IMPROVEMENTS IN FRYING TECHNOLOGY

Abstract

A method for preserving cooking oil comprises contacting the oil with oil-permeable cementitious material in the form of either stand-alone blocks, pellets, granules, or balls and which has been hydraulically hardened from a paste comprising (a) >50 wt % of (i) white OPC clinker, (ii) white OPC or (iii) a mixture of white OPC clinker and white OPC, and (b) optionally further ingredients selected from silica, titania, lime, calcium sulphate, hydrated alumina, natural feldspars, diatomaceous earth, Na and Ca forms of natural and synthetic zeolites, clays, pillared clays, activated clays/earths, silicate minerals selected from calcium silicate, magnesium silicate, aluminium silicate, agalmatolite, amphiboles, attapulgite, granite porphyry, kaolinite, porphyry, rhyolite, talc and wollastonite, wherein the porosity of the cementious material is 30-55%. The treatment of the cooking oil takes place in a location separate from the frying chamber.

Claims

1. A method for preserving cooking oil which comprises contacting the oil with oil-permeable cementious material in the form of either stand-alone blocks, pellets, granules, or balls and which has been hydraulically hardened from a paste comprising:— (a) >50 wt % of (i) white OPC clinker, (ii) white OPC or (iii) a mixture of white OPC clinker and white OPC, and (b) optionally further ingredients selected from silica, titania, lime, calcium sulphate, hydrated alumina, natural feldspars, diatomaceous earth, Na and Ca forms of natural and synthetic zeolites, clays, pillared clays, activated clays/earths, silicate minerals selected from calcium silicate, magnesium silicate, aluminium silicate, agalmatolite, amphiboles, attapulgite, granite porphyry, kaolinite, porphyry, rhyolite, talc and wollastonite, wherein the porosity of the cementious material is 30-55%, characterised in that the treatment of the cooking oil takes place in a location separate from the frying chamber.

2. The method of claim 1, wherein the paste also includes at least 5% by weight of microsilica.

3. The method of claim 1, wherein the paste also includes anhydrite.

4. The method of claim 1, wherein the paste also includes a non-toxic air entraining agent.

5. The method of claim 1, wherein the location where the treatment takes place is a tank.

6. The method of claim 1, wherein the oil to be treated is removed from the frying chamber via an inlet channel to a treatment tank and then returned to the frying chamber, after treatment in the treatment tank, via an outlet channel.

7. The method of claim 1, wherein the treatment tank is located integrally with the frying chamber.

8. The method of claim 1, wherein the inlet and outlet channels comprise pipes.

9. The method of claim 1, wherein pump means are used to effect circulation of the oil to be treated between the frying chamber and the treatment tank.

10. A method for preserving cooking oil which, comprises contacting the oil with an oil-permeable cementious material in the form of a pipe member or the lining for such a pipe member and which has been hydraulically hardened from a paste comprising:— (a) >50 wt % of (i) white OPC clinker, (ii) white OPC or (iii) a mixture of white OPC clinker and white OPC, and (b) optionally further ingredients selected from silica, titania, lime, calcium sulphate, hydrated alumina, natural feldspars, diatomaceous earth, Na and Ca forms of natural and synthetic zeolites, clays, pillared clays, activated clays/earths, silicate minerals selected from calcium silicate, magnesium silicate, aluminium silicate, agalmatolite, amphiboles, attapulgite, granite porphyry, kaolinite, porphyry, rhyolite, talc and wollastonite, wherein the porosity of the cementious material is 30-55%, characterised in that the treatment of the cooking oil takes place in a location separate from the frying chamber.

11. Equipment for the treatment of cooking oil which comprises an oil-permeable cementious material in the form of either stand-alone blocks, pellets, granules, or balls and which has been hydraulically hardened from a paste comprising:— (a) >50 wt % of (i) white OPC clinker, (ii) white OPC or (iii) a mixture of white OPC clinker and white OPC, and (b) optionally further ingredients selected from silica, titania, lime, calcium sulphate, hydrated alumina, natural feldspars, diatomaceous earth, Na and Ca forms of natural and synthetic zeolites, clays, pillared clays, activated clays/earths, silicate minerals selected from calcium silicate, magnesium silicate, aluminium silicate, agalmatolite, amphiboles, attapulgite, granite porphyry, kaolinite, porphyry, rhyolite, talc and wollastonite, wherein the cementious material has a porosity of 30-55% and is located in a treatment tank separate from the frying chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] How the invention may be put into effect will now be further described with reference to the accompanying drawings in which:—

[0056] FIG. 1 is general arrangement drawing.

