IES66233B2 - Production of smoked seafood - Google Patents

Abstract

Smoked fish which is fresh and moist in taste and has a relatively long shelf life is produced by receiving chilled raw fish at a temperature in the range of -1{C to +4{C and processed into fillets. Smoking is carried out in a chamber with three stages which lead directly into each other. The three stages are drying, smoking and purging, all of which are carried out at 22-26{C and a relatively humidity of 55-75%. Only 80-100 minutes is required for drying and 6-7 hours is required for smoking. An 80% beech/20% oak sawdust combination is used for smoke generation and the temperature of smoke entering the chamber is maintained below 28{C, this limit activating an alarm. Smoked fillets are immediately transferred to a chill area below 0{C and are left for a minimum of four hours. Post-smoking processing takes place at temperature of 12-16{C within a processing area. Salt may be applied to the fish before smoking.

Description

Production of Smoked Seafood The invention relates generally to production of smoked seafood, and more particularly fish.

Smoking of fish such as salmon is a traditional task which has been carried out for very many years. It was originally devised in order to prevent fish from decaying so that it could be stored for a long period of time. In more recent years, with major improvements in packaging there has been less need for smoking as a method for preserving fish. However, there is a strong demand for smoked fish because of its taste, which is appealing to very many people.

Probably the most important aspect of smoked fish production is to ensure that the end product is clean. A single example of an unhygienic product can have major adverse consequences for a producer. Because of this, one approach has been to use frozen fish. However, many consumers regard the end product as being inferior because the fresh taste is lost. Another approach has been to be use hot-smoking at which the fish is smoked at an elevated temperature at which bacteria are killed. In this approach, fish is smoked for a lengthy period of time. While this method generally does achieve the result of production of an hygienic product, taste of the product suffers as the pellicle is often relatively hard and the smoked taste is too strong. Another approach has been to use large quantities of salt - again causing taste to be impaired.

Another important criterion in production of smoked fish is to achieve a high efficiency and yield. A typical S 6 6 2 3 3 - 2 prior process is described in Soviet Union Patent Specification No. SU 651773, in which the fish is dried and then coated with an 80% glycerol solution, and then scalded. In Japanese Patent Specification No. JP 53038656, a process is described in which fish is immersed in a sugar solution, dried, smoked at 60 - 80°C, left standing for 20 - 24 hours and subsequently smoked again for 1 to 2 hours. It will be appreciated that both of these processes are quite complex and involve a high energy requirement.

The invention is directed towards providing an improved method for producing smoked fish in which an hygienic product is produced without comprising on taste.

According to the invention, there is provided a method of producing smoked fish, the method comprising the steps of : receiving fresh fish at a temperature in the range of 1°C to 4°C, and determining plate count of the fish, and rejecting fish having a plate count above 12,000; preparing fish fillets for smoking; within a smoking chamber, drying the fillets at a temperature in the range of 22°C to 26°C, at a relative humidity of 55% - 65%, and for a time duration in the range of 1 hour 20 minutes to 1 hour 40 minutes; subsequently smoking the fillets in the smoking chamber at the same temperature and relative humidity as for drying with smoke generated from a beech/oak sawdust combination, the temperature of the smoke at a chamber inlet not exceeding 28°C and the smoking duration being between 6 and 7 hours; purging the smoking chamber at the same temperature and relative humidity as the drying and smoking stages, the purging taking place over a time duration of 10 to 30 minutes; immediately after purging, transferring the fillets to a chiller room maintained at a temperature below 0°C, and storing the fillets in the chiller room for a minimum time duration of four hours; transferring the fillets to a processing area maintained at a temperature in the range of 12°C to 16°C and carrying out post-smoking processing operations; and packing and labelling the fillets and subsequently storing the packed fillets in a chill room at a temperature below 0°C until dispatch.

In one embodiment, the fish fillets are prepared by :detecting fat content of the fish; eviscerating and washing the fish to provide the fish fillets; and applying salt to the fillets according to fat content.

Preferably, salt is applied at a concentration of 3% for a fish fat content of 11 - 13%. In this latter embodiment, salt is preferably applied by depositing salt on the fillets and leaving standing for a time period of 4 to 10 hours in proportion to fillet weight in the range 2 to 7 kg.

