IES20060378A2 - Apparatus and process for the smoking of food articles - Google Patents

Abstract

An apparatus (10) for the smoking of food articles, such as fish, by impingement of an air/smoke mixture thereon, comprises an oven (20), an air/smoke handling unit (11) in communication with the oven(20), the air/smoke handling unit (11) having a regulated air inlet (12)and a regulated smoke inlet(13) for the independent introduction of air and smoke, and a fan (18) for drawing in the air and smoke and circulating the air/smoke mixture through the oven (20) and back to the air/smoke handling unit (11) resulting in an increase in pressure within the apparatus(10), means for heating the air/smoke mixture within the air/smoke handling unit (11) ,means for monitoring pressure changes within the apparatus (10) and means for intermittently venting part of the air/smoke mixture so as to reduce the pressure within the apparatus(10). The pressure within the oven (20) of the apparatus (10) can be raised to improve impingement of air/smoke mixture onto the food articles. The control of the level of impingement of the smoke onto the food articles means that the organoleptic properties, consistency and texture of the smoked product are reliably of a high standard. The smoking process is completed within a shorter period of time than a conventional processes, emissions to the atmosphere are reduced and labour, fuel and electrical costs are reduced. <Figure 1>

Description

This invention relates to apparatus for the smoking of food articles and, in particular, to an apparatus within which an air/smoke mixture is circulated so as to impinge on the food articles placed within. The invention also relates to a process for the smoking of food articles.

Current apparatus for smoking food articles includes smoking kilns or box ovens which include mechanical means such as an arrangement of fans for assisting the flow of smoke therethrough. For example, in a typical so-called English cold smoking kiln, smoke is drawn horizontally across racks holding the food articles, whereas in a typical so-called European smoking kiln the smoke is introduced through the roof of the kiln and travels a U-shaped path to exit the kiln through a second location in the roof, positioned upstream from the point of introduction.

In such apparatus, it is difficult to ensure that one obtains uniform impingement of the smoke onto the article of food, such as fish, and, consequently, the entire smoking process can take up to 12-15 hours to complete. The uniformity and consistency of the smoked product may be adversely affected by protracted smoking in such apparatus.

Irish Patent Specification No. S75677, which describes an improved process for the smoking of fish, overcomes many of the problems relating to the uniformity and consistency of the smoked product by ensuring that the temperature within the smoking apparatus is maintained at a temperature of no more than 5-15°C above the core temperature of the fish until a pre-set maximum temperature is reached.

However, impingement of the smoke onto the fish is aided by the creation of a slight positive pressure within the smoking apparatus and the length of the smoking process ranges from 5 hours for a hot smoking process to about 16 hours for a cold smoking process.

A problem of the process described in Irish Patent Specification No. S75677 is that, during the smoking process, the air/smoke mixture is continuously passed over the fish and a portion of the air/smoke mixture is vented to the atmosphere through an exhaust. Thus, smoke must be generated for the entire length of the smoking process.

Accordingly, there is a need for an apparatus for smoking food articles which allows control of the level of impingement of the smoke onto the food articles, resulting in a smoked product with excellent organoleptic properties and a firm texture.

Accordingly, the invention provides an apparatus for the smoking of food articles by impingement of an air/smoke mixture thereon, which apparatus comprises an oven, an air/smoke handling unit in communication with the oven, the air/smoke handling unit having a regulated air inlet and a regulated smoke inlet for the independent introduction of air and smoke, and a fan for drawing in the air and smoke and circulating the air/smoke mixture through the oven and back to the air/smoke handling unit resulting in an increase in pressure within the apparatus, means for heating the air/smoke mixture within the air/smoke handling unit, means for monitoring pressure changes within the 11 es«J>, apparatus and means for intermittently venting part of the air/smoke mixture so as to reduce the pressure within the apparatus.

The raising of the pressure within the apparatus according to the invention results in an improvement in the impingement of the air/smoke mixture onto the food articles. The control of the level of impingement of the smoke onto the food articles means that the organoleptic properties, consistency and texture of the smoked product are reliably of a high standard and the smoking process is completed in a shorter period of time than with current smoking processes. It will be appreciated that these features of the apparatus according to the invention compare favourably to conventional smoking apparatus in respect of which the organoleptic properties, consistency and texture of the smoked product can vary erratically.

