5. EQUIPMENT FOR FISH CANNING


5.1 Machines for Canning Sardine

5.1.1 Grading machines
5.1.2 Nobbing machines
5.1.3 Flash cookers
5.1.4 Smoking ovens

5.2 Machines for Canning Tuna

5.2.1 Pre-cookers
5.2.2 Filling machines

5.3 General Fish Processing Machinery

5.3.1 Brining machines
5.3.2 Exhaust boxes
5.3.3 Sealing machines
5.3.4 Retorting systems
5.3.5 Standard batch retorts for processing cans in steam
5.3.6 Crateless batch retorts for processing cans in steam
5.3.7 Batch retorts for processing glass containers in water
5.3.8 Hydrostatic retorts for processing cans in steam


For detailed descriptions of machinery used in production of the major , commercially canned fishery products, and for accompanying flowsheets, reference should be made to the FAO Fisheries Circular No 784. Planning and Engineering Data. 2. Fish Canning (1985), in which can be found also, examples of plant layouts for the major species canned. This Chapter contains a description of the processing equipment specifically used for the production of canned sardines and tuna (following the procedures outlined in Chapter 4), together with a description of the thermal processing equipment which is basic to most fish canning operations.

5.1 Machines for Canning Sardine

5.1.1 Grading machines

Grading machines are used to sort sardine and sardine-like fish into regular sizes. Machines are available which, in a single pass, segregate the fish into four different grades, with thicknesses ranging from between 5 mm and 33 mm. The fish pass, tail first, down inclined oscillating tracks which are separated by gradually widening gaps. When the gap between the tracks becomes greater than the thickness of the body, the fish fall through to belts below, from where they are segregated into storage bins or passed onto conveyors for further processing. The machines are fitted with water sprays which simultaneously wash the fish as they pass down the tracks.

Shown in Figure 24 is an example of a grading machine supplied by the Baader Company of West Germany. In the figure can be seen the feeding mechanism which deposits the fish onto the tracks down which the fish move while being graded for size. The Baader machine shown is designed to grade herring, mackerel, sprat and capelin.

Figure 24 Example of machine for size grading herring, mackerel, sprats and capelin (photograph courtesy of Baader)

5.1.2 Nobbing machines

There is a range of nobbing machines available for the removal of heads, tails and viscera of sardines and sardine-like fish; and there are also machines which automatically pack the nobbed fish into cans. Fish may be fed to the nobbing machines manually, by between three and five operators; however, there are also machines in which one supervisor can manage an automatic feeding operation. Shown in Figure 25 is an example of a Baader feeding machine designed to handle herrings, sardines, sprats and similar fish. The fish are raised on an elevator and passed to five feed channels for delivery to the nobbing machine (or other piece of processing equipment).

Once placed in the nobbing machine the fish are fed to cutting knives which shear the head from the body without cutting the throat. The head is then pulled away from the body, after which the rotating action of tapered fluted rollers remove the viscera. Shown in Figure 26 is a simplified sequential sketch of the fish as they pass through a Baader nobbing machine. The machines can be set to leave the tails on the fish, or alternatively, the tails can be removed and the body can be cut to standard lengths (in one or several pieces) to suit the size of the Cans. In Figure 27 are shown two pack styles available for sardines and other similar fish. Machines are available to handle fish ranging in length from approximately 10 to 45 cm, at a rate of 150 to 450 fish per minute (depending on fish size).

Figure 25 Example of automatic feeding machine designed to handle herrings, sardines, sprats and similar fish (photograph courtesy of Baader)

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Figure 26 Sequential stages of nobbing operation (photograph courtesy of Baader) .

In automatic nobbing and packing machines, fish are placed in moulded pockets (to suit the pack style) in which they are conveyed, in can lots, under rotating blades for the removal of the heads and tails. The fish bodies are then eviscerated by a suction process, after which they are automatically transferred to cans. In many traditional canneries the nobbing process is automatic but cans are still packed by hand on conveyors.

