GB2398370A

GB2398370A - Ice slurry cooling process for foodstuffs

Info

Publication number: GB2398370A
Application number: GB0303565A
Authority: GB
Inventors: Peter Adrian Hubbard
Original assignee: STARFROST
Current assignee: STARFROST
Priority date: 2003-02-17
Filing date: 2003-02-17
Publication date: 2004-08-18
Also published as: GB0303565D0

Abstract

An apparatus for use in cooling foodstuffs comprising means for suspending food items 16, means 19 for conveying an ice slurry to the food item, and one or more nozzles 21 through which the slurry is sprayed onto the foodstuff. The foodstuff may be conveyed through a chilled air stream to the or each nozzle. The apparatus may include a sensor 22 to determine the position of a foodstuff and trigger spraying of the ice slurry, which may include antifreeze agents to enable the slurry temperature to be below zero Celsius. The ice slurry may include water and ice in a ratio of between 30:70 and 80:20, by weight. The antifreeze agents may include for example, sodium chloride, carbonate or phosphate compounds. A warm air stream may also be passed across the food item when melting of ice is required. The ice slurry conveyer may be a pipeline 19, 20, which is controlled by a valve 23 triggered by the sensor 22. The food suspension means may be supported by a rail 11 and a chain drive 18 may provide movement. The foodstuff may be poultry.

Description

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APPARATUS FOR COOLING FOODSTUFFS

Field of the Invention

The present invention relates to an apparatus and to a method for cooling foodstuffs, in particular meat and fish products.

Background to the Invention

In the food production industry, there is a requirement to process large quantities of foodstuffs for sale to the consumer. As a result, a number of mechanised processes have been devised to carry out the variety of steps required to go from the initial raw material such as the animal or vegetable itself to the final product suitable for packaging and presentation on to the consumer.

Where these products are for consumption by humans, there must be particularly close control of the processing steps to ensure that the product remains fit for consumption and that the quality of the product does not deteriorate. In particular, the normal rate of decomposition of organic material needs to be slowed down and the chance of crosscontamination between any diseased items reduced to acceptable levels. Process controls need to be particularly strict and well monitored where meat products are concerned.

One of the processing steps with which the present invention is concerned is that of chilling the product which is, for example, carried out to increase the shelf-life or to facilitate later freezing. A number of methods of carrying out chilling are known which will now be described with reference to poultry.

ll Ite ttIt A need for rapid chilling of poultry, once the animal has been killed, can be more acute than with other meat products as the outer epidermis of the bird is often heated to facilitate the removal of the feathers. A plucked bird is thereby converted into an ideal substrate on which bacteria and other micro-organisms can grow. Following plucking and evisceration therefore, a common method of cooling has been to immerse the bird, along with a number of other birds into chilled water. The bird carcasses are agitated in the water to speed up the cooling process through the use of drag chains or by the use of a rotating cylinder having an internal scroll. This method of cooling has the drawback that the risk of cross contamination of any micro-organisms between the birds is high. For this reason, many countries have introduced legalization to ban the use of the method or the sale of imported birds to which the method has been applied.

An alternative method which has largely replaced the use of a chilled water tank is to pass chilled air across the plucked, eviscerated carcass. To assist the cooling, the carcass is normally suspended from, for example, a chain and conveyed through a chilled air environment. Water can also be sprayed onto the bird to accelerate the cooling as the evaporation of water removes heat. The method is however not efficient and has the undesirable side effect of dehydrating the bird.

It is therefore an object of the present invention to provide an apparatus and method which addresses the above problems.

Summary of the Invention

According to a first aspect of the invention there is provided an apparatus for use in cooling foodstuffs, the apparatus comprising: means for suspending food items; means for conveying an ice-slurry to a food item; one or more nozzles through which an ice-slurry is sprayed on to a foodstuff.

l tIt r ld l À The apparatus provides rapid cooling of the foodstuff and minimises energy consumption.

Advantageously, the foodstuff is conveyed through a chilled air stream to the or each nozzle. The chilled air assists in melting the ice and removing heat from the foodstuff.

The apparatus conveniently has a sensor to determine the position of a foodstuff and trigger spraying of an ice-slurry onto the foodstuff. There is thereby little wastage of the ice-slurry.

The ice-slurry advantageously includes one or more antifreeze agents to enable the temperature of the ice-slurry to be reduced below OC. The antifreeze agents are conveniently selected from sodium chloride, tripotassium phosphate, di potassium hydrogenphosphate, mono-potassium dihydrogenphosphate, potassium carbonate, potassium hydrogencarbonate, trisodium phosphate, all-sodium mono hydrogenphosphate or mono-sodium dihydrogenphosphate. Such antifreeze agents allow the temperature of the ice-slurry to be lowered but do not impair the quality or the edibility of the food items.

