CA2161367C

CA2161367C - Manufacture of cooked cereals

Info

Publication number: CA2161367C
Application number: CA002161367A
Authority: CA
Inventors: Osvaldo Geromini; Ernst Heck; Jean Noel Huet; Thierry Martin; Werner Pfaller
Original assignee: Societe des Produits Nestle SA
Current assignee: Societe des Produits Nestle SA
Priority date: 1995-04-28
Filing date: 1995-10-25
Publication date: 2001-12-25
Anticipated expiration: 2015-10-25
Also published as: DE69520491T2; CN1136897A; SI0739593T1; DE69520491D1; EP0739593B1; BR9504587A; ES2155879T3; NO954206L; AU711572B2; SG73351A1; CO4600737A1; PT739593E; RU2208369C2; MXPA95004522A; CA2161367A1; JPH08298974A; FI955075A0; DK0739593T3; AU3434095A; FI955075L

Abstract

A process for the manufacture of cooked cereals or dry pet food which comprises preparing a mixture of water and a dry premix mainly comprising cereal flour or semolina, cooking the mixture and extruding it by pressing it through an extrusion die with the aid of a gear pump.

Description

2~G~.~!~' Manufacture of cooked cereals Field of the Invention The subject of the present invention is a process for the manufacture of cooked cereals or dry pet food which comprises preparing a mixture of water and a dry premix of cereal flour or semolina, cooking the mixture and extruding it, as well as an apparatus for carrying out the process.
Background of the Invention Different processes are known which comprise at least one step of extrusion cooking a mixture of water and a dry premix mainly comprising cereal flour or semolina.
AU-A-4591389 (GERBER PRODUCTS COMPANY) discloses a process for producing instant cereals which comprises moistening a dry blend mainly comprising a cereal flour and including additional oil and vitamins, extrusion cooking the moistened blend into an expanded rope, slicing the rope into puffs, grinding and screening the puffs to give a fine powder-like particle size, and agglomerating the particles into granules.
EP-A-0524329 (SOCIETE DES PRODUITS NESTLE S.A.) discloses a process for the manufacture of precooked cereal foods by extrusion cooking a moist blend of cereals, wherein a compressed gas is injected into the blend at the end of the cooking stage, just before the extrusion stage.
Further, many uses of gear pumps are known, for example supplying well metered amounts of food materials into relatively complicated coextrusion apparatus.

EP-A-0202143 (NABISCO BR.~NDS INC. ) disc=Loses a triple coextruder capable of coaxially coextruding two cooking doughs having different compositions and textures separated by a layer of an oil-based material serving as a moisture barrier, the doughs and the oil-based material being metered into respective nozzle portions of the <:oextruder by gear pumps, for example.
EP-A-0280484 (KOBAYASHI, MASAO) discloses a coextrusion apparatus capable of forming a globular food product by wrapping a center material with one or more layers of other food materials, in which the different materials are also metered into respective nozzle portions of the coextrusion apparatus by gear pumps, for example.
Summary of the Invention The aim of the present invention is to provide a process for the manufacture of cooked cereals or dry pet food and an apparatus for carrying out the process which consumer relatively little energy and which subjects the said mixture to relatively little shear forces.
To this end, the process for the manufacaure of cooked cereals or dry pet food according to the present invention, which comprises preparing a mixture of water and a dry premix mainly comprising cereal flour oz- semolina, cooking the mixture and extruding it, distingui~~hes itself by the fact that the cooked mixture is extrudecL by pressing it through an extrusion die with the aid of: a gear pump.
Likewise, the apparatus for carrying out: the process according to the present invention comprises a mixing and/or cooking device, a gear pump and an extrusion die. ' -2a-According to one aspect of the present invention there is provided a process for the manufacture of cooked cereals or dry pet food, which comprises preparing a mixture of water and a dry premix comprising cereal flour or semolina, cooking the mixture to produce a gelatinized mixture having a degree of gelatinization of at least ~~50, pressurizing the gelatinized mixture using a gear pump comprising two toothed wheels or rollers which mesh with each other with the teeth being configured and dimensioned to avoid friction therebetween as they mesh; and forcing t:he gelatinized cooked mixture through an extrusion die using pressure generated by the gear pump to subject the mixture to compression with a minimum shear force t:o thus reduce the energy input into the mixture by 10%-25«; wherein the organoleptic properties of the cereal are enhanced.

