WO2009004292A1

WO2009004292A1 - Apparatus and method for applying a coating liquid

Info

Publication number: WO2009004292A1
Application number: PCT/GB2008/002120
Authority: WO
Inventors: Peter David Wilson
Original assignee: Peter David Wilson
Priority date: 2007-07-03
Filing date: 2008-06-23
Publication date: 2009-01-08
Also published as: GB0712835D0; GB2450866A

Abstract

Flavouring drums are used in the snack food industry to apply a flavouring mixture to snack food products such as potato chips, tortilla chips, corn chips, extruded snacks and the like. The invention provides an apparatus for applying flavouring slurry (or more generally a coating liquid) to food products as they pass through a flavouring drum (3). The apparatus includes a small mixing vessel (12) for mixing together a liquid such as an edible oil and flavouring particles to form a flavouring slurry. A pump (20) is provided to transfer the flavouring slurry from the mixing vessel (12) directly to a delivery means (8) for applying the flavouring slurry to the food products as they pass through the flavouring drum (3). The operation of the apparatus can be controlled in 'real time' and may include rate determining means for measuring or deriving the rate at which food products are supplied to the flavouring drum (3). Control means, optionally in the form of an electronic control unit (16), is provided to control the operation of the pump (20) such that that the rate at which the flavouring slurry is pumped directly to the delivery means (8) is selected in accordance with the rate at which the food products are supplied to the flavouring drum (3).

Description

Apparatus and method for applying a coating liquid

DESCRIPTION Technical Field

The invention relates to an apparatus and method for applying a coating liquid (e.g. a flavouring slurry such as an edible oil containing suspended solids such as flavouring particles, or a batter) to a variety of different food products including dried pasta, processed meat and fish products, and snack food products such as potato crisps, potato chips, tortilla chips, corn chips, extruded snacks and the like.

Background Art

Food products like dried pasta and snack food products such as potato chips, tortilla chips, corn chips, extruded snacks and the like can be flavoured by two known processes.

Process 1 :

In the first process the food products are flavoured by coating them with a dry flavouring mixture while feeding them through a rotating flavouring drum where they are tumbled to make sure the flavouring mixture is evenly distributed. The dry flavouring mixture will normally consist of flavouring particles such as granules or powder.

In some cases the food products are sprayed with a fine coating of edible oil such as vegetable oil before the flavouring particles are applied.

Process 2:

In the second process the food products are flavoured by coating them with a wet flavouring mixture or slurry that consists of flavouring particles suspended in an edible oil such as vegetable oil. Once again, the food products are fed through a rotating flavouring drum where they are tumbled to make sure the flavouring mixture is evenly distributed. The flavouring slurry is often prepared in a batch process where fixed quantities of edible oil and flavouring particles are mixed together slowly for a long period of time in a mixing vessel. The slurry is then stored in a storage vessel where it is constantly agitated to prevent the flavouring particles from coming out of suspension. Before it is supplied to a delivery nozzle and used to the coat the food products as they pass through the flavouring drum, the flavouring slurry is normally transferred from the storage vessel to a separate delivery vessel where once again it is constantly agitated.

The known processes are not capable of applying the flavouring particles to the food products in a consistently even manner. This means that significant amounts of the food products that exit the rotating flavouring drum will eventually be discarded because they have either been coated with too much flavouring or too little. A known problem with the second process in particular is the fact that the flavouring slurry that is applied to the snack foods will sometimes have the wrong proportion of edible oil to flavouring particles. This can result from incorrect quantities of edible oil and flavouring particles being supplied to the mixing vessel, for example. Since the flavouring slurry is prepared in a batch process, it is normally impossible to correct the error and the entire batch must be discarded.

Another problem is the tendency of the flavouring particles to come out of suspension when the flavouring slurry is being held in the storage and delivery vessels. Insufficient agitation or the creation of "dead zones" where the flavouring slurry remains substantially stationary is normally to blame for such separation. If the flavouring slurry is no longer properly mixed when it is applied to the snack foods then some of the food products will be coated with too much edible oil while others are coated with too much flavouring. So-called "spotting" can also occur where food products are coated with discrete clumps of flavouring particles instead of the flavouring particles being evenly distributed.

A further problem is known to arise when the flavouring slurry is transferred between the mixing vessel, the storage vessel and the delivery vessel using centrifugal or rotary lobe pumps. These can experience "compacting" problems where the action of the pumps themselves causes the flavouring particles to come out of suspension where they compact against the pump walls and lead to jamming.

WO 2007/008384 describes an apparatus for applying a coating liquid to snack food products made of sliced and fried potatoes. A dry seasoning mixture is mixed with omega-3 fatty oils in a mixing vessel and the resulting coating liquid is then supplied directly to a delivery nozzle. The delivery nozzle is located inside a rotating flavouring drum and applies the liquid coating to the snack food products as they pass through the flavouring drum.

US 2005/0169099 describes an apparatus for applying a batter for coating food products. A batter mixing apparatus includes a mixing vessel in which a dry batter mixture is mixed with a predetermined amount of water to form a batter. Once the batter has reached a desired viscosity, a variable speed supply pump is used to pump the batter to a batter applicator where food products are coated. The batter applicator delivers a pool of batter through which the food products are moved on a conveyor to coat them. Consistent coating of the food products is monitored and the viscosity of the batter can be varied accordingly. Excess batter from the batter applicator is collected and can be returned to the mixing vessel by a return pump.