As the air/smoke mixture is vented to the atmosphere intermittently and the smoking process is completed in a shorter period of time in accordance with the invention, the smoke emissions are reduced and, additionally, labour, electrical and fuel costs are reduced.

By food articles herein is meant any food which may undergo the smoking process according to the invention without suffering any adverse effects.

The smoking apparatus according to the invention is especially suited to the smoking of salmon and sea trout. In the following description, the invention will be illustrated with reference to such fish for reasons of clarity except where otherwise expressly stated. Ι£ 0β0378 Preferably, the performance of the fan determines the maximum obtainable pressure within the apparatus.

Control of the volume of the incoming air/smoke mixture is important in terms of the texture of the finished smoked product.

In one embodiment of the apparatus according to the invention, the pressure monitoring means is a pressure transducer.

In another embodiment of the apparatus according to the invention, the venting means is a regulating device located on an exhaust of the apparatus.

Preferably, the pressure transducer co-operates with the regulating device on the exhaust of the apparatus, causing the regulating device to be opened when the pressure within the apparatus reaches a pre-set level and causing the regulating device to be closed as the pressure within the apparatus approaches atmospheric pressure.

Optionally, once the pressure within the oven reaches a pre-set level, the pressure transducer emits a signal, said signal directing an operator of the apparatus to switch the regulating device to the open position. As the pressure within the oven approaches atmospheric pressure, the pressure transducer emits a second signal, thereby directing the operator of the apparatus according to the invention to switch the regulating device back to the closed position.

Preferably, the regulating device on the exhaust of the apparatus is a paddle valve.

Preferably, the pressure transducer operates in the range 0-200 mbar. uS<>27, Most preferably, the pressure transducer operates in the range ΟΙ 00 mbar.

It is well known in the art that the impingement of the smoke onto fish must be monitored so as to ensure that the degree of impingement is not too severe. The degree of impingement is determined by the colour of the fish and adjusted accordingly so as to achieve the desired dark red/orange colour. The advantage of the pressure transducer is that the level of impingement of the smoke onto the fish is predictable.

Additionally, if the pressure transducer co-operates directly with the regulating device on the outlet, the labour costs are reduced. It is also well-known in the art that the repeated introduction of fresh air/smoke during the smoking process results in a smoked product with excellent organoleptic properties and a firm texture.

In a further embodiment of the apparatus according to the invention, the air and smoke inlets are regulated by paddle valves.

Preferably, the paddle valves on the air and smoke inlets regulate the introduction of air and smoke to the air/smoke handling compartment in a desired ratio as hereinafter described.

The ratio of air : smoke in the air/smoke mixture is important in obtaining a smoked product with the required organoleptic properties, consistency and texture.

In a further embodiment of the apparatus according to the invention, the means for heating the air/smoke mixture is a heating element.

The heating element ensures that the air/smoke mixture is 5 sufficiently warm before entering the oven. If the temperature of the air/smoke mixture in the air handling compartment is cooler than the temperature within the oven, the air/smoke mixture may additionally act to cool the fish and prolong the smoking process.

In a further embodiment of the apparatus according to the 10 invention, the apparatus further comprises means for monitoring the core temperature of the food articles within the oven.

Preferably, the core temperature monitoring means is a temperature probe.

The advantage of monitoring the core temperature of the fish 15 within the oven is that a smoked product with superior organoleptic properties, consistency and texture is obtained when the temperature of the oven is maintained at no more than 5-15°C above the core temperature of the food articles within the oven.

The invention also provides a process for smoking food articles in 20 the smoking apparatus hereinbefore defined. °3?6 Accordingly, the invention provides a process for the smoking of food articles in a smoking apparatus, which process comprises the steps of: (a) independently introducing air and smoke to an air handling compartment of the smoking apparatus through distinct inlets; (b) mixing the air and smoke together within the air handling compartment; (c) heating the air/smoke mixture within the air handling compartment; (d) propelling the air/smoke mixture from the air handling compartment into an oven containing the food articles using a fan; (e) re-circulating the air/smoke mixture through the air handling compartment; (f) monitoring increasing pressure within the oven; (g) venting the air/smoke mixture from the apparatus through a regulated exhaust once the pressure within the oven reaches a pre-set level, the pre-set pressure level being dependent on the performance of the fan; (h) monitoring decreasing pressure within the oven; (i) closing the regulated exhaust as the pressure within the oven approaches atmospheric pressure and repeating steps (a) to (i) the process until the food articles have been sufficiently smoked.

