GB2149638A

GB2149638A - Processing of dairy products

Info

Publication number: GB2149638A
Application number: GB08425204A
Authority: GB
Inventors: Peter Hamish Fergusson
Original assignee: APV International Ltd
Current assignee: APV International Ltd
Priority date: 1983-10-05
Filing date: 1984-10-05
Publication date: 1985-06-19
Also published as: GB8425204D0

Abstract

A dairy product is processed by filtering it through at least one filter; passing it through one set of flow spaces of a plate heat exchanger wherein the shear rate of the dairy product does not exceed 100s<-1>; and, passing it through an apertured plate whereby homogenization of the said dairy product is facilitated. Also disclosed is a method of processing a diary product by passing it through one set of flow spaces of a plate heat exchanger and, passing a service fluid through the other set of flow spaces of the said plate heat exchanger, wherein; the shear rate of the dairy product does not exceed 100s<-1> and, the maximum temperature difference between adjacent flow spaces containing the dairy product and the service fluid respectively does not exceed 15 DEG C; whereby homogenization of the said dairy product is facilitated and thermal damage to the said dairy product is reduced. Apparatus for carrying out the above methods is provided.

Description

SPECIFICATION Processing of dairy products The present invention relates to the processing of dairy products.

Dairy products, such as milk, yoghourt, cream and cheese have a physical structure which is particularly easy to disrupt by mis-handling ofthe product. This is particularlytruewhenthe product is either being heated or cooled, whether for hygenic reasons of otherwise.

In the processing of dairy products,forexample in the manufacture of yoghurt orcream, considerable problems have been encountered due to a loss of viscosity in the productwhilethe product is being processed. It has been known to restore some of this viscosity bythe addition of artificial thickening agents tithe product, or to avoid the loss ofthisviscosity by employing a small batch vessel (e.g. a churn) rather than a continuous process. The first ofthese two suggested solutions results in a productwith unnatural additives whilethe second is uneconomical on a largescaie.

Afurther problem is that of "thermal shock", which causes irreversible changes in the product, which lead to its detriment.

Without wishing to restrict the method of operation ofthe present invention to any particulartheory of function, it is noted that both a high shear rate and a steep temperature gradient can cause disruption of the micellularstructure of the dairy product by altering the conformation ofthe proteins present in the product.

According to one aspect ofthe present invention there is provided a method of processing a dairy product, including the steps of: a) filtering said dairy productthrough at least one filter; b) passingthe said dairy productthrough one set of flow:spaces of a plate heat exchanger wherein the shear rate of the dairy product does not exceed I0Qsi; and d passing the said dairy productthrough an apertured plate whereby homogenization ofthe said dairy product is facilitated.

Accordingtoafurtheraspectofthe present invention there is provided a method of processing a dairy product including the steps of: a) passing the said dairy productthrough one set of flow spaces of a plate heat exchanger and, b) passing a service fluid through the other set of flow spaces of the said plate heat exchanger, wherein: the shear rate ofthe dairy product does not exceed 100ski and, the maximum temperature difference between adjacentflowspaces containing the dairy product and the service fluid respectively does notexceed 15 C; whereby homogenization ofthe said dairy product is facilitated and thermal damage to the said dairy product is reduced.

Conveniently,the method further comprising the steps of; a) passing the said dairyproductthrough an apertured plate, and, b) filtering said dairy productthrough at least one filter.

By employing the method ofthe present invention it is possible to obtain a homogeneous product, which does not suffer from the problems referred to in the art as "granulation" and "nodulation".

According to a fu rther aspect of the present invention, there is provided an apparatus for processing dairy products, which apparatus comprises; a) a filtration assembly including at least one filter and an outlet; b) a plate heat exchanger having an inlet connected to the outlet ofthefilter assembly, wherein in use, the shear rate of a said dairy product passing through the plate heat exchanger does not exceed 100ski seconds; and c) an apertured plate disposed in the flow path of said dairy product to facilitate homogenization ofthe said dairy product.

Conveniently, the filter is so chosen that its mesh prevents the passage of bodies greaterthan 1 mm in diameter.

According to a further aspect of the present invention there is provided an apparatus for processing dairy products, which apparatus comprises; a) a plate heat exchanger having an inlet and an outlet, wherein in use, the shear rate of a said dairy product passing through the plate heat exchanger does not exceed 100so' seconds; and b) an apertured plate disposed in the flow path of said dairy productto facilitate homogenization ofthe said dairy product.

Preferably, the plate heat exchanger is divided into at least a first and a second pack of plates.

More preferably, the arrangement is such that, in use, the throughput is in the range of 0.75 to 1.51 litres per second.