[0057] FIG. 2 is a general arrangement drawing showing a system wherein the frying chamber is integral with the treatment chamber.

[0058] FIG. 3 is a drawing showing the layout of the invention seen from above

[0059] FIGS. 4-7 are further general arrangement drawings of various embodiments of the invention.

[0060] FIGS. 8-9 are schematic drawings of a further embodiment of the invention.

[0061] FIG. 10 is a further general arrangement drawing.

DESCRIPTION OF PREFERRED EMBODIMENTS

Materials

[0062] The treatment materials that are suitable for use in embodiments of this invention are those cementious materials that are disclosed in the specifications of the BBM Patents, which are incorporated herein in their entirety by reference. Particularly suitable treatment materials are cementious materials made substantially from pastes comprising (a) >50 wt % of (i) white OPC clinker or (ii) white OPC or (iii) a mixture of white OPC clinker and white OPC, and (b) optionally further ingredients selected from silica, titania, lime, calcium sulphate, hydrated alumina, natural feldspars, diatomaceous earth, Na and Ca forms of natural and synthetic zeolites, clays, pillared clays, activated clays/earths, silicate minerals selected from calcium silicate, magnesium silicate, aluminium silicate, agalmatolite, amphiboles, attapulgite, granite porphyry, kaolinite, porphyry, rhyolite, talc and wollastonite, wherein the porosity of the cementious material is 30-55%.

[0063] Such pastes advantageously also contain minor amounts of microsilica/silica fume and suitable air entraining agents, as hereinafter described.

[0064] As an alternative to using a mixture of OPC and clinker, the man skilled in the art will readily appreciate that it is possible to make the treatment medium of the invention using either OPC alone or clinker alone, OPC alone being preferred because of its ready availability and ease of handling compared to clinker. Where clinker alone is used in place of a mixture of OPC and clinker then calcium sulphate (anhydrite) must be added to prevent flash setting.

Fryers

[0065] The invention is applicable to the treatment of cooking oils in deep fat fryers, which may be of the counter-top single-basket type (typically having an oil capacity of 3 to 10 litres) or twin-basket deep fat fryers (typically having an oil capacity of 7-16 litres) or in connection with medium duty freestanding deep fat fryers of oil capacity of e.g. 12-30 litres. The invention is also particularly suitable for use with larger industrial scale deep fat fryers having a capacity from 30 to 10,000 litres.

[0066] In one embodiment of the invention there is provided a treatment tank (1), capable of holding between 10 to 5000 litres, most preferably 30 to 200 litres of cooking oil, (2). The treatment tank (4) may be located integrally with the frying chamber (5) as part of one assembly (6) as depicted in FIG. 2. Alternatively the treatment tank (1) may also be located separately away from the frying chamber (3), as depicted in FIG. 1. The treatment tank may be made of stainless steel, another suitable metal, of a high temperature plastics material or of a ceramics material or from bricks or from any other material which is stable at the temperatures experienced during the food frying process (typically up to approximately 200° C.) and which is resistant to attack by virtue of a chemical reaction with the cooking oil.

[0067] An inlet channel (7) and an outlet channel (8) are provided between the frying chamber (3) and the filtration tank (1). The said channels may take the form of lengths of piping made from stainless steel, another suitable metal, of a high temperature plastics or rubber material or of a ceramics material or from bricks or from any other material, which is stable at the temperatures experienced during the food frying process (typically up to approximately 200° C.) and which is resistant to attack by virtue of a chemical reaction with the cooking oil. Both ends of the inlet channel (9, 10) and both ends of the outlet channel (11, 12) are preferentially located below the level of the oil to facilitate pumping and also to reduce exposure of the oil to the air.

[0068] The channels may also take the form of conduits (13, 14) between the frying chamber and the treatment tank, as illustrated in FIG. 2. During use of the invention the cooking oil flows from the frying chamber via inlet channel entrance (9) into the inlet channel (7) and out via inlet channel exit (10) into the treatment tank (1). After treatment in the tank, the cooking oil is returned to the frying chamber via the outlet channel entrance (12), the outlet channel (8) and out via the outlet channel exit (11) into the frying chamber (3). It is preferable that the end of the inlet channel that is in the frying chamber (9) is located as far away as possible in the frying chamber from the end of the returning outlet channel (11), so as to facilitate the treatment of all the oil in the frying chamber.

