GB1561190A

GB1561190A - Process for cooking and extruding food mixtures

Info

Publication number: GB1561190A
Application number: GB53607/77A
Authority: GB
Original assignee: Weetabix Ltd
Current assignee: Weetabix Ltd
Priority date: 1977-12-20
Filing date: 1977-12-20
Publication date: 1980-02-13
Also published as: CA1122849A

Description

(54) A PROCESS FOR COOKING AND EXTRUDING FOOD MIXTURES (71) We, WEETABIX LIMITED, a British Company of Weetabix Mills, Burton Latimer, Kettering, Northants, NN15 5JR, 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: e present invention relates to a process~for~cooking and extruding fooW mltxtures containing cereal bran. The invention relates particularly to a continuous cooking and extrusion process which can be carried out in an extrusion machine.

Extrusion machines are known for carrying out continuous cooking and extrusion processes whereby mixtures of powdered or granulated food solids and liquids or doughs are cooked under controlled conditions of temperature and pressure and thence extruded through die means. After extrusion, the cooked food may or may not expand, depending on the ingredients used, so that it has a honeycomb structure and be cut into size suitable for consumption. The food can be subjected to further processing such as drying or toasting if necessary.

Such machines generally comprise one or two intermeshing rotary screws which are located in a substantially cylindrical casing. An extrusion nozzle with die means is fixed at one end of the casing for egress of the food and an inlet is provided for the food at the other end of the casing. Between the inlet and the extrusion nozzle within the casing in certain extrusion machines, particularly in those with two intermeshing screws, three regions of processing can be defined. Immediately succeeding the inlet is a region wherein the food is mixed thoroughly by flight or flights of the screw or screws. Thereafter, pressure is progressively applied to the food by gradually decreasing the volume of that portion of the casing in relation to the volume of food therein. The temperature of the food is thereby raised and it is possible to reach temperatures sufficient to cook the food. Additional heat may be applied to the food if necessary, however, by heating the exterior of that portion of the casing which comprises the cooking region. In the final region, the pressure applied to the food is reduced and moisture in food which was raised above the boiling point of water during cooking may be allowed to flash off. In this region, the temperature and pressure applied to the food is carefully controlled so that the food egressing from the extrusion nozzle has a predetermined moisture content and the rate of expansion of same is regulated.

The die means may comprise a pair of die plates which define an aperture through which the food is extruded in a ribbon-like form. A cutting blade or shave can be located dose to the die aperture to cut the ribbon into small pieces and the die aperture can be of various shapes to produce food pieces of a variety of shapes.

An example of such a machine comprising two intermeshing rotary screws is the Twin Screw Extruder, Model No. BC45, produced by Creusot Loire, a French company of 5 rue de Montessuy 75007 Paris, France.

The object of the present invention is to provide a process for cooking and extruding food mixtures containing cereal bran which process may, for example, be carried out in a extrusion machine as described above.

According to the present invention there is provided a process for cooking and extruding a food mixture containing cereal bran and a binding agent in predetermined proportions with a total predetermined water content whereby the food mixture is cooked at a temperature within the range 100"C to 2700C inclusive at a pressure within the range 50 to 150 atmospheres inclusive, extruded through die means, and thereafter cut into pieces of a desired shape; Preferably, the total cereal bran content of the food mixture is within the range of 10% to 95% inclusive by dry weight.

Examples of the present invention will now be described with particular reference to processes for the production of breakfast cereals.

The basic ingredients of the food mixture are cereal bran, a binding agent and water, and these are combined in predetermined proportions as will be described. The binding agent permits the bran to be continuously extruded and may also be an expanding agent, for example an amylaceous flour or gum, so that a controlled degree of expansion takes place after extrusion of the cooked mixture. It should be noted that ingredients other than pure bran which may be included in the mixture, such as some amylaceous flours, also contain bran and it is anticipated that the total bran content of the mixture will be within the range of 10% to 95% inclusive by dry weight. The total water content of the mixture before processing will preferably be in the range of 5% to 30% inclusive by weight, the actual quantity depending on the particular process to be carried out on the food mixture. Again it should be noted that the total amount of water includes not only water which may be added to the mixture but also the moisture content of the various ingredients.

