Development of a Squid Skinningand Eviscerating System
R. PAUL SINGH and DANIEL E. BROWN
Despite its excellent food value, aNorth American market for squid is vir-tually non-existent. The appearance ofwhole squid is unappetizing to many inthe market place despite its relativelylow retail price ($0.69 to $0. 99/pound).The average consumer does not knowhow to clean or prepare whole squid forconsumption. Seafood restaurants serv-ing squid find the demand low and thehand-cleaning costs high. Hand clean-ing adds $1.50 to $2.00/pound to theprice of squid for the restauranteur.Prepared foods made from cleanedsquid meat have been well received inpreliminary tests (Berk, 1974), and thisshows that there is a potential marketfor squid in this country.
One species of squid abounds off thecoast of California, Loligo opalescensBerry (California Market Squid). Cur-rent methods for processing squid bythe California fishing industry involvecanning whole squid for foreign mar-kets and freezing whole squid for bothdomestic and foreign consumption.The high costs of manual cleaninglimits its use to small-scale special-order vendors. Cleaning involves re-moving the head, eyes, skin, viscera,ink sac, and backbone from the mantle.
ABSTRACT-A squid skinning and evis-cerating machine was designedfor Califor-nia market squid, Loligo opalescens. Vari-ous operations such as orientation, cutting,skinning, and evisceration were completely
This leaves a white flesh cone whichcan be split into a fillet. The tentaclesare saved intact for human consump-tion. Currently, there are no mechani-cal systems available commercially forcleaning squid. The development of anindustrial-scale machine for economi-cal cleaning of squid could have a rev-olutionary effect on this industry. Theoverall goal of the research reported inthis paper was to develop a completelyautomated squid processing system.
Squid and its various components areshown in Figure I. The body wallthickness is 3-5 mm (0.1-0.2 inch). Thecleaned body, called a mantle, resem-bles a hollow, flexible cone. This coni-cal shape is used in the alignment,ducting, skinning, and evisceratingprocesses of the machine.
R. Paul Singh is Associate Professor of FoodEngineering, Department of Agricultural En-gineering, Department of Food Science andTechnology, University of California, Davis, CA95616. Daniel E. Brown is Junior DevelopmentEngineer, Department of Agricultural Engineer-ing, University of California, Davis, CA 95616.This research was supported by Sea Grant ProjectNo. R/F-33, National Oceanic and AtmosphericAdministration.
automated. Solenoid valves were used tooperate the various components for thecleaning operations. The output from themachine was a cleaned white mantle intubular shape and tentacles. The machine
Orientation and Alignment
The basic data needed to design theorientation and alignment componentwas obtained by Brooks and Singh(1979). The coefficient of sliding fric-tion of the squid tentacles was found tobe higher than that of the mantle. Thisfact allowed the squid to rotate into thedesired alignment to slide mantle-firstinto the machine. Tests with themachine indicated that the squidoriented within their own length. Thisoperation is shown in a schematic inFigure 2.
The squid slid into an alignmenttrough to be positioned for separation oftentacles and was also cut near thebody-cavity opening for further proces-sing (Fig. 2). Cutting through the squidbody, 6.4 mm (0.25 inch) from thisbody-cavity opening, greatly facilitatedskinning, evisceration, and backboneremoval. The strongest attachmentpoints for the skin, viscera, andbackbone were located by Brooks( 1978) on the ring of flesh severed fromthe body cone with the head/eye mass(Fig. I).
The alignment trough, 19.1 mm(0.75 inch) wide, accepted the squidfrom the orientation slide in any axialposition and supported it so that the
operates with a low consumption oj water.The pilot-scale machine cleaned squid at arate oj Jour squid per minute. Industrialscale-up Jor processing 10 tons oj squid per8-hour shift is explored in the paper.
