A process and a device for cleaning used cooking oils and fats as well as a deep fat fryer provided with such a device

Abstract

 A process and a device for cleaning used cooking oils and fats, in which the used oils and fats are sucked from a deep well at service temperature and are passed through a filtering device which carries out a filtration to a particle size in the order of 1 micron. The filtering device comprises one or more closed filter units with at least one filter element, as well as supply and discharge conduits and a pump for passing the oils and fats to be cleaned through the filter unit. The filter element used may be a bag made of filter paper and put over a support.

Description

[0001] This invention relates to a process for cleaning used cooking oils and fats, which comprises filtering the used oils and fats. The invention also relates to a filtering device suitable for using the process as well as to a deep fat fryer provided with such a filtering device.

[0002] Practice has shown that oils and fats used for deep fat cooking will age after a certain service life. This is a consequence of the high service temperature of about 180°C, resulting in oxidation, polymerization and lipolytic reactions, and of substances originating from the cooked products, such as water and the visible particles fallen from the cooked products as they are fried.

[0003] Oxidation and polymerization will lead to substances, such as dimeric and polymeric triglycerides, that may be injurious to public health, while lipolytic reactions will lead to compounds, such free fatty acids, that give the fat or oil an unpleasant taste.

[0004] According to the standards of the Dutch Food and Drugs Inspection cooking oils and cooking fats are unsuitable for further use when the contents of polymers exceed 10% and/or the acid number is higher than 4.5. In practice, this means that fat for cooking French fried potatoes and breaded products can be used for about 27 hours and that oil for cooking fish can be used for about 2 hours.

[0005] Ageing of cooking oils and fats can be established visually by means of the following phenomena: smoking, frothing, thickening, darkening, a stronger odour, inferior cooking properties, a fatty and insufficiently crisp final product.

[0006] Consequently, both from a viewpoint of public health and from a viewpoint of business economics, there is a need for an effective technique of cleaning cooking oils and cooking fats so as to remove injurious substances, extend the service life of the oils and fats and obtain a cooked product that is always good and palatable.

[0007] US patent 4,052,319 discloses a kind of sieve for manually filtering cooking oil. The hot oil is to be poured through the sieve, collected and poured again into the deep well. It is a drawback of this method that by thus treating hot oil there is a considerable risk of scalds caused by oil splashes. Furthermore, the visible particles fallen from the cooked products as they are fried are removed indeed but not the invisible injurious materials. Also, this way of pouring the oil will enhance the absorption of oxygen and consequently the oxidation of the oil. Finally, sieving the hot oil requires relatively much time, during which the deep well in question is out of use.

[0008] Practice has further shown the use of filter arrangements comprising a pump which pumps hot fat or hot oil from a deep well into a reservoir via a hose. The reservoir contains a paper filter on a metal sieve. A filter aid is scattered into the oils or fats pumped into the reservoir followed by sucking the oils or fats through the sieve and pumping them again into the deep well. The filter aid will then form a so-called filter cake on the paper filter, and this filter cake has a filtering effect. Although a certain cleaning effect thus occurs indeed, this prior method has some drawbacks. The result of the treatment largely depends on the filter cake formed. The forming of the filter cake, however, is not controllable which, in general, leads to a non-uniform filter cake. Another drawback is that the oil is sucked vigorously through the filter cake and the paper filter so that there is a risk of the paper filter being torn. Besides, oxygen can be absorbed by the oil. Furthermore, the deep well cannot be used during the cleaning treatment.

[0009] It is an object of this invention to satisfy the above need and to remove the drawbacks of the prior art.

[0010] To this end, a process for cleaning used cooking oils and cooking fats is characterized according to the invention by sucking the oils and/or fats from a deep well at service temperature and passing them in a substantially continuous stream through a filtering device which carries out a filtration to the order of 1 micron.

[0011] A filtering device for cleaning used cooking oils and fats is characterized according to the invention by at least one closed filtering unit comprising at least one filter element and provided with a supply conduit and a discharge conduit for the oils and/or fats to be cleaned; and by a pump for passing the oils and/or fats to be cleaned through the filtering unit.

