CA1041714A - Method of, and apparatus for removing skin from salted, seasoned or otherwise pre-treated fish, preferably herring filets - Google Patents

Abstract

INVENTORS

STIG LINDBLADH AND WALLIS STAHLBERG

TITLE

A METHOD AND APPARATUS FOR REMOVING SKIN FROM
SALTED, SEASONED OR OTHERWISE PRE-TREATED FISH, PREFERABLY HERRING FILETS

ABSTRACT OF THE DISCLOSURE
A method and apparatus for removing skin from pre-treated fish, preferably from herring filets, wherein the opened fish is passed skin side up on a conveyor belt through a cutting and cleaning apparatus in which the skin of the fish is contacted with an acid to produce a denaturization of the fish and liquid jets are directed against the skin at a suitable angle to remove the skin which is flushed away together with other parts of the fish severed during the cutting and skin removing opreation.

Description

The pre~ent inyention ~elates to ~ ~ethod o~ re~oving skin from s~ltedg seasoned or ot~erwise pre treated fish~
prefera~ly herring $ilets. T~e ~nvention also relates to an apparatus for carrring out said method.
It has been necessary until now, for various reasons, to manually remove skin rom salted, seasoned or otherwise pre-treated fish. This method is o~viousl~ ver~ time consuming~ especially when dealing with small herrlng filets.
; It is therefore an object of the present invention to provide a method enabling skin to be removed mechanically `~
from saltedJ seasoned or otherwise pre-treated fish without any or with an insignificant loss in fish meat. The method of the invention is defined in and by the appended claims.
An additional object of the present invention resides in the provision of suitable apparatus for carrying out the method in question. This inventive apparatus has the eatures which are also deined in the appended claims.
The invention will be described in greater detail ~0 hereafter with reference co the acco;~panying dra~ingj~
in which: ~-Fig. 1 is a side elevational view diagrammatically illustrating a skinning machine for carrying out the method of the invention;
Fig. 2 illustrates the machine in top plan view;
Fig. 3 illustrates the ~achine in a front elevational view; and Figs.4 and 5, in side elevation and front elevation, respectively, illustrate a fin cutting device connected to the mac}line.
Kefe~ring to the dra~ings, the machine ~llustrated therein comprises a framework 1 having our su~por~ legs 2, . .

)4~L4 an endless conveyor belt 3, a li~uid su~plying unit 4 and a li~uid draining unit 5.
The conveyor ~elt 3 is arranged to travel around two end rollers 6 and 7, at least one of ~hlc~ is operat~vely connected to a relativel~ lo~ powered variable speed worm ~-gear motor ~not shown). Bet~een said end rollers 6 and 7 the load carrying run 8 of the conveyor belt 3 extends substantially horizontally~ and the conveyor belt 3 is `~ driven to cause its load carrying run to mo~e in the sense indicated by an arrow l'A" in the drawing. `
The load carrying run of conve~or belt 3 - as seen in its direction of advance - will first pass beneath a station 9 forming part of the liquid supplying unit 4 and having for its purpose to supply a treatment liquid. Such treatment liquid is supplied through tubes 10 having spray nozzles 11. The latter are arranged and shaped to project I spray jets 12 directed downward towards objects carried by the run 8. The load carrying run 8 advances above ia chute ", , ~
or trough 13 forming part of the liquid-draining unit 5 `~

2~ a.nd servirlg to cnllect the liquid origi~zting from t~e spray nozzles 11 in the station 9 situated thereabovè. The - trough 13 is suitably provided with an incli~ed bottom wall 14 discharging into a drain pipe 15. Liquid ~rom the ~ , spray nozzles 11 thus will collect in the troug~ 13 and is caused to flow out through the discharge or drain p~e 15.
Thereafter the liquid is suitably fed back to the tu~es - lO by a pump tnot shown) to be discharged through the spray nozzles, ie. the liquid is recirculated.
The load carrying run 8 of the con~eyor belt 3 then will pass beneath a station 16, which also forms part of ;~
the liquid supplying unit 4 and is adapted to sùpply clea~
; .
' ~ .

- .; - , - - . - . ...... .. , ~ ...... .. . . .