The apertures ofthe apertured plate constitute preferably less than 25% of the cross-sectional area of the plate and more preferably constitute from 2 to 10% ofthe cross-sectional area ofthe plate.

In an embodiment of the invention,thefine mesh filter may be eitherconical or cylindrical and may or may not be supported by a backing mesh.

The apertures ofthe apertured plate may be parallel-walled cylindrical holes in the plate or may be tapered from one or each end of the aperture.

In a particular embodiment ofthe present invention, the product is passedthroughthe apertured plate between the first and second pack a divided plate heat exchanger.

In afurther particularembodiment ofthe present invention the apertured plate is disposed in the filtration assembly and may be located either before orafterthefilter in the productflowpath.

The invention will be further described with reference to the single accompanying figure, wherein a method ofapparatusfor use in the manufacture of yoghurt are illustrated.

A bio-reactor 1 maintained at a temperature of 30 to 48"C is used for the bio-reaction step at the start of yoghurt production. The raw material is run into the tankthrough line 14 and an innoculum is added through line 13.Atypical raw material would be pasturised yoghurt mix comprising skimmed milk, with a solids level before the addition of sweetening agentsoftypically 12to 16% which is incubatedfora period of between 4 and 12 hours depending on the particulartemperature of incubation.

Atthe end of this period the acidity produced by growth ofthe innoculum culture has caused coagulation ofthe milk, forming a typical yoghurt gel. The yoghurtgel isthen pumped by pump 15 along line 2.

The pump maybeforexample,a positive pump such as a Mono or SSP pump.

Theyoghurt gel is passed through a filter3 which comprises,forexample,a conical mesh pointing in a downstream direction and supporting backing mesh.

Thefirstfilter3 is intended to retain particles having a diameterofgreaterthan 1 mum.

The filtered gel passes along line 4to the orifice plate 5. The orifice plate is shown in the example as being inthefiltration assemblytogetherwith the filter 3 and the connecting line 4. However, it is possible to locate the orifice plate elsewhere in the apparatus as is further described below.

The orifice plate comprises an apertured plate having holes which constitute less than 25% ofthe cross-sectional area ofthe plate and preferably constitute 2 to 10% ofthe cross-sectional area ofthe plate. An exemplary apertured plate is 82mm in diameterwith 173 regularly spaced holes comprising 8.2% ofthe cross-sectional area of the 4mm thick plate.

The pressure drop across the filtration assembly 3, 4,5 is typically 3 psi, in the example given, with a throughput oftypically 0.75 to 1.51 litres per second.

The yoghurt gel passes along line 6to the first pack7 ofthe plate heat exchanger 7, 10. The yoghurt gel passes through a first set of flow spaces ofthe plate heatexchanger7, 10 with a countercurrentofcooled water circulating in the second set of flow spaces. The countercurrent of cooled water is provided by a cooling tower circuit 8 or mains water and typically enters at a temperature of to 1 5"C. The pressure drop in the product, across this first pack7 ofthe plate heat exchanger7, 10 is typically 5 psi, inthe example given.

The yoghurt gel leaves the pack7 along line 11 at a temperature of 5to 1 5"C and enters the second pack 10 ofthe plate heat exchanger. The yoghurt gel flow through one set of flow spaces of the pack 10, with a countercurrent of chilled waterflowing through the second set offlow spaces of the heat exchanger 10.

The chilled water is provided by a chilling circuitand plant 9 and typically entersthe plate heat exchanger at a temperature of O to 2"C.

The process flow pressure drop across the second pack of plates 10 is typically 13 psi, in the example given.

It is possible to divert the water in the cooling tower circuit 8 via valve 12 to re-circulate in the flow spaces ofthefirst pack of plates 7, hence towerwaterfrom the outlet ofthe first plate pack7 is used to heat up the incoming tower water. This allows fine control over the temperature at which the tower-cooled water enters the second set offlow spaces ofthe first pack 7.

It is possible, by ehe provision of such a recirculation route to ensure that the temperature difference between the dairy product and the cooling water is minimised and therefore to considerably reduce the damage caused to the dairy product by thermal shock.

Atypical temperature difference of5 to 1 00C is employed in the present example.

It is possible to include a similarsystem in the chiiled water circuit9 either in addition or as an alternative to the system described above.

It is also possible thatthe apertured plate may be disposed in the line 11 ratherthan in the filtration assembly 3, 4and 5 in which case a similar plate to that described above would be employed.

On leaving the pack 'IOofthe heat exchanger7, 10 by line 12the product now at atemperature of 5 to 10 C is either packed directly or held in a holding tank (not shown in the figure) in orderthatsome viscosity may be recovered. If the chilled watercircuit 9 is not in operation a typical product temperature of 1 5-250C would result.

