The subject of the present invention is an expanded cereal which can be obtained by extrusion, and a method for manufacturing such a cereal.

EP 0,898,890 (SOCIETE DES PRODUITS NESTLE S.A.) describes an extrusion die for producing, by extruding a single substance, a product which has the overall shape of a nucleus surrounded by a ring, the die comprising a feed orifice plate opening onto a distribution chamber communicating, on the one hand, with a central extrusion duct with the overall shape of a converging cone, via a circular central orifice plate for pre-expansion and/or for slowing, and communicating, on the other hand, with at least one coaxial tubular extrusion duct with the overall shape of a converging cone, via at least one annular orifice plate for pre-expansion and/or slowing, the coaxial central and tubular extrusion ducts having concentric central and annular respective outlet orifices.

US 2,858,218 (J.O. BENSON) describes a cereal in the form of flakes which has a relief comparable with the surface of a raspberry, and a method for obtaining such a cereal, in which method a mixture of cereal and water is cooked at atmospheric pressure, the cooked paste thus obtained is extruded, driving it with a piston through a die which has a number of holes so as to form parallel filaments of cooked paste, the filaments are combined into a bundle and compressed laterally in a tubular extension of the die so that they stick together, the cylinder thus obtained is dried and cut transversely into thin slices and the slices are then made to puff under the action of heat (see Fig. 6 of US 2,858,218).

US 3,482,992 (J.O. BENSON) describes a cereal in the form of flakes made up of touching pieces, the lines where the pieces meet being coloured, and a method for obtaining such a cereal, in which method a mixture of cereal and water is cooked in a cooking device, the cooked paste is extruded through a die which has a number of circular outlet orifices, particularly six holes arranged in a circle around a central hole, and a colorant is injected through small intermediate holes, so as to form parallel strands of cooked paste which are coloured at their interface, the strands are combined into a bundle and compressed laterally in a tubular extension of the die so that they stick together, the diameter of the composite strand thus obtained is reduced by drawing it longitudinally, the composite strand is cut transversely into thin slices, the slices are dried and then made to swell under the action of heat.

WO 98/49902 (General Mills Inc.) describes in connection with its Fig. 11 a multiple coloured or flavoured extruded cereal product made by leading together two different dough streams to a centre zone and a periphery, the peripheral dough stream converging and being compressed against the central dough stream shortly before the led-together dough streams are extruded through a single die opening, and slicing the extruded merged mass. The product (Fig. 11) has for example the general shape of a flower with a central zone originating from the central dough stream and petals originating from the peripheral dough stream. Since there is only one die opening with a central zone, the different components of the product (central portion and petals) form one merged multicoloured mass.

US 3,139,342 (E.F.LISKEY) describes the production of animal food pellets by extruding a stream of plasticized material through a cylindrical orifice and cutting the material into short lengths equal approximately to the diameter of the orifice. The extruded material expands or puffs to form individual spherical pellets shown in Fig. 3 of US 3,139,342. These individual pellets can be collected into a 3-dimensional agglomerated mass or cluster as shown in Fig. 4 of US 3,139,342.

The object of the present invention is to propose an expanded cereal with a particularly attractive three-dimensional shape, namely the overall shape of an array of 2-30 touching balls that are all made from one given thermoplastic mass, obtainable by extruding the given thermoplastic mass with a rotating-screw extruder, whereby the given thermoplastic mass exits an extrusion outlet as a bundle of separate parallel strands of the given thermoplastic mass to obtain a bundle of strands of expanded thermoplastic substance, which extruded strands have a porous texture obtainable by the escape of steam from the thermoplastic mass during expansion and which stick together, and cutting the bundle of strands of porous texture at the extrusion outlet into a slice that forms the array of touching balls which stick together.

Further aspects of the invention are set out in the claims.

The expanded cereal can be produced using an extrusion die which comprises a feed ring opening onto a cylindrical distribution chamber communicating with an array of parallel extrusion tubes provided in a front wall, a cylindrical distribution insert extending axially from the centre of the ring as far as a predetermined distance from the array of tubes.

An extruder for producing the expanded cereal comprises an elongate barrel containing one or two processing screws, at least one such extrusion die, and chopping means.

The expanded cereal that can be obtained by extrusion through such a die has the overall shape of an array of touching balls formed by the sliced strands of expanded thermoplastic material which stick together.

A method of manufacturing an expanded cereal with the overall shape of an array 2-30 of touching balls consists in cooking-extruding-expanding a mixture comprising, in parts by weight, 60-90 parts of starchy material, up to 15 parts of sugar, up to 10 parts of oil and water added until the mixture has a water content of 15-25% by weight, in performing the extrusion with a rotating-screw extruder wherein the given thermoplastic mass exits through at least one die comprising an array of parallel extrusion tubes so as to obtain a bundle of strands of expanded thermoplastic substance, which extruded strands have a porous texture obtainable by the escape of steam from the thermoplastic mass during expansion and which stick together, and in cutting the bundle of strands of porous texture into slices at the outlet orifices of the extrusion tubes.