Figure I. -Cleaned squid parts above.whole squid below
Half at troughpivots aftersquid is cut
Ducts for tentacles.eyes, and body
Sl1uld rotates 90° induct and falls onto peg,
open end down
When squid IS positionedon peg, high pressurewater Jets rei nove skin~
:J'.'____~ Water nozzles force
F'an shaped \ squid body onto pegspray 50°
Peg rotates at",...1 I '\400-1,000 rpm '-LJ..../
Waler lets aid thesliding motion~
ElectriC eye senses passingof squid and starts thealignment process -f';;/1
Telltacles of squid dragwhile moving down slide,
body rotates 90° clockwiseor counterclockwise
Figure 2. -Alignment. cutting. and dueting systems of squ id cleaning machine.
Marine Fisheries Review
Figure 3. -Squid skinning and evisceration system.
body-cavity opening protruded abovethe rest of the squid. Alignment pinsengaged the protruding lip of thebody-cavity opening, as shown inFigure 2, and pushed the squid in thetrough forward until it was correctlypositioned opposite the rotary knives.
The tip speed of the rotary kni veswas 5.6 m/second (18 feet/second).The squid were cut quickly and cleanly.Since the body-cavity opening wasused as the alignment point, the bodylength, L 1 (Fig. I), and the tentacle/head length, L 2 , may vary without af-fecting the alignment efficiency. Thelength L J may vary from 88.9 mrn (3.5inches) to 170.2 mm (6.7 inches) andL 2 may vary by the same extremes(Fig. I). The size variance and sizeratio of tentacles to mantle was there-fore el iminated as a factor in aligningand preparing squid for processing.
Ducting of Squid
The elongated, conical shape of thesquid mantle facilitated its ducting fromthe alignment trough to the skinning/evisceration peg. The mantle was firmenough to remain oriented longitudi-nally in a close-fitting duct, 38 mm (1.5inches) to 51 mm (2.0 inches) in diam-eter, and could be transported by gravityor with the aid of moving water overany distance required.
The hollow conical mantle wasducted onto a rotating peg, as shown inFigures 2 and 3. The viscera, attachedto the dorsal side of the mantle interior,was displaced to one side as the mantleslid onto the peg. The squid is shown inplace in Figures 4 and 5. The mantleassumed the rotation of the peg, 400-1,000 rpm, and rotated along its majoraxis below the water jets used for skin-ning. The longer the mantle, the moreof the peg was covered. Again, the sizeand length variation problems wereavoided using this holding technique.The body-cavity opening was kept openand circular as it was ducted onto thepeg by a flexible-tube water-jet funnel(Fig. 2, 3). The tubes of the funnelsupported all sides of the flexible man-tle wall as it passed through, keeping itcircular. Jets of water issued from these
July-A ugusl 1980
Skinn ing ----;--++--.1peg
:t:I IWater in
tubes along the length of the body, ac-celerating the conical mantle onto thepeg.
One nozzle, producing a fan-shapedwater spray, was used to skin the man-tle. The mantle draped over and sup-ported by the peg, received an evenblast of water as it rotated under thewater nozzle. The fins were shearedfrom the mantle by the skinning nozzleand were propelled out and away fromthe rotating peg. The fins dragged much
Evisceration clamps, stops rotationof squid for gutting step..
Water jets remove viscera,backbone, ink sac
of the skin off with them because of theskin's firm attachment at their edges.The remainder of the skin was peeleddown the length of the mantle by thedownward blast from the water nozzle.
Evisceration and Pen Removal
The remaining cleaning operationsnamely, evisceration, ink sac removal,and backbone (pen) removal were ac-complished by water jets provided in-side the rotating peg (Fig. 3) over
- ...... -
Ring of water jetsremoves squid
Squid, skinnedand eviscerated
L Retra::table deflection plateYL..-_Jjf---i--l-Z---IB;~o
[::J~ :Water jets direct squid7 I
out of machine I
Figure 4. -System tv remove cleaned squid from machine.
which the mantle was still draped. Apair of clamps closely matching theconically shaped mantle exterior en-gaged the squid body, stopping its rota-tion relative to the peg, and supported itfor evisceration. The rotating peg'swater jets swept past the interior of themantle, giving an even 360 0 coverage,shearing off the viscera and membranesholding the backbone. The eviscerationclamps kept the mantle from blowingup like a balloon. The viscera wereflushed out the open bottom of the man-tle. The viscera, skin, and backboneswere collected in a large pan under themachine. The water was drained off.