[0012] A deep fat fryer is characterized according to the invention by a filtering device comprising at least one closed filtering unit with at least one filter element, said filtering device being provided with a supply conduit connected to each of the deep wells through valves and with a discharge conduit likewise connected to each of the deep wells through valves.

[0013] The invention will be understood in greater detail from the following description with reference to the accompanying drawings.

Fig. 1 diagrammatically shows an example of a device according to the invention;

Figs. 2-5 diagrammatically show a front view, a left-hand and a right-hand side view and a top view of a device according to the invention of a mobile type;

Fig. 6 shows a detail of a device according to the invention;

Fig. 7 shows a method of producing a filter element for a device according to the invention;

Fig. 8 diagrammatically shows a deep fat fryer provided with a device according to the invention;

Fig. 9 shows an example of a modification of a part of Fig. 1; and

Fig. 10 shows a variant of Fig. 9.

[0014] Fig. 1 diagrammatically shows an exemplary embodiment of a filtering device according to the invention suitable for use in the process according to the invention. The invention is based on the insight that it is not necessary to use (expensive) filter aids if there is applied a sufficiently fine filtration of the oils and fats to be cleaned. The cleaning effect obtained according to the invention is at least comparable to the effect obtained using a filter aid if the oils or fats are passed through a filter element having openings in the order of 1 micron. With such a fine filtration not only are particles fallen from the cooked products removed, but also invisible undesirable chemical substances, such as free fatty acids and polymers, are at least partly removed, too.

[0015] As will be apparent from the following, such a fine filtration can be advantageously effected in a plurality of steps so as to reduce the risk of the filter element becoming clogged prematurely. Furthermore, because of the lack of filter aids that are to form a filter cake the cleaning step can be effected according to a recycling method so that a deep well the oil of fat of which is being cleaned need not be put out of service.

[0016] The exemplary embodiment of a filtering device according to the invention as diagrammatically shown in Fig. 1 comprises two filtering units 1 and 2 arranged in series and a vacuum pump 4 driven by an electric motor 3 or in another suitable manner. During operation of the vacuum pump 4 the hot oils or fats supplied to the device via a supply conduit 5 are sucked through the filtering units. The filtering units can in principle be of different types. It is important, however, that the cleaning process should not lead to the absorption of oxygen into the oils or fats, because the oxidation process would then be accelerated.

[0017] The filtering units are closed units connected to each other and to the pump 4 via conduits 6, 7. There is thus obtained a device fully closed between the inlet of the supply conduit 5 and the outlet of a discharge conduit 8 of the pump.

[0018] In order to prevent oxygen from being absorbed into the oils or fats during the inflow into the supply conduit 5 and the outflow from the discharge conduit 8, respectively, the pump 4 is so controlled that the suction force is just sufficient to permit the hot oils or fats to pass through the filtering units at a low rate of flow. The risk of damage to the employed filter elements is thereby substantially eliminated.

[0019] In the exemplary embodiment as shown in Fig. 1 each filtering device consists of a substantially vertical, elongate cylindrical housing 10 closed at the top and, at the bottom, secured sealingly but detachably, e.g., by means of screw thread 11, to a bottom flange 12. The substantially disc-shaped bottom flange is provided with a centrally arranged trough-shaped element 13 extending from the bottom flange 12 into the housing 10 and slightly flaring from the bottom flange. The discharge conduits, e.g., the conduits 6 and 7 of the filtering units, open into the bottom flanges 12 within the trough-shaped elements 13. Furthermore, the supply conduits 5 and 6 of the filtering units 1 and 2, respectively, open into the bottom flanges beside the trough-shaped elements.

[0020] Positioned inside each trough-shaped element is a tapering bottom part 14 of an otherwise substantially cylindrical coil spring 15. Placed around each coil spring 15 is a filter element in the form of an elongate filter bag 16 of suitable material, which is slipped over the coil spring. For clarity's sake, this is shown once again in Fig. 6. Once the housing 10 has been removed, the spring 15 can be taken from the trough-shaped element. Then, if required after removal of an old filter bag, a filter bag 16 is slid over the spring in such a manner that the opening of the bag is located at the tapered part 14 of the spring. In order to prevent the bag from rolling up when the spring is placed back in the trough-shaped element 13, the bag is preferably somewhat longer than the spring so that it can be folded into the interior of the spring at its tapered end, as shown in Fig. 6 at 60.

