GB2320667A

GB2320667A - Smoking fish

Info

Publication number: GB2320667A
Application number: GB9626994A
Authority: GB
Inventors: Peter Gerard Curtin
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-12-18
Filing date: 1996-12-27
Publication date: 1998-07-01
Also published as: IES75677B2; GB9626994D0; IES960895A2

Abstract

A process for the smoking of fish or portions thereof, especially salmon, comprises increasing the temperature of the fish in the smoking apparatus from ambient temperature in a step-wise manner, so that the temperature in the apparatus is maintained at a temperature of no more than 5-15{C above the core temperature of the fish or portion thereof at each stepped increase until a pre-set maximum temperature is reached. The process is suitable for both hot and cold smoking. The smoked fish thereby obtained has consistently good organoleptic properties, including firm texture, distinctive flavour and good colour.

Description

This invention relates to the smoking of fish and, in particular, to a process for the smoking of fish which results in a uniform and consistent texture in the smoked product and improved organoleptic properties.

The primary aim of all fish processing is to retard or eliminate the activities of spoilage agents. Smoking or smoke preserving ensures partial inhibition of bacterial growth and is generally combined with chilling, brining and drying.

Traditional wood smoking was carried out by hanging fish or fish fillets in a chimney structure and drawing smoke by convection through the chimney. This traditional method results in blank spots on the smoked product, namely spots which do not have the requisite firm texture and colour, resulting in a non-uniform product because smoke does not impinge on these spots throughout the smoking process.

Traditional smoking is a very slow procedure and is not suitable for commercial or large-scale smoking of fish.

Other and more modern methods of smoking involve the use of 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 of fish or fish fillets, whereas in a typical so-called European smoking kiln the smoke is introduced at the top of the kiln and travels a U-shaped path to exit the kiln at a point upstream from the point of ingress of smoke, in each case for a period of 4-5 hours following a drying period of circa 4 hours. In each of these processes a single temperature is used for each of the drying and smoking steps. It is difficult to ensure that one obtains a uniformly smoked product with either type of process. For example, if the product to be smoked is salmon, frequently the resulting smoked product has a soggy, rather than a firm texture and the fish does not have the desired red/orange colour.

Accordingly, there is a need for a process for smoking fish which results consistently in a smoked product having the desired colour, flavour and texture.

Accordingly, the invention provides a process for the smoking of fish or portions thereof, which process comprises increasing the temperature of the fish in the smoking apparatus from ambient temperature in a step-wise manner, so that the temperature in the apparatus is maintained at a temperature of no more than 5-15 0C above the core temperature of the fish or portion thereof at each stepped increase until a pre-set maximum temperature is reached.

The process according to the invention, which can be carried out in times corresponding to those used in conventional processes of the type described above, results consistently in a smoked product having a firm texture throughout and an excellent flavour because of the use of a step-wise increase in temperature during the smoking procedure The term smoking as used herein and as used in the art includes a pre-smoking drying process, unless it is clear from the context that reference is being made only to smoking as such.

By fish or portion thereof herein is meant both fresh and salt water fish, including eels.

The process is especially suited for the smoking of salmon and sea trout.

Preferably, the temperature of the incoming air or air/smoke mixture is allowed to increase by no more than 1O"C at each stepped increase so as to maximise results.

The process according to the invention is suitable for both cold smoking and hot smoking of fish.

Thus, in one embodiment the smoking is carried out over the range l00-300C for a cold smoking procedure. Typically, a cold smoking procedure is carried out for a period of 14-16 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 7-8 hours.

In a separate embodiment the smoking is carried out over the range of 10-80"C for a hot smoking procedure. Typically, a hot smoking procedure is carried out for a period of 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 3-4 hours.

In a cold smoking procedure the stepped increase in temperature is preferably completed during the pre-smoking drying process.

Typically, there will be 2-3 stepped increases in temperature during the drying process.

In a hot smoking procedure the stepped increase in temperature will normally not be completed at the end of the drying process and thus will continue in the smoking process. Typically, there will be in excess of 5 stepped increases in temperature in a hot smoking process.