Summary of the Invention

The present invention provides an apparatus for applying a coating liquid to food products, comprising a coating region, a mixing vessel for mixing together a liquid and a dry mixture to form a coating liquid, a pump for pumping the coating liquid to a delivery means for applying the coating liquid to the food products as they pass through the coating region, and control means for controlling the operation of the pump such that the rate at which the coating liquid is pumped to the delivery means is selected in accordance with the rate at which the food products are supplied to the coating region. The dry mixture may be in the form of flavouring particles, in which case the coating liquid may be a flavouring slurry that can be used to coat a wide variety of different food products including dried pasta and snack food products such as potato crisps, potato chips, tortilla chips, corn chips, extruded snacks and the like. The flavouring particles may be supplied in the form of granules or powder. The dry mixture may also be a dry batter mix in which case the coating liquid will be a batter that can be used to coat food products such as processed fish and meat products and the like.

The liquid may be water or an edible oil such as a vegetable, seed or nut oil, for example.

A significant advantage of the present invention is that the coating liquid can be pumped directly from the mixing vessel to the delivery means "on demand" (i.e. only when it is actually needed to coat the food products) rather than having to be produced in advance in a batch process and then held in storage and delivery vessels before it can be applied to the food products. In the case where food products are coated with flavouring slurry then the problems arising from the flavouring particles coming out of suspension are avoided.

The mixing of the liquid and dry mixture in the mixing vessel and the rate at which the coating liquid is supplied to the delivery means can also be carefully controlled in "real time" to adapt to changing circumstances and processing demands. This ensures that the coating liquid is evenly and consistently applied to the surface of the food products at all times during operation of the food processing plant of which the present apparatus forms a part.

It also means that the storage and delivery vessels associated with the second process are no longer required, leading to significant cost reductions.

The size and configuration of the mixing vessel is important in making sure that the liquid and dry mixture are properly mixed in a short period of time. The best mixing results are achieved by using a small capacity vessel (preferably holding no more than about 30 litres of coating liquid) together with high-speed impeller rotation (typically about 1450 rpm). The average mixing time (i.e. the average time that an individual particle of the dry mixture will remain within the mixing vessel) will preferably be no less than about 3 minutes and no more than about 5 minutes.

The actual capacity of the mixing vessel will normally be selected with reference to the operating parameters of the food processing plant, and in particular to the maximum rate at which the food products that need to be coated are to be supplied to the coating region, because this will determine the maximum rate at which the coating liquid will need to be supplied to the delivery means. Two or more mixing vessels can be provided if necessary. The mixing vessels can be arranged entirely independently of one another such that each mixing vessel has its own pump for pumping the coating liquid to a separate delivery means for applying the coating liquid to the food products as they pass through the coating region. The mixing vessels can also be arranged to supply coating liquid to the same delivery means. A single pump can be used to pump coating liquid from each of the mixing vessels to the same delivery means. Alternatively, each mixing vessel can have its own pump for pumping the coating liquid to the same delivery means.

The volume of coating liquid within the mixing vessel is preferably kept relatively constant (or at least within certain accepted limits) and liquid and dry mixture are supplied to the mixing vessel to replace the coating liquid that is pumped to the delivery means. As a result, the total volume of coating liquid that is supplied to the delivery means over the period of time when the present apparatus is operating will normally significantly exceed the capacity of the mixing vessel. One advantage of this is that if production has to be stopped for any reason then only the coating liquid that is currently being mixed in the mixing vessel and flowing though the delivery circuit between the mixing vessel and the delivery means will have to be discarded.

There will often be a short lead time (typically about 3 minutes) when the present apparatus is operated for the first time before the liquid and the dry mixture are properly mixed and the pump can be operated to pump the coating liquid from the mixing vessel to the delivery means. Subsequently, the liquid and dry mixture that are supplied to the mixing vessel will be mixed together with any existing volume of coating liquid to achieve a constant supply of coating liquid for the delivery means.

The pumping of the coating liquid to the delivery means can be carefully controlled in an automated manner. A rate determining means is preferably provided for measuring or deriving the rate (either volumetric or mass flow rate, for example) at which the food products are being supplied to the coating region. The rate at which the food products are being supplied to the coating region can be determined at any suitable point. For example, if the food processing plant includes an extruder for making extruded snack food products and a drier for drying the extruded snack food products before they are supplied to a rotating flavouring drum (i.e. coating region) then the rate at which the food products are being supplied to the flavouring drum can be determined at any point between the raw ingredients being supplied to the extruder all the way through to the extruded snack food products arriving at the near end of the flavouring drum. However, it is generally preferred that the rate determining means is a weighing means (e.g. a vibro weigher or belt weigher) located immediately before the coating means. The weighing means can provide information about the weight of food products passing over it and this can be used to determine the rate at which the food products are being supplied to the coating means. The food products will normally be passing over the weighing means on a conveyor and the speed of the conveyor may need to be taken into account when determining the rate. The speed of the conveyor can be assumed to be constant for any given food processing plant or measured by any suitable means.