[0021] Hot oils or fats that have reached the space outside the filter bag via a conduit 61 (Fig. 6) can now only reach the discharge conduit 62 via the wall of the filter bag.

[0022] It is therefore very easy to exchange the filter bags.

[0023] Of course, the filter bags can also be supported by an element other than a coil spring, e.g., by a tapering cylinder of perforated metal or wire mesh.

[0024] The filter bags can be easily made of a rectangular piece of filter material by doubling this material and sewing it along two edges. This is shown in Fig. 7. An elongate rectangular piece of filter material has longitudinal edges 71, 72 and short edges 73, 74. The filter material is doubled along the longitudinal axis so that the edges 71 and 72 come to lie over each other. These edges are then secured to each other in one of the known manners suitable for the purpose, e.g., by sewing. Moreover, one of the doubled edges 73 or 74 is sewn so as to form a bag.

[0025] As stated above, a good cleaning requires a fine filtration to the order of 1 micron.

[0026] In the example shown, this fine filtration is effected in two steps. The filtering unit 1 comprises a filter element having openings of 25 microns, and the filtering unit 2 comprises a filter element having openings of 1 micron.

[0027] The first filter bag can be made of, e.g., prepared paper impregnated with, e.g., activated carbon. The second filter bag can then also be made of prepared paper impregnated with, e.g., diatomaceous earth.

[0028] Various modifications are possible. The first bag can be designed in such a manner that, e.g., particles exceeding 3 microns are held back.

[0029] It is further possible to make filter bags of prepared paper provided both with diatomaceous earth and with activated carbon.

[0030] Moreover, the filtration can be effected in one step, e.g., by using a single filtering unit or a plurality of filtering units arranged in parallel and each filtering to 1 micron. This purpose is served by using, e.g., the above filter bags provided with both diatomaceous earth and activated carbon.

[0031] Another possibility is the use of a single filtering unit which, however, comprises two filter elements. An example is diagrammatically shown in Fig.9.

[0032] According to Fig. 9 a filtering unit comprises a first wide filter element 90 based on a wide cylindrical support 91 having a conical lower end. Positioned inside the wide support is a second filter element 92 having a support 93. Disposed on a bottom flange 94, on which a housing 95 is detachably mounted, are two through-shaped elements 96, 97, capable of receiving the conical lower ends of the supports provided with filter bags in the above described manner. In a manner similar to that shown in Fig. 1, supply and discharge conduits open into the bottom flange. Furthermore, an additional drain conduit 98 is provided with a tap for draining the space between the two filter elements.

[0033] A similar effect can be obtained with the filtering unit shown in Fig. 10. In the embodiment shown in Fig. 10, however, there is used a relatively high trough-shaped element 100 retaining with a lower narrow part the inner filter element 92 and with an upper wider part a filter element 90-with-support placed over the inner filter element.

[0034] A device according to the invention must be so designed that the complete filtering device can be drained so as to prevent it from being clogged owing to fats or oils solidified during standstill.

[0035] In the device shown in Fig.1 the different conduits are of such construction that every conduit has a lowest point where a drain tap is provided. The supply conduit 5 is provided with a tap K1 disposed at the lowest point, which also allows of draining the space between the housing 10 and the filter element 16.

[0036] The discharge conduit 6 of the first filtering unit 1 also forms the supply conduit of the second filtering unit 2 and has a drain tap K2 disposed at a lowest point, which allows of draining the space within the filter element of the first unit and simulta­neously the space outside the filter element of the second unit as well as the conduit 6 itself.

[0037] Disposed in the discharge conduit 7 extending from the second filtering unit 2 to the pump, again at a lowest point, is a tap K3 for draining the space within the second filter element, the conduit 7 itself and partly the pump.

[0038] Finally, the discharge conduit 8 has a lowest point with a tap K4 for draining the pump and the discharge conduit.

[0039] Figs. 2-5 show a device of the type shown in Fig. 1 in greater detail. For corresponding parts the same reference numerals are used in these figures as in Fig. 1. Fig. 2 diagrammatically shows a front view of a device according to the invention. Starting from the orientation of Fig. 2, Fig. 3 shows a left-hand side view, Fig. 4 a right-hand side view, and Fig. 5 a top view. In this example the device shown is mounted within a suitable mobile frame 20 of, e.g., stainless steel or aluminum, provided with caster wheels and/or road wheels 21.