~1~~.3~6~~

Throughout the present specification and claims, the expression "mainly comprising cereal flour or semolina"
means comprising at least about 50~ or preferably at least about 800 of cereal flour or semolina.
Similarly, the expression "a mixture of water and a dry premix" means "either a mixture of water and dry premix or a mixture of steam, water and dry premix".
It has been observed, surprisingly, that it is possible to manufacture cooked cereals or dry pet food which have remarkable organoleptical properties, especially as to their texture and flavour, while consuming relatively little energy and subjecting the mixture of water and cereal material to relatively little shear forces, in spite of the fact that this mixture passes through a gear pump and that it is briefly subjected therein to a severe compression.
Indeed, between the teeth of a gear pump comprising two toothed wheels or rollers which mesh which each other, the mixture may be subjected to a compression of several hundreds of bar during a fraction of a second, for example.
To carry out the present process for manufacturing cooked cereals, it is possible to prepare a dry premix comprising about 80-88$ of a flour or semolina of a cereal such as wheat, oat, corn or rice, about 2-12~ of sugars such as sucrose and dextrose, and other traditional ingredients such as about 1-2~ of sodium chloride, up to 15~ of modified starches such as modified corn or wheat starches, up to 10$ of powdered milk or other protein source, up to about 0.5~ of mineral salts, up to about 0.5~ of vitamins, up to 2~ antioxidants and 21~~.'~!~P~
possibly even enzymes which can reduce the viscosity of the mixture to be prepared, for example.
For manufacturing dry pet food, it is possible to prepare a dry premix comprising at least about 50~ of cereal flour or semolina, about 25-35~ of meat flour and animal by-products, about 5-15$ fat and tallow, up to 10$
vegetable by-products and up to 6$ vitamins and minerals, for example.
For manufacturing either cooked cereals or dry pet food it is possible to prepare a mixture of water and the premix such that the mixture has a water content of about 10-40o by weight, with the aid of a high speed blade mixer, a twin-screw intermeshing and corotating mixer or extruder, or a single-screw extruder, for example.
It is possible to cook this mixture by heating it to about 80-200°C for about 20 s to about 180 min, with the aid of a mixing and cooking device such as a twin-screw intermeshing and corotating mixer or extruder, or a single-screw extruder, and/or a cooking device such as a double jacketed cylindrical vessel enclosing internal transporting means such as an Archimedes screw, for example.
Preferably, the various possible screw configurations of the above devices which may be used for carrying out the present mixing and cooking steps are chosen in order to subject said mixture to relatively low shear forces. Such screws generally comprise a shaft upon which bilobes each having the shape of a screw section are fitted and attached onto each other. The length and the direction of the screw pitch associated with a bilobe can be chosen in function of the type of work which it is desired to perform in numerous successive and/or alternating zones of the screw, a relatively long pitch rather corresponding to a mixing zone and a relatively short pitch rather corresponding to a cooking zone, for example.
It is possible to maintain a pressure of less than about 2000 kPa, preferably of from about 100 to about 1000 kPa upstream of the gear pump and to have the gear pump exerting a pressure of from about 2000 to about 20000 kPa on the mixture upstream of the die, for example.
In order to press the mixture through said extrusion die, it is possible to exert the pressure on the mixture during the cooking step, especially by connecting the gear pump between a mixing and cooking device and a cooking device, for example. In such an embodiment, the present process permits the use of a mixture having a relatively high dry matter content, that means a relatively high viscosity, while using a cooking device which itself would not be capable of transporting such a mixture.
It is possible to further enhance the dry matter content by using enzymes which lower the vicosity of the mixture.
A relatively high dry matter content, especially of from about 78~ to about 90$, may be necessary if one wishes to obtain an expanded product at the exit of the die, for example.
It is also possible to exert the pressure on the mixture after the cooking step, by connecting the gear pump between a mixing and cooking device and the die, for example.