Where such a weighing means does not form part of the food processing plant then the extruder itself may effectively function as the rate determining means by providing information about the amount of food products it is producing, for example. In general terms, it will therefore be readily appreciated that the rate determining means may form an integral part of the present apparatus or may be a component part of the food processing equipment of which the present apparatus forms a part. In the latter case, control signals indicative of the rate at which the food products are supplied to the coating region (e.g. the rate of supply of raw materials to the extruder, the rate of production of the extruder, the speed of any conveying means etc.) can be transmitted to the control means from the relevant component part.

The control means controls the operation of the pump such that the rate (volumetric flow rate, for example) at which the coating liquid is pumped to the delivery means is selected in accordance with the rate at which the food products are being supplied to the coating means.

The control means is preferably configured to automatically alter the rate at which the coating liquid is pumped to the delivery means in response to a change in the rate at which the food products are being supplied to the coating means. For example, the control means can be configured to increase the rate at which the coating liquid is pumped to the delivery means in response to an increase in the rate at which the food products are being supplied to the coating means, and to decrease the rate at which the coating liquid is pumped to the delivery means in response to a decrease in the rate at which the food products are being supplied to the coating means. In practice, this automated matching or tracking of the respective rates means that the correct amount of coating liquid is applied to the food products by the delivery means at all times. Close tracking between the respective rates is therefore preferred so that a change in the rate at which the food products are supplied to the coating region results in a "real time" change in the rate at which the coating liquid is pumped to the delivery means. However, the control means may apply averaging or any other suitable mathematical or processing techniques to make sure that the rate at which coating liquid is pumped to the delivery means is varied within acceptable physical operating limits for the component parts of the apparatus in the event that there are sudden and/or significant changes in the rate at which the food products are supplied to the coating region (e.g. caused by discontinuities in the production of the food products during the course of a batch run).

The control means may also have to delay making any changes to the rate at which coating liquid is pumped to the delivery means so that the change is made at the appropriate time. For example, if the extruder is effectively functioning as the rate determining means then there will probably be a delay between the extruder changing the amount of food products it is producing and the food products made under the new production conditions reaching the coating region.

The rate at which the coating liquid is pumped to the delivery means is preferably changed by altering the operating speed of the pump. _r

It will normally be the case that for any given food product there will be a known relationship between the rate at which the food products are supplied to the coating region and the rate at which the coating liquid is to be pumped to the delivery means.

The control means will preferably make use of this known relationship when controlling the operation of the apparatus. Deviations from the known relationship are possible in certain circumstances, for example in response to the results of post- production testing or the moisture content of the food products, or when discontinuities in the production of the food products causes sudden and/or significant changes in the rate at which the food products are supplied to the coating region.

The apparatus may further comprise sensor means for measuring or deriving the volume of the coating liquid within the mixing vessel. In practice, the sensor means may monitor the level of the coating liquid within the mixing vessel and may be of any suitable type (e.g. acoustic).

The rate at which the liquid and/or dry mixture are supplied to the mixing vessel may be fixed. In this case, the control means can be configured to alter the rate at which the coating liquid is pumped to the delivery means if the volume of the coating liquid exceeds certain accepted limits. For example, the control means can be configured to increase the rate at which the coating liquid is pumped to the delivery means if the volume of the coating liquid in the mixing vessel increases above a certain volume, and to decrease the rate at which the coating liquid is pumped to the delivery means if the volume of the coating liquid in the mixing vessel decreases below a certain volume. The control means can also be configured to alter the rate at which the liquid and/or dry mixture are supplied to the mixing vessel in response to a change in the rate at which the food products are supplied to the coating region or the rate at which the coating liquid is pumped to the delivery means. For example, if the rate at which the coating liquid is pumped out of the mixing vessel to the delivery means happens to be increased then the rate at which the liquid and/or dry mixture are supplied into the mixing vessel can also be increased.

It will be readily appreciated that a zero rate setting can be used to prevent any liquid and/or dry mixture from being supplied to the mixing vessel. Similarly, a zero rate setting can be used to prevent any coating liquid from being pumped out of the mixing vessel to the delivery means. In practice, a zero rate setting may be equivalent to the pump being stopped.

The control means can be used to alter the proportion (or ratio) of the liquid and dry mixture supplied to the mixing vessel. More particularly, if post-production testing of the coated food products indicates that the amount of liquid or dry mixture is not within certain limits then the control means can alter the proportion of liquid and dry mixture accordingly. The post-production testing will normally be carried out in a laboratory setting and the results can then be used to manually vary the proportion of the liquid and dry mixture being supplied to the mixing vessel. For example, if the results of the post-production testing indicate that the coating liquid contains too much dry mixture then an operator can use the control unit to reduce the rate at which the dry mixture is supplied to the mixing vessel while keeping the corresponding rate for the liquid unchanged. If post-production testing can be carried out in "real time" by some sort of sensing means then the results could be used by the control means to automatically alter the proportion of the liquid and dry mixture being supplied to the mixing vessel and/or to alter the rate at which the coating liquid is supplied to the delivery means. Although the intention is that the operation of the apparatus will be as automated as possible, it is generally preferred that some level of manual control is still provided for. The control means may therefore include a user interface (such as a graphical user interface (GUI)) to enable the apparatus to be manually controlled as required. Direct control of the supply of coating liquid to the delivery means and the supply of

' liquid and dry mixture to the mixing vessel may therefore be achieved manually by an operator through the control means.