[0069] Flow of oil from the frying chamber to the treatment tank is effected either by gravity flow and/or by the use of suitable pump means, (15). Flow of oil from the treatment tank back to the frying chamber can also be accomplished by gravity flow and/or by the use of suitable pump means (16).

[0070] The location of the exit of the inlet channel (12) and the outlet channel entrance (13) are such as to afford the oil entering the treatment tank (14) an opportunity to come into intimate contact with the treatment material (17) made in accordance with the disclosures effected by the BBM patents. In one embodiment for example, as shown in FIG. 1, the inlet channel is on one side of a substantially vertical treatment member (18) on one side of which is the inlet channel exit (10) and on the other side of which is the outlet channel entrance (12) so that oil passing from the inlet channel exit (10) to the outlet channel entrance (12) has the opportunity for intimate contact with the treatment material (17) in the vertical treatment member (18). So as to aid effective treatment of the oil, multiple such treatment members (19) may be used in the treatment tank (20) between the inlet channel exit (21) and the outlet channel entrance (22) as shown in FIG. 3.

[0071] The treatment member will now be described in more detail. The treatment member comprises elements containing treatment material made in accordance with the inventions disclosed in the specifications of the BBM Patents.

[0072] In one embodiment of the invention, illustrated in FIG. 4, the vertical treatment member (20) comprises treatment briquettes (21) stacked on top of each other so as to form a more or less continuous barrier as shown in FIG. 5 between the inlet channel exit (24) and the outlet channel entrance (25).

[0073] In another embodiment of the invention, illustrated in FIG. 5, the treatment briquettes are held in a cartridge (26), held in place by a frame (27) so as to form a more or less continuous barrier of treatment briquettes (28) as shown in FIG. 5, which affords cooking oil to be treated in the treatment tank (29) an opportunity for intimate contact with the treatment media. There may be more than one separate treatment cartridge in each such barrier.

[0074] In yet another embodiment of the invention, illustrated in FIG. 6, the treatment material is in the form of loose pellets, granules or balls (30) which are located in a cartridge (31), the foraminous side walls of which allow intimate contact between at least some of the oil circulating in the tank between inlet channel exit (32) and outlet channel entrance (33) and the treatment material. The walls of the cartridge may be porous, perforated or mesh-like so as to achieve the requisite degree of contact between the circulating oil and the treatment material. The cartridge can be made out of a metal such as steel, another suitable metal, or of a high temperature plastic or similar material or of a ceramics material or from any other material which is stable at the temperatures experienced during the food frying process (typically up to approximately ° C.) and which is resistant to attack by virtue of a chemical reaction with the cooking oil. The cartridge can be rigid or alternatively could be made from flexible mesh like materials. The cartridge can be fitted with handles (34) or other means so as to allow for its ready removal, which is important in practice as with larger units the treatment media and cartridge may be quite heavy. An advantage of using a cartridge is that it facilitates the changing of the treatment material when it has reached the end of its useful life without the requirement to drain the oil from the treatment tank or to stop the treatment process taking place. This is particularly advantageous for the operators of large-scale industrial food frying equipment who wish to run such machinery substantially continuously and/or with as few interruptions as possible.

[0075] The treatment material, in the form of pellets or balls, can also be located in mesh bags which can either be free standing or contained within a cartridge with foraminous side walls, so as to allow intimate contact between at least some of the oil circulating in the tank between the inlet channel exit and the outlet channel entrance and the treatment material.

[0076] In one embodiment of the invention the side walls of the tank are fitted with female grooves or tracks (35) so as to receive and interconnect with male members (36) on the cartridge side walls and to hold them in place during the treatment operation, as shown in fig FIG. 6.

[0077] In a still further embodiment of the invention, illustrated in FIG. 7, the treatment material is stacked substantially vertically in towers (37) located in the treatment tank, (38). The cross section of the towers may be rectangular, circular or any other convenient shape. The side walls of the towers may be longer than the towers are high or may be shorter. In this embodiment the towers do not form a more or less continuous partition in the chamber but their relatively large cumulative surface area of the treatment material in such towers allows sufficient intimate contact between the cooking oil to be treated and the treatment material so as to effect efficient treatment. In this embodiment, the filter material can be in the form of standalone briquettes, blocks, pellets, granules or balls, which may as necessary be held in location by the use of foraminous cartridges (39), made of materials similar to those described previously in this patent specification. The towers may sit on the lower surface of the tank or may be suspended from a frame (not shown) into the tank. Whichever embodiment is chosen it is important that the treatment material is fully covered by the cooking oil to be treated so as to prevent the treatment material, which is strongly hygroscopic, from absorbing water vapour from the air which can lead to foaming in the oil.

