GB1564485A

GB1564485A - Process and a device for converting a gellified product into a jomogeneously-smooth viscous liquid

Info

Publication number: GB1564485A
Application number: GB4924777A
Authority: GB
Original assignee: STICHTING BEDRIJVEN VAN HET
Current assignee: STICHTING BEDRIJVEN VAN HET
Priority date: 1976-11-26
Filing date: 1977-11-25
Publication date: 1980-04-10
Also published as: FR2371886B1; DK523477A; FR2371886A1; DE2752751A1; NL7613236A

Description

(54) A PROCESS AND A DEVICE FOR CONVERTING A GELLIFIED PRODUCT INTO A HOMOGENEOUSLY-SMOOTH VISCOUS LIQUID (71) We, STICHTING BEDRIJVEN VAN HET NEDH(LANDS INSTITUUT VOOR ZUIVE U)NDERZOEK, a Dutch Company, of Ede, Holland, 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: The present invention relates to a process and apparatus for converting a gellified product into a homogeneously-smooth viscous liquid by moving a perforated plate through a space for this conversion, said plate being moved by a plugstream of the gellified product through said space and returned rapidly thereafter so that the product flows through the perforations to obtain the said conversion.

An example of one application of such a process is the continuous manufacture of fermented milk products such as yoghurt in which liquid fermented milk is transmitted from a prefermentation vessel gradually to the coagulation vessel in which a plugstream is formed, the milk under continuing fermentation gradually becoming more acid as it moves downwards in the vessel and coagulating to form a gel. Within a certain range of acidity through which the milk in the vessel passes, said plugstream may not be disturbed, but in the lower part of the vessel the gel should be stirred to form a smooth viscous liquid without causing by such stirring that the viscosity becomes too low.

According to one aspect of the invention, there is provided a process for converting a gellidied product into a homogeneouslysmooth viscous liquid comprising the steps of allowing a perforated plate to be moved through a space in which conversion occurs from a first position to a second position with a plugstream of the gellified product, there being exerted by said plate on the gellified mass in a direction contrary to its direction of movement a counter pressure which is less than that corresponding to the yield stress of the part of the gellified mass which is in contact with the plate, until it reaches said second position when said pressure is substantially increased for a short duration to a value greater than that corresponding to the yield stress of the product whereby the plate is rapidly returned to its first position and the product flows through the perforations to obtain said conversion.

According to another aspect of the invention, there is provided apparatus for converting a gellified product into a homogeneously-smooth liquid, comprising a vessel, a perforated plate movable therein between first and second positions with a plugstream of the product, the vessel having a product inlet located on one side of the plate and a liquid outlet on the other side thereof, pressure generating means operable to exert a counter-pressure on the perforated plate as it moves through the vessel between its first and second positions and return means for rapidly returning the plate from its second position to its first position. Said yield stress or yield value is a known concept in rheology, among others also for gels.

When a shearing force acts on a gel this will only begin to flow at a minimum value of said force, i.e. after the yield stress at which the gell is converted into a viscous liquid is exceeded.

It will be clear that it is not necessary for the plugstream and the stirring plate to move vertically. The invention may be applied as well for other directions thereof and of course also for other liquids in which comparable problems occur.

During the rapid return movement of the perforated plate the yield stress has to be exceeded so that the gel will flow through the perforations of the plate and will appear as a viscous liquid on the other side of the plate and to this end the pressure between gel and plate is considerably increased for a short duration.

The invention aims at keeping the speeds of the plugstream and the perforated plate during movement of this plate together with the plugstream continuously and completely mutually equal with simple means.

In the manufacture of yoghurt one will always stay below the yield value as long as the pressure of the plate onto the gellifled mass remains in the vicinity of a pressure of a water column with a height of 1 cm. The yield value will of course depend on different circumstances, not only on the kind of material of the gel but also on the temperature and the acidity.

It might be possible to realise the process of the invention by driving the plate also when moving with the plugstream positively with a speed which is derived from the observed speed of the plugstream or from a measure of this speed derived from the rate of discharge of liquid from the vessel. It is thus possible to make the speed of the plate equal to the speed of the plugstream but the time at which the movement of the plate with the plugstream begins should be chosen so that meanwhile some pressure has been built up between plugstream and plate.

Much more simple is, however, a preferred embodiment of the process according to the invention according to which the plate is freely displaceable in the direction of movement with the plugstream so that the plugstream is able to push the plate in front of it, a force being exerted on the plate to give rise to the appropriate pressure, which is less than that corresponding to the yield stress of the product.

Said force is preferably entirely or in part derived from the pressure of a column of liquid with an overflow, acting for example on a pistton or the like mechanically connected to the plate. The said force may be adjusted by adjusting the height of the overflow. The force may be only in part dependent upon the pressure of the liquid column because a role may also be played by the weight of moving parts and by mechanical friction, etc.

The invention will now be elucidated with reference - to the accompanying somewhat diagrammatic drawing of-a device for embodying the process according to the invention.

