GB1570521A

GB1570521A - Extrusion process for the treatment of cereal

Info

Publication number: GB1570521A
Application number: GB886/76A
Authority: GB
Original assignee: Golden Wonder Ltd
Current assignee: Golden Wonder Ltd
Priority date: 1976-02-09
Filing date: 1976-02-09
Publication date: 1980-07-02
Also published as: NL162547B; DE2704880A1; BE851158A; FR2340058A1; FR2340058B1; NL7701028A; DE2704880B2; NL162547C

Description

(54) EXTRUSION PROCESS FOR THE TREATMENT OF CEREAL (71) We, GOLDEN WONDER LIMITED a British Company of Edinburgh House, Abbey Street, Market Harborough, Leicestershire LE16 7NT, England do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to an extrusion process for the treatment of cereal, i.e. edible grain, to provide an expanded cooked product in the preparation of a snack food.

A known cooker extruder for maize grit has an inlet for the cereal which leads into an extrusion chamber comprising a sleeve within which a conveyor screw is arranged to rotate.

The outlet end of the extrusion chamber comprises a die housing which provides a restricted outlet. Maize grit fed to the extrusion chamber is subjected to high pressure and the friction generated between the screw and sleeve maintains a temperature of about 150 C which gelatinises the maize. As the latter is extruded through the orifices in the die plate it expands due to the drop in pressure. A rotating knife cuts the extrudate into specified lengths.

Due to the friction fit of the screw in the sleeve, wear takes place in the sleeve. The density of the extrudate is dependent on several factors, notably the condition of the sleeve but also the rate of feed to the chamber, the rotational speed of the screw, the temperature in the chamber, the orifice area and the moisture content of the cereal. With a new sleeve the maize extrudate normally has a high density and a hard texture and often contains small particles of unexpanded maize. As the sleeve becomes worn the density of the extrudate decreases, finally becoming unacceptable in the finished product, in other words the density of the product is uncontrollably affected by wear of the extruder sleeve. When the density is high, the weight of raw cereal required is correspondingly high and this is reflected in the raw material costs.

If the feed rate or the screw speed is reduced to provide a high density product the volumetric output of the extruder will be correspondingly reduced. Alternatively, if the die plate is changed to vary the die orifices or, if a different sleeve is fitted, to vary the screw fit the extruder has to be temporarily shut down, thus interrupting production.

One object of the present invention is to provide an extrusion process for a cereal grit, e.g. maize grit, wherein a controlled variation in density of the cooked extrudate is achieved without adversely affecting the volumetric output from the extruder.

According to the invention there is provided an extrusion process for producing an expanded, cooked cereal product comprising the steps of: a) subjecting a raw cereal to heat and pressure in an extrusion chamber of a cooker extruder having a sleeve and a co-operating screw, which sleeve during operation is subject to wear which affects the density of the extrudate; b) adding to the raw cereal upstream of the cooker extruder an additive comprising particles of cereal which have already been expanded and milled; c) monitoring the density of the extrudate; d) utilizing the results of the monitoring to determine the amount of said additive to be added to the raw cereal upstream of extrusion so as to keep the density of the subsequent extrudate within a predetermined range; and e) adding the determined amount of said additive to the raw cereal to keep the density of the extrudate within said range, the percentage by weight of the additive not exceeding 15% of the extrudate.

The temperature in the extrusion chamber is preferably controlled by cooling units to lie within the range 115-165"C.

The density-controlling additive is preferably cereal which has already been expanded in a cooker extruder and has then been reduced to a suitable particle size.

The expanded cereal may be milled in a known rotary sieve wherein the expanded cereal is fed into a mesh cylinder where a rotating paddle scrapes it against the mesh. The resulting particle size which can be varied by changing the cylinder is not uniform but does not exceed 1400 microns.

The proportion by weight of additive to ran cereal is at a maximum when the extruder sleeve is new and is then progressively decrease to zero as sleeve wear takes place. The maximum proportion of additive is 15% because above this figure mixing problems arise, viz. the raw cereal settles out from the lighter cereal additive.

EXAMPLE 1 In this Example the machines used comprise a cooker extruder and a rotary sieve, each of the kind described above, and a ribbon blade mixer. The mixer is used to mix water with the raw cereal and then to mix additive with the moist raw cereal.

The raw cereal is a maize grit and the additive cereal is a maize grit which has been expan ded in a previous extrusion process and then milled to a particle size not greater than 1400 microns. The additive cereal may comprise waste material from a previous extrusion process. A sampling container of known weigh and capacity for periodically taking a sample of the extrudate is also provided.

The extruder is preheated to approximately 1 500C (but not above 165"C) then started up and the extrusion chamber is fed with raw cereal only. The extrudate is collected and a sample taken with the sampling container. If the extrudate is found to have an unacceptably high density, an estimated suitable quantity of the cereal additive is mixed with the raw cereal in the ribbon blade mixer. Since the cereal additive is drier than raw cereal, a compensating quantity of water is added to the raw cereal in the mixer before the cereal additive is introduced. The resultant mixture having a moisture content of about 13-15% by weight is then fed to the extrusion chamber. The extrudate will now show a decrease in density when a sample is taken with the sampling container. If the density decrease is too great, the addition of cereal additive is reduced until an acceptable extrudate is obtained. The original high-density extrudate made from the raw cereal only and also any unacceptably low-density extrudate are collected and then milled in the sieve to provide future cereal additive. During production of the expanded cereal the extrusion chamber sleeve becomes progressively worn and as this wear takes place so the density of the extrudate decreases. This density decrease is detected using the sampling container and the amount of cereal additive to keep the extrudate within acceptable predetermined density limits is immediately reduced. When the extruder sleeve is almost worn out, the extrudate density has decreased to such a level that no further cereal additive is necessary. The density of the TABLE