The gear pump may comprise two toothed wheels, or toothed rollers which mesh with each other. The two rollers can rotate in a housing on axles situated in a plane perpendicular to the direction of a mixture stream. They can each rotate in the opposite direction, the teeth coming apart upstream and closing again downstream. The outer edge of the teeth can slide against a corresponding inner wall of said housing, thus defining intersticial spaces intended for transporting the mixture to be extruded downstream. The shape of the teeth may be especially designed to avoid as much as possible any friction between the teeth which mesh with each other and any shearing on the mixture transported.
The gear pump is preferably provided with a double jacketed body.
It is possible to cut the extruded rope of cooked mixture into pellets or puffs just at the exit of the die, with the aid of a cutting device such as a rotating knife, for example.
The extrusion die may comprise one or more extrusion conduits, especially cylindrical conduits, generally oriented in the same direction as that of a stream of mixture to be extruded, preferably in a direction perpendicular to the plane in which the roller axles are situated, for example. The shape of the extruded rope may be determined in particular by the shape of the outlet opening or orifice of said conduits.
The die is preferably enclosed in a double jacketed casing in which a cooling or heating fluid can be circulated.

Brief description of the Drawings Embodiments of the invention are described below by way of example only with reference to the: accompanying drawings in which:
- Figure 1 is a schematic view of an embodiment where the gear pump is connected between a mixing and cooking device and a cooking device, and - Figure 2 is a schematic view of an embodiment where the gear pump is connected between a mixing and cooking device and the extrusion die.
Detailed description of the Invention In the embodiment represented in Figure l, the apparatus comprises a mixing and cooking device l, a cooking device 2, a gear pump 3 connected between the mixing and cooking device 1 and the cooking device 2, and an extrusion die 4.
The mixing and cooking device 1 is in the form of screws 13 which int-er_mesh and corotate. In other words, the screws 13 rotate in the same direction and mesh with each other. They are driven by a motor 5. 'They are enclosed in a barrel 14 having at its upstream end an inlet 15 for feeding water and a dry premix. Suitable devices are commercially available and may be obtained from Wenger;
Clextral, Teledyne~and the like.
The gear pump 3 comprises two toothed rollers 9 which mesh with each other. Suitable devices are commercially available and may be obtained from Maag~
* Trade-mark The cooking device 2 comprises a doublE~ jacketed cylindrical vessel 7 enclosing an Arch_Lmedes screw 6 driven by a motor 8.
The extrusion die 4 comprises a plate pierced with several cylindrical conduits 10. A cutting device is provided at the exit of the die 4 in form of a rotating knife 11 driven by a motor 12. Suitable extrusion dies and cutting devices are well known in t:he art and may be obtained from Wenger and Clex,tral, for example.
In the embodiment represented in FigurE: 2, the apparatus comprises a mixing and cooking device 7_, an extrusion die 4 and a gear pump 3 connected between t:he mixing and cooking device 1 and the extrusion die 4.
The mixing and cooking device 1, the gear pump 3 and the extrusion die 4 are similar to the corz-esponding devices described above with reference to Figure 1.
The process according to the present invention is described in greater detail in the examples presented below by way of illustration. The percentages are given therein by weight.
Example 1 An arrangement corresponding to the embodiment represented in Figure 1 was used, in which the mixing and cooking device was a twin-screw intermeshing and corotating READCC~type TELEDYNE~mixer. This mixer had a screw diameter of 127 mm and a total processing length of 7.2 times the screw diameter. It was driven by a motor the speed of which was adjustable between 50 and 510 rpm at a maximum power of 37 kW. Its barrel was temperature * Trade-mark _ _g_ controlled either with the aid of steam or hot water heat exchangers.
The gear pump was a VACOREX VX 70/70~type MAAG pump. It was driven by a motor the speed of which was adjustable.
It was provided with a double jacketed body which was temperature controlled with the aid of a hot water exchanger.
The cooking device was a cylindrical vessel with double jacket enclosing an Archimedes screw. The temperature of the double jacketed vessel was contra lled-with the aid of a hot water heat exchanger.
The extrusion die was a plate pierced with two cylindrical conduits each 4mm in diameter. It was enclosed in a double jacketed casing which was temperature controlled with the aid o f a water heat exchanger.
The cutting device was a rotating knife driven by a motor the speed of which was adjustable.
With the aid of this apparatus, cooked cereals were manufactured in the following way:
20 kg/h of water heated to 80°C and a0 kg/h of a dry premix mainly comprising corn semolina were fed into the mixing and cooking device. The premix had a water content of about 11$. The mixture of water and dry premix thus had a water content of about 36.4$.
The composition of the premix was:
- corn semolina 88$
- sucrose 8$
* Trade-mark --10- ~ ~16~.3~7 - sodium chloride 2$