[0078] In a still further embodiment of the invention, illustrated in FIG. 8, the inlet channel (40) is removably connected to a number of cementious pipe members (41), made from the cementious materials described in the specifications of the BBM Patents. Such pipes can be manufactured in sections and attached together or optionally made as one piece. Protruding members (42) also made from the cementious materials described in the BBM Patents may optionally be provided on the inside of the side walls of the cementious pipe members so as to increase still further the area of surface contact between the oil to be treated and the cementious treatment material.

[0079] The oil to be treated (43) runs along the cementious pipe members situated between the inlet channel (40) and the outlet channel (44), which thereby allows for intimate contact between the cooking oil and the cementious filter material. Pipe sections can be replaced when the cementious material comprising them is spent. There is one tap (45) fitted for each removably connected pipe member, the tap being located upstream of the removably connected pipe member so as to allow the operator to turn the supply of cooking oil into that removably connected pipe member off completely. Any cooking oil in the removably connected pipe member is then allowed to drain into outlet channel (44) before removal of the spent removably connected pipe member and its replacement by a new removably connected pipe member. Each removably connected pipe member is optionally fitted with an openable/closable air inlet valve (46) so as to facilitate pumping out of the removably connected pipe member by pump 47. Each of the removably connected pipe members may also optionally be fitted with a close fitting full length sleeve (48) made of a suitable impermeable material (such as stainless steel) so as to allow any cooking oil permeating right through the side walls of the removably connected pipe member to return back to outlet conduit (44) via channels in the said sleeve (which are not shown on FIG. 8 for simplicity). Alternatively the oil may be allowed to penetrate right through the removably connected pipe members so that it is on the outside surface of such removably connected pipe members (49), as illustrated in FIG. 11, and can thereafter drain to a collecting device (50) for recirculation back into the frying chamber via the outlet channel (44). Such an embodiment is however not preferred as it allows for greater exposure of the hot oil to the air which will promote oxidation and hydrolysis breakdown reactions, thus producing more of the very breakdown products that the treatment media are intended to remove.

[0080] In a variant of the above mentioned embodiment, illustrated in FIG. 9, the exit of the inlet channel is removably connected to a single or to a number of inline cementious pipe members (52) in series, each made from the cementious materials as generally described in the BBM Patents. The cementious pipe members may optionally be fitted with protruding members on the inside side walls (53) also made from the cementious materials described in the BBM Patents, so as to increase still further the area of surface contact between the oil to be treated and the cementious material.

[0081] The oil to be treated (54) runs along the length of the cementious pipe members (52) situated between the exit of the inlet channel (53) and the entrance of the outlet channel (55), which thereby allows for intimate contact between the cooking oil and the cementious filter material. Pipe sections can be replaced when the cementious material comprising them is spent. There is one tap (56) fitted in close proximity to the exit of the inlet channel and one tap (57) located in close proximity to the entrance of the outlet channel (55). To drain the pipe members of oil prior to changing them, the valve nearest the inlet channel (56) is turned to the closed position and optional air inlet valve (58) is opened. Any remaining oil in the pipe sections is then pumped clear of outlet channel (55) by the use of pump means (59) or by gravity flow as appropriate. Once emptied then tap (57) is turned to the off position and the removably connected pipe members are then removed and replaced with fresh ones. The removably connected pipe members may also optionally be fitted with a close fitting sleeve (60) made of a suitable impermeable material, so as to retain any oil permeating right through the sides walls of the pipe members and allow it to return via channels in the sleeve (not shown) back to the outlet channel (55) back and on to the frying chamber.

[0082] The treatment tank may optionally also be fitted with other filtering means, not shown. These may include for example a conventional particulate filter suitable for the removal of food debris. Other known filtering equipment may also be used in combination with and/or part of the equipment here in described.

[0083] The treatment tank may optionally also be fitted with a heating element or gas burner, under thermostatic control, so as to maintain the oil at the required temperature.