The, food products will normally be supplied to the coating region on some sort of conveying means (such as a conveyor belt, for example) moving at constant speed. Changes in the speed of the conveying means may result in a change in the rate at which the food products are supplied to the coating region and the speed of the conveying means can be monitored by the rate determining means. This provides a convenient way of automatically controlling the pump to ramp down to a stop if the conveying means happens to stop for any reason. The control means may control the operation of the pump such that the rate at which the coating liquid is pumped to the delivery means is selected in accordance with the rate at which the food products are supplied to the coating region by the conveying means.

Although it is the volume of the food products being supplied to the coating region that is normally most important in determining the amount of coating liquid that needs to be applied, this is difficult to measure directly. If the bulk density of the food products is assumed to be relatively constant then the volume can be determined by taking a measurement of the weight of the food products. (However, care should be taken to make sure that changes in the weight are a direct result of changes in the volume of the food product rather than a change in moisture content, for example.) The rate determining means may therefore include weighing means for weighing the food products as they are supplied to the coating region. Any change in the volume or weight of the food products being supplied to the flavouring drum over a predetermined period of time may result in a corresponding change in the volumetric or mass flow rate, respectively. The pump is preferably a peristaltic pump (either rotary or linear) operating at variable speed. It has been found that peristaltic pumps do not suffer from the problem of "compacting" mentioned above. In addition, the moving parts of the peristaltic pump do not come into contact with the coating liquid and there is no risk of contamination. The pump will normally be selected with reference to the operating parameters of the food processing plant, and in particular to the maximum flow rate at which the food products are to be supplied to the coating region because this will determine the maximum flow rate at which the coating liquid will need to be supplied to the delivery means. Two or more pumps can be provided (either in parallel or series) if necessary. The speed of the pump will always be controlled to be within safe operating limits.

The delivery means can take the form of a nozzle and is preferably located at the coating region.

The coating region can take the form of a standard rotating flavouring drum, for example. An alternative would include a coating region defined by a pool of coating liquid through which the food products must pass to be coated. The flavouring drum is normally open-ended and is mounted so that its longitudinal axis is inclined relative to the horizontal. The food products are fed into the higher of the two openings where they are coated with the coating liquid and move through the rotating flavouring drum in a rumbling motion under gravity.

^■ The control means may be implemented using a single electronic control unit, for example. Alternatively, a number of linked electronic control units can be provided.

The present invention further provides a method of applying coating liquid to food products, the method comprising the steps of mixing together a liquid and a dry mixture to form a coating liquid, using a pump to supply the coating liquid to a delivery means for applying the coating liquid to the food products as they pass through a coating region, measuring or deriving the rate at which food products are supplied to the coating region, and controlling the operation of the pump such that the rate at which the coating liquid is supplied to the delivery means is selected in accordance with the rate at which the food products are supplied to the coating region.

The step of controlling the operation of the pump such that the rate at which the coating liquid is supplied to the delivery means is selected in accordance with the rate at which the food products are supplied to the coating region will normally be carried out continuously (i.e. in "real time") over the whole of the batch run.

The liquid and dry mixture are preferably mixed together in a mixing vessel to form the coating liquid.

The rate at which the liquid and/or dry mixture are supplied to the mixing vessel can be altered in response to a change in the rate at which the food products are supplied to the coating region or in the rate at which the coating liquid is supplied to the delivery means.

The method may further comprise the step of altering the rate at which the coating liquid is supplied to the delivery means in response to a change in the volume of the coating liquid in the mixing vessel. For example, the rate at which the coating liquid is supplied to the delivery means can be increased if the volume of the coating liquid in the mixing vessel increases above a certain volume, and the rate at which the coating liquid is supplied to the delivery means can be decreased if the volume of the coating liquid in the mixing vessel decreases below a certain volume.

The method may further comprise the step of altering the proportion of liquid and dry mixture that are mixed together to form the coating liquid.

The step of measuring or deriving the rate at which food products are supplied to, the coating region may further comprise measuring or deriving one of the weight, volume and bulk density of the food products being supplied to the coating region. . Drawings

Figure 1 shows a process flow diagram for the present invention; Figure 2 shows a schematic representation of an apparatus for applying a flavouring slurry according to the present invention; and Figure 3 shows an alternative flow diagram for the present invention.

With reference to Figure 1, raw ingredients (e.g. dry ingredients and water) are supplied to an extruder 1 which processes the raw ingredients and provides snack food products at a particular rate, which may vary over the course of a particular batch run. The snack food products are then dried in a dryer 2 and fed to a conveyor. The operation of the dryer 2 may be at least partially controlled by the extruder 1 during a batch run and the extruder transmits control signals (which are represented in all of the various Figures by dashed arrows) to the dryer. For example, if the rate at which the snack food products are produced is varied, the extruder 1 may automatically vary the temperature within the dryer 2.

