Technical field

The invention relates to a tubular food casing comprising a carrier casing covered by a net, the shape and diameter of the net being freely adjustable. Said food cas¬ ing is suitable for food products such as meat, poultry, fish, vegetable, and cheese products.

Prior art

Traditionally, tubular casings covered by cylindrical nets having uniform diame¬ ters are particularly used for sausages of the salami type, and originally, the pur- pose of the covering net being the improvement of the mechanical properties such as strength of the natural gut used as the casing. With respect to mechanical prop¬ erties, modern artificial sausage casings are strong enough, and thus such covering nets on sausages primarily provide a rustic and esthetic impression. When a sau¬ sage product covered by a net is sliced up, the net may provide the outer edge of the slice with a desired decorative shape, resembling for instance a gingerbread.

The carrier casing is normally made from an elastic and stretchable material, ex¬ emplified by collagen and cellulose casings. The carrier casing is stretched when filled with sausage emulsion. The net covering the carrier casing for sausages is generally virtually unstretchable. The carrier casing then expands through the meshes of the net due to the filling pressure of the sausage emulsion, and thus bulges are formed separated by groove-like depressions between the net meshes. In case the net is not intergrally fixed to the surface of the carrier casing, the net may be loosened therefrom during cooking and drying, and accordingly, the sur- face structure provided during filling may be lost. For a desired decorative surface structure, it is essential that the net firmly remains in place on the food product during the whole production and storage processes thereof.

DE 2801545 discloses a cylindrical sausage casing having a network fabric im- pregnated with collagen bound on the surface of the carrier casing with a collagen dispersion.

A cylindrical sausage casing comprising cellulose, polyamide, or polyester, hav¬ ing net-like tube bound on the surface thereof with starch, size, or a gelatine or casein solution is known from DE 1217238.

Application FI 891392 presents an artificial cylindrical sausage casing having a carrier casing based on polyamide or polyester, preferably based on cellulose, and optionally reinforced with fibers. On the carrier casing, there is a covering net having a cylindrical shape and having a uniform circumference. Said covering net is bound on the surface of the carrier with a reactive adhesive. Polyurethane adhe- sives are mentioned as preferable reactive adhesives, having at least one polyiso- cyanate component and at least one polyol component. During the production of the casing, the inner surface of the covering net is coated with a sufficient amount of the reactive adhesive, individual fibers of the covering net optionally being totally covered or even impregnated with the adhesive. The covering net is then adhered on the surface of the tubular carrier.

US 5712007 discloses a cylindrical food casing comprising a knitted tubular car- rier casing having a net-like structure made on the outer surface thereof during the knitting process, and thus, when the casing is stuffed, said net-like structure al¬ lows the formation of corresponding bulges comparable to those provided with collagen casings covered by a net.

EP 0962148 describes a tubular carrier casing containing thermoplastic starch and/or thermoplastic starch derivative and at least another polymer, preferably polyester urethane, covered by a cylindrical net. This carrier casing material is very stretchable, and thus controlling the expansion of the casing may cause prob¬ lems.

In the industrial production of meat products and sausages, particularly hams, producers mostly use separate collagen films and separate tubular nets that are superimposed on each other only during the production of the product. In the pro¬ duction of hams, stretchable nets made of elastic materials are often used. It is also possible to use net stockings alone, but considerable amounts of humidity escape through such a highly porous net, and thus, the productivity of the food product remains low. A drawback of the collagen film is the fact that the wetting of the film prior to filling results in considerably increased friction that may then cause film ruptures during filling. Other disadvantages of the process include high material losses and low productivity (kg of the product / h).

Meat products such as sausage products and hams are typically suspended from one end for cooking and storage. Then the weight of the product often causes stretching of the net structure widthwise at the lower end of the product, and lenghtwise at the upper end of the product, thus resulting in an irregular, so-called pear-like shape. The narrow conical upper end of this pear must in many cases be removed from the product by cutting, thus giving rise to losses. For this reason, especially nets for sausage products are produced, if only possible, from almost unstretchable material to give cylinders having uniform diameters, thus being able to maintain the dimensional stability and shape of the product such as the sausage during cooking and storage.

