DEVICE FOR PASTEURIZING A MASS OF FOODSTUFF

The invention relates to pasteurizing of a mass of foodstuff. Such a mass can for instance contain soya, fruits, potatoes, and/or meat. The mass can also contain other ingredients, such as sugar, salt, spices and the like.

The invention provides a device for pasteurizing a mass of foodstuff, such as a mass containing soya ingredients, a mass containing eggs, a mass containing fruits, for instance jam, a mass containing potatoes, or a mass containing meat, or the like, which device comprises : a feed through which said mass can be supplied under pressure to the device at a determined flow rate/ a first tube, connecting to the feed, of an electrically and magnetically inert material suitable for contact with food; two plate-like electrodes which are situated on either side of the first tube and which are connected to an RF power generator which generates energy at a frequency in the range of about 10-50 MHz to the electrodes such that the mass present in the first tube is heated dielectrically during its first residence time in this first tube; a first jacket filled with a heatable first liquid and extending around the first tube; a second tube which connects to the first tube and in which the hot mass is held at practically constant temperature during its second residence time in this second tube; and a second jacket filled with a heatable second liquid and extending around the second tube for this purpose, at the end of which second tube the hot mass is discharged for further processing, such as cooling, portioning and packaging. The pasteurizing processing which is performed by the device according to the invention can also serve for allowing the treated mass to cure for some time by the

occurring heating. A mixture of meat ingredients, salt, spices and binding agents can thus be formed in one continuous movement with the device according to the invention into a continuous sausage which is then portioned under sterile conditions, packaged and if necessary further confectioned, whereafter transport to the customers can take place.

For further processing of the mass thus pasteurized in the device, this will in many cases have to have the opportunity to cool before being portioned and packed. If desired, this cooling can take place after portioning and packing. An embodiment is often recommended comprising a third tube which connects to the second tube and in which the hot mass is given the opportunity to cool during its third residence time in this third tube, at the end of which third tube the thus cooled mass is discharged for further processing. Such a third tube can be wound in the form of a helix, thereby obtaining a great length in a relatively small space, whereby, optionally in combination with an external cooling medium, for instance flow-by air, a rapid cooling is obtained. Other than in the dielectric heating in the first tube, in this cooling section the heat is removed from the pasteurized mass solely by conduction. Necessary for this purpose is time, and therefore a relatively great length. Use can also be made in per se known manner of a portioning process, optionally followed by a packing process, wherein the portions are guided through a cooling space by means of trolleys. A per se known lift-tower is suitable in this respect.

Attention is drawn to the fact that the inner diameter of the tubes does not have to be round. Any desired and technically realizable form can be chosen. A device is known from WO-A-88/02222 for cooking and thus curing a meat-containing mass. For heating of the mass carried through the device under pressure use is made of a field, described as an electromagnetic field, with a frequency between 10 and 41 MHz, such that the mass is exposed to an efficient heating.

The medium is carried through the device by a pipe, leaves the device in hot state and in this state is cut into pieces or slices and, if desired, packed immediately thereafter. WO-A-2004/039164 relates to a method and system for manufacturing a sausage product without casing. According to this known art the mass is heated by a first heating element based on heat conduction, then heated to an increased temperature by a second heating element, whereby a sausage without casing is obtained, whereafter the product is finally cooled in forced manner through the action of a cooler.

This specification mentions the possible application of microwave energy or radiofrequency or RF energy. The frequency ranges in question are not further defined in this publication. Since microwaves have by definition a frequency of more than 300 MHz, it is not possible as a result of the associated wavelengths to prevent hot and cold zones occurring in the mass to be heated. In respect of the wish for fully homogeneous heating this is highly undesirable, and even impermissible in respect of requirements set down for food products. The temperature to be reached is after all chosen with a view to a pasteurizing treatment, which requires a minimum temperature of 72°C everywhere in the heated mass, which temperature must be maintained for a time period in the order of at least 2 minutes . In this respect frequencies over 300 MHz are certainly not suitable according to the invention. This is the reason that an RF frequency in said range of about 10-50 MHz has been chosen according to the invention.

Compared to the two stated prior art references, it is deemed essential according to the invention that use is made of the liquid-filled jackets. Each of the tubes preferably has the same cross- sectional shape everywhere.

A material which is completely transparent for said frequencies is for instance PTFE (polytetrafluoroethylene) . This material has the further advantage of being very suitable for contact with food. It is a smooth material to which food products do not

adhere, or hardly so. The material can further be very easily given a smooth finish, and thus be cleaned regularly in accordance with set requirements .

The electrodes can be of any suitable material. Aluminium plates can for instance be applied.

The device has an in-line arrangement and is able to perform a continuous and very homogeneous heating, wherein it can be ensured that the temperature difference between the hottest and the coldest zones in the heated mass is less than 5°C.

The system is capable of a rapid heating into the core of the mass, for instance at a speed in the order of magnitude of l°C/s.

The temperature of the supplied mass can be assumed to be about 0 ⁰ C-IO ⁰ C. Said required temperature is reached at the end of the electrodes .

According to a determined aspect of the invention, the device has the special feature that the material of the second tube is stainless steel. The device can also have the special feature that the material of the third tube is stainless steel. Very practical is the embodiment in which the second and the third tube are embodied together as an integral tube . According to a subsequent aspect according to the invention, the device has the special feature that the first residence time and the RMS RF voltage over the electrodes can be adjusted such that the temperature of the mass at the end of the first tube has a value in the range of about 70°C-90°C.