~ . . . , . -4~7~4 f~ushin~ uid Th~s liquid is supplied to the objects throu~ a nu~ber o~ Cpreferably t~o) slot orifice nozzles 17 and 18, Each such slot orifice n~zzle 17, 18 is designated and arranged to project a uni~orm and kni~e blade shaped flush jet 19, 20 directed at an angle o~ 30 to 60, pre~erabl~ 45, relative to the load carryi~g run 8 of the conveyor belt and oriented o~liquel~ against t~ direc~ion of advance of the run.
Th~ ~lushing liquid together ~ith the entrails o the I0 ish is collected by a chute or trough 21 forming part of the liquid draining unit 5 and having a bottom ~all 22 in-clining downward towards a discharge conduit 23. Disposed in the trough 21 or in the conduit 23 is at least one ~ilter or strainer (not shown), whereby the entraiIs can be filtered o~f and about 80~ of the liquid can suitably be recirculated to ~aid slot orifice nozzles 17, 18 by ; a pump ~not shown~
The conveyor belt 3 is suitably made of a nett~ng which is relatively coarse meshed in order, together ~ith liquid, to pass therethrough residual skin fragments and an~ ~in remnants.
The machine thus described is fairly well suited ~or carrying out the method of the present in~ention. According to th.is method, salted9 seasoned or otherwise pre treated (for instance vinegar prepared) fish, preferabl~ herring filets, is treated to cause denaturation of the skin of the fish by contacting the skin with an acid; pre~erably acetic or citric acid, which is capable of separating proteins, ie. of breaking up peptide bonds. The acid is suitably - 30 maintained at a temperature of 14 to 20C, preferabl~ 15 to 17 C. In addition to acetic or citric acid, an~ other acid suitably for use in the ~ood production industrr and h.aving the propertie~ just described may be u$ed.
To carry out the method of the invention~ the fish is ;:
placed on th.e load carrying run 8 of the conveyor belt, ~;
and if fish filets, preferably herring filets, are to be treated they are d~sposed ~ith.t~eir skin side up. T~e converor ~elt 3 is started and t~e flsh is passed through station 9 at ~hich the fish is sprayed with the ac~d ~hich is supplied under pressure through the spra~ nozzles 11.
Th~ denaturation takIng place durlng the spra~ing o~eration '.;
is caused by the act th.at the distance fro~ the iso-elect~
rical point increases, meaning a pH-displacement towards the acidic region. At the same time sodium chloride will ..
disappear, which involves an increase of the bonding ~orces .
between the peptide chains at the acidic.side of.the iso-electrical point. This is true for sodium concentrations below 5~. This treatment gives the skin a gelatinous . ...
I consistency, caused by th.e drop below the iso-electrical `;~
point. The effectiveness of the treatment is adjustable -by varying the speed of advance of the conveyor ~elt 3, ie. the speed of conveyance of the fish, through station 9, and said effectiveness can also, or alternatively, be adjusted by.varying the pressure of the spra~ jets and/or : -:,~, . . .
the spacing of the spray nozzles 11 from the load carrying run 8. It is preferred to project the spray jets or to -dispose the fish on the conveyor belt in such a ~ay as to ~:.
cause the spray jets to hit skin covered portions of the ~.. :
,. . . .
ish only, ,-~ue to the treatment thus described at least the ~ :
major portion of the skin will have a gelatinous con$.ist~ ..
ency when the fish is leaving the station 9~ t~e treatment liquid used being si~ultaneouSl~ recirculated $or reuse, thus permitting a very low acid co~sumptlon. :~

~04~L7~4 :~ Afte~ this treatment o~ th.e fish skin (~h.ich can now .
easily be ~lushed away), the fish. is transferred into the clean flushing station 16. The skin and any fin remnants are flushed away by means of th.e knife-like jets l9, 20 from the nozzles 17, 18. To this end the fishes should be placed in such positions on the load carrying run 8 of the con~eyor bel~ 3 that the jets will not impinge the fish against its meat ~i~re structure, since other~ise there would be a risk of splitting up the meat. For example, the firs:t jet l9, as seen ~n the direction of advance, may be directed to impinge the skin only ..
slightly inclined relative to the direction of advance, : while the second jet 20 is caused to impinge the skin from a more inclined direction relative to the direction of advance It is preerred7 however, to direct the jets in relatively parallel directions and so as to form ! an angle of 30 to 60, for instance 45, with the load . carrying run 8.
These jets l9, 20 operate to roll the skin, being in ~ :
a gelatinous condition after said denaturation step, off the 1sh without causing an~ damage to the same. Th.e skin ~.
is flushed mainly downward th.rough the conveyor belt run 8 and is discharged through the trough 21 and conduit 23.
The flushing liquid is su~plied at a pressure o~ for example, about 2 kp/cm2 and this pressure can be ~aried according to the fish size and the degree of skin dena~
turation. The liquid may suitably be water which might be recirculated for reuse, while any skin remnants are filtered off in the course of the recirculation, t~us ~
involving a low consumption of fresh water.
Thus, at station 9 a chemical treatment, and at ..
station l6 a mechanical processing o~ the fisl~ is carried o~t. : `