For a long time, there exists a need to provide different types of food casings with predetermined shapes and diameters covered by a net, having dimensions accord¬ ing to the wishes of producers of food products, and having for instance a repeat- ing regular shuttle, oval, elongated oval or tubular form with spheres, for indus¬ trial production and filling of food products. At present, there are no suitable food casings for this purpose; especially since conventional cylindrical casings covered by nets are associated with uncontrollable stretching phenomena.

Summary of the invention

An object of the invention is a food casing covered by a net, comprising a carrier casing having thereon a net with a freely adjustable shape and diameter.

Another object of the invention is a method for producing a food casing covered by a net, comprising a carrier casing having thereon a net with a freely adjustable shape and diameter.

Further, an object of the invention is also the use of a food casing covered by a net, comprising a carrier casing having thereon a net with a freely adjustable sha- pe and diameter, for producing food products such as meat, poultry, fish, cheese and vegetable products.

The characteristic features of the food casing, the use and the method for the pro¬ duction thereof according to the invention are presented in the appended claims.

Detailed description of the invention

It was now surprisingly found that a carrier casing having a constant diameter may be united in a controlled manner with a tubular net having a variable diame- ter and shape to obtain a taylored net casing with dimensions and shape predeter¬ mined by the food producer. In this way, a novel solution for food casings covered by a net may be offered. With this inventive solution, problems associated with food casings covered by nets of the prior art may be avoided or at least substan¬ tially reduced. The food casing according to the invention comprises a carrier casing covered by a net having a freely adjustable shape and diameter.

The term food product refers to fresh or processed food products, particularly fresh or processed meat, fish, poultry, cheese, or vegetable products such as sau¬ sages, hams and the like.

In this specification, a carrier casing refers to casings made of synthetic or natural materials that may be used as food casings. In the casing according to this inven- tion, a casing based on collagen, or a casing based on cellulose may be used as the carrier casing, said casings and the methods for the production thereof being as such very known in the art. Said cellulose casing is preferably reinforced with fibers, including casings reinforced with paper, acaba, sisal, jute or hemp fibers. Preferably a paper reinforced fibrous casing is used.

The carrier casing may also be a plastic casing of the prior art, comprising a po¬ lymer known for food casings, or a combination of several such polymers. Food quality thermoplastic polymers are preferably used. The plastic casing has at least one or several layers, preferably one layer.

The polymer may for instance be selected from the group consisting of polyam- ides, PVDC, EVOH, EVA, EMA, EEA, polyolefins, polyesters, polyurethanes, and modified derivatives and block copolymers thereof. Preferable block copoly¬ mers include block copolymers comprising polyether and polyamide blocks.

The carrier casing may comprise at least one polymer (a) with polyamide blocks and polyether blocks. The carrier casing may also comprise a combination of at least one polyamide (b), and at least one polymer having polyamide blocks and polyether blocks. Suitable polyamides (b) may be selected from the group consisting of the follow¬ ing polyamides: PA6 (nylon 6), PAI l (nylon 11), PA12 (nylon 12), PA66 (nylon 66), PA6.12 (nylon 612), PA6/66 (nylon 6/66), PA6/12 (nylon 6/12), PA6/69 (ny¬ lon 6/69), polyamides containing MXDA, particularly aromatic polyamides, and mixtures of the above polyamides.

Suitable polymers (a) with polyamide blocks and polyether blocks may be se¬ lected from thermoplastic polymers with polyether chains, these chains being op¬ tionally present as side chains (copolymer B) or blocks (or sequences) in the main chain (copolymer A), or as side chains or blocks.

As examples of the polymers having polyether side chains, ethylene/polyalkylene glycol (meth)acrylate copolymers may be mentioned, including those presented in EP 848,019, the teachings of which are incorporated into the present application. As an example of the polymer A having polyether blocks, the copolymer (A) of the application WO 98/26004 may be mentioned, that is, a block copolymer hav¬ ing polyoxyalkylene chains and other polymer chains linked together, or a poly¬ mer having polyoxyalkylene chains linked together through linking regions.

Polyether blocks comprise alkyleneoxide units that may be selected among ethyl- eneoxide, propyleneoxide, and the group -CH2-CH2-CH2-CH2-O-. Water vapour permeability increases with increasing proportions of polyether, depending on the nature thereof. The higher the amount of polyethyleneglycol, the higher is the water vapour permeability.