The snack foods products proceed along the conveyer to a standard rotating flavouring drum 3, which is shown in more detail in Figure 2. Before the snack food products reach the flavouring drum 3 they are weighed by a weighing means 4 (e.g. a vibro weigher or a belt weigher). It will be readily appreciated that the process of drying the snack food products in the dryer 2 will reduce their weight as the water content is reduced. If the extruder 1 and the dryer 2 are both operating normally then the weight measured by the weighing means 4 should be within normal predetermined tolerances. A control signal is transmitted from the weighing means 4 to both the extruder 1 and the dryer 2. In the event that the weight measured by the weighing means 4 exceeds the normal predetermined tolerances then the control signal can be used to either control the operation of one or both of the extruder 1 and the dryer 2 or provide an alert that they may not be working correctly. For example, if the weight measurements exceed the normal predetermined tolerances then the extruder 1 may be malfunctioning such that the snack food products are not being made to their correct size or composition) or the temperature inside the dryer 2 may be too high or too low. In some situations, the control signals might be used to completely halt the batch run to enable maintenance or repairs to be made.

The snack food products are coated with flavouring slurry within the flavouring drum 3 and the coated snack food products are then subjected to post-production testing 5. This can be carried out in a laboratory setting or in "real time" using any suitable sensing means. The purpose of the post-production testing 5 is to check that the correct amount of flavouring slurry has been applied to the snack food products and that the flavouring slurry itself has the correct composition.

After post-production testing 5 the coated snack food products proceed to packaging 6 where they are packaged ready for transport.

The flavouring slurry is applied to the snack food products by an apparatus 7, which is shown in Figure 2. Flavouring particles and oil are supplied to the apparatus 7 where they are mixed to form a flavouring slurry. This is then pumped to a delivery nozzle 8 located within the flavouring drum 3. To ensure the correct amount of coating is applied to the snack food products as they pass through the flavouring drum, the flavouring slurry is pumped to the delivery nozzle 8 at a rate that is determined in accordance with the rate at which the snack food products are supplied to the flavouring drum 3. The rate at which the snack food products are supplied to the flavouring drum 3 is determined by measuring the weight of the snack food products leaving the dryer 2 as they pass over the weighing means 4 during a predetermined timeframe. Control signals transmitted from the weighing means 4 to the apparatus 7 can therefore be used to control the rate at which the flavouring slurry is pumped to the delivery means 8 and hence the rate at which it is applied to the snack food products.

The results of the post-production testing 5 can also be used to alter the amount of flavouring particles and oil being supplied to the apparatus 7 to change the composition of the flavouring slurry and/or the rate at which the flavouring slurry is pumped to the delivery means 8. Figure 2 shows the flavouring drum 4 and the apparatus for applying the flavouring slurry 7 in more detail. The standard rotating flavouring drum 3 has a near opening 3a and a far opening 3b and its longitudinal axis is inclined relative to the horizontal such that the near opening is elevated with respect to the far opening. The inner surface 9 of the flavouring drum is corrugated with alternating ridges and valleys (not shown) to promote tumbling.

Snack food products SF are extruded by the extruder 1 from a mixture of dry ingredients and water. The extruded snack food products are then dried in the dryer 2 before being fed to an input conveyor 10. The moisture content of the snack food products is measured before and after drying and is assumed to be constant once the extruder 1 has reached its steady-state operating condition. The snack food products SF are moved along the input conveyor 10 and fed into the near opening 3a of the flavouring drum 3 where they are coated with flavouring slurry that is delivered by the delivery nozzle 8 and tumbled to make sure the flavouring is evenly distributed. The snack food products SF pass through the flavouring drum 3 in a tumbling motion under gravity until they fall out of the far opening 3b onto an output conveyor 11 and are taken to a different part of the food processing plant for packaging.

The apparatus for applying the flavouring slurry includes a mixing vessel 12. Vegetable oil is supplied to the mixing vessel 12 along a first inlet pipeline 13 from a storage vessel (not shown). In practice, the food processing plant may include a common pipeline through which vegetable oil is conveyed from the storage vessel to the various component parts of the food processing plant. In this case, the first inlet pipeline 13 may be connected to the common pipeline by any suitable coupling. Flavouring particles are supplied to the mixing vessel 12 along a second inlet pipeline 14 from a storage container or hopper (not shown). The respective rates at which the vegetable oil and flavouring particles are supplied to the mixing vessel 12 are determined independently by any convenient means such as a valve arrangement 15 or auger screw, for example operated under the control of an electronic control unit 16. The mixing vessel 12 includes an impeller 17 for thoroughly mixing the vegetable oil and flavouring particles together to form a flavouring slurry.

The mixing vessel 12 includes an outlet pipeline 18 that connects to a common outlet pipeline 19 through which the flavouring slurry is supplied to the delivery nozzle 8 located within the flavouring drum 3. The flavouring slurry is transferred from the mixing vessel 12 to the delivery nozzle 8 by the action of a variable speed peristaltic pump 20 that is located in the common pipeline 19 and operated under the control of the control unit 16. The speed of the pump 20 can be altered to change the rate at which the flavouring slurry is supplied to the delivery nozzle 8.