It will be appreciated that the volume of heat used is important in achieving a gradual rise in core temperature.

Preferably, the heat is supplied for a cold smoking process at a rate of 12-15kw, more especially of the order of 13.75kw.

Preferably, the heat is supplied for a hot smoking process at a rate of the order of 35-38kw, more especially of the order of 37kw.

In conventional cold smoking and hot smoking the values used are higher, typically 20kw and 40-45kw, respectively.

Fish core temperature can be measured by means of a suitable probe.

The smoking will suitably be carried out in the same apparatus as the drying procedure which precedes the smoking procedure as such.

Such apparatus, namely a kiln or box/static oven, during the smoking step operates under conditions of positive pressure. Suitably, the conditions of positive pressure are achieved by means of curved fans which push rather than pull the air/smoke mixture through the apparatus.

Preferably, the combustible wood material used for generating the smoke combusts at a temperature of less than 400"C.

Typically, in conventional commercial smoke generation, a smoke box generator is used in which the combustion takes place at a temperature of the order of 800"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 the 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. No highly resinous timber should be used.

A particularly good and distinctive flavour is obtained when furze bush chippings are included during the smoking procedure, especially over the last third of the smoking period as such.

The velocity of the air/smoke mixture on introduction to the smoking zone is of the order of 560-620 cubic feet per min, more especially of the order of 600 cubic feet per min.

The control of the velocity of the incoming air/smoke mixture is important in terms of the texture of the finished smoked product.

However, if the velocity of the mixture is outside of the lower limit indicated above, this can lead to an imbalance in the kiln.

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

Preferably, the ingress of the incoming air/smoke mixture is fanassisted. Further, preferably the air/smoke mixture enters the smoking apparatus through a plurality of vents disposed in a side wall of the apparatus, so that the mixture enters horizontally therein and passes over the product to be smoked which is disposed on racks (similar to the situation in the so-called English smoking procedure referred to above). However, the smoke exits through an exit port located in the roof of the smoking apparatus (similar to the situation in the so-called European smoking procedure referred to above).

Because the kiln operates under conditions of positive pressure during smoking, the smoke impinges on the fish product under conditions of positive pressure. This impingement 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 pre-smoking drying is suitably carried out for a period of the order of 1 hour in the case of a hot smoking procedure and for a period of 7-8 hours i.e., typically overnight, in the case of a cold smoking procedure. Drying results in the curing of the fish or fish portions 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 fish cells, apart from removing surface moisture. This negative pressure is achieved by an arrangement of fans operatively connected to the air inlet(s) and outlet(s).

Warm air is drawn into the drying vessel. The humidity of the drying air is important. Thus, depending on the relative humidity of the ambient air, it may be necessary to add or remove moisture from the incoming air. For example, in the West of Ireland the humidity of the ambient air is typically 77-99%. Thus removal of moisture from the drying air may be necessary in conditions of such ambient humidity.

Typically the fish or fish portions are dried at a temperature in the range 2-4OOC. Suitably for a cold smoking procedure, the drying step is carried out over a range of 10-30"C, whereas for a hot smoking procedure the drying step is carried out over a range of 10-40 C.

Fish flesh is very delicate and one must ensure that the drying thereof is achieved without denaturing the fish protein which would have an adverse effect on the texture of the end product.

The fish is generally filleted and then salted. The legal minimum for the salt concentration is 3.2% by weight in order to prevent bacterial spoilage.

In the process according to the invention the salt concentration used is preferably less than 3.5% by weight, more especially 3.2% by weight. The salt is then washed off in conventional manner and the fish products spread on racks in the drying apparatus where the wash water is first removed followed by intemal moisture resulting in curing.

In the accompanying drawings: Fig. 1 is a graph of fish core temperature ("C) versus time (hours) for a cold smoking procedure in accordance with the invention; and Fig. 2 is a graph of fish core temperature ( C) versus time (hours) for a hot smoking procedure in accordance with the invention.

The invention will be further illustrated by the following Examples.