The polyether blocks may comprise from 5 to 85 % of the weight of (A). The po¬ lyether blocks may contain other units than ethyleneoxide units, such as propyle¬ neoxide or polytetrahydrofuran, resulting in polytetramethyleneglycol bonds. It is also possible that PEG blocks, that is blocks consisting of ethyleneoxide units, PPG blocks, that is blocks consisting of propyleneoxide units, and PTMG blocks, that is blocks consisting of tetramethyleneglycol units also known as polytetrahy- drofurane blocks are used simultaneously. It is preferable to use PEG blocks or blocks obtained by oxyethylation of bisphenols, such as bisphenol A. The latter products are presented in the application EP 613,919. The amount of polyether blocks (A) is preferably from 10 to 50 % relative to the weight of (B).

The polyamide blocks consist of polyamide-6, or polyamide-12, and preferably polyamide-6.

Number average molecular weight of the polyamide sequences varies between 300 and 15,000, preferably between 600 and 5,000. Molecular weight of the poly¬ ether sequences varies between 100 and 6,000, preferably between 200 and 3,000.

The polyether is polyethyleneglycol (PEG) ot polytetramethyleneglycol (PTMG) also known as polytetrahydrofurane (PTHF), and preferably polyethyleneglycol (PEG).

In the polymer comprising polyamide blocks and polyether blocks, the polyamide blocks and polyether blocks are preferably of single type, respectively. Suitable polymers are polymers with PEG blocks having water vapour permeability that is higher that that of the polymers with PTMG blocks. Also a mixture of the poly¬ mers containing polyamide blocks and polyether blocks is useful.

Preferably, the polymer containing polyamide blocks and polyether blocks is such that polyamide is the major component by weight, that is, the amount of polyam- ide present in the polymer as blocks and optionally statistically distributed in the polymer chain comprises 40 % or more of the weight of the polymer containing polyamide blocks and polyether blocks. The ratio of the amount of polyamide to that of polyether (polyamide/polyether) is preferably between 1/1 and 3/1.

In case a breathing food casing made of thermoplastic polymer is desired, the car¬ rier casing is made of polymer with polyether blocks and polyamide blocks hav- ing a moisture vapour transmission rate (MVTR) of more than 200 g/m2/24 hours, preferably more than 400 g/m2/24 hours, as measured by ASTM E96 BW method.

In case a smokable food casing made of thermoplastic polymer is desired, the car- rier casing preferably comprises polymer (a) with polyether blocks and polyamide blocks having a moisture vapour transmission rate (MVTR) of more than 100 g/m /24 hours, preferably from 250 to 20,000 g/m /24 hours, as measured by ASTM E96 BW method.

According to a preferable embodiment, a smokable polymeric carrier casing com¬ prises from 15 to 85 %, by weight, preferably from 50 to 70 % by weight of poly- amde (b) or a combination of polyamides (b), and from 15 to 85 % by weight, preferably from 30 to 50 % by weight of the polymer (a) with polyamide blocks and polyether blocks, or a combination of said polymers (a). This smokable car- rier casing preferably contains PA6 or PA6/66 as the polyamide (b), and a poly¬ mer with PA6 polyamide blocks and PEG polyether blocks as the polymer (a), said polymer (a) being hydrophilic with a high MVTR, being more than 100 g/m2/24 hours, preferably from 250 to 20,000 g/m2/24 hours. The polymer (a) may also be based on PA6 polyamide blocks and PTMG polyether blocks, and further, combinations of said polymers (a) may also be used.

The polymeric carrier casing may be produced with any known method of the prior art, such as with an extrusion method. The polymer or polymers are con¬ verted into a homogenous melt that is extruded through an annular die to form a seamless tube, followed by stretching thereof lengthwise and widthwise and, if desired, thermal treatment to adjust the shrinkage to a desired range. Mixing and melting may also be carried out in separate mixing extruders. The polymeric car¬ rier casing comprises a single layer or several coextraded layers comprising the same or different polymers. The diameter of the carrier casing is at least equal to, preferably at least 2 % and particularly preferably 15-20 % larger than the maximum diameter of the covering net. The larger the diameter of the carrier casing is in comparison to the maximum diameter of the covering net, the bigger bulges or protrusions at each mesh of the net after stuffing the casing, and the stronger impressions on the surface of the finished product are obtained.