The size of the mixing vessel 12 will normally be chosen with reference to the intended production parameters of the food processing plant, and in particular to the intended rate at which the snack food products will be supplied to the flavouring drum 3 along the input conveyor 10. However, it is generally preferred that the capacity of the mixing vessel 12 does not exceed 30 litres in order to promote thorough mixing of the vegetable oil and flavouring particles within a short period of time. The relatively small capacity of the mixing vessel 12 places limits on the rate at which the flavouring slurry can be supplied to the delivery nozzle 8. If the intended rate at which the snack food products will be supplied to the flavouring drum 3 requires the flavouring slurry to be supplied to the delivery nozzle 8 at a rate that is higher than that which can be provided by a single mixing vessel then the apparatus can include one or more additional mixing vessels. A second mixing vessel 21 can be located in parallel with the first mixing vessel 12 and is shown ghosted in Figure 2. An outlet pipeline 22 of the second mixing vessel 21 is connected to the common pipeline 19 in parallel with the outlet pipeline 18 of the first mixing vessel 12. Flavouring slurry is therefore transferred from the second mixing vessel 21 to the delivery nozzle 8 by the action of the pump 20. Although not shown, the pump 20 could be replaced by a pair of variable speed peristaltic pumps located in the outlet pipelines 18 and 22 (i.e. upstream of the common pipeline 19). The weighing means 4 includes a belt weigher 23 that is located at the input conveyor 10 and weighs the snack food products SF as they pass along the input conveyor to the flavouring drum 1. The weight measurements (which can be made continuously or at regular short intervals) are fed back to the control unit 16.

A sensor 24 (which in practice may take the form of an acoustic sensor) is located in the mixing vessel 12 and measures the fluid level of the flavouring slurry in the mixing vessel. Since the dimensions of the mixing vessel are fixed, the fluid level measured by the sensor 24 corresponds to the volume of the flavouring slurry within the mixing vessel 12. The fluid level measurements (which can be made continuously or at regular short intervals) are fed back to the control unit 16.

The apparatus is highly automated and is designed to function during normal operation with little or no manual intervention. However, the valve arrangement 15 and the pump 20 can also be controlled manually by an operator, preferably through the electronic control unit 16. For this reason the control unit 16 includes a graphical user interface (GUI) that enables an operator to manually alter the various rates etc.

The operation of the apparatus will now be explained in more detail.

Prior to the start of a batch run, the valve arrangement 15 is opened by the control unit 16 to allow vegetable oil and flavouring particles to flow into the mixing vessel 12 at predetermined rates. The impeller 17 is rotated to mix the vegetable oil and flavouring particles together to form a flavouring slurry. After a predetermined period of time (typically about 3 minutes), or when it is otherwise determined that the vegetable oil and flavouring particles are thoroughly mixed, the pump 20 is operated by the control unit 16 and ramps up to a predetermined speed that corresponds to a predetermined rate for the transfer of the flavouring slurry from the mixing vessel 12 to the delivery nozzle 8. Flavouring slurry is therefore pumped under the action of the pump 20 at the predetermined rate to the delivery nozzle 8. At the same time, snack food products SF are supplied to the flavouring drum 3 along the input conveyor 10. The snack food products SF are coated with the flavouring slurry inside the flavouring drum 3 and move through the flavouring drum under the influence of gravity to arrive at the output conveyor 11.

The weight of the snack food products SF on the input conveyor 10 is measured by the belt weigher 23 of the weighing means 4 and the control unit 16 uses the weight measurements to automatically alter the speed of the pump 20 and hence the rate at which the flavouring slurry is supplied to the delivery nozzle 8.

The normal rate at which the snack food products will be supplied to the flavouring drum 3 along the input conveyor 10 will often be known in advance. For example, if the input conveyor 10 is moving at the normal speed and the extruder 1 has reached its steady-state operating condition then it can be expected that a certain amount of snack food product will be supplied to the^ flavouring drum 3 over a given timeframe. The normal rate will correspond to a normal weight measurement being fed back to the control unit 16 by the belt weigher 23 as the snack food products pass over the belt weigher.

The normal rate at which flavouring slurry must be supplied to the delivery nozzle 8 can therefore be determined by the control means 16 and the pump 20 will be ramped up to a speed that corresponds to the normal rate for the supply of flavouring slurry to the delivery nozzle 8 so that all of the snack food products are properly coated as they pass through the flavouring drum 3.

The weight measurements provided by the belt weigher 23 will never stay completely constant during the course of a particular batch run. For example, the extruder 1 may be specifically controlled to increase the amount of snack food products that it produces over a given timeframe (e.g. production may be ramped up gradually during the start of the batch run until normal steady-state operation is achieved). Even during normal steady-state operation, the amount of snack food products being produced by the extruder 1 will vary slightly within accepted limits. Such changes in the weight measurements provided by the belt weigher 23 will usually indicate that there is a corresponding change in the rate at which the snack food products are being supplied to the flavouring drum 3. If there is a change in the current rate then the control unit 16 will determine a new rate for the supply of flavouring slurry to the delivery nozzle 8 and then ramp the pump 20 to a new speed that corresponds to that new rate. For example, if the belt weigher 23 measures an increase in the weight of the snack food products SF passing over it, indicating an increase in the rate at which the snack food products are being supplied to the flavouring drum 3, then the control unit 16 will ramp up the speed of the pump 20 to increase the rate at which the flavouring slurry is supplied to the delivery nozzle 8. Such tracking of the rate at which the flavouring slurry is applied to the delivery nozzle 8 to the rate at which the snack food products are being supplied to the flavouring drum 3 happens in "real time" and consistently ensures that the correct amount of flavouring slurry is applied to the snack food products over the course of the entire batch run. The control unit 16 has the ability to correct for very small changes in the rate at which the snack food products are supplied to the flavouring drum 3, even those changes that would normally be considered to be within acceptable production limits.