[0084] The treatment tank may further optionally be fitted with insulation means to reduce the heat loss occurring in the tank.

[0085] How the invention may be put into effect will now be further described by reference to the following examples.

Example 1

[0086] Filters were made with Alborg white cement clinker and Alborg White OPC. Alborg white clinker is made using an extremely pure limestone originating from a marine deposit which is now located in Denmark and was obtained from Aalborg Portland A/S—Denmark, Aalborg Portland A/S, Rørdalsvej 44, P.O. Box 165, 9100 Aalborg, Denmark.

[0087] The unmilled clinker was obtained from Hanson Cement, Ketton Works

[0088] Ketton, Stamford, Lincolnshire.

[0089] A typical composition of the Alborg clinker used is:—

SiO.SUB.2 .25.0%

[0090] Al.sub.2O.sub.3 2.00%
Fe.sub.2O.sub.3 0.30%

CaO 69.0

[0091] This gives a calculated Bogue composition as follows:—

C.SUB.3.S 65.0%

C.SUB.2.S 21.0%

C.SUB.3.A 5.0%

C.SUB.4.AF 1.0%

CaSO.SUB.4 .0%

[0092] The equivalent typical figures for the OPC used in this experiment were:—

SO.SUB.3 .2.03%

SiO.SUB.2 .24.4%

[0093] A.sub.l2O.sub.3 1.97%
Fe.sub.2O.sub.3 0.34%

CaO 68.6%

MgO 0.58%

Cl 0.01%

TiO.SUB.2 .0.09%

[0094] P.sub.2O.sub.5 0.30%

K.SUB.2.O 0.16%

Na.SUB.2.O 0.19%

[0095] Thus giving a calculated Bogue composition (corrected to take into account a free lime content of about 3%):

C.SUB.3.S 66.04%

C.SUB.2.S 20.1%

C.SUB.3.A 4.64%

C.SUB.4.AF 1.04%

CaSO.SUB.4 .3.45%

[0096] Importantly the clinker has a very low free iron content which is important as iron is a powerful pro-oxidant trace metal, (see for example Sonntag 1979 in Bailey's industrial Oil and fat Products, New York, John Wiley and Sons, Vol 1. pp 152).

[0097] The clinker was milled by an external ball-miller to a “ready-to-use” grain-size of nominally 14.5 μm, with the particle size distribution being such that the d50 was 13.33 μm±4.7%, which was approximately the same size as the cement used. Once milled the clinker was kept in a dry sealed plastic container to prevent clumping, until use.

[0098] Both the clinker and the cement were fine sieved immediately prior to mixing to remove any large clumps before addition of the water.

[0099] The mix to make the filters comprised three parts of clinker to one part of OPC as well as relatively minor amounts of microsilica (12% by weight of the paste) and a small amount of Microair 119, an air entraining agent manufactured by BASF, added in accordance with user instructions.

[0100] The incorporation of micro silica into the mix has several effects due to its strong pozzolanic activity. It accelerates the hydration reactions of the clinker phases (particularly alite). The fine microsilica particles fill the spaces between clinker grains thereby producing a denser paste and stronger overall cement. The addition of microsilica further reduces the amount of free calcium hydroxide produced by the hydration of alite and belite and promotes the production of calcium silicate hydrate gel. This reduces foaming.

[0101] For many years entrained air has been deliberately incorporated into concrete and cement mixtures in parts of the world which experience freezing so as to reduce the damage caused by repeated cycles of freezing and thawing. Chemical additives, known as air entraining agents, are used to produce a stable system of discrete air voids, which are typically extremely small being between 10 μm and 1 mm. There are normally more than 1 million such bubbles in one cubic inch of treated paste or more than 60,000 per cubic centimetre. The entrained air void system in cement can be viewed and determined from the examination of a cut and polished section of a hardened cement sample, using microscopic techniques in accordance with ASTM C457 (standard test method for microscopical determination parameters of the air void system in hardened concrete).