The net, or the covering net, comprises a net stocking, preferably a seamless net stocking or tube having meshes or openings. The net stocking is knitted in a way to produce expanded or enlarged portions and contracted portions having prede¬ termined sizes and shapes, preferably at regular intervals.

The appended figures 1 - 6 show some preferable food casings of the invention surrounded by a net. In each case, the shape and diameter of the net is adjusted for stuffing food products having different weights and shapes.

Figure 1 shows an unfilled flat (in the flattened form) food casing of the invention covered by a net. In Figures Ia - Ic, the net mesh is a hexagon, a rhombus, and a square, respectively. In the food casing, there are enlarged portions 1 having lar- ger mesh size, and contracted portions 2 having smaller mesh size at regular inter¬ vals. Mesh size may gradually be increased and decreased to be different in each row, or it may remain constant in several rows. The net is formed by the meshes 3.

Figure 2 illustrates the food casing shown in Figure Ia stuffed with sausage emul¬ sion, and closed only at one end. Enlarged and contracted portions 1 and 2, re¬ spectively, may be clearly seen. Sausage emulsion protrudes through the meshes to form bulges or protrusions. Figure 3 shows an unfilled flat (in the flattened form) food casing of the invention covered by a net, the casing having a clearly spherical form, the meshes thereof being hexagons.

Figure 4 shows a food product stuffed into a spherical (4a), or an oval (4b) food casing of the invention, having hexagonal meshes 3, the casing being closed and cut at both ends.

Figure 5 shows a food product stuffed into a spherical (5a), or an oval (5b) food casing of the invention, having rhombic meshes 3, the casing being closed and cut at both ends.

Figure 6 shows a food product stuffed into a spherical (6a), or an oval (6b) food casing of the invention, having square meshes 3, the casing being closed and cut at both ends.

The net may be knitted with any known knitting method to obtain loops for pro¬ viding meshes to the net. All known needling methods for net knitting are particu¬ larly suitable.

Expanded (enlarged) portions may be accurately knitted to the net according to a predetermined pattern to obtain, by filling or stuffing into each expanded (enlar¬ ged) portion of the food casing, a food product having a predetermined weight, shape and diameter in each of the expanded portion.

Adjustment of the shape and size of the enlarged portion is accomplished by de¬ fining the size of the meshes or openings in each of the knitted row by means of the number of the loops in each knitting direction. In addition, the number of rows to be knitted using each loop size is defined. Said adjustment is preferably carried out by means of an automatic logistic control attached to the knitting machine of the net. In the knitted net, this results in a desired shape, size and diameter for each expanded (enlarged) and contracted (narrowed) portions, and further, in the desired the distance between the expanded portions accurately according to the wishes of the producer of the food product such as sausage or ham. During the production process of the food product, the producer of the food product binds or closes the stuffed product at each contracted portion using any known method of the prior art.

The net comprises meshes having polygonal, hexagonal, octagonal, decagonal, dodecagonal, rhombic, square, circular, oval, or triangular shapes that may be freely selected.

The net material may be any fiber of food quality. The net should be such that it may be readily adhered onto the surface of the carrier casing, and moreover, it should be sufficiently strong to give patterns (bulges) on the surface of the prod- uct, if desired, but it should, however, also be sufficiently elastic to force the cas¬ ing firmly against the surface of the product during cooking and shrinkage the¬ reof, and yet the removal of the net should be easy. Suitable fibers include cotton, linen, viscose, polyamide, polyester, polyolefin, and cellulose. If desired, the net may be provided with elasticity by means of elastane, for instance by using elas- tane fibers.

The covering net may be formed from single fibers or from several fibers wound together depending on the application, and the size of the protrusions, that is, whether high bulges, low bulges or no bulges at all are desired on the product sur- face. Suitable combinations include combinations of cotton, polyethylene and elastane, and a combination of cotton and polyethylene. The net may also contain coloured fibers, preferably coloured with any food dye.

The covering net is attached on the carrier casing with a suitable food quality ad- hesive, or thermoplastic thread may be co-knitted in the net, the thread melting and thus acting as an adhesive during heating. Suitable adhesives for attaching the net include adhesives based on collagen, starch, and gelatine, and reactive adhe- sives, for instance polyurethane adhesives containing isocyanate. Preferably, an adhesive based on collagen is used for cellulosic fiber casings.