The rate at which the snack food products are supplied to the flavouring drum 3 will normally change in quite a gradual manner over the course of a batch run. However, the control unit 16 can also cope with more sudden and/or significant changes by averaging the measurements provided by the belt weigher 23 over a predetermined timeframe. For example, the extruder 1 may suddenly experience a temporary malfunction and stop producing snack food products for a short period of time. The input conveyor 10 will therefore contain a gap where there are no snack food products corresponding to the short period of time when the extruder 1 experienced the temporary malfunction. The belt weigher 23 will measure a sudden and significant reduction in weight as the gap passes over it. This will be followed shortly after by a sudden and significant increase in weight as the snack food products produced by the extruder 1 after the malfunction had cleared pass over it. Making sudden changes in the speed of the pump 20 and the amount of vegetable oil and flavouring particles that are supplied to the mixing vessel 12 will not normally be desirable because, for example, it may place unnecessary mechanical stresses on the pump and result in unsatisfactory mixing of the vegetable oil and flavouring particles in the mixing vessel 12. By averaging the measurements provided by the belt weigher 23 over a predetermined period of time, the control unit can therefore track the respective rates in a more general way without having to make sudden changes to the speed of the pump 20 or the operation of the valve arrangement 15. For the example mentioned above, the control unit 16 will start to reduce the speed of the pump 20 as soon as the gap starts to pass over the belt weigher 23. The speed of the pump 20 will continue to be reduced for as long as the gap continues to pass over the belt weigher 23. It will therefore be readily appreciated that if the gap in the snack food products was long enough then the speed would eventually be reduced to zero such that no flavouring slurry is supplied to the delivery nozzle 8. However, for a short gap the speed of the pump 20 will still not have reached zero when the snack food products start to pass over the belt weigher 23 and the control unit 16 starts to increase the speed again. The tracking is therefore not quite as closely matched during sudden and/or significant changes as it is when the rate at which the snack food products are supplied to the flavouring drum 3 changes gradually.

In the arrangement shown in Figure 2 the belt weigher 23 is immediately in front of the near opening 3 a of the flavouring drum 3. The control unit 16 can therefore start to change the speed of the pump 20 as soon as the measurements from the belt weigher 23 indicate a change in the rate at which the snack food products are supplied to the flavouring drum 3. However, in other arrangements it may be necessary for the control unit 16 to delay any changes in the speed of the pump 20 to take account of an increased distance between the weighing means 4 and the flavouring drum 3.

In general terms, the normal rate at which the snack food products are supplied to the flavouring drum 3 (i.e. during steady-state operating conditions) may be represented by X₁ kg/sec and the normal rate at which the flavouring slurry is supplied to the delivery nozzle 8 may be represented by yj m³/sec. During operation of the apparatus, the rate at which the snack food products are supplied to the flavouring drum 1 may increase to X₂ kg/sec. Once this is determined by an increase in the weight measurements provided by the belt weigher 23, the control unit 16 will automatically increase the speed of the pump 20 so that the rate at which the flavouring slurry is supplied to the delivery nozzle 8 is increased to y₂ m /sec. The relationship between xj kg/sec and yj mVsec, and between X₂ kg/sec and y₂ m³/sec, for any given snack food product is stored in the control unit 16, optionally in the form of a look-up table or a mathematical function.

If the speed of the pump 20 is changed then the control unit 16 may automatically control the valve arrangement 15 to change the rate at which one or both of the vegetable oil and the flavouring particles is supplied to the mixing vessel 12.

The control unit 16 can automatically control the valve arrangement 15 to change the rate at which one or both of the vegetable oil and the flavouring particles is supplied to the mixing vessel 12 in response to changes in the fluid level (and hence the volume) of the flavouring slurry within the mixing vessel as measured by the sensor 24. The control unit 16 can also use the fluid level measurements provided by the sensor 24 to automatically control the speed of the pump 20 and hence the rate at which the flavouring slurry is supplied to the delivery nozzle 8. These provide useful feedback loops to try and keep the volume of flavouring slurry within certain agreed limits where possible.

An operator may use the control unit 16 to make small adjustments to the proportion (or ratio) of vegetable oil and flavouring particles supplied to the mixing vessel 12. The control unit 16 can achieve this by independently controlling the valve arrangement 15 in a suitable manner.

It will be clear from the above description that the control unit 16 uses control signals from the belt weigher 23 and the sensor 24 and processes this information to control the operation of the pump 20 and the valve arrangement 15 and hence alter the rate at which the flavouring slurry is supplied to the delivery nozzle 8 and the amount of flavouring particles and oil that are supplied to the mixing vessel 12, respectively. In an alternative embodiment to that shown in Figure 2 the control signals indicative of the rate at which the snack food products are supplied to the flavouring drum 3 may be received from another suitable component part of the apparatus 7 or the food processing plant rather than the belt weigher 23.

The control signals can be transmitted by any suitable means such as cables or wireless transmission, for example.

Figure 3 shows an alternative process flow diagram for the present invention. It is similar to the process flow diagram of Figure 1 and the same reference numerals have been used where appropriate. In this case, the weighing means is not present between the dryer 2 and the apparatus 7. Control signals are therefore transmitted from the extruder 1 to the apparatus 7 to indicate the rate at which the snack food products are being produced by the extruder and hence the rate at which they are being supplied to the flavouring drum 3. The apparatus 7 can therefore use the control signals from the extruder 1 to control the rate at which the flavouring slurry is pumped to the delivery means 8 as described above.