[0102] Such air voids provide empty spaces within the cement or concrete and are known to act as storage sites for freezing water moving in the capillary pores, thereby relieving the pressure generated during freezing and preventing damage to the cement or concrete. However it has surprisingly been found that the addition of relatively small amounts of air entraining agents to mixtures of the type used to make the filters of the type described in the BBM Patents produces very much more porous filters, which absorb very considerably much more free fatty acids and aldehydes than filters without such air entraining agents. There are a number of well-known types of air entraining agents. Typically these are surfactants and include for example wood derived acid salts, wood rosin, tall oil, vegetable oil acid salts such as the alkanolamine salt of coconut oil, synthetic detergents such as alkyl-aryle sulfonates and sulfates such as dodecylbenzenesulfonate. The surfactant used in the invention disclosed herein must be non-toxic. The man skilled in the art will readily be able to identify numerous such non-toxic air entraining agents suitable for use in the invention herein described.

[0103] Thorough mixing of the clinker, the OPC, the air entraining agent and the microsilica, using an industrial mixer took place and then sufficient water was added to give a good paste in accordance with the following mix design:—

TABLE-US-00001 Mix Design WHITE CEMENT Kg 0.900 CLINKER Kg 2.700 DEIONISED WATER Kg 1.800 ANHYDRITE Kg 0.054 MICROSILICA Kg 0.400 Microair 119 ml 24.000 Dry Total 4.05

[0104] Assuming about 10% of the mix was wasted in the mixer and in the moulds this 4.05 kg of mix would typically produce about 15 treatment blocks, each with a weight before drying of 240 gms.

[0105] The paste was then placed into moulds, of the type depicted in FIGS. 1 to 4 of WO/2013/121206 and as further described in that patent application. The moulds used in this embodiment had however 30 holes of diameter of 0.5 cm so as to promote intimate contact between the oil to be treated and the treatment material. The paste was allowed to cure until fully set. Thereafter the filter units were dried in an industrial oven for 6 hours at 130° C. to remove excess water and were then individually sealed in water impermeable wrapping.

[0106] The dimensions of the filter were approximately 15 cm×2 cm×9 cm with 30 holes each with a diameter of approximately 0.5 cm: (these figures ignore slight tapering of the filter to facilitate extraction from the mould).

[0107] The porosity of hardened cement paste is discussed e.g. by Alford et al. in their article entitled “An assessment of porosity and pore sizes in hardened cement pastes”, J. Materials Sci., 16, (1981) 3105-3114. The porosity of a cementious article can be estimated by firstly weighing the article after it has been dried in an industrial oven for 72 hours at 130° C. (to give weight A) and then immersing it in water at room temperature until the article is fully saturated with water and then weighing it fully saturated (weight B). The total weight of the water taken up is then weight B minus weight A, which when multiplied by the density of the cement/density of water gives a figure which as a percentage of weight A represents the porosity of the filter.

[0108] The filters made for the purposes of this example had a porosity determined in accordance with the above described method of between 45 to 50%.

[0109] 200 filters made in this manner were then located into twenty cartridges which were located in a tank with a capacity to hold approximately a 90 litre capacity. The general arrangement is shown in FIG. 10 but for simplicity only one such cartridge (61) is shown, fitted to the treatment tank (62). The treatment tank and the frying equipment are not shown drawn to scale in FIG. 10.

[0110] Each cartridge could hold ten treatment briquettes (63), stacked on top of each other with the largest face (9×15 cm) containing the 30 holes facing forwards. Two male ridges on each of the cartridges (64) fitted into corresponding female groves (65) of the treatment tank (62).

[0111] The treatment tank was connected, via an inlet channel (66) and an outlet channel (67), each being a stainless steel pipe, to a large scale continuous cycle industrial chip fryer, which was used to manufacture bagged, frozen pre-fried potato chips. The exit of the inlet channel (68) was located on one side of the rows of treatment elements and the entrance to the outlet channel (69) was located on the other side of the rows of treatment elements so as to enable intimate contact between the cooking oil to be treated and the treatment medium.

[0112] The frying tank of this fryer held approximately 1,650 litres of cooking oil during use. The auto-top up oil feature of the fryer was disabled so as to keep the amount of oil in the frying chamber at a constant. The entrance of the inlet channel (70) was inserted through a side wall of the frying chamber (71) at one end of the fryer and the exit of the outlet channel (72) was inserted through the sidewall of the fryer at the other end of the fryer, such that the distance between entrance points of the inlet and outlet channels in the frying chamber was in excess of 450 cm. The stainless steel pipes were lagged, outside the frying tank and treatment tank with glass mineral wool (73) to reduce heat loss.

[0113] Pump means (74) was used to bring the oil into the treatment chamber via the inlet valve and then other pump means (75) were used to pump the oil out after treatment back into the frying chamber.