According to a second aspect of the invention there is a provided a method of cooling food items, the method including the steps of; (i) suspending the food item; (ii) spraying a slurry of water/ice onto the food item; (iii) passing chilled air across the food item.

Conveniently, an antifreeze agent is included in the water/ice-slurry to enable the temperature of the slurry to drop below OC. By using a lower temperature slurry, heat can be removed more rapidly from the foodstuff. The antifreeze agent is preferably selected from sodium chloride, tripotassium phosphate, all-potassium hydrogenphosphate, mono-potassium dihydrogenphosphate, potassium All carbonate, potassium hydrogencarbonate, tri-sodium phosphate, all-sodium mono hydrogenphosphate or mono-sodium dihydrogenphosphate.

The water to ice ratio is optionally from 30:70 to 80:20% w/w. It is preferable that the ratio is from 40:40 to 60:40% w/w. Such ratios enable the slurry to be pumped whilst having sufficient ice to rapidly cool the food item.

The food item is advantageously conveyed through a chilled air stream.

Optionally, a warm air stream +3 to +5C can be passed across the food item when ice on the food item needs to be more rapidly melted. Such a step is particularly useful when an ice crust forms on the surface of the food item.

Advantageously, the food item is conveyed through a sensor, activation of the sensor triggering spraying of the ice/water slurry.

Brief Description of the Drawings

The invention will now be described with reference to the accompanying drawings which show by way of example only, one embodiment of chilling apparatus. In the drawings: Figures la to 1c illustrate respectively, a top, side and end view of a conveyor for foodstuffs; Figure 2 illustrates the conveyor of Figures la to 1c in more detail; and Figure 3 is a graph of cooling time for chicken carcasses.

Detailed Description of the Invention

In order to chill a particular food item, the food item needs to undergo a continuous period during which it is maintained at a low temperature. In order to reduce the space taken up by the apparatus used to carry out the chilling, the food item is normally conveyed along a circuitous route guided by a system of rails l which traverse back and forth, across and along the chilling area. In order to lower energy costs, the area in which the food item is chilled is normally enclosed and often insulated. In the following description, the chilling is described as applied to eviscerated chicken carcasses. The apparatus and method used are S however generally applicable to other foodstuffs.

Referring initially to Figures la to 1c, chilling is carried out within the walls of an air-conditioned insulated room 10. The chicken carcasses are suspended from rails 11 which are laid out across the room 1O, passing around guides 12 in order to maximise the rail length contained within the room 10. The rails 11 are laid out on two levels 13,14 again to maximise space utilization. Each level has itself two tiers. In total there is a sufficient space for approximately 6,500 birds to be passing through the room 10 at any one time.

Chilled air at a temperature of -3 to +5C is continually circulated throughout the room by a series of evaporators and fans 15. In general, air is drawn on from the lower portion of the room 10 and circulated in direction A by means of the fans 15.

Turning to Figure 2, it can be seen that a chicken carcass is hung from shackles 16 beneath the conveyor rail 11. The shackles 16 run on rollers 17 along the conveyor rail 11 and are pulled along the rail 11 by chains 18 attached to the shackles 16.

In order to reduce rapidly the temperature of the carcass, a cooling system is provided. The cooling system is capable of delivering an ice slurry onto the surfaces of the chicken carcass. Running parallel to and above the conveyor rail 11 is a pipe 19 through which a slurry of ice and water is pumped. At a number of points along the length of the pipe 19, spray pipes 20 depend downwardly therefrom. Each spray pipe 20 includes a number of nozzles 21 which are so orientated that they combine together to ensure that the entire surface of the carcass, including the inner cavity is sprayed.

1 1 4 1 ' I À 1 e 4 A sensor array 22 is triggered by the passage of a carcass along the rail 11. The triggering activates, with a time delay dependent on the speed of conveyance of the carcass, a control valve 23 which permits passage of the ice slurry from the spray pipe 19 through the nozzles 21 onto the carcass. The amount of ice slurry sprayed onto the carcass depends, amongst other stings, upon the original temperature of the carcass and its size determined by a weight cell in the conveyor prior to the sensor. Without being limited to theory, it is believed that the primary source of cooling is through the latent heat of liquefaction of the ice. Cooling is accelerated by passage of air, at a temperature above the freezing point of water, across the carcass. The air causes water to evaporate and in order to maintain the ice/water equilibrium, ice melts taking heat from the carcass. Due to the use of water in the cooling process there is a significant reduction in dehydration of the carcass when compared with conventional drying methods which use air alone.