In this description, the expression "processing screw" is to be understood as meaning the extruder screw or screws rotated inside a bore or two secant bores made in the barrel and to which processing members such as flights helically wound about their axis, are attached. The configuration, pitch, depth and hand of such flights may be configured in various ways along the axis so as to define zones for various processing operations such as conveying, wetting, mixing, shearing, compressing and/or cooking, for example. Such screws may be made as a single piece or by assembling elements slipped in succession onto a spindle, for example.

A corresponding extrusion die therefore comprises a feed ring opening onto a cylindrical distribution chamber communicating with an array of parallel extrusion tubes provided in a front wall, a cylindrical distribution insert extending axially from the centre of the ring as far as a predetermined distance from the array of tubes.

The feed ring may be produced in the form of two concentric annuli connected by radial bars or by juxtaposed tubular hoops, for example.

The distribution insert may have a first cylindrical upstream part and a second frustoconical downstream part, for example. It is intended to even out the rate of displacement of a stream of thermoplastic substance to be extruded across the entire width of an extrusion front that corresponds to the width or diameter of the array of parallel extrusion tubes.

The tubes of the array of tubes may have cross sections of varying shape, such as circular, oval and/or polygonal, particularly triangular, square, rectangular and/or trapezoidal, for example.

The tubes of one and the same array may therefore have cross sections of the same or different shapes and sizes.

The array comprises 2-30 tubes, particularly 12-30 tubes arranged, when viewed in cross section, in alignment along a number of axes or curves, or in no particular order but relatively close together, for example.

The cross section of the tubes may have dimensions, particularly diameters, lengths or widths of between 1.0 and 4.0 mm, or in other words may have a surface area or aperture of 1-16 mm², for example.

The distance between two tubes of the array may be from 0.2-0.6 mm, for example.

An extruder for producing the expanded cereal of the given shape therefore comprises an elongate barrel containing one or two processing screws, at least one extrusion die as described above, and chopping means.

The chopping means may be produced in the form of a rotary cutter with a number of blades, particularly 2-4 blades, rotating against the outlet orifices of the tubes of the array, or in other words against the front wall of the die.

In one preferred extruder with several dies, particularly 2-30 dies, a downstream part of the barrel containing a downstream end of the processing screw or screws ends in a front plate secured to the barrel and in which there is a predistribution orifice opening, via a predistribution orifice plate, onto a bell-shaped predistribution chamber, communicating with the distribution chambers of the dies via the feed rings.

In an extruder such as this one with several dies, the number of dies that can be used can be adjusted according to the output of the extruder, particularly by barring one die in two or one die in three by closing off its feed ring with a cover fixed at its centre in place of the distribution insert, for example.

The expanded cereal according to the present invention which can be obtained by extrusion through such a die therefore has the overall shape of an array of touching balls balls formed by the sliced strands of expanded thermoplastic material which stick together.

The touching balls of the array may be of similar or different shapes, and may, in particular, be round and/or elongated, and may or may not be aligned along axes or in curves, for example. The array may have an overall thickness of about 4-16 mm, for example.

The array may be flat on the whole or may be somewhat curved. It may have a periphery of varying overall shape, particularly square, rectangular, circular or oval, modulated by the bumps formed by the balls located at the edges, for example.

It is possible to envisage different embodiments of the present cereal, such as breakfast cereals or crunchy pet food, for example.

In an embodiment as a breakfast cereal, the present cereal can be eaten as it is or coated, particularly with a chocolate coating, a sugar syrup, a fruit syrup, a honey syrup, or a coating containing vitamins and flavourings, for example.

A method of manufacturing an expanded cereal with the overall shape of an array of 2-30 touching balls consists in cooking-extruding-expanding, at a pressure of 40-180 bar at 105-180°C, a mixture comprising, in parts by weight, 60-90 parts of starchy material, up to 15 parts of sugar, up to 10 parts of oil and water added until the mixture has a water content of 15-25% by weight, in performing the extrusion of the given mixture with a rotating-screw extruder wherein the thermoplastic mass is extruded through at least one die comprising an array of parallel extrusion tubes so as to obtain a bundle of strands of expanded thermoplastic substance, which extruded strands have a porous texture obtainable by the escape of steam during expansion and which stick together, and in cutting the bundle of strands of porous texture into slices at the outlet orifices of the extrusion tubes.

The mixture may further contain up to 1.5 parts of calcium, in the form of calcium carbonate or calcium triphosphate, for example.

Vitamins, trace elements and sodium chloride, for example, may be added to the mixture.

Colorants, flavourings or even flavouring ingredients such as cocoa may, for example, be added to it. For example, up to 6 parts of cocoa may be added.

The starchy material may be a cereal flour, particularly wheat, barley, rice and/or cornflour, and/or a starch, particularly wheat, barley, rice, tapioca, potato and/or corn starch, for example.

The sugar may be sucrose, glucose or fructose, for example.

The oil, preferably added in the proportion of 4-10 parts, may be butter oil or a vegetable oil such as palm nut oil, for example.