[0114] Oils develop acidity during frying due to oxidation, hydrolysis and other decomposition routes. Different oils have different oxidation and hydrolysis rates. The free fatty acid level in any given oil in a fryer is determined by the starting FFA level, the subsequent rate of FFA generation and the amount of its elimination by distillation and absorption by food. It is essential therefore if meaningful data on FFA levels are to be obtained to use the same oil throughout all experiments.

[0115] The trials described herein were all conducted with sunflower oil from the same manufacturer's batch, which contains E900 (PDMS anti-foaming agent). 16,500 litres of such cooking oil was then added to the frying tank and it was switched on and the thermostatic control was set to 185° C. Two taps (76, 77), fitted respectively near the entrance of the inlet channel and the exit to the outlet channel, were then opened to as to allow cooking oil from the frying chamber to enter into the treatment tank. 65 litres of additional cooking oil were then added to the frying chamber so as to ensure both that the cooking oil was maintained at the appropriate level for the frying operation and that the top layer of treatment blocks in the treatment tank were fully covered by cooking oil. A lagged close fitting lid was then placed on top of the treatment tank (not shown in the drawings) so as to reduce heat loss and reduce oxidation/hydrolysis through contact with the air.

[0116] Ten tonnes of washed, peeled and cut potatoes were put through the fryer in an eight hour shift. Two shifts were run a day and at the end of each day's two production shifts, 50 gm samples of the oil were taken, after the oil had cooled and been filtered using the fryers own internal particulate filter. The samples were then flushed with nitrogen and kept at minus 20° C. away from any source of light until analysed so as to prevent further breakdown of the oil.

[0117] These were then compared with the oil taken from the same fryer at the end of each day for four days (two shifts per day, ten tonnes per shift) but with the inlet value and outlet valves to the treatment tank (77, 78) in the closed position and the treatment tank pump and heater turned off.

[0118] The free fatty acid was measured for each sample (in accordance with the procedure laid down in IUPAC (1979), Standard Methods for Oils, Fats and Derivatives, 6.sup.th edn, Pergamon Press, Oxford, reference 2) and the averaged results are tabulated below:—

TABLE-US-00002 FFA % with FFA % with the treatment tank treatment tank Day connected* disconnected 0 0.04 0.05 1 0.32 0.45 2 0.36 0.55 3 0.35 0.67 4 0.43 0.79

[0119] * Note that the results for the oil used in the fryer connected to the treatment tank were adjusted to compensate for the fact that in that experimental run there were 1715 litres of cooking oil in the system compared to 1650 in the fryer not connected to the treatment tank. The extra oil was assumed to dilute the free fatty acids on a linear basis so that the results actually obtained were divided by a correcting factor being 1715/1650=1.04.

[0120] It can be seen that the use of the treatment tank materially reduced the rate of build-up of the free fatty acids, the increased presence of which would otherwise have decreased the smoke point and flash point of the oil and increased the oil absorption into the food cooked into the oil. High levels of free fatty acid have also been shown to catalyse further hydrolysis of triglycerides and to promote oxidation reactions, thus causing a feedback driven process to create yet more free fatty acid/oil degradation.

[0121] An alternative method of testing acidity is to use the CNS 3647 method which gives a result in gm of KOH per gm of oil, which is a good proxy for acid concentration.

Total Polar Compounds

[0122] Some authors and experts in the field have questioned how reliable free fatty acid concentration is as a measure of oil quality, (see for example effective Process Control in Frying by GB Quaglia et al at page 237 of Frying, Improving quality, edited by J. B. Rossell, Woodhead Publishing Limited). Accordingly the amount of total polar compounds was also measured as it is (along with acid value) a very commonly used indicator of oil quality and is widely use in many international regulations: (see for example Fritch, C. W. 1981. Measurements of frying fat deterioration. A brief review. J. Am. Oil Chem Coc. 58: 272-274 and Firestone, D. 2007. Regulation of frying fat and oil, In “Deep Frying: Chemistry, Nutrition, and Practical Applications”. 2.sup.nd ed. Pp. 373-385. Erickson, M. D. ed. AOCS Press, Urbaba, USA.)