During passage ofthe product through the heat exchanger7, 0 the shear rate of the product does not exceed 1 OOs-1 thereby preventing irreversible chemical changes in the product. These chemical changes prevent a recovery of viscosity on storage and result in a thin product. The apparatus and method of the present invention results in a product which will recover this viscosity on storage in part or in whole.

Furthermore, the product produced by the present apparatus and method does not contain local inhomogeneity (such as granulations and nodulations) such as has been obtained with previous methods.

The shear rate ofthe product may be kept below 100so' by employing an oversize heat exchanger which has a cooling capacity in excess ofthat required by any particularthroughput and therefore is not running at its maximum throughput.

Further modifications may be made within the scope of the present invention, for example the plant may include further apparatus for cleaning in place.

Claims

1. A method of processing a dairy product, including the steps of: a) filtering said dairy product through at least one filter; b) passing the said dairy productthrough one set of flow spaces of a plate heat exchangerwherein the shear rate ofthe dairy product does not exceed 100s-';and c) passing the said dairy productthrough an apertured plate whereby homogenization ofthe said dairy product is facilitated.

2. A method of processing a dairy product including the steps of; a) passing the said dairy productthrough one set of flow spaces of a plate heat exchanger and, b) passing a service fluid through the other set of flow spaces ofthe said plate heat exchanger, wherein; the shear rate ofthe dairy product does not exceed 1 00ski and, the maximum temperature differ- ence between adjacent flow spaces containing the dairy product and the service fluid respectively does not exceed 1 5 C; whereby homogenization ofthe said dairy product is facilitated and thermal damage to the said dairy product is reduced.

3. A method as claimed in claim 2, further compris ingthe steps of; a) passing the said dairy productthrough an apertured plate, and, b)filtering said dairy productthrough at least one filter.

4. An apparatus for processing dairy products, according to the method of claim 1 or claim 3, which apparatus comprises; a) a filtration assembly including at least one filter and an outlet; b) a plate heat exchanger having an inlet connected to the outlet ofthefilter assembly, wherein in use, the shear rate of a said dairy product passing through the plate heat exchanger does not exceed 1 oos- seconds; and c)an apertured plate disposed in the flow path of said dairy product to facilitate homogenization ofthe said dairy product.

5. An apparatus as claimed in claim 4, wherein the filter is so chosen that its mesh prevents the passage of bodies greater than 1 mm in diameter.

6. An apparatus for processing dairy products, according to the method of claim 2, which apparatus comprises; a) a plate heat exchanger having an inlet and an outlet, wherein in use, the shear rate of a said dairy product passing through the plate heat exchanger does not exceed 100ski seconds; and b) an apertured plate disposed in the flow path of said dairy productto facilitate homogenization of the said dairy product.

7. An apparatus as claimed in claim 4,5 or 6, wherein the plate heat exchanger is divided into at least a first and a second pack of plates.

8. An apparatus as claimed in any of claims 4-7, wherein, the arrangement is such that, in use, the throughput is in the range of 0.75 to 1.51 litres per second.

9. An apparatus as claimed in any of the preceeding claims 2-8, wherein the apertures ofthe apertured plateconstitute lessthan 25% ofthecross-sectional area of the plate.

10. An apparatus as claimed in any ofthe preceeding claims 2-9, wherein the apertures ofthe apertured plate constitute from 2 to 10% ofthe cross-sectional area of the plate.

11. An apparatus as claimed in any ofthe preceeding claims 4-5 wherein the fine mesh filter is conical.

12. An apparatus as claimed in any of the preceed- ing claims 4-5 wherein the fine mesh filter is cylindrical.

13. An apparatus as claimed in any of the preceeding claims 4-5 or 11-12 wherein the fine mesh filter is supported buy a backing mesh.

14. An apparatus as claimed in any ofthe preceeding claims 4-13 wherein the apertures of the apertured plate are parallel-walled cylindrical holes in the plate.

15. An apparatus as claimed in any of the preceeding claims 4-13wherein the apertures ofthe apertured plate are tapered from one or each end ofthe aperture.

16. An apparatus as claimed in claim 7 wherein, the product is passed through the apertured plate between the at leastfirst and second pack of the divided plate heat exchanger.

17. An apparatus as claimed in any of claims 4-5 or 11-13 wherein the apertured plate is disposed in the filtration assembly and is located before the filter in the productflow path.

18. An apparatus as claimed in any of claims 4-5 or 11-13 wherein the apertured plate is disposed in the filtration assembly and is located afterthe filter in the productflow path.

19. An apparatus for processing a dairy product, substantially as hereinbefore described by way of example, and in the accompanying drawings.