The advantages of this process have already been described in relation to the apparatus according to the invention hereinbefore defined.

The term smoking as used herein and as used in the art includes a pre-drying smoking process, unless it is clear from the context that reference is being made only to smoking as such.

Drying results in the curing of the food articles so that they are ready for smoking. The drying step is preferably carried out under conditions of negative pressure which results in moisture being drawn out of the food articles, apart from removing surface moisture. The exhaust is connected to an extractor fan during the drying/curing cycle.

The extractor fan co-operates with the air inlet of the air handling compartment and the fan so as to achieve the negative pressure within the oven.

The drying/curing process will preferably be carried out in the same apparatus as the smoking procedure which precedes the smoking procedure as such.

According to one aspect of the process according to the invention, combustible wood material is used for the generation of smoke in a separate smoke generator.

IE 0 60J7j Preferably, the combustible wood material used for the generating the smoke combusts at a temperature of less than 400°C.

The use of a temperature less than 400°C is found to result in a smoked product with an improved and more distinctive flavour relative to the flavour obtained in conventional processes.

Preferably, the wood material used is in the form of wood chippings, more especially containing a major proportion of hard woods and a minor proportion of semi-hard or soft woods. This combination is found to maximise the colour of the end-product. Highly resinous timbers are not recommended.

Preferably, the air and smoke are present in the air/smoke mixture in a ratio of 1:4.

Preferably, the volume of the air/smoke mixture entering the oven is in the range 580-620 cubic feet per min, more especially 600 cubic feet per min.

Control of the volume of the incoming air/smoke mixture is important in terms of the texture of the finished smoked product.

According to a further aspect of the process according to the invention, the smoking is carried out over a temperature range of 1020 80°C for a hot smoking process.

Typically, a hot smoking procedure according to the invention is carried out for a period of 2.5 - 4.5 hours.

In a hot smoking procedure according to the invention drying/curing is preferably carried out for a period of 1 hour and smoking is carried out for a period of 1.5 - 3.5 hours.

In the case of a hot smoking process, the temperature of the oven 5 is increased in a stepwise fashion from ambient temperature to 40°C during the drying process and further increased to 80°C in a stepwise fashion during the smoking process.

According to another aspect of the process according to the invention, the smoking is carried out over a temperature range of ΙΟΙ 0 35°C for a cold smoking process.

Typically, a cold smoking procedure according to the invention is carried out for a period of 11 -15 hours.

In a cold smoking procedure according to the invention drying/curing is preferably carried out for a period of 7-8 hours and smoking is carried out for a further period of 4 - 7 hours.

In the case of a cold smoking process, the temperature of the oven is increased in a stepwise fashion from ambient temperature to 30°C during the drying process and maintained at this temperature during the cold smoking process.

In both the hot and cold smoking processes, the temperature within oven is maintained at a temperature of no more than 5-15 °C above the core temperature of the food articles.

The advantage of maintaining the temperature of the central compartment of the smoking apparatus at no more than 5-15°C above the core temperature of the food articles is that a smoked product with superior organoleptic properties, consistency and texture is obtained.

Preferably, the process according to the invention is automated.

An automated process according to the invention is more efficient in terms of time and labour costs.

The invention will be further illustrated by the following description of an embodiment thereof, given by way of example only with reference to the accompanying Figure which is a schematic representation of the apparatus according to the invention.

Referring to the Figure, there is indicated generally at 10, a smoking apparatus, in accordance with the invention, the smoking apparatus 10 comprising an air/smoke handling unit 11, the air/smoke handling compartment 11 having an inlet 12 for the introduction of air and an inlet 13 for the introduction of smoke generated in a smoke generator 14. The inlets 12 and 13 are regulated by regulating devices in the form of paddle valves 15 and 16, respectively, mounted therein.

The air/smoke handling unit 11 also comprises a heating unit 17 which heats the air/smoke mixture and a fan 18 which circulates the air/smoke mixture through the smoking apparatus 10.

The fan 18 propels the air/smoke mixture along an air duct 19, the air duct 19 connecting the air/smoke handling unit 11 to an oven 20. The air/smoke mixture is propelled through a plurality of vents 21 positioned on an internally disposed side wall 22 of the oven 20, so that the air/smoke mixture enters horizontally therein and passes over the fish to be smoked which is disposed on racks (not shown). The fan 18 circulates the air/smoke mixture through the oven 20 and returns the air/smoke mixture to the air/smoke handling unit 11 via a further air duct 23.