[0123] The content of total polar compounds in oil can be determined by the use of the methods set out in AOCS Cd_20-91 and ISO 8420. Typically a glass column (for example 35 cm in length and 2.1 cm in diameter) is used to effect the chromatography. A suitable eluent is a mixture of petroleum and diehthyl ether in the ration of 87: 13 (v/v). The oil sample to be tested (2.5 g) is loaded into the packed column and the non-polar compounds (%) is calculated as the mass fraction of the total polar compounds in the oil sample as a percentage.

[0124] However the AOCS Cd_20-91 and ISO 8420 procedures need to be carried out in a laboratory with proper equipment by a skilled technician and is not suitable for on site testing. Accordingly, we used a Testo 270 Deep frying oil tester (Testo Inc. Germany), which gives a more or less instantaneous reading of total polar compounds as a percentage when its probe is put into the oil to be tested and used in accordance with the manufacturer's instructions. The oil to be tested was tested at 55° C.

[0125] Oil samples collected during the previous FFA testing were analysed using the Testo 270 and the results are tabulated below:—

TABLE-US-00003 TPC % with TPC % with the treatment tank treatment tank Day connected disconnected 0 5.5 5.5 1 8.3 9.9 2 10.2 14.3 3 12.8 17.1 4 15.8 19.8

[0126] It can be seen that the use of the treatment tank materially reduced the presence of total polar compounds.

Aldehydes

[0127] The aldehyde concentration of the oil was also ascertained as described below. Aldehydes are a good indicator of oil quality for several reasons. Firstly aldehydes, even in very low concentrations, are known to cause many of the off-flavours observed in used cooking oils and in food fried in such cooking oils. Secondly such aldehydes are secondary oxidation products, resulting from the breakdown of primary oxidation products and therefore can be seen as a good proxy for the concentration of such primary oxidation products.

[0128] Thirdly many aldehydes are considered to be injurious to human health, (see Warning: thermally-stressed polyunsaturates are damaging to health, Martin Grootveld, Christopher J. L. Silwood and Andrew W. D. Claxson Food Chemistry 67 (1999) 211-213). During frying, polyunsaturated fatty acids oxidize and form degradation products with proven toxicity, such as 4-hydroxy-2-(E)-nonenal: (see for example Seppanen C M, Csallany A S (2001) Simultaneous Determination of Lipophilic Aldehydes by High-Performance Liquid Chromatography in Vegetable Oil. J Am Oil).

[0129] Particular aldehydes of interest include:—

(a) trans-2-alkenals
(b) trans,trans-alka-2,4-dienals,
(c) 4,5-epoxy-trans-2-alkenals
(d) 4-hydroxy-trans-2-alkenals
(e) cis,trans-alka-2,4-dienals and
(f) n-alkanals.

[0130] Detection and measurement of the concentrations of such aldehydes in cooking oils taken from the frying chamber, after four days of frying (two shifts a day, 10 tonnes of pealed, washed and cut potatoes per shift) was determined in accordance with the methodology as set out on pages 22 to 23 of WO 2008/015481 A2, which is incorporated by reference herein and the results are tabulated below as between (a) the fryer with the treatment tank functioning and (b) the fryer with the treatment tank not functioning, samples being taken at the end of each day of 4 consecutive days of frying. 50 gm samples of the oil were taken, after the oil had cooled and been filtered using the fryers own internal particulate filter. The samples were then flushed with nitrogen and kept at minus 20° C. away from any source of light until analysed so as to prevent further breakdown of the oil. The results are tabulated below:—

TABLE-US-00004 trans, cis, trans- 4,5- 4-OH- trans- trans- alka- epoxy- trans- alka- 2- 2,4- trans-2- 2- 2,4- n- 4 Days alkenal dienal alkenal alkenal dienal alkanal treatment tank 26.0 38.4 5.1 3.9 8.2 4.6 not functioning treatment tank 10.8 24.2 2.3 1.6 2.7 3.1 functional

[0131] All units are mmol/kg oil detected in .sup.1HMR experiments conducted on sunflower oil.

[0132] Note that the same adjustment factor of 1.04 was again applied to the results obtained from this set of experiments for the reasons set out above.

[0133] It can again be seen that the use of the treatment tank materially reduced the presence of these toxic aldehydes.

[0134] Thus these experiments demonstrate that the use of an out of frying tank treatment facility as described herein does effect useful treatment of the used cooked oil, notwithstanding the considerable amount of cooking oil required to be treated. The cooking oil so treated was capable of being used for an additional four days before being finally discarded for recycling.