- vitamins 0.5~

- mineral salts 0.50 - antioxydant 1~

The screw speed of the mixing and cooking device (n-mixcook) was set to 200 rpm. The temperature of the barrel of the mixing and cooking device was maintained between 127 and 137°C. The residence time of the mixture within the mixing and cooking device (t-mixcook) was about 30 s. At the end of the mixing and cooking device the mixture was totally gelatinised and it had a temperature (T-mixcook) of 104°C. The pressure in the mixing and cooking device and at the inlet of the gear pump (p-gear) was 100 kPa.
The speed of the toothed rollers of the gear pump (n-gear) was set to 9 rpm. The temperature of the body of the gear pump was maintained at 100°C. The residence time of the gelatinised mixture within the gear pump was about 8 s.
The temperature of the double jacket of the cooking device was maintained at 90°C. The residence time of the mixture within the cooking device was about 3 h. At the end of the cooking device the cooked mixture had a temperature of 84°C. The pressure at the end of the cooking device and in front of the extrusion die (p-die) was 2000 kPa.
The temperature of the double jacketed casing of the extrusion die was maintained at 90°C.
The cooked cereals thus manufactured were ball-shaped, partly expanded pellets, ready to be processed with ~1~~~~ r further down-stream equipment in order to be either puffed or rolled into flakes, for example.
The smell and the taste of the mixture improved noticeably during its long residence time in the cooking device. Before entering the cooking device, the gelatinised mixture was light yellow and did not really have the smell and taste of well cooked cereal. After leaving the cooking vessel, the color of the cooked mixture had changed to dark yellow-light brown and its smell and taste were more intensive, namely similar to those of fresh baked bread.
It is important to note that the mixture was totally gelatinised, namely totally precooked before entering the cooking device which rather functioned as a holding device without transferring any further heat into the mixture.
Thus, a specific energy input into the mixture (E-mixture) may be defined as the sum of the respective power consumption of the mixing and cookig device (W-mixcook) and of the gear pump (W-gear) divided by the flowrate of the mixture. In the present example, W-mixcook was 9.8 kW, W-gear was 0.8 kW and E-mixture was 0.15 kWh/kg.
Examples 2 to 5 An arrangement corresponding to the embodiment represented in Figure 2 was used.
In Example 2, the mixing and cooking device was a twin-screw intermeshing and corotating READCO type TELEDYNE
mixer identical to the one used in Example 1.

In Example 3, the mixing and cooking device was a twin-screw intermeshing and corotating BC--72 H type CLEXTRAL
extruder. This extruder had a screw diameter of 88 mm and a total processing length of 17 times the screw diameter.
It was driven by a motor the speed o~° which was adjustable. Its barrel was temperature controlled with the aid of induction heating coils.
In Example 4, the mixing and cooking device was a single-screw X-25 type WENGER extruder. This extruder had a screw diameter of 133 mm and a total processing length of 8:8 times the screw diameter. It was driven by a motor the speed of which was adjustable. Its barrel was temperature controlled with the aid of induction heating coils.
In Example 5, the mixing and cooking device was an OE
15.2 type KHAL~expander which is a k~_nd of single screw extruder.
In Example 2 the composition of the premix was the same as in Example 1.
In Example 3 and 4 the composition oi: the premix was:
- corn semolina 25$