The pressure within the oven 20 is monitored and controlled by a pressure transducer 24, such as a PTH Air Differential Pressure Transducer manufactured by Bailey & Mackey Ltd, located therein. The pressure transducer 24 co-operates with a regulating device in the form of a paddle valve 25 located in an exhaust 26 of the apparatus. The exhaust 26 is located at position 27 on roof 28 of the oven 20.

In use, the pressure within the oven 20 increases as the air/smoke mixture is propelled into the oven, the regulating device 25 being in the closed position.

The maximum pressure obtainable within the oven 20 is determined by the performance of the fan 18, i.e., the pressure within the oven 20 will continue to increase up to the point where the fan 18 can no longer propel the air/smoke mixture into the oven 20.

The pressure transducer 24 monitors the pressure within the oven 20 and, once the pressure within the oven 20 reaches a pre-set upper level (the pre-set level generally being a pressure approaching the maximum obtainable pressure within the oven but may also be lower if 06°3?9 desired), the pressure transducer 24 communicates directly with the paddle valve 25 causing the paddle valve 25 to be switched to the open position. The pressure within the oven 20 falls as part of the air/smoke mixture is vented from the oven 20 through the exhaust 26. As the pressure within the oven 20 approaches atmospheric pressure, the pressure transducer 24 communicates directly with the paddle valve 25 again, causing the paddle valve 25 to be switched back to the closed position.

During the venting step, part of the air/smoke mixture continues to be circulated through the apparatus 10 by the fan 18. The inlets 12 and 13 are controlled by the paddle valves 15 and 16 such that the collective rate of introduction ofthe air and smoke through the inlets 12 and 13 is less than the rate of egress of the air/smoke mixture from the smoking apparatus 10 through the exhaust 26. This allows the pressure within the apparatus and, consequently, the oven 20, to approach atmospheric pressure once more.

The smoking cycle is repeated until the food articles within the oven 20 have been sufficiently smoked. Increasing the pressure within the oven 20 increases the level of impingement of the smoke onto the fish and the resultant smoked product has excellent organoleptic properties and a firm texture.

The temperature within oven 20 is maintained at a temperature of no more than 5-15°C above the core temperature of the fish until a preset maximum temperature is reached. A temperature sensor 29 monitors the temperature within the oven 20 and a temperature probe 30 is used to If Q6q monitor the core temperature of the fish and controls the temperature within the oven by way of feedback communication.

The exhaust 26 is connected to an extractor fan (not shown) during the drying/curing cycle. The extractor fan co-operates with the paddle valve 15 on the air inlet 12 and the fan 18 so as to achieve a negative pressure within the oven 20.

The entire smoking process may be either manual or automated. An automated process is more efficient in terms of time and labour costs. The automated process is managed by a control panel 31, situated on one of exterior walls 32 of the oven 20.

The invention will be further illustrated by the following Examples.

Example 1 Cold Smoking of Salmon Fillets A selection of salmon was filleted, salted and washed in conventional manner. The filleted salmon was then spread across racks in an oven of the smoking apparatus 10 of the type hereinabove described and dried for a period of 7.5 hours under negative pressure conditions. The temperature of the oven 20 was increased in a stepwise fashion from ambient temperature to 30°C during the drying process and maintained at this temperature during the cold smoking process. The temperature within oven 20 was maintained at a temperature of no more than 10°C above the core temperature of the salmon fillets during both the drying and smoking processes.

Smoke was generated in a smoke generator 14 from the combustion of wood material. The wood material used consisted of wood chippings containing a major proportion of hard woods and a minor proportion of semi-hard or soft woods. Combustion of the wood chippings in the smoke generator took place at a temperature of less than 400°C.

Air and smoke were independently introduced to the air/smoke handling unit 11 of the smoking apparatus through the inlets 12 and 13, mixed together and heated by the heating element 17 within the air air/smoke handling unit 11. The air and smoke were present in the air/smoke mixture in a ratio of 1:4. The air/smoke mixture was propelled from the air/smoke handling unit 11 into the oven containing the salmon fillets by the fan 18 at a volume of 600 cubic feet per minute.

The pressure within the oven was monitored by the pressure transducer 24 as an increasing volume of air and smoke was introduced to the smoking apparatus 10. The increase in pressure within the oven 20 improved the impingement of the air/smoke mixture onto the salmon fillets.