Cooking-extrusion may be performed in a cooker-extruder with a length to diameter screw ratio of about 9-24, with the screws rotating at 240-370 rpm, at a pressure chosen from the range from 40-180 bar and at a temperature chosen from the range of 105-180°C so as to obtain an expansion coefficient of about 2-4, for example, for the extruded strands.

Water escapes from the thermoplastic mass in the form of steam during expansion so that the extruded strands have a porous texture and may have a residual water content of 5-12%, for example.

The expanded cereal thus obtained may then be dried, particularly by passing it continuously through a hot air oven, until the residual water content is down to 1-3%, for example.

The cereal according to the present invention and a die and extruder for producing it are described hereinafter with reference to the appended drawing given by way of example, and in which:

• Figure 1 is a view in axial section of one type of die,
• Figure 2 is a view in cross section of a detail of the die depicted in Figure 1,
• Figure 3 is a partial cross section view of one type of extruder comprising a number of dies,
• Figure 4 is a face view of the extruder depicted in Figure 3, and
• Figure 5 is a photograph showing one embodiment of the expanded cereal having the overall shape of an array of touching balls shown from three different angles.

In Figure 1, the extrusion die comprises a feed ring 1 opening onto a cylindrical distribution chamber 2 communicating with an array of parallel extrusion tubes 3 provided in a front wall 4, a cylindrical distribution insert 5 extending axially from the centre of the ring 1 as far as a predetermined distance from the array of tubes 3.

As can be seen depicted in Figures 1 and 2, the distribution ring 1 is produced in the form of two annuli 11 and 12 connected by juxtaposed tubular hoops 13.

The distribution insert 5 has a first cylindrical upstream part 16 and a second frustoconical downstream part 17.

The array of tubes 3 comprises 24 cylindrical parallel tubes of the same circular cross section arranged in two groups with parallel axes intersecting at angles, namely six groups of four tubes in one direction, and three groups of six tubes bounded by two groups of three tubes in an intersecting direction, as shown.

In Figures 3 and 4, the extruder comprises an elongate barrel (not depicted) containing one or two processing screws (not depicted), a number of extrusion dies as depicted in Figures 1 and 2, and chopping means 14.

A downstream part of the barrel containing a downstream end of the processing screw or screws ends in a front plate 7 secured to the barrel and in which is provided a predistribution orifice 8 opening, via a predistribution orifice plate 10 onto a bell-shaped predistribution chamber 9 communicating with the distribution chambers 2 of the dies via the feed rings 1.

The chopping means are produced in the form of a rotary cutter 14 rotating against the outlet orifices of the tubes 3.

As can be seen in Figure 3, one die in two is barred, its feed ring being blanked off with a cover 15 fixed at its centre in place of the distribution insert 5, for example.

Figure 5 depicts one embodiment of the cereal which can be obtained by extrusion through a die similar to those depicted in Figures 1 and 4.

In this embodiment, the cereal therefore has the overall shape of an array of touching balls of the same round shape and of the same dimensions aligned in two groups with parallel axes intersecting at angles. The array of balls is slightly curved (on the side where the cutter detached the cereal from the composite strand leaving the die, as can be seen on the left-hand view of Fig. 5) and has a periphery of rectangular overall shape modulated by the bumps formed by the balls located at the edges.

The example hereinafter illustrates the production of a preferred form of the present cereal, in this instance an expanded breakfast cereal, by cooking-extruding a mixture based on flour and water in a cooker-extruder comprising several dies according to the present invention. In this example, just as in the entirety of this description, the percentages and parts are given by weight.

A twin-screw cooker-extruder comprising several dies like the one illustrated in Figures 3 and 4 is used to produce expanded cereals with the shape of an array of touching round balls as illustrated in Figure 5.

To do this, a mixture with the following composition (in parts, except for the added water): Rice flour 40 Cornflour 12 Wheat flour 22 Sucrose 10 Palm nut oil 5 Salt/spices 3 Water added to a water content of 18% was prepared.

To prepare the mixture, the dry powders were first mixed. The dry mixture, the oil and the water added to the extruder, in this instance a CLEXTRAL type BC-72 twin-screw extruder with a screw diameter of 88 mm and screw length of 900 mm were then mixed.

The mixture was then cooked-extruded at 170°C at 100-120 bar, with the extruder screws rotating at 310 rpm.

The thermoplastic mass thus obtained was extruded through 6 arrays of 24 tubes, the tubes having a diameter of 1.3 mm and the distance between two tubes being 0.3 mm.

The thermoplastic mass was extruded into the ambient space and immediately cut into slices using a four-bladed cutter rotating at 800 rpm against the front wall of the dies.

The cereal obtained had the overall shape of an array of 24 touching balls with the same round shape and the same dimensions aligned in two groups with parallel axes intersecting at angles. The array of balls was slightly curved (on the side where the cutter detached the cereal from the composite strand leaving the die) and had a periphery of rectangular overall shape.

The cereal had a thickness of about 6 mm, a width of about 15 mm and a length of about 20 mm.