Removal of Squid From Machine
The cleaned squid mantle was thenpropelled off the peg and out of themachine by a ring of water jets at thebase of the skinning/evisceration peg(Fig. 4). A deflection plate was movedinto position between the skinning pegand water-jet funnel. Water nozzles di-rected the flight of the cleaned squidmantles out of the machine.
The tentacles and eye/head portion ofthe squid, having been severed from thebody by the rotary knives, were ductedout of the machine for further process-ing (Fig. 2). No attempt was made toskin the tentacles or to remove the beakfrom them. The tentacles are never-theless highly desirable for humanconsumption.
Allied Design Features
Half of the trough, which supportedthe squid for the cutting process,pivoted to allow the th.ree parts ofthe squid-mantle, head/eyes, andtentacles-to fall into their respectiveducts, as shown in Figure 2. Water jetsaided in cleaning the trough of squidparts. The contour of the duct intowhich the body portion falls (Fig. 2)ensured that the squid was ducted to andinserted on the skinning peg properly,body-cavity opening first.
The water nozzle used in skinningproduced a thin fan-shaped high-velocity cutting sheet. The operationpressure used was 60-80 psi. Watersupplied to the nozzles and other waterjets was controlled by solenoid valves
80 Marine Fisheries Review
Figure 5. -Squid mantle in place on skinning and evisceration peg.
mounted on a manifold. The manifoldwas pressurized by a positive displace-ment roller pump.
The water jets used in eviscerationcut in the support peg are visi ble inFigure 3. The peg was hollow and thewater supply to it was also controlled bya solenoid valve. A rotary seal at itsbase allowed for its rotation.
The operation of the pilot-scale squidprocessing machine (Fig. 6) was fullyautomatic. The control system for thevarious functions performed by themachine was activated by an electriceye. It sensed the squid entering themachine via the orientation slide(Fig. 2). It set in motion a rotary step-ping switch. This activated the solenoidvalves supplying water to the nozzles,or the solenoids, providing linear mo-tion to devices like the alignment pinsor evisceration clamps. Fifteen secondswas required to run through the se-quence producing a cleaned squid.Another squid was then inserted intothe machine initiating the sequenceagain.
The pilot-scale squid processingmachine has been tested extensively toobtain information on its performance.Two samples of squid were used. Thefirst was obtained frozen in I .5-kg(3.3-pound) boxes from Meredith FishCo. t, Sacramento, Calif. The secondsample was obtained 24 hours after itwas caught in the ocean from Sea Pro-ducts Co., Moss Landing, Calif. Thissample had been placed in cold storagein 10-kg (22-pound) plastic-linedboxes. The top layer of squid in theseboxes was found to be frozen and theremainder was unfrozen. These squidhad been stored in ice water prior topackaging. The unfrozen squid weresorted into three groups by mantlelength before being fed into themachine. The groups were: 80-110 mm(3.2-4.4 inches), 110-150 mm (4.4-6inches), and 150+ mm (6+ inches).
Frozen whole squid were thawed,
I Mention of trade names or commercial firmsdoes not imply endorsement by the NationalMarine Fisheries Service, NOAA.
July-A ugusr 1980
drained of excess water, and weighedbefore being fed into the machine. Theoutput of the machine was also drainedand weighed. The yield by weight con-sisted of cleaned mantles and severedtentacles (beak not removed) drained ofwater. In 22-25 percent of the sampleoutput the viscera were still connectedto the body by a thread of tissue even
though the viscera had been removedfrom the body cavity. These viscera andbits of skin could be separated easily byhand. These squ id were included in theyield by weight data. Those squidwhich were clearly not an acceptableproduct, i.e., unskinned or uneviscer-ated, were not included in the yieldweight.