~ 04~7~
In order to effect a completely automated p~cessing of th.e fis.h., the latter, acco~ding to a development of ., . . . . , -the invention, .can be processed in a fin cutting device 24. . ..-This device comprises a machine frame 25 (indicated diagrammaticall~ only~ w~.ich is disposed close to, or is rigidly secured to, the machlne frame 1. The frame 25 ..
carries a power-driven conveyor belt 26 extending in an ~. .
endless loop about two end rollers 27, 28 and a guide ~.
roller 29. These rollers 27 to 29 are mounted on the machine frame 25, and at least one of them is power ~.
driven for driving the conveyor belt to cause its top run ..
to move ln the sense indicated by arrow 'IB" and to form a load carrying run or conveying part 30 which extends from a fish deposition or feed table 51 to the load .~.;
carrying run 8 of the conveyor belt 3. .
The conveyor belt 26 is composed of a plurality of ! endless conveyor elements 31, for instance flexible plastic tubes, disposed closely side by side, and the .. -belt is divided by stationary frame mounted, elongated :.
guide members 32 into longitudinally extending section 33, 34, 35, 36, each including ai pluraltiy of, for . .
instance four or five, conveyor elements 31. ;~.:
The guide members 32 preferably project upward to the level of the top surface of the load carrying run ` ;.
(ie..flush with the conveying path 30 formed by this run) or project slightly above this top surface. :
The guide members 32 are directed towards a fin cutting asse~bly 37 including a pluraltiy of cutting members in the ~orm of knie~edge cutters 38 ~hich are mounted on a stationary frame mounted shaft 39 arranged to be driven by a driving mech.anism Cnot s~own). Each cutter 38 comprises two circular knife element$ 40 and `~

co-ope~ates ~ith an as$ociated guide mem~er 32 which pro-jects into the space between the t~o circular knife elements 40. T~e width o~ this- space is variable at least in that one of th.e knife elements 40 of each cutter 38 is displaceably mounted on the shaft 39 and adapted to be clamped in place by a clamping screw 41 or the like. Each knife element 40 depends beneath the conveying path 30 ~ and rotates in the sense indicated by arrow "C".
To guide the fins cut away downward, and beside the - knife elements, elongated stripper 42 are disposed ~hich, by means of holders 43, are mounted on the machine frame 25 above the conveying path 30. Each stripper extends towards one of the cutters 38 and also downward to term~
inate between the knife elements 40 thereof at the level of j the conveying path 30 or slightly therebelow or thereabove.
The holders 43 are preferably so designed as to enable all the strippers 42, or each individual stripper 42, to be adjustable into different angular positions andlor into different height levels relative to the conveying path 30.
, 20 The fin cutting assembly 37 further comprises a Knife-; protection cowling 44 which is movably mounted on the machine frame 25 by hinges 45 or the like. The cowling 44 can be swung upward from a protecting position (arrow ?l~t) for uncovering the cutters 38~ so that the latter can ~easily be cleaned or readjusted when required.
To ensure removal of cut off fins, it may be of advantage to equip the fin cutting assembly 37 with a flushing device 46. The latter preferably comprises a conduit 47 which is fixedly or rotatably mounted on the cowling 44 and extends along the underside of th.e co~ling 44. The conduit 47 is ~ro~ided ~ith nozzles 48 adapted to project relatively forceful liquid-jets 49 from a~ove - 8 - l ~7~
,., ~: in an ~nclinea dir~ction ~n~rdly ~et~een the kni~e ele~ents 4Q of each cutter 38, so as to cause the jets 49 to ~ass at t~.e upstre~m or in~eed side o~ the s~.aft 39 of the fin-cutting assembly 37. ~--- Th.e jets 49 ejected by t~e nozzles 48 are e~-Eective to press the cut off fins guided do~n~ard b~ the strippers 42 downward into a chute or gutter 50 extending ~eneath .
the knives and ~hose bottom ~all is inclined so that th.e -, fins can flo~ over laterally from the machine and can be collected as waste. ~. .
For processing the fish. filets are placed on the table 27 and are then fed sepa~ately or individually ont~
the conveying path. 30 with their skin side u~. Each filet, .
which has normally a longitudinally extending recess beneath its back fin portion, is placed in a ~anner to ~
cause this recess to be disposed above and to extend .
along one of the guide members 32. The filet thereb~ ~ill . .:
: .
be disposed ~uite properly relative to one of the cutters .~:
38. The guide member 32, when t~.e file* is being conveyed :~
in the directiGn indicated by arrow !IB~ towards the ~in ~
cutting assembly 37, will guide the filet in such a ~ay towards one of the cutters 38 that the knife element 40 of the actual cutter will cut the filet into three parts, vix. one "central part" containing the back fin of the fish ~.
and being discarded as ~aste, and t~o "side parts" which `.
are advanced to the conveyor run 8 for dena~uration. 1:
The method and apparatus thus described by ~ay o~
example a~e intended to elucidate principles o:E the inventive in a non~limiting sense.

