown in Figs. 4 and 5 comprises a vertical cylinder 100 having a side inlet 102 connected with a receiver hopper 104 through an inlet sluice arrangement 106. Bottomwise the cylinder 100 is provided with an outlet sluice system 108 and an outlet 110, and topwise it projects into a top chamber 112 having a sloping bottom 114 communicating with an outlet sluice arrangement 116 and an associated outlet 118. Topwise the closed top chamber 112 is provided with a pipe 120

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connected to a vacuum source (not shown) .

The product as delivered from the outlet 88 of the apparatus shown in Figs. 2 and 3 is supplied to a conventional air separator (not shown) , in which the loose shell portions are separated from the product, and the remaining product as consisting of shelled and partly shelled crustaceans are then fed, in a flow of water, to the hopper .104 of the separator according to Figs. 3 and 4. The product is chargewise sluiced into the cylinder 100 through the sluice 106. - - -

Because of the vacuum in the cylinder 100 the same type of separation as in the water bath 22 of Fig. 1 will now take place, i.e. the shelled crustaceans will sink to the bottom and the partly shelled will rise to the top end of the cylinder 100. By admission of further water through the hopper 104 an overflow is created from the cylinder top, whereby the partly shelled crustaceans ^r will enter the top chamber 112 and be sluiceable out through 116 to the outlet 118. In its turn this outlet 118 is connected to the inlet vat 2 of Figs. 2 and 3, for the already discussed recirculation of the partly shelled crustaceans.

The ready shelled crustaceans are sluiced out through 108 to the bottom outlet 110 of the cylinder 100. Even this output may be recirculated, should the need arise. It should be strongly emphasized that different types of crustaceans may separate invertedly in the cylinder, i.e. for some types the fully shelled bodies will rise to the top while the partly shelled bodies sink to the bottom. Furthermore, for a perfect separation it may be necessary to adjust the vacuum according to the character of the product.

Preferably the water in L.he cylinder 100 should be held at a temperature which is just below the boiling temperature of the water at the particular vacuum. hereby a certain bubble production will take place in

the water, and the rising bubbles promote an effective separation.

It will be appreciated that the separator as shown in Figs. 2 and 3 is advantageously applicable independtly of how the crustaceans are otherwise treated for the shelling thereof.

In Fig. 6 is shown another modification of the shelling system according to the invention. It comprises a pressure cylinder 130 having an inlet valve 132 for crustaceans and a bottom outlet valve 134 located e.gV ^* some 50 cm above the surface of an open water bath 136 in a vat 138. The cylinder 130 further has a top valve 140 for connecting the cylinder top to a compressed air chamber 142. Moreover the cylinder 130 has a lower steam inlet valve 144 and an upper vent valve 146. In the vat 138 is arranged a bottom conveyor 148 serving to convey precipitated goods to a receiver such as a sorting conveyor 150.

When a charge of crustaceans has been filled into the cylinder 130 the inlet valve 132 is closed and the steam valve 144 and the- ent valve 146 are opened. The vent valve 146 is closed when the steam fills out the cylinder 130, and thereafter a steam pressure of some 2-4 atm is rapidly built up therein, e.g. with steam at ca. 120°C. Short time thereafter, e.g. after some 10 seconds, the steam valve 144 is closed, and the compres¬ sed air valve 140 is opened, whereby the pressure in the cylinder 130 may increase further. Shortly or immediately thereafter the bottom outlet valve 134 is opened, whereby the charge of crustaceans will be "fired" down into the water bath 136, As in Fig. 1 the crustaceans will be exposed to a sudden pressure drop, here down to ambient pressure and here in a preheated condition, such that the said vivid boiling just inside the shells will take place, and rapidly thereafter they will hit the water bath 136 and get shelled thereby. Since the water bath

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is here under ambient pressure it will not normally show any separator effect by flotation, and all parts of the product sink to the bottom, where they are conveyed by the conveyor 148 and brought to the sorter conveyor 150.

Hereafter some examples shall be given:

Example 1 : Shelling of fresh-caught Northsee shrimps. The shrimps are boiled in water of 100 C for 2 - - minutes and are then cooled in running, cold water for complete cooling. Immediately prior to the shelling process they are caused to pass through the vat 2 of the Fig. 3 apparatus with a passing time of ca. 5 seconds through water of 100°C, and a charge of ca. 1 kg is let into the chamber 70, of which the volume is ca. 4-5 liters. Then the pressure in the chamber .is lowered to a vacuum of ca. 500 mm Hg, and immediately thereafter the charge is fired into the tank 20 as holding a still lower pressure, viz. a vacuum of ca. 700 mm Hg. The product in the bath 22 is sluiced out for external separation and for recirculation of partly shelled shrimps. Alternatively the separation may be effected in the brake water under vacuum (Fig. 1 ) .

Example 2: Shelling of frozen, thawed out, unboiled krill. Frozen krill in blocks are thawed out in running water for ca. 3 hours. Excess liquid is drained off and the krill is thoroughly rinsed with cold water. Immediate¬ ly prior to its being processed for shelling the krill is portionswise (1 kg) warmed for ca. 15 seconds in water of 40 C and is then supplied to the vacuum chamber 70 (Fig. 3) , in which a vacuum of 350 mm Hg is provided. From chamber 70 the krill is fired into the tank 20, in which the vacuum has been set to 720 mm Hg. The combined

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product as delivered through the outlet 88 is supplied to an ordinary water frotation separator which separates the loose shells from the shelled and partly shelled krill, and this remaining krill product is fed to a vacuum separator according to Fig. 5, in which the fully shelled krill is separated from the partly shelled or unshelled krill at a water temperature of 20°C and a vacuum of ca. 720 mm Hg.

Example 3: - - Shelling of seaboiled, frozen Greenland shrimps.

The loose frozen shrimps are thawed out in running water for ca. 20 min. and are supplied to a steam heater 130, Fig. 6. Here they are heated by steam of 3 atm (121°c) for 10 seconds, whereafter they are fired into water bath at ambient pressure and temperature. The combined product is let out from the bath, and excess water is drained off from the product. The loose shells are separated away by air separation, and shelled and partly shelled shrimps are separated in a separator according to Fig. 5; water temperature 25°C and vacuum 700 mm Hg. Partly shelled shrimps are recirculated to the steam heater.