5.1.3 Flash cookers

Sardines are cooked and dried in flash cookers in open cans which are automatically transported through continuous machines. There are at least two systems available, however in each, the mode of operation is similar. Filled cans are automatically fed into a steam heating section where the sardines are cooked. For machines in which pre-cooking takes place while the cans are in the upright position, the filled containers are inverted to allow draining; however, when cans are inverted during pre-cooking, draining is continuous. At the completion of draining the sardines are dried, and the cans then proceed to the automatic discharge unit. In Figure 28 is a simplified line drawing showing the side elevation of a pre-cooking machine (supplied by Trio) in which the fish are pre-cooked and then the cans drained for approximately three minutes, prior to being returned to the upright position for drying.

The speed of the machines may be altered to suit the load and container size, typically the machines process in excess of 10 000 filled cans per hour.

5.1.4 Smoking ovens

In the manufacture of Norwegian style sardines, the fish are smoked either in a batch or a continuous system. The units consist of the drying chamber into which hot air (at around 40 C) is drawn. and a smoking section. Smoking ovens may be either simple batch operations into which are placed trolleys containing the smoking frames loaded with fish; or they may be automatic systems which continuously draw the fish on their frames through the drying and smoking chamber.

Figure 27 Examples of pack style available with .automatic nobbing machine (Photograph courtesy of Baader)

Equipment used for the remainder of the sardine canning process is similar to that described under the heading "General fish processing machinery" (see section 5.3).

5.2 Machines for Canning Tuna

5.2.1 Pre-cookers

The most common pre-cookers are live-steam cookers. fitted with condensate drains. vents and safety valves. The pre-cookers operate on a batch system. with doors at each end (so that fish may be rolled in and out on a flow-through basis). The fish are loaded into galvanized iron baskets. and the baskets are placed on racks which are rolled into the cookers for steaming.

Other preparatory stages taking place before filling are completed manually. and in many canneries. filling is also a manual operation. There are. however. fully automatic filling machines suitable for packing tuna in all pack styles in round and oval cans.

Figure 28 Side elevation of continuous flash cooker for pre-cooking sardines; (diagram Courtesy of Trio Mask in Industry A/S)

5.2.2 Filling machines

Machines are available for filling chunk and grated (shredded) tuna which operate at speeds of between 80 and 350 cpm with cans ranging from 112 to 445 9 (approx.). There are a number of manufacturers with various operating procedures, but one manufacturer (Carruthers Equipment Co., USA) has several machines for automatic tuna filling. In one machine (the Pack-Former) fish is discharged into filler bowls from where it is transferred into a series of piston pockets positioned around the circumference of the machine. As the filling heads complete a revolution, the fish is compressed into a cylindrically shaped slug in the pocket, in which form it is pushed out the bottom of the piston and is trimmed to the correct length, so that the weight of the pack in each can is controlled. The fish is then fed into the can which has been located below. A machine (a Carruthers Nu-Pak) operates on a similar principle, at speeds ranging from 200 to 600 cpm, with 225 g cans (and smaller).

Solid style tuna loins are packed fully automatically by a machine (a Carruthers Pak.-Shaper) which handles cans ranging in size from 112 g to 1.8 kg (approx.) at speeds from 30 to 130 cpm. The machines are fed with solid loins which are transferred to a forming hoop in which the flesh is molded into the desired shape and then cut off cleanly to produce segments of the required length (and therefore weight).

Equipment used for the remainder of the tuna canning process is described in the following section.

5.3 General Fish Processing Machinery

5.3.1 Brining machines

Brining machines are sometimes coupled with washing machines, so that the two operations occur simultaneously. In continuous applications, the machine is usually a rotating perforated drum partially immersed in a brine bath and through which the fish pass at a predetermined rate. In less sophisticated operations. brining can be a batch process in which the fish are loaded into perforated drums which rotate and, because of the tumbling action, gently transport the fish through the salt solution. Whether using automatic, semi-automatic or batch equipment, it is important that, the salt concentration be maintained at the desired level -this means that periodically the effects of gradual dilution must be monitored and salt added. The material used for construction of the equipment must resist the corrosive effects of the salt.