Figure 6. - The squid skinning and eviscerating machine.
in Figure 7 seem to indicate the skin-ning percentage was higher in the fro-zen sample. The fresher squid ap-peared harder to skin. Data presented inFigure 8 indicate that squid greater than150 mm (6 inches) were very difficult toskin totally; squid less than 110 mm(4.4 inches) were easier to skin. Smallportions of fins and/or skin could beeasily removed manually. Only thosesquid from which all of the viscera hadbeen removed by the machine werecounted as being part of the fractiontotally eviscerated. Figure 7 indicates
that 63-73 percent of the squid weretotally eviscerated. An additional 22-25percent of the output was then includedin the yield after hand separation of theviscera, removed from the body by themachine but still attached by a thread oftissue. It is clear in Figure 8 howdifficult it is to totally eviscerate thesquid over 150 mm (6 inches). Theevisceration rates in these samples were33-53 percent. Manual separation waslargely feasible in the fraction of theselarge squid that were not evisceratedtotally.
r--:---J--.........,._-:~-::;s: - - It.ll l · t 'I'-: .. I 1_"_'''_'__..Results and Discussion
2Ghio, T. 1979. Ghio Seafood Products, Inc.,San Diego, Calif. Personal commun., 10 July.
An important parameter in mechani-cally assisted cleaning of squid is theyield of edible portion. The yield byweight of hand-cleaned squid rangesfrom 50 to 55 percent according toGhi02 • In the tests performed with thepilot-scale machine, the previously fro-zen squid samples yielded 45 percentedible meat, and the unfrozen samples52 percent edible meat as shown inFigure 7. The lower edible meat yieldin the frozen sample is due to dehy-dration of the frozen sample duringstorage.
The dimension of mantle length ap-pears to have a significant influence onprocessing rates. The unfrozen samplewas sorted by mantle length into threesize classes. The 110-150 mm (4.4-6inch) squid, numerically composing 70percent of the catch, and 72 percent byweight, averaged 51 percent ediblemeat return as shown in Figure 8.Squid over 150 mm (6 inches), 21 per-cent of the catch by weight, yielded 58percent edible meat. Squid less than110 mm (4.4 inches) yielded 36 percentedible meat. These small squid may notbe worth processing since they com-pose only 14 percent of the catch nu-merically and only 7 percent by weight.Thus, yield of edible meat from thepilot-scale machine depends on the ini-tial size of individual squ id processed.This fact clearly indicates the need todevelop a size grading device thatwould allow the system to achieve highprocessing rates.
It should be noted that a small portionof the trailing edge of the mantle is cutand discarded in the alignment step. Inaddition the fins are removed during theskinning step. However, these opera-tions do not significantly reduce theyield since, although these lost piecesare edible, they are very thin in crosssection.
The quality of the cleaned squidwas evaluated in terms of the desiredattributes, e.g., samples completelyskinned, eviscerated, and boned. Data
82 Marine Fisheries Review
Figure 8. -Processing data for unfrozen S4uid sorted by mantle length.
aliGned forc" lIinet n ivel
Handseporolionof visceran.c ••• ary
evisceratedI 0 tally
Fratt ionof ,quid101t inlII.ttll",
Figure 7 .-Processing data tor frozen and unfrozen S4uid.
Unfrozon Squid, Montle LonQth:
~IIO-I~O mIT'. acmple sizt: 196
\.::':.) 150-+ mm, sample size; 41
eO-IIO mm, sonaple lize: 40
Yield by F fOC I io n Fr oc lion F· ac I ion H 0 n d Fr a eli on Fr a eli 0 n
wei 9111 of squid skinned eVlsceroted seporotion booed aligned for
10 sl ;n to' oIly I oto 11 y of viscera to 10 11, cutting
machIne nee e sso r y k ni yes
o L.-----'-""'·ccJ··L....L.._~ ",,'.:L-J._....lll.lL:./'-'-•. -L----l:uL\c:.L:---'-_
[?ZZLI Frozen Squid, Sample Size' 356
o Unfrozen Squid I Sample Size 277
During processing it was observedthat the ink sacs removed with the vis-cera from the frozen sample came outintact without much ink release. How-ever, in unfrozen samples, a stream ofink flowed with the evisceration waterfrom the interior of the squid. The ink,however, was completely flushed fromthe squid body cavity, and it did notcontaminate or discolor the meat.