The pressure within the oven 20 continued to increase up to the point where the fan 18 could no longer circulate the air/smoke mixture through the smoking apparatus 10. Part of the air/smoke mixture was then vented from the smoking apparatus through the exhaust 26 located on the roof 28 of the oven 20.

During the venting step, the air/smoke mixture was continually circulated through the apparatus 10 by the fan 18. However, the collective rate of introduction of the fresh air and smoke through the inlets 12 and 13, respectively was less than the rate of evacuation of the air/smoke mixture from the smoking apparatus 10 through the regulated exhaust 26.

The pressure within the oven 20 was monitored by the pressure transducer 24 as the air/smoke mixture was vented from the smoking apparatus. The regulated exhaust 26 was closed as the pressure within the oven 20 approached atmospheric pressure.

The smoking process continued until the salmon fillets had been sufficiently smoked, approximately 7 hours.

The control of the level of impingement of the smoke onto the food articles means that the organoleptic properties, consistency and texture of each individual batch of smoked salmon were consistent with one another and were reliably of a high standard.

Example 2 Hot Smoking of Salmon Fillets A selection of salmon was filleted, salted and washed in conventional manner. The filleted salmon was then spread across racks in the oven 20 of the smoking apparatus 10 of the type hereinabove described and dried for a period of one hour under negative pressure conditions. The temperature of the oven 20 was increased in a stepwise fashion from ambient temperature to 40°C during the drying process.

Smoking was carried out as for Example 1, except that the temperature of the oven 20 was further increased to 80°C in a stepwise fashion during the smoking process. The temperature within oven 20 was maintained at a temperature of no more than 10°C above the core temperature of the salmon fillets during both the drying and smoking processes.

The smoking process continued until the salmon fillets had been sufficiently smoked, approximately 3.5 hours.

Again, the control of the level of impingement of the smoke onto the salmon fillets means that the organoleptic properties, consistency and texture of each individual batch of smoked salmon were consistent with one another and were reliably of a high standard.

Claims (5)

1. An apparatus for the smoking of food articles by impingement of an air/smoke mixture thereon, which apparatus comprises an oven, an air/smoke handling unit in communication with 5 the oven, the air/smoke handling unit having a regulated air inlet and a regulated smoke inlet for the independent introduction of air and smoke, and a fan for drawing in the air and smoke and circulating the air/smoke mixture through the oven and back to the air/smoke handling unit resulting in an increase in pressure within the apparatus, means for 10 heating the air/smoke mixture within the air/smoke handling unit, means for monitoring pressure changes within the apparatus and means for intermittently venting part of the air/smoke mixture so as to reduce the pressure within the apparatus.

2. An apparatus according to Claim 1, wherein the 15 performance of the fan determines the maximum obtainable pressure within the apparatus.

3. An apparatus according to Claim 1 or 2, wherein the monitoring means is a pressure transducer, the venting means is a regulating device located on an exhaust of the apparatus, said regulating 20 device being a paddle valve, and the pressure transducer co-operates with the paddle valve on the exhaust of the apparatus causing the paddle valve to be opened when the pressure within the apparatus reaches a preset level and causing the paddle valve to be closed as the pressure within the apparatus approaches atmospheric pressure.

4. An apparatus according to any preceding claim, wherein the air and smoke inlets are regulated by paddle valves that regulate the introduction of air and smoke to the air/smoke handling compartment in a desired ratio. 5 5. A process for the smoking of food articles in a smoking apparatus according to Claim 1, which process comprises the steps of: (a) independently introducing air and smoke to an air handling compartment of the smoking apparatus through distinct inlets; 10 (b) mixing the air and smoke together within the air handling compartment; (c) heating the air/smoke mixture within the air handling compartment; (d) propelling the air/smoke mixture from the air handling 15 compartment into an oven containing the food articles using a fan; (e) re-circulating the air/smoke mixture through the air handling compartment; (f) monitoring increasing pressure within the oven; 20 (g) venting the air/smoke mixture from the apparatus through a regulated exhaust once the pressure within the oven reaches a pre-set level, the pre-set pressure level being dependent on the performance of the fan; (h) monitoring decreasing pressure within the oven; (i) closing the regulated exhaust as the pressure within the

5. Oven approaches atmospheric pressure and repeating steps (a) to (i) until the food articles have been sufficiently smoked.