5.3.2 Exhaust boxes

The exhaust box is used to heat the contents of cans, so that they may be sealed hot, thus ensuring that, after cooling, a vacuum has formed in the container. Exhausting also drives entrapped air from the pack. Exhaust boxes may i take many shapes and forms, depending on the requirements of the cannery; basically they consist of a tunnel through which the open and filled cans pass while being exposed to atmospheric steam. They require a feed and a discharge mechanism, and a conveying system for transporting the cans from one end to the other. Recent models are frequently constructed with stainless steel, however many canneries still find painted mild steel systems adequate.

5.3.3 Sealing machines

When selecting can sealing machines. fish canners must consider the following factors:

In order to cater for the diverse requirements of fish canners, there is a wide range of machines from which manufacturers can choose a model to suit their operations. Since many sealing machines have features in common, the following is confined to a general description of the major categories which are readily available.

The simplest of machines are required by those packers who run their lines at speeds of from 8 to 25 cpm using hand operated or semi-automatic single-head equipment with motorized drives. For those with a low output (i.e., < 20 cpm), hand operated models are ideal -as with seasonal production or in those plants which are required to prepare test packs.

Single head seaming machines may be fitted with steam-flow closing or mechanical evacuation apparatus as a replacement for, or as an adjunct to, hot filling or exhausting. When mechanical vacuum closing is required the operator places the container (with the can end sitting in place on top of the can) in a chamber, which is then closed and evacuated by opening a line leading to a vacuum pump. When the desired vacuum is obtained in the chamber, the sealing operation is initiated by depressing a foot pedal which lifts the can up to the chuck on the sealing head and into position for double seam rolling. The first and second action rollers are sequentially brought into action while the can is rotated by the spinning seaming head. At the completion of the seaming operation the sealing chamber is opened to the atmosphere and the hermetically sealed container is removed. Machines of the type described can frequently have the facility for steam flow closing, in which case steam is injected across the headspace of the container (while it is positioned in the sealing chamber) immediately prior to double seaming.

Fully automatic in-line single-head steam flow closing machines which operate in the range of 70-90 cpm are available; while for canneries operating at higher speeds there is a variety of multiple-head machines from which to choose. Of the latter, three, four and six spindle machines are common and can be selected to cover seaming speeds of from 200 to 600 cpm, depending on can sizes and production capacity.

Machines for sealing glass containers generally do not operate at the speeds of can closing equipment, however, they can be fitted for steam-flow closing or mechanical evacuation. Fully automatic steam flow closing machines are available to apply caps at around 400 to 500 cpm (depending on container size), while semi- automatic machines can be operated at around 15 cpm. As with cans, vacuums in glass jars may be also obtained by hot filling, or by addition of hot brine, or by exhausting.

Laminated packaging materials are sealed by the fusion of the two facing layers of the innermost ply. The material is heated while clamped between jaws of the sealing machine for sufficient time for the two layers (usually polyethylene or polypropylene) to fuse and form an hermetic seal. One of the greatest difficulties faced by users of laminated packaging materials is that of ensuring effective seal formation. Under all circumstances the sealing surface must be clean and free of particulate matter, which can present difficulties when packing fish products, as it is not always possible to prevent flakes of flesh from contaminating the sealing surfaces. The solution to the problem is to clean the seal area before passing the package to the sealing machine, however, this further retards what is in many cases an already slow sealing operation.

5.3.4 Retorting systems

For a detailed description of recommended retorts and retort fittings reference should be made to the following publications:

The main types of retorts used in the manufacture of low-acid canned foods include the following:

  1. Batch retorts heated with saturated steam. These may be either vertical or horizontal and are by far the most common retorts used by fish canners. Simplified drawings of these types of retorts are shown in Figures 29 and 30; in Figure 31 is shown a less frequently used batch system for processing cans in saturated steam. The latter system is referred to as a crates. Brief descriptions of these systems are found in sections 3.6.1, 5.3.5 and 5.3.6.
  1. Batch retorts heated with water under pressure. These retorts are vertical or horizontal and are most frequently used for processing glass containers which cannot be processed in pure steam because of the risks of thermal shock breakage. They are also widely used for sterilization of products packed in aluminium cans with score-line easy open ends. Simplified drawings of these types of retorts are shown in Figures 32 and 33; operational guidelines are given in section 3.6.2 and features of the system are described in section 5.3.7.