Example 1 Cold Smoking Salmon was filleted, salted at a concentration of 3.2% by weight and the salt washed off in conventional manner. The filleted salmon was then spread on racks in a combined drying/smoking static oven of the type hereinabove described and dried for a period of 7.5 hours, the temperature of the oven being increased in steps from ambient temperature (14"C) to 210C, and then to 29.5 C under negative pressure conditions. The core temperature increased in the manner indicated in Fig. 1.

At the end of the drying period an air/smoke (1:4) mixture at a velocity of 600 cubic feet per min was introduced horizontally through a plurality of inlets in side walls of a custom-built static oven and caused to circulate under conditions of positive pressure within the oven to exit via an outlet in the roof of the oven. The temperature of the oven was maintained at approximately 30"C throughout the smoking process. The smoking was carried out for a period of 8 hours.

The smoke was generated from the combustion of wood chippings containing mainly hard woods such as oak and beech but also a small amount of semi-hard and soft woods such as non-resinous pines. Furze chippings were added after a period of 5 hours.

Combustion of the chippings was conducted throughout at a temperature of the order of 350"C.

The smoked salmon had excellent organoleptic properties including a firm texture and excellent flavour together with a deep red/orange colour.

Example 2 Hot Smoking Filleting, salting, washing and drying of salmon was carried out as for Example 1, except that drying was carried out for 1 hour and the temperature of the oven was increased during that period from ambient temperature (14"C) to 21 C, and then in further steps to 30"C and then to 40"C. Smoking was carried out as for Example 1, except that the smoking continued for 4 hours and the temperature of the oven was again raised in step-wise fashion throughout the smoking process from a temperature of 400C to a final temperature of 80"C in 10 C steps.

The fish core temperature increased throughout the entire 5 hour period in the manner indicated in Fig. 2.

Again the smoked salmon had excellent organoleptic properties with a firm, but not tough texture and good flavour.

Claims

Claims:

1. A process for the smoking of fish or portions thereof, which process comprises increasing the temperature of the fish in the smoking apparatus from ambient temperature in a step-wise manner, so that the temperature in the apparatus is maintained at a temperature of no more that 5-15"C above the core temperature of the fish or portion thereof at each stepped increase until a pre-set maximum temperature is reached.

2. A process according to Claim 1, wherein the temperature of the incoming air or air/smoke mixture is allowed to increase by no more than 10 C at each stepped increase.

3. A process according to Claim 1 or 2, wherein the smoking is carried out over a temperature range of 10-30 C.

4. A process according to Claim 1 or 2, wherein the smoking is carried out over a temperature range of 10-80 C.

5. A process according to any preceding claim, wherein the smoking is carried out in a kiln under conditions of positive pressure.

6. A process according to any preceding claim, wherein combustible wood material used for the generation of smoke combusts at a temperature of less than 400" C.

7. A process according to Claim 5 or 6, wherein the velocity of the smoke entering the kiln is of the order of 560-620 cubic feet per min., more especially 600 cubic feet per min.

8. A process according to any preceding claim, wherein the ratio of air to smoke in the air/smoke mixture is of the order of 1:4.

9. A process according to Claim 1, substantially as hereinbefore described and exemplified.

9. A process according to any one of Claims 5-8, wherein the ingress of the incoming air/smoke mixture is fan-assisted.

10. A process according to Claim 1, substantially as hereinbefore described and exemplified.

AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS

1. A process for the smoking of fish or portions thereof, which process comprises increasing the temperature of the fish in the smoking apparatus from ambient temperature in a step-wise manner, so that the temperature in the apparatus is maintained at a temperature of no more than 5-150C above the core temperature of the fish or portion thereof at each stepped increase until a pre-set maximum temperature is reached, wherein the smoking is carried out in a kiln under conditions of positive pressure.

5. A process according to any preceding claim, wherein combustible wood material used for the generation of smoke combusts at a temperature of less than 4000 C.

6. A process according to any preceding claim, wherein the velocity of the smoke entering the kiln is of the order of 560-620 cubic feet per min., more especially 600 cubic feet per min.

7. A process according to any preceding claim, wherein the ratio of air to smoke in the air/smoke mixture is of the order of 1:4.

8. A process according to any preceding claim, wherein the ingress of the incoming air/smoke mixture is fan-assisted.