- rice flour 55$

- sucrose 12~

- modified corn starch 4$

- sodium chloride 2~

- vitamins 0.5~

- mineral salts 0.5~

antioxydant 1~

* Trade-mark In Example 5 the composition of the premix was:
- corn semolina 50$
- meat flour and animal by-products 29~
- fat and tallow 9~
- vegetable by-products 8~
- vitamins, minerals 4g In all of Examples 2 to 5, the gear pump was a VACOREX VX
70/70 type MAAG pump. It was driven by a motor the speed of which was adjustable. It was connected at the end of the mixing and cooking device and in front of the die. It was provided with a double jacketed body in which a temperature of 120°C was maintained with the aid of a high pressure water based heat exchange system. The speed of its toothed rollers was adjusted in order to keep a constant pressure of about 100-200 kPa at its inlet.
The gelatinised mixture was pressed through a die plate pierced with one or more cylindrical extrusion conduits, each a few mm in diameter (Example 2 to 4) or star shaped extrusion conduits (Example 5).
The expanding ropes were cut at the exit face of the die into ball- or star-shaped pellets with a cutting device which was a standard CLEXTRAL pelletizer.
The different processing parameters are presented in table 1 below in which the abbreviations used correspond to those defined in Example 1:

Table 1 Example No 2 3 4 5 water flow rate (kg/h) 18 18 37 90 dry mix " " (kg/h) 83 230 150 350 water content of 27 17.5 28.5 28.5 mixture (%) t-mixcook (s) 30 20 35 30 T-mixcook (C) 132-142 139-148 124-134 120-140 n-mixcook (rpm) 200 286 315 330 W-mixcook (kW) 11.6 30 24 33 p-gear (kPa) 100 100 200 150 n-gear (rpm) 12 21.5 20.5 20 W-gear (kW) 0.8 1.4 1.3 1.2 E-mixture (kWh/kg) 0.115 0.122 0.131 0.073 p-die (kPa) 4400 11400 8000 10500 die conduits (mm) 1 x 3.5 3 x 4 3 x 4 The cooked cereals manufactured in Examples 2 and 4 were ball-shaped semi-expanded pellets, ready to be processed with further down-stream equipment in order to be either puffed or rolled into flakes, for example.
The cooked cereals manufactured in Example 3 were ball-shaped expanded pellets, ready to be processed with further down-stream equipment in order to be toasted, for example.
The shape of the pellets manufactured in Examples 2 to 4 were similar to, and their smell, taste and texture were also similar to but could even be said to have improved as compared to those of corresponding pellets manufactured without the support of the gear pump.

-15- 2~~~
The dry pet food manufactured in Example 5 were star shaped expanded pellets, ready to be processed with further down-stream equipment in order to be dried and coated, for example.

Claims

1. A process for the manufacture of cooked cereals or dry pet food, which comprises preparing a mixture of water and a dry premix comprising cereal flour or semolina, cooking the mixture to produce a gelatinized mixture having a degree of gelatinization of at least 95%, pressurizing the gelatinized mixture using a gear pump comprising two toothed wheels or rollers which mesh with each other with the teeth being configured and dimensioned to avoid friction therebetween as they mesh; and forcing the gelatinized cooked mixture through an extrusion die using pressure generated by the gear pump to subject the mixture to compression with a minimum shear force to thus reduce the energy input into the mixture by 10%-25%; wherein the organoleptic properties of the cereal are enhanced.

2. A process according to claim 1 in which the mixture is extrusion cooked, passed through the gear pump, and then further cooked by holding the mixture at, a cooking temperature.

3. A process according to claim 1 in which the mixture of water and dry premix has a water content of about 10 to about 40% by weight.

4. A process according to claim 2 in which the mixture is cooked at a temperature of about 80 to about 200°C. for about 20 seconds to about 180 minutes.

5. A process according to claim 1 in which the pressure of the mixture prior to the gear pump is less than about 2000 kPa and the gear pump increases the pressure on the mixture to between about 2000 kPa and about 20000 kPa.

6. A process according to claim 5 in which the pressure of the mixture prior to the gear pump is from about 100 kPa to about 1000 kPa.

7. A process according to claim 1 in which the mixture is extrusion cooked.