The food casing covered by a net according to the invention is produced by apply¬ ing an adhesive on a net knitted to have a predetermined shape, diameter, and pat¬ tern with respect to expanded and contracted portions, followed by pulling the net over a carrier casing having a diameter at least equal to the maximum diameter of the net, and drying this assembly. The application of the adhesive may be carried out using any known method, preferably by spraying.

Drying is carried out for instance by blowing warm air on the inflated tube. Fi¬ nally, the casing may be shirred to obtain a tube of desired size, or a "caterpillar", or it may be cut in lenghts according to the wishes of the producer of the food product, and then, depending on the application of the casing, one end of the lenghts may be finished by closing it.

Advantages of the invention

The food casing covered by a net according to the invention comprises both the net and the carrier casing as a finished combination. With respect to shape and diameter, the food casing of the invention is produced according to the dimen¬ sions predetermined by the producer of the food product to obtain a casing with expanded portions, into which constant amounts of the product may be stuffed by the producer of the food product, and contracted portions at which the closing clips may be applied. In this manner, it is possible to adjust the weight of the food product stuffed into or present in each expanded portion very accurately, and fur¬ ther, to produce uniform products with respect to weight and shape thereof. The food casing covered by a net according to the invention may be used for pro¬ ducing fresh or processed meat, fish, poultry, cheese, and vegetable products, in¬ cluding sausage products, hams and the like.

By using the food casing of the invention, it is possible to considerably reduce losses during the stuffing process and increase the rate of stuffing the product into the casing (kg/h) since with respect to mechanical properties, the casing is strong without any rupture risk. It is thus possible to produce products such as sausage, ham, cheese, fish, poultry and vegetable products and the like from any stuffable emulsion at high speed, the products having an appealing appearence and a regu¬ lar shape that may, however, be selected freely, and further, to accurately prede¬ termine the shape and weight thereof. A product having a regular shuttle-like, oval, spherical or any other elongated form is thus obtained, having strong, weak or no surface patterns.

With respect to its mechanical properties, said food casing covered by a net is strong, and the caliber stability thereof is high. The properties of the product may be taylored as desired according to the food product to be produced by selecting a suitable carrier casing and a suitable net structure, and moreover, the colour of the net and the carrier casing may vary.

By using a cellulosic fiber casing as the carrier casing, all advantages of fiber cas¬ ings are attained, including different colour alternatives, impregnation options, printing options, and further, shirrability and almost unlimited applicability.

If a plastic casing is used as the carrier casing, it is possible to produce a food cas¬ ing impermeable to water vapour and to minimize printing losses, or alternatively to produce a breathing food casing or a smokable food casing, if desired. In this manner, also the advantages of different plastic casings may be attained. Combining a net to a collagen casing according to the invention allows the pro¬ duction of salami covered by mould according to desired specifications.

The invention is now illustrated with the following example without wishing to limit the invention thereto.

Example 1

A net was made of cotton, polyethylene and elastane fibers by knitting it to form hexagonal meshes to the net, the size of the meshes being minimal at the con¬ tracted portions and maximal at the expanded portions. The net was knitted using a automatic knitting method with a logistic control, for the purpose of stuffing 2.5 kg of sausage emulsion of the "mortadella" type into each expanded (enlarged) portion, the expanded portions having a shape of the "mortadella" sausage. In each knitting direction, the mesh size was adjusted by means of the number of loops. The width of the flat net stocking was 165 mm at the widest portion, and 115 mm at the narrowest portion, the distance between two consecutive narrowed portions being 240 mm.

The net stocking was adhered on a cellulosic fiber casing having a flat width of 175 mm. The fiber casing was produced by the known viscose method.

Collagen dispersion adhesive was sprayed on the net, followed by pulling the net over the inflated fiber casing, and drying with warm air. In this manner, a desired food casing comprising desired expanded portions and contracted portions at regular intervals was obtained, each portion having a desired shape. At the ex¬ panded portion, the maximum diameter of the inflated food casing was 125 mm, and at the contracted portion, the minimum diameter was 95 mm. The food casing was shirred to give a 420 mm "caterpillar". The casing was stuffed with sausage emulsion, followed by cutting and closing at each contracted portion. This resulted in "mortadella" sausages having a desired shape, weighing 2.5 kg.