A squid was counted as boned totallyif the pen was completely removed andnot retained by the body or unremovedviscera. The fraction boned totally washigh. The pen was at times hung up inthe viscera which was out of the bodybut still attached by a thread of tissue.These squid were not counted as beingboned totally and the pens were re-moved manually.
The cut provided through the squid atthe body-cavity opening assisted insevering the attachments for the penand viscera making them easier to re-move. Proper alignment ensured thatthis cut was made with the minimumloss of edible meat. Inspection of the
• output from the machine indicated thatthe fraction of squid aligned pruperlyfor cutting knives was very high. Theproper cut was made in at least 80 per-cent of the squid fed into the machine.The data for unfrozen, sorted squidshow that squid over 110 mm (4.4inches) were aligned at an 84-88 per-cent rate (Fig. 8). Squid under 110 mm~4.4 inches) were aligned at a signi-ficantly lower rate (47 percent) in thissample. In addition, they were boned ata slightly lower rate (68 percent vs. 78and 79 percent for the I 10-150 clnd150+ mm (4.4-6 and 6+ inches) squid,respectively). However, in the 80-110mm (3.2-4.4 inch) sample the squidwere headed, skinned, and evisceratedat a high rate compared with the othersize ranges. Their smaller size probablymakes them easier to skin and eviscer-ate, despite improper alignment.
Flesh firmness also had an effect onthe frequency of alignment. Squidbodies that were not firm were not en-gaged properly by the alignment pins.The edible meat loss was then higherthan necessary.
Water consumption rates were mea-sured in operating the pilot-scale
July-August 1980 83
machine. The maximum water con-sumption rate was 0.38 I/second (6.0gallons/minute).
In an industrially-viable squid-processing machine it is anticipated thatthe single channel unit can be dividedinto two stages, namely, J) alignmenttrough, and 2) skinning and eviscera-tion peg. Each stage could be controlledindependently and thus could processsquid simultaneously. The processingtime for each stage is 7 -8 seconds andthis would have the effect of doubl ingthe output from its current 4 squid/minute or 18 kg/hour (40 pounds/hour).The number of pegs and troughs couJdthen be multiplied to get the requiredtonnage. Using a 6 squid/pound aver-
age, an 8 squid/minute operation, and aprocessing goal of 10 tons/8 hours,from 30 to 35 peg units would berequired.
Hydraulic conveyance of squid toeach of these units can be accompl ishedwith a fluidized ducting system of a38-5J mm (1.5-2.0 inch) diameter tub-ing. This has been tried on a small scalein our laboratory. Squ id were separatedfrom a batch loaded holding tank andducted to another location one at a time.Further work on this component of pro-cessing squid is currently underway.
In summary, a pilot-scale squ idcleaning machine has been developedto automate the cleaning process. Theedible yield from the machine, 45-52percent of the total body weight, wascomparable to hand-cleaned squid. Theyield depended on initial size of the
individuaJ squid and prior handling op-erations. The processing efficiency washighest for squid with a body length ofJJO-150 mm (4.4-6 inches). The pilot-scale machine forms the basic unitaround which an industrial-scale squidprocessing machine could be built. Theprocessing rate in the pilot-scalemachine was 4 squid/minute or 18 kg/hour.
Berk, Z. 1974. Processing squid for food. MITSea Grant Rep. MITSG 74-13, Mass. Inst.Techno!., Cambridge, 41 p.
Brooks, L. A. 1978. Development and testing ofa device to automatically clean California mar-ket squid (Loligo opalescens). Master'sThesis. University of California, Davis.
___ ,and R. P. Singh. 1979. Properties ofsquid useful in designing of cleaning and han-dling systems. Trans. ASAE 22(3):658-663.
Marine Fisheries Review