In the drawing, 1 shows a vertically positioned coagulation vessel, provided in the bottom with a discharge duct 2 and with a guide bearing 3, through which a piston rod 4 is adapted to move, which rod at its upper end is connected to a perforated plate 5 and at its lower end to a piston 6 in a hydraulic cylinder 7. The plate 5 is shown with - several cylindrical perforations, but in practice the number of perforations may be much higher and said perforations may have a shape differing from a cylinder, for instance diverging upwardly so that the top face of the plate only has sharp intersecting edges of the openings as described in Patent No. 1,508,252 in order to avoid any part of the gel being retained by the plate.

The perforated plate may make a vertical translation between an upper position 8 and a lower position 9. Switch contacts acting as position signalling means react on the plate reaching one of these positions. Preferably said contacts do not cooperate immediately with the plate itself, but are provided in the piston-cylinder-system 6, 7 outside the vessel. The downwardly directed movement of the plate is the result of the continuous contact of the plate with the lower limit of a plugstream 10. The upward movement of the perforated plate takes place by an increase of short duration in the hydraulic pressure in a liquid 11 present below piston 6 in cylinder 7, of short duration.

A duct 12 leads from cylinder 7 to a threeway-valve 13 which on the one hand is connected by a duct 14 to an overflow 15 with a take-up receptacle 16 and on the other hand by the duct 17 to a pump 18 and to a pressure-relief valve 19 in circulation duct 22. The overflow 15 is adjustable in height and may be placed either below or above the top end of the vessel 1. The pump 18 sucks the hydraulic liquid from a supply vessel 20 through duct 21. A duct 23 leads from take-up receptacle 16 for the overflow back to said vessel 20.

If it is desired by way of example to use this device- for the continuous manufacture of yoghurt, one operates as follows. In the top part of vessel 1 fermented liquid milk is supplied and from discharge duct 2 a substantially equal quantity of stirred yog- hurt is discharged. During said flow the combination of perforated plate 5, piston rod 4 and piston 6 is moved to and fro periodically between the highest position 8 and the lowest position 9 of the plate, viz.

rapidly upwardly and slowly downwardly.

The downward movement takes place with the same speed as that at which the plugstream of coagulating yoghurt flows gradually downwards in the vessel 1. This movement is caused by having continuous contact existing between the lower limit of the plugstream, gellified and not yet stirred, and the top surface of the perforated plate, in such a way that a low contact pressure is maintained. To this end duct 12 is connected by threeway-valve 13 and duct 14 to overflow 15 which is provided at such a height that the pressure in the hydraulic liquid below piston 6 results in an upwardly directed force which is somewhat greater than the weight of the aggregate of perforated plate in submerged condition and rod and piston. By the upwardly directed resulting force the perforated plate is continuously maintained pressed against the lower limit of the plugstream. The pressure difference which is generated across the perforated plate as a result thereof is, however, so small that the yield stress of the yoghurt gel is not exceeded so that the downwardly directed movement takes place in that the gel pushes the perforated plate in front of it with the same speed as the plugstream itself. Liquid from cylinder 7 therewith flows by way of overflow 15 into receptacle 16 and through duct 23 back to supply vessel 20.

When reaching the lowest position 9 the plate or a part moving with the plate such as the piston 6 will contact a sensor element of a position signalling means associated with said position and thereby threewayvalve 13 is switched into the position shown in the drawing separately at the left. The connection between duct 12 and duct 14 is thus interrupted and duct 17 is now connected to duct 12. Pump 18 now pumps liquid into the space below piston 6. As the pressure in duct 17 drops, pressure relief valve 19 will close, so that the perforated plate is moved at high speed upwardly through the plugstream to its highest position at 8, during which movement the yield stress of the gel is substantially exceeded.

The coagulated yoghurt thereby passes through the perforations in the plate and is thus stirred into a smooth condition without the viscosity of the liquid becoming too low.

When the stirring plate has reached its highest position at 8, threeway-valve 13 is again switched to its original position by a position signalling means as indicated, by which pressure relief valve 19 will be opened again under influence of the pressure of the pumped liquid, so that the pumped liquid will circulate while simultaneously the connection of cylinder 7 with overflow 15 is restored so that the stirring plate will move downwardly again with the speed of the plugstream by the continuous contact with the as yet un-stirred yoghurt.

WHAT WE CLAIM IS:- 1. A process for converting a gellified product into a homogeneously-smooth viscous liquid comprising the steps of allowing a perforated plate to be moved through a space in which conversion occurs from a first position to a second position with a plugstream of the gellified product, there being exerted by said plate on the gellified mass in a direction contrary to its direction of movement a counter-pressure which is less than that corresponding to the yield stress of the part of the gellified mass which is in contact with the plate, until it reaches said second position whereupon said pressure is substantially increased for a short duration to a value greater than that corresponding to the yield stress of the product whereby the plate is rapidly returned to its first position and the product flows through the perforations to obtain said conversion.