Figure 29 Controls and fittings for a vertical batch retort for processing in saturated steam and pressure cooling

Figure 30 Controls and fittings for a horizontal batch retort for processing 1n saturated steam and pressure cooling (For code to symbols see Figure 29)

Figure 31 Crateless retort -operating sequence (Courtesy of FMC Corporation)

  1. Continuous retorts (other than hydrostatic retorts). Containers are passed through a mechanical inlet port into a pressurized chamber containing steam where they are processed before passing through an outlet port and. depending on the make of the retort. into either another pressurized shell. or an open water reservoir. for cooling. The motion of the cans through the retort causes some forced agitation which aids the rate of heat transfer to the SHP of the container.
  1. Hydrostatic retorts. A simplified drawing of this type of retort is shown in Figure 34 and the system is described in section 5.3.8.
  1. Retorts heated by a mixture of steam and air. The containers are processed under pressure in a system which relies on forced circulation (by a fan or a blower) for the continuous mixing of the steam with the air. Inadequate mixing can result in the formation of cold spots which could lead to under-processing spoilage. As with water filled retorts. this system is suitable for retortable pouches which require a counterbalancing overpressure to prevent their rupture.

Code to symbols:

A Water line
B Steam line
C Temperature control
D Overflow line
El Drain line
E2 Screens
F Check valves
J Petcocks
L Steam spreader
M Temperature control probe
N Reference thermometer
O Water spreader
P Safety valve
Q Vent
R Pressure gauge
T Pressure control
U Air line
V To pressure control instrument
W To temperature control instrument
X Wing nuts
Y1 Crate support
Y2 Crate guides
Z1 Constant flow orifice used during come-up
Z2 Constant flow orifice valve used during cook

Figure 32 Vertical retort for processing glass containers

There is a comparatively rarely used retorting system whereby sterilization is achieved by directly heating cans with flames from gas burners positioned underneath containers which spin past on guide rails. This system is suitable for packs which contain a high proportion of liquid, thus permitting rapid transfer of heat by convection, but it is not used commercially in fish canning operations.

The most frequently used style of retort found in commercial fish canneries today, is the static batch system for processing cans in saturated steam. A description of the fittings for these retorts is given in the following section; however, many of the other retorting systems referred to above are similar with respect to fittings and methods of operation. The most significant difference between static retorts and continuous systems, is that the latter must have container transfer mechanisms to regulate the movement of cans at a predetermined rate through the heating and cooling sections.

Code to symbols:

A Water line
B Steam line
C Temperature control
D Overflow line .
E Drain line
I El Screens
F Check valves
G Line from hot water storage
H Suction line and manifold
I Circulating pump
J Petcocks
K Recirculating line
L Steam spreader
M Temperature control probe
N Reference thermometer
O Water spreader
P Safety valve
Q Vent
R Pressure gauge
S Inlet air control
T Pressure control
U Air lines
V To pressure control instrument
W To temperature control instrument
Z Constant flow orifice valve

Figure 33 Horizontal retort for processing glass containers

Figure 34 Hydrostatic retort (Courtesy of Churchill Livingstone)

5.3.5 Standard batch retorts for processing cans in steam

Irrespective of whether retorts for processing cans in steam are vertical, horizontal or crateless, they have a number of features in common. The major fittings are as follows:

The steam supply should be capable of bringing a fully loaded retort to operating temperature within 15 min from "steam on" and to regulate temperature to within 1 C during the process.

The water supply should be sufficient to fill a fully loaded retort, against the pressure of the steam, within 10 min.