Apart from the basic ingredients, other subsidiary ingredients may also be added. These include flavouring and sweetening agents for example sugars, syrups, honey, malt extract, salt and monosodium glutamate. Proteins may be added such as gluten, soya protein, casein, egg albumen or fish flour and similarly many types of flour may be added as binding/expanding agents and to vary the taste of the finished product. Examples of such flours are wheat, rye, barley, rice, maize and oat flours as well as ground millet and other sorghum flours in addition. As is usual in the production of foodstuffs, colouring, added vitamins and texture modifiers in the form of emulsifiers may also be added to the mixture.

With particular reference to the production of breakfast cereals, fruit or fruit products can also be added to the mixture. The fruit may be added into the mixture in a dried disintegrated form or be a paste or puree. Fruit concentrates may also be used.

Preferred food mixtures for the production of breakfast cereals fall into two main categories, those in which the major ingredients are all cereal products and those in which there are fruit or fruit products included. In the examples which follow, lists of ingredients are given for the production of various products. For each of the lists of ingredients is quoted a range of percentage weights for each ingredient together with an exact percentage weight which is that preferred. Although the food mixture could be cooked in and extruded by any extrusion machine as described above, the process details are quoted with particular reference to the machine which is Model BC45 of Creusot Loire as mentioned above.

Example 1 In this example, a sugar acts as the binding agent for the food mixture, which does not include any fruit and has a high bran content. No expanding agent is included in the ingredient. Water, however, is added and it should be understood that the water content quoted below is that water which is added to the dry ingredients and not necessarily the total water content of the mixture.

Ingredient Preferred percentage Preferred percentage weight weight range Cereal bran 78% 70% - 85% inclusive Sugar (Sucrose) 15% 10% - 20% Dry malt extract 5% 3% - 7% Salt 2% 1.5% -2.5% - 2.5% Water 2% 0% - 3% The food mixture comprising the above ingredients is preferably cooked at a temperature of 195"C with a screw speed of 250 revolution per minute. However, the temperature may be varied within the range 1500C to 195"C inclusive and the screw speed altered to fall within the range 200 to 300 revolutions per minute inclusive.

Example 2 This example has a lower bran content than example 1 but includes wholemeal flour which acts both as a binding agent in addition to the sugar content and as an expansion agent. Again, the water content quoted below is that water which is added to the other ingredient.

Ingredient Preferred percentage Preferred percentage weight weight range Cereal bran 50% 40% - 55% inclusive Wholemeal flour 35% 30% - 50% Sugar (Sucrose) 10% 5% - 15% Dry malt extract 3% 3% - 6% Salt 1% 1% - 2% Caramel 1% 1% - 2% Water 2% 0% - 3% The food mixture is preferably cooked at a temperature of 195"C with a screw speed of 250 revolution per minute. However, as for example 1 above, the temperature may be varied within the range 1500C to 1950C inclusive with a variation in screw speed within the range 200 to 300 revolutions per minute inclusive.

Example 3 This example includes dried fruit as an ingredient and has a high bran content. A sugar is used as the binding agent and no expanding agent is included. The dried fruit may include any chopped and prepared dried fruit such as, for example, date, apricot, peel or similar.

Ingredient Preferred percentage Preferred percentage weight weight range Cereal bran 82.5% 70% - 85% inclusive Sugar (Sucrose) 7.5% 5% - 10% Dried fruit 6% 2% - 10% Dry malt extract 2% 1% - 3% Salt 2% 1.5% -2.5% - 2.5% Water None 0% - 3% The food mixture is preferably cooked at a temperature of 140"C with a screw speed of 300 revolutions per minute. The temperature may, however, be varied within the range 125"C to 1450C inclusive and the screw speed varied withir the range 250 to 350 revolutions per minute inclusive.