Claims

1. An apparatus for applying a coating liquid to food products, comprising: a coating region; a mixing vessel (12) for mixing together a liquid and a dry mixture to form a coating liquid; a pump (20) for pumping the coating liquid to a delivery means (8) for applying the coating liquid to the food products as they pass through the coating region; and control means (16) for controlling the operation of the pump (20) such that the rate at which the coating liquid is pumped to the delivery means (8) is selected in accordance with the rate at which the food products are supplied to the coating region.

2. An apparatus according to claim 1, further comprising: rate determining means for measuring or deriving the rate at which food products are supplied to the coating region.

3. An apparatus according to claim 1 or claim 2, wherein the control means (16) is configured to automatically alter the rate at which the coating liquid is pumped to the delivery means (8) in response to a change in the rate at which the food products are supplied to the coating region.

4. An apparatus according to any preceding claim, wherein the control means (16) is configured to alter the rate at which the liquid and/or dry mixture are supplied to the mixing vessel (12) in response to a change in the rate at which the food products are supplied to the flavouring delivery region.

5. An apparatus according to any preceding claim, wherein the control means (16) is configured to alter the rate at which the liquid and/or dry mixture are supplied to the mixing vessel (12) in response to a change in the rate at which the coating liquid is pumped to the delivery means (8).

6. An apparatus according to any preceding claim, wherein the control means (16) is configured to control the proportion of the liquid and dry mixture supplied to the mixing vessel (12).

7. An apparatus according to claim 2; wherein the rate determining means includes weighing means (4,23) for weighing the food products.

8. An apparatus according to any preceding claim, wherein the coating liquid is pumped directly from the mixing vessel (12) to the delivery means (8).

9. An apparatus according to any preceding claim, wherein the coating region is a rotating flavouring drum (3).

10. An apparatus according to any preceding, further comprising conveying means (10,11) for supplying the food products to the coating region.

11. An apparatus according to any preceding claim, further comprising sensor means (24) for measuring or deriving the volume of the coating liquid within the mixing vessel (12).

12. An apparatus according to claim 11, wherein the control means (16) is configured to alter the rate at which the coating liquid is pumped to the delivery means (8) in response to a change in the volume of coating liquid in the mixing vessel (12).

13. An apparatus according to claim 11 or claim 12, wherein the control means (16) is configured to alter the rate at which the liquid and/or dry mixture are supplied to the mixing vessel (12) in response to a change in the volume of coating liquid in the mixing vessel (12).

14. An apparatus according to any preceding claim, wherein the pump (20) is a peristaltic pump.

15. An apparatus according to any preceding claim, further comprising a plurality of mixing vessels (12,21).

16. A method of applying coating liquid to food products, the method comprising the steps of: mixing together a liquid and a dry mixture to form a coating liquid; using a pump (20) to supply the coating liquid to a delivery means (8) for applying the coating liquid to the food products as they pass through a coating region; measuring or deriving the rate at which food products are supplied to the coating region; and controlling the operation of the pump (20) such that the rate at which the coating liquid is supplied to the delivery means (8) is selected in accordance with the rate at which the food products are supplied to the coating region.

17. A method according to claim 16, wherein the rate at which coating liquid is supplied to the delivery means (8) is altered in response to a change in the rate at which the food products are supplied to the coating region.

18. A method according to claim 16 or claim 17, wherein the rate at which the coating liquid is supplied to the delivery means (8) is altered automatically by a control means (16).

19. A method according to claim 16 or claim 17, wherein the rate at which the coating liquid is supplied to the delivery means (8) is altered manually.

20. A method according to any of claims 16 to 19, wherein the liquid and dry mixture are mixed together in a mixing vessel (12) to form the coating liquid.

21. A method according to claim 20, wherein the rate at which the liquid and/or dry mixture are supplied to the mixing vessel (12) is altered in response to a change in the rate at which the food products are supplied to the coating region.

22. A method according to claim 20 or claim 21, wherein the rate at which the liquid and/or dry mixture are supplied to the mixing vessel (12) is altered in response to a change in the rate at which the coating liquid is supplied to the delivery means.

23. A method according to any of claims 20 to 22, further comprising the step of altering the rate at which the coating liquid is supplied to the delivery means (8) in response to a change in the volume of the coating liquid in the mixing vessel (12).

24. A method according to any of claims 20 to 23, wherein the rate at which the liquid and/or dry mixture are supplied to the mixing vessel (12) is altered in response to a change in the volume of the coating liquid in the mixing vessel (12).

25. A method according to any of claims 16 to 24, further comprising the step of altering the proportion of liquid and dry mixture that are mixed together to form the coating liquid.

26. A method according to claim 26, wherein the proportion of liquid and dry mixture that are mixed together to form the coating liquid is altered automatically by a control means (16).

27. A method according to claim 26, wherein the proportion of liquid and dry mixture that are mixed together to form the coating liquid is altered manually.

28. A method according to any of claims 16 to 27, wherein the step of measuring or deriving the rate at which food products are supplied to the coating region further comprises measuring or deriving one of the weight, volume and bulk density of the food products being supplied to the coating region.