2. A process according to claim 1 wherein the plate is freely displaceable in the direction of movement of the plugstream so that the plugstream is able to push the plate in front of it, a force being exerted on the plate to provide said counter pressure.

3. A process according to claim 1 or claim 2 wherein said force is entirely or in part derived from the pressure of a column of liquid, acting on a movable member mechanically linked to the plate.

4. A process according to claim 3, wherein the column of liquid includes an overflow, the said force being adjusted by adjusting the height of the overflow relative to said space.

3. Apparatus for converting a gellified product into a homogeneously-smooth liquid, comprising a vessel, a perforated plate movable therein between first and second positions with a plugstream of the product, the vessel having a product inlet located on one side of the plate and a liquid outlet on the other side thereof, pressure generating means operable to exert a counter-pressure on the perforated plate as it moves through the vessel between its first and second positions and return means for rapidly returning the plate from its second position to its first position.

6. Apparatus as claimed in claim 5 wherein the pressure generating means com- prises a hydraulically operated piston connected to a hydraulic system including switching means operable in a first position to cause a high pressure to be supplied to said piston whereby the plate is rapidly moved against the direction of flow of the liquid and in a second position to cause a lower pressure to be supplied to the piston to provide said counter pressure.

7. Apparatus as claimed in claim 6, wherein said switching means in its first position connects the piston with a pump or a pressure fluid accumulator, whereas in its second position the switching means connects the piston with a liquid column exerting an adjustable pressure in said system.

8. Apparatus as claimed in claim 7, wherein the said liquid column has a heightadjustable overflow associated therewith.

9. Apparatus as claimed in claim 7 or claim 8, wherein said switching means is a three-way valve, said valve being connected to the pump by a duct including a pressure relief valve and return duct, the arrangement being such that in its first position the three-way valve makes the liquid from the pump flow to the said hydraulic piston, the pressure relief valve being closed and the connection to the liquid column being interrupted, whereas in its second posi

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. perforated plate as a result thereof is, however, so small that the yield stress of the yoghurt gel is not exceeded so that the downwardly directed movement takes place in that the gel pushes the perforated plate in front of it with the same speed as the plugstream itself. Liquid from cylinder 7 therewith flows by way of overflow 15 into receptacle 16 and through duct 23 back to supply vessel 20. When reaching the lowest position 9 the plate or a part moving with the plate such as the piston 6 will contact a sensor element of a position signalling means associated with said position and thereby threewayvalve 13 is switched into the position shown in the drawing separately at the left. The connection between duct 12 and duct 14 is thus interrupted and duct 17 is now connected to duct 12. Pump 18 now pumps liquid into the space below piston 6. As the pressure in duct 17 drops, pressure relief valve 19 will close, so that the perforated plate is moved at high speed upwardly through the plugstream to its highest position at 8, during which movement the yield stress of the gel is substantially exceeded. The coagulated yoghurt thereby passes through the perforations in the plate and is thus stirred into a smooth condition without the viscosity of the liquid becoming too low. When the stirring plate has reached its highest position at 8, threeway-valve 13 is again switched to its original position by a position signalling means as indicated, by which pressure relief valve 19 will be opened again under influence of the pressure of the pumped liquid, so that the pumped liquid will circulate while simultaneously the connection of cylinder 7 with overflow 15 is restored so that the stirring plate will move downwardly again with the speed of the plugstream by the continuous contact with the as yet un-stirred yoghurt. WHAT WE CLAIM IS:-

1. A process for converting a gellified product into a homogeneously-smooth viscous liquid comprising the steps of allowing a perforated plate to be moved through a space in which conversion occurs from a first position to a second position with a plugstream of the gellified product, there being exerted by said plate on the gellified mass in a direction contrary to its direction of movement a counter-pressure which is less than that corresponding to the yield stress of the part of the gellified mass which is in contact with the plate, until it reaches said second position whereupon said pressure is substantially increased for a short duration to a value greater than that corresponding to the yield stress of the product whereby the plate is rapidly returned to its first position and the product flows through the perforations to obtain said conversion.

tion, the three-way valve re-opens the said connection to the column and interrupts the discharge flow from the pump whereby this flow re-opens the pressure relief valve and will thereupon flow through the return duct.

10. Apparatus as claimed in any of claims 5 to 9, wherein the switching means include two position observing and signalling means, co-operating with the moving parts of the device in such a way that they signal the attainment by the perforated plate of the extreme positions of its range of movement and that the said signals control the said switching means, e.g. by switching the said three-way valve.

11. Apparatus as claimed in claim 10 when dependent on any one of claims 6 to 9, wherein the position observing means are positioned at and co-operate with a moving part of the hydraulic piston outside the vessel.

12. Apparatus substantially as herein described with reference to the accompanying drawings.

13. A process for converting a gellified product into a homogeneously smooth viscous liquid substantially as herein described with reference to the accompanying drawings.