Example 4 This example again includes dried fruit but has a low bran content. Wholemeal flour is used with a sugar as the binding agent and additionally acts as an expansion agent.

Ingredient Preferred percentage Preferred percentage weight weight range Cereal bran \ 50% 40% - 55% inclusive Wholemeal flour 29% 25% - 45% Sugar (Sucrose) .10% 5% - 15% Dried fruit 10% 5% - 15% Salt 1% 0.5% -1.5% - 1.5to Water None 0% - 3% The food mixture is preferably cooked at a temperature of 1300C and with a screw speed of 300 revolutions per minute. As with example 3, however, the cooking temperature may be varied within the range 125"C to 145"C inclusive and the screw speed varied within the range 250 to 350 revolutions per minute inclusive.

In each of the above examples, it should be appreciated that the cereal bran percentage weights quoted are those for bran per se. The total bran content is calculated by adding the percentage weight quoted for bran to the percentage weight of the bran content of the other mgredients such as wholemeal flour. In example 2 and 4 it is also possible to substitute wheat germ for some of the bran or wholemeal flour.

From the above examples, it can be seen that food mixtures containing fruit are cooked at a lower temperature with a higher screw speed than those mixtures which are predominately cereal. This is to prevent burning of the fruit. It will be appreciated that a balance has to be found between the prevention of burning and the attainment of a crisp final product, so that it is important to cook the mixtures at a temperature high enough to remove sufficient moisture from the mixture but only for a period of time long enough to cook the food adequately. The temperature should, therefore, fall within the range 100"C to 2700C inclusive. The residence time of the food mixture within the machine will depend on the screw speed, as is specified above and in each example is calculated according to the cooking temperature to produce the desired crispness of the food. The pressure within the machine will be determined in part by the screw speed and with speeds as mentioned above, the pressure can be expected to be in excess of 50 atmospheres but below a maximum 150 atmospheres.

The pressure is additionally controlled by the die means and particularly by the aperture between the die plates of the machine through which the food mixture is extruded. For the production of breakfast cereals, the food is extruded through the die means and cut by a rotating shaver located in close proximity to the aperture of the die means whereby the extruded ribbon of food is chopped into small pieces suitable for consumption without being further cut up. Flakes, pellets or balls can be produced in a variety of different shapes according to the shape of the die aperture. For example, flat dics, flakes, star-shapes and twists can be produced. However, for the various food mixtures listed in the aforementioned examples it is preferred that a concave flake is produced.

To produce a flake of suitable size, the die aperture is preferably of arcuate shape with width and length dimensions in the range 0.4 mm to 1.0 mm inclusive by 7 mm to 20 mm with a slit radius of curvature in the range 10 mm to 20 mm inclusive. The preferred dimensions are 0.6 mm by 10.0 mm with a radius of 10 mm. It will be appreciated however that the aperture need not be curved and may be simply rectangular when a flat disc or flake is produced.

As is stated above, the food mixture cooked and extruded according to the present invention may or may not contain an expanding agent. The specific density of the finished product varies according to the process conditions but typically example 1 above will produce a food having a density of approximately 0.8 grams per millilitre whereas example 4 will produce a food having a density of approximately 0.5 grams per millilitre.

The product bulk density will vary with the specific density and also with the shape of the die aperture. For example, food mixtures processed according to the present invention and extruded through a die aperture of 0.6 mm by 10 mm with a radius of curvature of 20 mm have bulk densities within the range 0.1 to 0.3 grams per litre. With particular reference to example 1, such a food has a bulk density of approximately 0.2 grams per litre.

Breakfast cereals produced using food mixtures as specified in the examples above and by a process according to the present invention require no further processing other than cooling after the extrusion and cutting of the product. In particular, no further cooking, such as toasting, of the product is necessary.