In one embodiment, the drying, smoking and purging stages are carried out at a temperature of approximately 24°C and a relative humidity of approximately 60°C.

Ideally, the time duration for the drying stage is approximately 1 hour and 30 minutes.

In one embodiment, the time duration for the smoking stage is approximately six hours and thirty minutes.

In one embodiment, the time duration for the purging stage is approximately 15 minutes.

Preferably, the smoke is generated from sawdust having an 80% beech and 20% oak combination.

Ideally, an alarm is generated if the temperature of inlet smoke to the chamber rises above 28°C.

In a further embodiment, the smoked fillets are processed in a processing area maintained at a temperature of approximately 14°C.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which :Fig. 1 is a stylised plan view of a production plant illustrating the process steps of a method of the invention; Fig. 2 is a diagrammatic side view of a smoking plant which is used in the process; and Fig. 3 is a diagrammatic flow chart, showing postsmoking processing steps.

Referring to the drawings, and initially to Fig. 1, there is shown a production process for smoked salmon. Fig. 1 shows a production plant 1 having a raw fish intake area 10. The fish which is received is chilled at a temperature in the range of -1°C to +4°C and immediately when it is received, a test is carried out to determine the plate count and also the temperature. The plate count should be below 12,000. For the process, it is very important to check quality of the fish at intake as the fish is fresh and contamination may arise due to lack of temperature control by the fish supplier, contamination by pathogens, hydrocarbons or parasites (particularly for wild salmon), or contamination by antibiotic residues (farmed salmon). Another test which is carried out in the intake area 4 is a test of the fat level which should be below 15% and is ideally in the range of 11 - 13%. While the fat level does not directly affect hygiene, it does have a bearing on downstream processing steps.

After intake, the fish is transferred to a chill room 11 at a temperature of -1°C. The temperature of the fish is checked to ensure that it does not exceed +2°C. This ensures that microbial growth is prevented.

In general, the fish will be retained in the chill room 11 for only a short period of time, generally a few hours and rarely more than 24 hours. This is because the production process is organised on the basis of production on demand. It has been found that while such an approach does place heavy emphasis on maintenance of hygiene during the production process as the fish is not frozen, a better quality end product is achieved because it has a fresher taste. The fish is removed from the chill area 11 and washed in a wash area 12 under controlled hygienic conditions and is then transferred to an evisceration area 13. In this area, the heads and tails are removed and the fish is filleted. During these steps, it is essential to prevent cross-contamination from offal and contamination from knives, gloves, and unclean water. Accordingly, the offal is removed regularly and stored in covered bins and objects such as knives and gloves are sterilised regularly and water input is tested regularly to ensure that it is within the EU Directive 80/778. After filleting, the fillets are washed using the clean water and are transferred to a salt area 14. In the area 14, pure dried vacuum salt is applied to the fillets and they are left to stand for a pre-determined period of time. The period of time is in the range of 4 - 10 hours in proportion to the weight of the fillets, 4 hours corresponding to 2 kg fillets and 10 hours corresponding to 7 kg fillets. It has been found that this salting time provides a concentration in the range of 2 - 4 % and generally 3%, for fish having a fat content in the range of 11 - 13%. Where the fat content is higher, then the salt concentration must be higher. It has been found that by ensuring that fish is received from certain suppliers at which they are farmed in a manner to avoid a high fat content, this problem rarely arises.

After salting, the fillets are mounted on racks and are transferred to a smoking chamber 17 of a smoker 15 which also comprises a smoke generator 16. The smoker 15 is now described in detail with reference to Fig. 2. The smoke generator 16 comprises a housing in which a set of paddles 40 agitate sawdust 41 over a mesh 42. The sawdust 41 is a combination of 80% beech and 20% oak. It has been found that by using this combination, the consistency of the burning operation and the resulting taste in the fish is particularly good. The sawdust drops from the mesh 42 to a perforated hot plate 43 and smoke, driven by incoming air at an inlet 44 rises through an outlet duct 45. The outlet duct 45 has a number of access covers 46 which are easily removable for access to the ducting for cleaning. These are used for regular cleaning of the ducts to ensure that hygienic conditions are maintained and the risk of fire is minimised. A purging outlet 47 is mounted adjacent the end of the outlet duct 45 for taking exhaust from the duct 47 into a tube which extends over a ceiling line 67 in an upper part of the building. The part of the building above the ceiling line 67 is used for maintenance of the smoker 15 and for supporting various tubes such as the air inlet tube 44 and the exhaust tube. Further, the top portion of the smoking chamber 17 is within this compartment and therefore, access to the smoking chamber for maintenance may be achieved via an access hatch 65 mounted above the ceiling line 67.