The setting of said parameters for reaching said temperature depends inter alia on the salt content of the mass. The choice of the parameters must therefore also be made in the light thereof. According to a following aspect of the invention, the device has the special feature that the average effective internal diameter of the first tube is in the range of about 40-130 mm. A value of 50-115 mm is particularly envisaged here. Another aspect of the dimensioning of the device can lie in the length of the electrodes being in the

range of about 0.3-3 m. The electrodes preferably have a length in the order of 0.5-1.5 m.

The greatest efficiency of the RF heating is realized with an embodiment in which the electrodes each have a form corresponding with the external shape of the tube.

A constant speed at a given mass flow rate and a total absence of discontinuities is realized with an embodiment in which the internal cross-sectional forms of the three tubes are the same as each other.

Diverse liquids can be considered for filling the jackets. An embodiment is recommended in which the first and/or the second liquid is water or an oil.

For the safety of operating staff and others present, the embodiment is recommended in which all RF voltage-carrying components are accommodated in a housing, in particular a Faraday cage. The mesh of the Faraday cage can be relatively coarse in respect of the relatively large wavelength, relative to microwave radiation, associated with the frequencies applied according to the invention.

In order to maximize the efficiency of heating of the mass for cooking and pasteurizing, the embodiment is recommended in which the liquid in the first jacket is held at a temperature in the range of about 20°C-80°C. During a residence of a minimum of two minutes in the section in which the mass is kept warm, i.e. the second tube, the temperature of the mass for pasteurizing may not fall below a determined prescribed temperature, usually in the order of magnitude of 72 ⁰ C- 75 ⁰ C.

A preferred aspect according to the invention lies in the fact that the electrodes are coupled to the RF generator via an adjustable impedance matching circuit. The device can for instance have the feature that the feed is adapted for coupling to a preproduction device, for instance a meat pump. For this purpose the inlet side of the first tube can be provided with a flange, which is adapted for sealing coupling to a correspondingly formed outlet flange of a known meat pump .

The device can have the particular feature that the frequency lies in the range of 12-29 MHz.

According to yet another aspect of the invention, the device has the feature that the frequency has a value of 27 + 2 MHz. The frequency 27.12 MHz is for instance a frequency allowed for industrial applications such as the present ones.

According to yet another aspect of the invention, the device has the special feature that the frequency has a value of 13.5 ± 1 MHz. The frequency 13.56 MHz is likewise allowed for industrial applications such as the present ones .

It is noted that the third tube subjects the cooked and pasteurized mass to a gradual cooling by conduction on the inside and convection on the outside. The third tube will therefore generally have to have a relatively great length compared to the first and the second tube.

The invention will now be elucidated with reference to the accompanying drawings . In the drawings : Fig. 1 shows a highly simplified representation of the device according to the invention, partially in the form of a block diagram and partially in cross-section; and

Fig. 2 shows a longitudinal section through the device according to Fig. 1.

The figures show a device 1 for cooking and pasteurizing a meat-containing mass 4, which mass 4 is supplied to device 1 by a meat pump 2 of known type. The device comprises a feed 3 through which a mass 4 is supplied under pressure to device 1 at a determined flow rate; a first tube 5, connecting to feed 3, of an electrically and magnetically inert material suitable for contact with food, in particular PTFE; two plate- like electrodes 6, 7 situated on either side of first tube 5 and having a form corresponding to the external shape of first tube 5, which electrodes are connected to an RF power generator 8 which generates energy with a frequency in the range of about 10-50 MHz to electrodes β, 7 such that mass 4 present in first tube 5 is heated dielectrically during its first residence time in this first tube 5; a first jacket 10 extending around first

tube 5 and filled with a first liquid 9; a second tube 11 which connects to first tube 5 and in which the mass heated in first tube 5 is held at practically constant temperature during its second residence time of a minimum of two minutes in the second tube; a second jacket 13 extending around second tube 11 and filled with a second liquid 12; and a relatively long third tube 14 which connects to second tube 11 and in which the hot mass is given the opportunity to cool during its third residence time in this third tube, at the end 15 of which third tube 14 the thus cooled mass is discharged for further processing, for instance portioning and/or packing.

Second tube 11 and third tube 14 are embodied together as one integral, monolithic tube of stainless steel .

The first residence time and the RMS RF voltage over the electrodes can be adjusted such that the temperature of mass 4 has a value in the range of about 70°C-90°C at the end 16 of first tube 5. For an energy transfer, and thus heating of mass 4, with the highest possible efficiency the electrodes 6, 7 are coupled to RF generator 8 via an impedance matching circuit 17. Circuit 17 comprises a variable capacitor 8 connected in series and a variable second capacitor 19 connected in parallel to electrodes 6, 7.

The RF generator 8 can be adapted to generate energy with a frequency of for instance 27.12 MHz or 13.56 MHz. These are both legally permissible frequencies for industrial applications of this type.

The first liquid is held at a desired temperature of for instance 40°C by means of a heating device 20 having a heat exchanger with a pump. In this embodiment a demineralizing unit 22 is also incorporated in supply conduit 21. In this case use is made of water. Other liquids such as thermal oil are also suitable.

The second liquid 12 can be brought to and held at the desired temperature in similar manner.

With a view to the requirements set down for pasteurization, the residence time of the hot mass in second tube 11 must be a minimum of two minutes.

The RF voltage-carrying components are all accommodated in a Faraday cage 23. This Faraday cage is earthed via an earth wire 23. Electrode 6 is also earthed, via an earth wire 25, with which the electrode is also coupled to the RF generator. This is therefore also earthed. Both the Faraday cage and said earthings are essential for the safety of operating staff.