,i .' ;' . . .'.~

Claims (15)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. A method for removing skin from salted, seasoned or otherwise pre-treated fish, preferably herring filets, comprising the steps of denaturing the skin on the fish by. contacting the skin with an acid, preferably acetic or citric acid, removing the denatured skin, and flushing the fish with a medium, preferably a liquid, supplied under pressure.

2. The method of claim 1 wherein the acid used for the denaturation has a temperature of 14 to 20°C, preferably 15 to 17°C.

3. The nethod of claim 2 wherein the fish is conveyed along a predeterminal path and is first passed through a spraying station for the denaturation, and then passed through a flushing station for flushing off the skin and any fin remnants.

4. The method of claim 3 wherein the fish is conveyed through the spraying station so that the spray jets impinge only skin covered portions of the fish, preferably herring filets.

5. The method of claim 4 wherein the denaturation effect at the spraying station is adjusted by selectively varying the conveying speed of the fish, the pressure of the spray jets and the spacing of the spray nozzles from the conveying path.

6. The method of claim 5 wherein the flushing off of the skin and any fin remnants is effected initially by subject-ing the skin covered parts of the fish. to at least one first knife-blade shaped flushing jet which is directed against the direction of conveyance, and subsequently by subjecting the skin covered parts of the fish to at least one second flushing jet which is also directed against the direction of conveyance.

7. The method of claim 6 wherein said first flushing jet is directed slightly against the direction of conveyance and said second flushing jet is directed against the direction of conveyance so as to cause it to form an angle of 30 to 60°C, preferbaly about 45°, with the path of conveyance.

8. The method of claim 7 wherein the denaturation acid is maintained in contact with the skin until at least a major portion of the skin to be removed will have achieved a gelatinous consistency.

9. The method of claim 8 wherein the acid used for the denaturation step is capable of separating proteins, ie.
of breaking up peptide bonds.

10. The method of claim 9 wherein water is used for flushing off the skin.

11. The method of claim 10 wherein the acid used in the denaturation step is recirculated after it has been used to treat the skin.

12. The method of claim 11 wherein at least a major portion of the flushing water, after having flushed off skin, is drained through the conveyance path.

13. The method of claim 12 wherein before said denaturation step the fish is conveyed in the form of filets along a path to cause each filet to pass a cutter adapted to cut the filet into three parts, viz. a central part containing the back fin of the fish and discarded as waste, and two side parts which are advanced to the denaturation step

14. Apparatus for carrying out the method of claim 1 for removing skin from salted, seasoned or otherwise pre-treated fish, preferably fish filets, comprising a first conveying path (30) including, on the one hand, a plurality of longitudinally extending, endless conveyor elements (31) and, on the other hand, a plurality of stationary guide members, (32), each guide member projecting towards a double-edged rotary cutter (38), said conveying path (30) being longitudinally juxtaposed to a succeeding conveying path (3) which extends beneath a denaturation station (9) including spray nozzles (11) for supplying acid, and beneath a clean-flushing station (16) including flushing-jet nozzles (17, 18) for supplying a flushing medium.

15. Apparatus according to claim 14 wherein a nozzle (48) is associated with each rotary cutter (38) and adapted to direct a flushing jet into the space between the two knife elements (40) of the rotary cutter (38) to flush away fin remnants which have been cut off by said cutter (38).