A temperature sensor 49 is connected at the junction between the outlet duct 45 and the smoking chamber 17 and this is connected to a control panel 48. The control panel includes a convection heater which prevents condensation in the components, which condensation could possibly cause faulty operation of components such as circuit breakers and switches generally. A humidity spray device 50 is mounted just above the control panel and this is constructed for generation of a fine mist of clean water for control of the humidity within the smoking chamber 17. Also shown in Fig. 2 are a pair of trolleys 55 having racks 56 at which fillets 57 of salmon are placed. The fillets 57 are spread evenly on the racks 56. A heat exchanger 58 is mounted above the trolleys 55 and there is a pair of air fans 59 and 60 which are of the reverse flow type. The trolleys 55 are mounted between an inlet diffuser wall 61 and an outlet diffuser wall 62 for control of the atmosphere around the fillets 57. - 8 An important aspect of the production process is the manner in which the conditions within the smoking chamber 17 are controlled for smoking of the fillets. There is a three-stage process within the smoking chamber 17, namely drying, smoking and purging. These three stages are carried out directly one after the other without any delay. A further important aspect of the three stages is that the parameters of temperature and relative humidity are maintained constant throughout. This has been achieved by selection of appropriate values for these parameters which apply to all stages. By doing this, the time required for smoking is significantly lower than has heretofore been the case and secondly, sufficient smoking is achieved to provide the necessary taste, without the pellicle being too dry or crusty.

The first stage is drying which is carried out when the dry bulb temperature of the chamber 17 is between 22°C and 26°C, and most preferably 24°C. The relative humidity is between 55% and 65% and preferably 60%. These parameter values are achieved by operation of the fans 59 and 60, the heat exchanger 58 and the humidity spray 50. It is found that by drying under these conditions, the fillets are sufficiently dry after a time between 80 and 100 minutes, and preferably 90 minutes.

The second stage, smoking, is carried out at the same temperature and humidity as the drying stage and therefore it may begin immediately without any delay. The smoke generator 16 is activated and smoke enters the smoking chamber 17. The temperature of the smoke is well below 28°C and is preferably approximately 24°C. The temperature sensor 49 performs the dual function of both ensuring that the temperature of the smoke does not exceed a certain limit which would cause an imbalance in the environment within the chamber 17, and secondly to provide an early alarm of fire at some part of the outlet duct 45. The temperature sensor 49 is connected to an alarm device in the control panel 48 for this purpose. Again, both of the fans 59 and 60 are operated in a manner whereby their directions of rotation are changed at regular intervals for comprehensive distribution of air and smoke throughout the chamber 17. It has been found that by smoking under these conditions, a time duration in the range between 6 and 7 hours, and preferably only six hours and 30 minutes is required.

The final stage is purging and again, the temperature and humidity remain the same, the fans 59 and 60 are both operated, the smoke generator 16 being switched off. A valve connected to the purge outlet 47 is opened and under these conditions the chamber 17 is purged of smoke in a period of only 15 minutes although the duration could be at a level between 10 and 30 minutes.

It has been found that this three-stage cycle is very short because of the manner in which the parameters are controlled and further, a high quality smoked product is achieved. The pellicle of the fillets is not crusty, the flesh is moist and there is little or no loss due to burning at the edges of the fillets.

At regular intervals, the sawdust is analysed to ensure that there is no chemical contamination. By ensuring that the sawdust is pure, contamination of the products in the smoking chamber 17 is avoided provided that this has been correctly handled before entry to the chamber, and the racks are cleaned regularly to avoid such things as buildup of smoke deposits.