Density Machine Output of Product Extrusion Mixture in Consumption Extrudate GMS/Litre in LBS/Hour In Cu Ft/Hour STANDARD (i.e. without 47 180 60.0 cereal additive) A CONTAINING 5% by weight 44 180 65.4 cereal additive A CONTAINING 7% by weight 37 154 66.5 cereal additive STANDARD (i.e. without 65 210 53.3 cereal additive B CONTAINING 3% by weight 62 210 54.2 cereal additive B CONTAINING 6% by weight 55 195 56.2 cereal additive B CONTAINING 9% by weight 51 180 56.4 cereal additive B CONTAINING 12% by weight 47 180 61.2 cereal additive extrudate continues to decrease until the extrudate density becomes unacceptable. The extruder is now stopped operating and the worn sleeve is replaced. Cereal additive is then added to the raw cereal in the mixer. When a new sleeve is fitted the extrudate density is at its highest. In order to reduce this density a maximum amount of 15% by weight of additive is necessary to reduce the density to an acceptable level.

The cut lengths of extrudate are baked to crispness, flavoured and put into bags or other marketing containers.

EXAMPLE 2 The machines used are the same as for Example 1. The procedure followed is also the same as for Example 1 except that in the mixer ordinary potato powder is mixed in with the moistened raw maize grit. The percentage by weight of the potato powder is 10%. The density-controlling additive remains the same, viz.

maize grit which has been expanded by a previous extrusion process and then milled to a particle size not exceeding 1400 microns. Likewise, the maximum proportion of cereal additive should not exceed 15% by weight of the maize/potato mixture.

With reference to the Table on the previous page which relates to the same extruder typical extrudates containing only maize (Example 1) are Products A whilst typical extrudates containing maize and potato (Example 2) are Products B.

WHAT WE CLAIM IS: 1. An extrusion process for producing an expanded, cooked cereal product comprising the steps of: a) subjecting a raw cereal to heat and pressure in an extrusion chamber of a cooker extruder having a sleeve and a co-operating screw, which sleeve during operation is subject to wear which affects the density of the extrudate; b) adding to the raw cereal upstream of the cooker extruder an additive comprising particles of cereal which have already been expanded and milled; c) monitoring the density of the extrudate; d) utilizing the results of the monitoring to determine the amount of said additive to be added to the raw cereal upstream of extrusion so as to keep the density of the subsequent extrudate within a predetermined range; and e) adding the determined amount of said additive to the raw cereal to keep the density of the extrudate within said range, the percentage by weight of the additive not exceeding 15% of the extrudate.

2. A process according to claim 1, wherein the proportion of weight of the cereal additive to the raw cereal is at a maximum to start with and is then decreased with wear of the sleeve in the extrusion chamber to keep the density of the extrudate within a predetermined range.

3. A process according to claim 1 wherein the particles of the cereal additive are the milled product of a former extrusion process.

4. A process according to claim 1, wherein the cereal is maize grit and the cereal additive is maize grit which has been expanded by an extrusion process and milled.

5. A process according to claim 1, wherein water is added to the cereal before the addition of the cereal additive so as to compensate for a drying effect produced by the subsequent addition of the cereal additive.

6. A process according to claim 1, wherein the temperature in the extrusion chamber does not exceed 165"C.

7. A process according to claim 1, wherein potato powder is added to the cereal before extrusion.

8. A process according to claim 1 wherein the size of the particles of additive does not exceed 1400 microns.

9. A process according to claim 1 wherein the temperature in the extrusion chamber is maintained within the range of 150C to 1650C.

10. A process for producing a maize product as claimed in claim 1 substantially as described in Example 1 hereof.

11. A process for producing a maize and potato product as claimed in claim 1 substantially as described in Example 2 hereof.

12. An extrudate produced by the process of any of claims 1 - 9.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. extrudate continues to decrease until the extrudate density becomes unacceptable. The extruder is now stopped operating and the worn sleeve is replaced. Cereal additive is then added to the raw cereal in the mixer. When a new sleeve is fitted the extrudate density is at its highest. In order to reduce this density a maximum amount of 15% by weight of additive is necessary to reduce the density to an acceptable level. The cut lengths of extrudate are baked to crispness, flavoured and put into bags or other marketing containers. EXAMPLE 2 The machines used are the same as for Example 1. The procedure followed is also the same as for Example 1 except that in the mixer ordinary potato powder is mixed in with the moistened raw maize grit. The percentage by weight of the potato powder is 10%. The density-controlling additive remains the same, viz. maize grit which has been expanded by a previous extrusion process and then milled to a particle size not exceeding 1400 microns. Likewise, the maximum proportion of cereal additive should not exceed 15% by weight of the maize/potato mixture. With reference to the Table on the previous page which relates to the same extruder typical extrudates containing only maize (Example 1) are Products A whilst typical extrudates containing maize and potato (Example 2) are Products B. WHAT WE CLAIM IS:

1. An extrusion process for producing an expanded, cooked cereal product comprising the steps of: a) subjecting a raw cereal to heat and pressure in an extrusion chamber of a cooker extruder having a sleeve and a co-operating screw, which sleeve during operation is subject to wear which affects the density of the extrudate; b) adding to the raw cereal upstream of the cooker extruder an additive comprising particles of cereal which have already been expanded and milled; c) monitoring the density of the extrudate; d) utilizing the results of the monitoring to determine the amount of said additive to be added to the raw cereal upstream of extrusion so as to keep the density of the subsequent extrudate within a predetermined range; and e) adding the determined amount of said additive to the raw cereal to keep the density of the extrudate within said range, the percentage by weight of the additive not exceeding 15% of the extrudate.

12. An extrudate produced by the process of any of claims 1 - 9.