5.3.6 Crateless batch retorts for processing cans in steam

Crateless retorting systems are available in which loading, processing, cooling and unloading are all carried out fully automatically, often with the aid of computer control systems which enable one operator to supervise eight to ten retorts simultaneously.

Cans are automatically loaded through the top of the retort and fall into the cushion water below (step 1). When the prescribed number of containers have been loaded, the oncoming stream of cans is automatically diverted into the next retort, and the top of the retort is closed (step 2). Steam is forced into the retort and as it enters it displaces the cushion water through the bottom drain valve (step 3). Once all the air and water have been vented from the system and the retort reaches operating temperature, the process commences (step 4). At the completion of the scheduled retorting time, the steam is turned off, and water and compressed air are pumped into the vessel and initial cooling commences (step 5). After partial cooling, cans are released into the cushion water canal (step 6), which runs underneath the bank of retorts, and from there they are automatically transferred, on conveyors, into the cooling water canal.

Although offering considerable labour savings and flexibility, it is important that care be taken while loading and unloading the cans. In the former case there is a danger that, if the retorts are overloaded, or the cushion water level in the retort is too low, or if there are "floaters" (caused by insufficient removal of air prior to sealing the cans), incoming cans will damage the double seams of the uppermost layer of cans. Similarly, during unloading, seam damage can occur if the cans are permitted to drop out of the retorts in an uncontrolled manner. The risks to the seam are heightened at this stage if the cans are still hot, because the compound will be soft and the cans under positive internal pressure, so that damage to the double seam area may cause momentary venting of the seal. Because of the potential danger to the hermetic seals during unloading, it is strongly recommended that the water level in the cushion water canal be maintained above the level of the exit door (as shown in stages 5 and 6 of Figure 31). If this procedure is adopted, the cans gently float down and out of the retort, which means that their double seams are not exposed to as much physical abuse as when they are dropped directly into the cushion water lying below the level of the exit.

5.3.7 Batch retorts for processing glass containers in water

The operating principles for processing glass under water in counterbalanced retorts have been discussed in section 3.6.2. The similarities in retort fittings for processing glass in water and cans in steam are evident when comparing Figures 29 and 30, with Figures 32 and 33, respectively. The main functional characteristics peculiar to systems for processing glass are that:

5.3.8 Hydrostatic retorts for processing cans in steam

In the diagram of the cross section of the hydrostatic retort shown in Figure 34 can be seen the columns of water in the inlet and outlet legs which balance the pressure in the steam dome and give this style of retorts their name. As the height of the column controls the steam pressure, it also controls the temperature in the steam dome. Cans are automatically loaded onto the chain which carries them through a preheating zone at the top of the inlet leg and down into the column where they are heated by water which becomes progressively hotter the further into the leg they move. At the bottom of the inlet leg the cans emerge from the water seal and then travel up into the steam dome (or steam chamber). In some hydrostatic retorts the cans have two passes through the dome (one up and the other down), while in others the cans have multiple passes. In Figure 34 a two-pass system is illustrated. The severity of the process depends upon the residence time that the cans are in the dome (which is controlled by chain speed and chain length). and the temperature of the steam (which is controlled by the height of the water column). At the completion of the process the cans move back through the water seal, on the cooling side of the retort, and up into the cooling leg where they are exposed to progressively colder water. At the top of the cooling leg the cans pass through an air cooling section and then pass down a final cooling section where they are sprayed with cool water. The cooling water canal shown in the illustration is omitted in some hydrostatic retorts.

Because of the high capital investment, the time taken to adjust the conveyor systems to handle different can sizes, and the time required to bring the retorts to operating temperature, hydrostatic cookers are best suited to long I production runs. When dual chain systems are used, it is possible to process cans I of different sizes simultaneously, for different times but at the same temperature. While savings of floor space, gentle can handling, and gradual

changes in temperature and pressure, are attractive features of these retorts, the systems are expensive to install and maintain, and the costs of breakdowns can be high.