Referring again to Fig. 1, after smoking the fillets are transferred to a chill area 18. This is a direct transfer without any delay and the temperature of the chill area 18 is maintained at -1°C in order to reduce the temperature of the fillets to below 4°C in four hours. This may be referred to as blast chilling and it is a very important aspect of the process as it ensures hygiene of the fillets before processing steps are carried out.

Processing is carried out in a processing area 19 within which the chill room 18 is located. There is strict temperature control of the processing area 19 and the temperature is maintained at a level between 12°C and 16°C and preferably 14°C to prevent bacteria growth, while at the same time providing tolerable working conditions for personnel.

At a station 25, the fillets are boned by hand and at a station 26 they are skinned and sliced. Referring now to Fig. 3, a device 70 for skinning the fillets is illustrated. This device is relatively simple and it comprises a rotating perforated drum 71 which has cutting faces extending a small distance proud of the surface of the drum to tear the skin from the fish as it is slid on a feed table 72 to an output table 73. Slicing is then carried out at a machine 80, comprising a feed chute 81 which delivers the fillets to a rotary cutter 82, the slices dropping onto an output conveyor 82. It has been found that this is a particularly effective method of slicing the fillets. For some grades of fillets such as the larger sizes, a reciprocating blade slicing machine is used to better effect. The fillets are then trimmed manually at a station 27 (shown in Fig. 1).

A vacuum packing machine 90 is then used at a station 28, Fillets 95 are placed in a bag 91 of plastics material together with a backing board 92 having a smooth surface for hygiene. The head 96 of the vacuum machine 90 is moved downwardly to press around the edges of the bag 91 to heat seal it after removal of air.

After packing, the packs are immediately labelled at a labelling station 29, using a labelling machine 100. The machine 100 has a display 101 which indicates weight, unit price, and total price of each pack and has a controller which prints a label 102 which is immediately adhered to the pack. This helps to ensure that incorrect labelling does not take place and important information such as a shelf-life indicator are correct.

Immediately after packing, the packs are transferred to a final chill room 30, which is also at a temperature of -1°C. It is from the room 30 that the packs are retrieved directly for dispatch from a dispatch area 31.

It will be appreciated that the invention provides for production of a smoked fish product which is hygienic. This is achieved by virtue of the relative locations and the manner in which the chill rooms and the processing area are used. The manner in which temperature is controlled in the processing area 19 is also important, as is the manner in which the smoking is controlled. It has also been found that the manner in which seafood is inspected at the intake area 10 is very important. In addition, the end product has a very desirable taste as it is moist throughout with a sufficiently smoked flavour without excessive salt. It will further be appreciated that the efficiency of the process is very high, particularly in view of the short smoking cycle which is involved.

The invention is not limited to the embodiments hereinbefore described, but may be varied in construction and detail.

Claims (4)

1. A method of producing smoked fish, the method comprising the steps of :receiving fresh fish at a temperature in the range of 1°C to 4°C, and determining plate count of the fish, and rejecting fish having a plate count above 12,000; preparing fish fillets for smoking; within a smoking chamber, drying the fillets at a temperature in the range of 22°C to 26°C, at a relative humidity of 55% - 65%, and for a time duration in the range of 1 hour 20 minutes to 1 hour 40 minutes; subsequently smoking the fillets in the smoking chamber at the same temperature and relative humidity as for drying with smoke generated from a beech/oak sawdust combination, the temperature of the smoke at a chamber inlet not exceeding 28°C and the smoking duration being between 6 and 7 hours; purging the smoking chamber at the same temperature and relative humidity as the drying and smoking stages, the purging taking place over a time duration of 10 to 30 minutes; immediately after purging, transferring the fillets to a chiller room maintained at a temperature below 0°C, and storing the fillets in the chiller room for a minimum time duration of four hours; transferring the fillets to a processing area maintained at a temperature in the range of 12°C to 16°C and carrying out post-smoking processing operations; and packing and labelling the fillets and subsequently storing the packed fillets in a chill room at a 5 temperature below 0°C until dispatch.

2. A method as claimed in claim 1, wherein the time duration for the drying stage is approximately 1 hour and 30 minutes.

3. A method as claimed in claims 1 or 2, wherein the time 10 duration for the smoking stage is approximately six hours and thirty minutes.

4. A method substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings. 15 5.A smoked fish product whenever produced by a method as claimed in any preceding claim.