WHAT WE CLAIM IS: 1. A process for cooking and extruding a food mixture containing cereal bran and a binding agent in a predetermined proportions with a total predetemined water content whereby the food mixture is cooked at a temperature within the range 1000C to 2700C inclusive at a pressure within the range 50 to 150 atmospheres inclusive, extruded through die means, and thereafter cut into pieces of a desired shape.

2. A process as claimed in claim 1, in which the total cereal bran content of the food mixture is within the range of 10% to 95% inclusive by dry weight.

3. A process as claimed in claim 1 or 2, in which the binding agent comprises a sugar.

4. A process as claimed in claim 1 or 2, in which the binding agent is also an expanding agent whereby after being cooked and extruded the food mixture is permitted to expand before being cut into the pieces of desired shape.

5. A process as claimed in claim 4, in which the binding and expanding agent comprises an amylaceous flour.

6. A process as claimed in any of claims 1 to 5, in which the die means comprises two die plates which define an aperture through which the cooked food mixture is extruded.

7. A process as claimed in claim 6, in which the aperture has length and width dimensions within the ranges 7 mm to 20 mm inclusive and 0.4 mm to 1.0 mm inclusive respectively.

8. A process as claimed in claim 6 or 7, in which the aperture is arcuately shaped.

9. A process as claimed in claim 8, in which the radius of curvature of the aperture is in the range 10 mm to 20 mm inclusive.

10. A process as claimed in any of claims 1 to 9, in which the food mixture contains fruit or a fruit product.

11. A process as claimed in claim 3, in which the food mixture comprises cereal bran with a percentage weight within the range 70% to 85% inclusive and sucrose with a percentage weight within the range 10% to 20% inclusive and is cooked at a temperature within the range 1500C to 1950C inclusive.

12. A process as claimed in claim 10 when dependent on claim 3, in which the food mixture comprises cereal bran with a percentage weight within the range 70% to 85% inclusive, sucrose with a percentage weight within the range 5% to 10% inclusive, and dried fruit with a percentage weight within the range 2% to 10% inclusive, and is cooked at a temperature within the range 125"C to 1450C inclusive.

13. A process as claimed in claim 4, in which the food mixture comprises cereal bran with a percentage weight within the range 40% to 55% inclusive and wholemeal flour with a percentage weight within the range 30% to 50% inclusive, and is cooked at a temperature within the range 1500C to 195"C inclusive.

14. A process as claimed in claim 10 when dependent on claim 4, in which the food mixture comprises cereal bran with a percentage weight within the range 40% to 55% inclusive, wholemeal flour with a percentage weight within the range 25% to 45% inclusive, and dried fruit with a percentage weight within the range 5% to 15% inclusive, and is cooked at a temperature within the range 125"C to 145"C inclusive, 15. A process for cooking and extruding a food mixture substantially as hereinbefore described with reference to example 1, example 2, example 3 or example 4.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. example 1, such a food has a bulk density of approximately 0.2 grams per litre. Breakfast cereals produced using food mixtures as specified in the examples above and by a process according to the present invention require no further processing other than cooling after the extrusion and cutting of the product. In particular, no further cooking, such as toasting, of the product is necessary. WHAT WE CLAIM IS:

1. A process for cooking and extruding a food mixture containing cereal bran and a binding agent in a predetermined proportions with a total predetemined water content whereby the food mixture is cooked at a temperature within the range 1000C to 2700C inclusive at a pressure within the range 50 to 150 atmospheres inclusive, extruded through die means, and thereafter cut into pieces of a desired shape.

14. A process as claimed in claim 10 when dependent on claim 4, in which the food mixture comprises cereal bran with a percentage weight within the range 40% to 55% inclusive, wholemeal flour with a percentage weight within the range 25% to 45% inclusive, and dried fruit with a percentage weight within the range 5% to 15% inclusive, and is cooked at a temperature within the range 125"C to 145"C inclusive,

15. A process for cooking and extruding a food mixture substantially as hereinbefore described with reference to example 1, example 2, example 3 or example 4.