[0040] In this example two filtering units 1 and 2 are used again, the housings 10 of which are provided with handles 22, so that the housings can be easily unscrewed. Fig. 2 clearly shows that the conduit 6 slopes upwards from the tap K2 to the second filtering unit 2, so that the tap K2 is at the lowest point which is vertically below the first filtering unit 1.

[0041] Similarly, Fig. 3 shows that the conduit 7 slopes upwards from the tap K3 vertically below the second filtering unit to the pump 4. Furthermore, Fig. 3 shows that the tap K4 is at the lowest point of the discharge conduit 8, and Fig. 4 shows that the tap K1 is at the lowest point of the supply conduit 5.

[0042] The supply conduit and the discharge conduit each comprise a flexible part 23 and 24, respectively, which may be, e.g., a wire-reinforced and plastic-­coated teflon hose. The flexible parts are coupled to mouthpieces 25 and 26, respectively, each provided with heat insulating handles 27 and 28, respectively, of a suitable material.

[0043] The mobile device is particularly suited for use in large equipments with several and/or spaced deep wells. The device can be used for pumping hot oils or fats from a deep well, filtering the oils and fats and then pumping them into a suitable receptacle.

[0044] Preferably, however, the process is carried out according to the recirculation principle, with both mouthpieces 25 and 26 being disposed within one and the same deep well and the pump being operated. Since the contents of the device are small, the deep well can remain in operation during the cleaning process without inconvenience, which is of great advantage to the user.

[0045] According to a further elaboration on the inventive idea a filtering device according to the invention can also be integrated into a deep fat fryer assembly. Such an assembly is diagrammatically shown in Fig. 8.

[0046] The assembly shown comprises three deep wells 40, 41, 42, each of which is connected via suitable valves to the supply conduit 5 and to the discharge conduit 8 of a filtering device according to the invention diagrammatically shown at 43.

[0047] The valves releasing or blocking the connection to the conduit 5 are designated by 44, and the valves releasing or blocking the connection to the conduit 8 are designated by 45.

[0048] These valves can be manually operable valves, but preferably they are electrically or magnetically or, if required, pneumatically or hydraulically operable valves controlled by an electronic control unit 46.

[0049] The electronic control unit is designed to control, at predetermined times and in a predetermined order, the valves and the assembly 43 so that the contents of each deep well are regularly cleaned according to the recirculation principle. For safety's sake, a bypass with manually operable valves 47 and 48, respectively, can be provided for each automatically operable valve. By way of alternative, the valves 44 and 45 could be so designed that manual operation is possible.

[0050] The control unit preferably comprises a programmable microprocessor and can advantageously be designed so that an indication is automatically given when the filter bags are to be replaced. To this end, a sensor by which the reduced pressure is detected and passed on to the unit 46 might be disposed in the suction conduit 7 of the pump.

[0051] After reading the above, various modifications will readily occur to a skilled worker.

[0052] Thus, for instance, the pumpt 4 can be arranged at a different place in the device or can be driven by a means different from an electric motor. The housing 10 of a filtering unit may be composed of, e.g., a lower part secured firmly to the bottom flange or even being integral therewith and an upper part secured sealingly but detachably to the lower part. It is shown in Fig. 1 by way of example for the filtering unit 2 at 99.

[0053] Such modifications are deemed to fall within the scope of the invention.

Claims

1. A process for cleaning used cooking oils and fats, which comprises filtering the used oils and fats, characterized by sucking the oils and/or fats from a deep well at service temperature and passing them in a substantially continuous stream through a filtering device which carries out a filtration to the order of 1 micron.

2. A process according to claim 1, characterized by carrying out the cleaning process according to the recirculation principle, which comprises returning the cleaned oils and/or fats directly to the deep well.

3. A process according to claim 1 or 2, characterized by carrying out the filtration in at least two successive steps with increasing fineness.

4. A process according to claim 3, characterized by a filtration step to the order of 25 microns preceding the filtration to the order of 1 micron.