As a final step in the cooling process, when the temperature of the carcass has reached a desired value (the determination of the temperature being carried out by the use of an infrared temperature detector or similar non-contact measurement), a final current of air is applied which absorbs some of the latent and sensible heat from the ice remaining on the carcass surface and also dries off some surface water. Up until the final air drying step, ice slurry is sprayed in sufficient amounts to maintain ice on all possible surfaces of the carcass. If necessary, where the outer temperature drops too far and the iced water freezes too much on the carcass, warm air, at a temperature of +3 to +5C can be passed across to melt a portion of the ice.

The ice slurry is primarily a suspension of ice crystals in water. In order to keep the water/ice ratio at a desired temperature an antifreeze agent is included. Care must be taken when selecting the antifreeze agent that the agent complies with food regulations, as a residue of the agent can be left on the carcass which would then be passed on to the consumer. Amongst agents which can be used are sodium chloride (common salt), potassium phosphate, mono - or all-potassium hydrogenphosphate (often referred to as E340), potassium carbonate / potassium hydrogencarbonate (often referred to as E501) or sodium phosphate, mono - di sodium hydrogenphosphate (often referred to as E339) or mixtures thereof. Other À ': l l additives can be included without further inventive thought.

With the use of antifreeze agents, a pumpable ice-slurry at a temperature of -2C can be achieved. Typically the ice/water ratio is 40:60%ww, but other values can be used depending on the particular carcass and drying conditions to be used. A ratio within the range of 30:70 to 80:20% w/w has been found to be effective, although those from 40:60 to 60:40% w/w are preferred.

A further advantage of the use of an ice slurry is that the slurry can be generated overnight for use during the following working day. The cooling agent can therefore be generated during the night when energy rates and ambient temperatures are lower. Costs are therefore significantly reduced.

In order to demonstrate the efficiency of the use of an ice slurry a comparison with conventional air chilling was carried out. The results of the comparison are shown in the graph in Figure 3. The graph shows the time required to reduce a 2.4kg chicken from 34C to 4C. When air-chilling alone was used, the time required was 145 minutes. This compares with 95 minutes for the use of an ice slurry coolant. The significant time saving is therefore demonstrated. In addition, the carcass showed a weight gain of 2% during the process in contrast to the undesired dehydration processes which use air alone. Such a weight gain is often desirable on economic and aesthetic grounds.

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible with the scope of the appended claims. : l:

Claims

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Claims 1. An apparatus for use in cooling foodstuffs, the apparatus comprising: means for suspending food items; means for conveying an ice-slurry to a food item; one or more nozzles through which an ice-slurry is sprayed on to a foodstuff.
2. An apparatus according to Claim 1, wherein the foodstuff is conveyed through a chilled air stream to the or each nozzle.
3. An apparatus according to either Claim 1 or Claim 2, wherein the apparatus has a sensor to determine the position of a foodstuff and trigger spraying of an ice-slurry onto the foodstuff.
4. An apparatus according to any preceding claim, wherein the ice-slurry includes one or more antifreeze agents to enable the temperature of the ice-slurry to be reduced below OC.
5. An apparatus according to Claim 4, wherein the or each antifreeze agent is selected from sodium chloride, tri-potassium phosphate, all- potassium hydrogenphosphate, mono-potassium di-hydrogenphosphate, potassium carbonate, potassium hydrogencarbonate, tri-sodium phosphate, all-sodium mono-hydrogenphosphate or mono-sodium di-hydrogenphosphate.
6. A method of cooling food items, the method including the steps of; (i) suspending the food item; (ii) spraying a slurry of water/ice onto the food item; (iii) passing chilled air across the food item.

at: #:' It: :
7. A method according to Claim 6, wherein one or more antifreeze agents is included in the water/ice-slurry to enable the temperature of the slurry to drop below OC.
8. A method according to Claim 7, wherein the or each antifreeze agent is selected from sodium chloride, tri-potassium phosphate, all-potassium hydrogenphosphate, mono-potassium di-hydrogenphosphate, potassium carbonate, potassium hydrogencarbonate, tri-sodium phosphate, all-sodium mono-hydrogenphosphate or mono-sodium di-hydrogenphosphate.
9. A method according to Claims 6 to 8, wherein the water to ice ratio is from 30:70 to 80:20% w/w.
10. A method according to Claim 9, wherein the ratio is from 40:60 to 60:40% wlw.
A method according to Claims 6 to 10, wherein the food item is conveyed through a chilled air stream.
12. A method according to Claims 6 to 11, wherein a warm air stream at a temperature of +3 to +5C is passed across the food item when ice on the food item needs to be more rapidly melted.
13. A method according to Claims 6 to 12, wherein the food item is conveyed through a sensor, activation of the sensor triggering spraying of the ice/water slurry.
14. An apparatus substantially as herein described with reference to an as illustrated by the accompanying drawings.