5. A process according to claim 3 or 4, characterized by a filtration step with a fineness of substantially 3 microns.

6. A process according to any of the preceding claims, characterized by passing the oils and fats to be cleaned through the filtering device by means of a relatively low vacuum.

7. A process according to any of the preceding claims, characterized by carrying out the filtration with at least one paper filter.

8. A process according to claim 7, characterized by using a paper filter prepared with diatomaceous earth.

9. A process according to claim 7 or 8, characterized by using a paper filter prepared with activated carbon.

10. A process according to any of claims 7-9, characterized by using a paper filter prepared with diatomaceous earth and activated carbon.

11. A filtering device for cleaning used cooking oils and fats, characterized by at least one closed filter unit comprising at least one filter element and provided with a supply conduit and a discharge conduit for the oils and/or fats to be cleaned; and by a pump for passing the oils and/or fats to be cleaned through the filter unit.

12. A filtering device according to claim 11, characterized in that the closed filtering unit comprises a cylindrical housing substantially vertical during operation, which has a bottom flange and is closed at the top, and that a support for a filter element substantially cylindrical during operation is provided within the housing, said filter element being smaller in diameter than the housing.

13. A filtering device according to claim 12, characterized in that the bottom flange is provided with a holder for the filter element support, and that the bottom flange is provided with a bore which opens into the holder and has a discharge conduit connected thereto.

14. A filtering device according to claim 13, characterized in that the bottom flange is provided with a bore which opens outside the holder and has a supply conduit connected thereto.

15. A filtering device according to claim 13 or 14, characterized in that the holder is trough-shaped and that the support has a tapering bottom capable of being positioned within the holder.

16. A filtering device according to any of claims 12-15, characterized in that the support is a coil spring.

17. A filtering device according to any of claims 12-16, characterized in that the filter element is an elongate bag made of filter paper, which can be slipped over the support.

18. A filtering device according to claim 17, characterized in that the filter element is made of a rectangular piece of filter paper doubled and sewn along two free edges.

19. A filtering device according to any of claims 12-18, characterized in that in the housing a second cylindrical wider support with accessory filter element is placed over the support with the filter element.

20. A filtering device according to claim 19, characterized in that the bottom flange is provided with concentric holders for the filter element supports.

21. A filtering device according to claim 19, characterized in that the bottom flange is provided with a trough-shaped flaring holder, the bottom past of which can receive a tapered bottom end of a support, while the upper part can receive a tapered bottom end of a wider support.

22. A filtering device according to any of claims 11-21, characterized by at least one similar second filtering unit arranged in series with the first filtering unit and carrying out a finer filtration than the first filtering unit.

23. A filtering device according to any of the preceding claims, characterized in that each conduit used in said device for cooking oils and/or fats is so positioned that the conduit has a lowest point and that at the lowest point of each conduit a drain tap is provided for draining the respective conduit and the part of a filtering unit communicating with this conduit or the pump.

24. A filtering device according to any of the preceding claims 11-23, said device being a mobile unit.

25. A filtering device according to any of claims 11-24, characterized in that the supply conduit and the discharge conduit are at least partly flexible and are provided with insulating handles.

26. A filtering device according to any of claims 17-25, characterized by a bag prepared with diatomaceous earth.

27. A filtering device according to any of claims 17-26, characterized by a bag prepared with activated carbon.

28. A filtering device according to any of the preceding claims, characterized by a pressure sensor placed in at least one of the conduits.

29. A deep fat fryer comprising a plurality of deep wells, characterized by a filtering device comprising at least one closed filtering unit with at least one filter element, said filtering device being provided with a supply conduit connected to each of the deep wells through valves and with a discharge conduit likewise connected to each of the deep wells through valves.

30. A deep fat fryer according to claim 29, character­ized in that said valves are automatically controllable and that a control unit is provided which controls said valves in a predetermined manner and energizes the filtering device so as to successively clean the oils and/or fats in the different deep wells.

31. A deep fat fryer according to claim 30, charac­terized in that said control unit is designed to operate the valves and the filtering device according to a predetermined time cycle.

32. A deep fat fryer according to any of claims 29-31, characterized in that said control unit is designed to give an indication when a filter element requires replacement.

Drawing