WO1988007821A1

WO1988007821A1 - Continuous treatment process

Info

Publication number: WO1988007821A1
Application number: PCT/US1988/001106
Authority: WO
Inventors: Michael Mark Blumenthal; Bernard Friedman
Original assignee: Oil Process Systems, Inc.
Priority date: 1987-04-06
Filing date: 1988-04-06
Publication date: 1988-10-20

Abstract

Methods for controlling the quality of cooking fluids such as oils comprising triglycerides used in food frying processes in which degradation products including surfactants are produced therein are disclosed, including continuously recirculating the oil through a cooking zone and a recirculation zone, and continuously treating the recirculating oil with a treatment compound so as to selectively reduce the surfactants in the oil below the level of such surfactants normally produced during the frying process, so that the useful life of this oil is substantially increased. The preferred treatment compounds are porous rhyolitic materials containing from 33 to 75 wt. % water as well as a food compatible acid such as citric acid.

Description

DESCRIPTION CONTINUOUS TREATMENT PROCESS Technical Field

This invention relates generally to methods for controlling the quality of fats and oils. More particularly, this invention relates to methods for controlling the quality of cooking oils generally comprising triglycerides. Still more particularly, this invention relates to methods for controlling the quality of such cooking oils used in continuous food cooking processes in which degradation products including surfactants are produced or introduced therein. Background Art

In conjunction with the use of various cooking oils or heated frying oils there has been a recognized tendency for these oils to decompose, forming various chemical products therefrom. These products include not only free fatty acids, but various other impurities and contaminants, which are formed both by the breakdown of the oil itself as well as by the interaction of the oil with food products added thereto. It has been known that the presence of these materials in the cooking fluid or oil, and the degradation of the fluid itself, result in the degradation of its frying properties, until it eventually becomes non-usable. Thus, foods which are fried using such contaminated or degraded oil products often become far too browned on the outside before proper cooking takes place on the inside. Also, oily residues can then be obtained on these food products themselves, and furthermore the oils tend to foam or boil during cooking, which is yet another undesirable effect of such oil degradation.

One highly successful approach to this problem is set forth in U.S. Patent No. 4,330,564 to Friedman, which discloses a fryer oil treatment which utilizes expanded rhyolitic material and water, in amounts of from about 33 to 75 wt. % of the composition, for such treatment purposes. This material is preferably used in combination with a food compatible acid. The material itself has thus become commercially significant in connection with the various batch-type processes generally encountered in the retail food industry in which the used fryer cooking oil is mixed with this composition, including the porous carrier material, and the residue is then filtered from the oil. The presence of the water in these compositions thus results in dispersion of the porous carrier material throughout the hot oil.

Furthermore, the use of such food compatible acids was previously disclosed in Clewell, Jr. et al, U.S. Patent No. 3,947,602, which also discloses the use of various absorbents, such as diatomaceous earth, activated carbon and the like, to remove contaminants from the used cooking oil.

Methods have also been developed for determining the presence of contaminants in fats and oils. For example, Blumenthal et al, U.S. Patent No. 4,349.,353, discloses a method for determining the amount of alkaline substances in fats and oils. This patent thus relates in part to the feasibility of determining the cooking quality of used frying fats and oils based on the amount of alkaline substances, including soaps, ^"present therein. The search has continued, however, for processes for improving cooking with such fats or oils, particularly on a continuous basis, and without the need to continuously replace the degraded oil. Disclosure of Invention

In accordance with the present invention, these and other objects have now been realized by the discovery of a method for controlling the quality of a cooking fluid, such as a fat or oil used in a food frying process in which degradation products including surfactants are produced during the frying process which comprises continuously recirculating the cooking fluid through a cooking zone and a recirculation zone, and continuously treating the recirculating cooking fluid with a treatment compound so as to selectively reduceύvthe surfactants in the cooking fluid below the level of such surfactants normally produced during the frying process, whereby the useful life of the cooking fluid can now be substantially 5 increased.

In accordance with one embodiment of the method of the present invention, the treatment compound is capable of selectively absorbing and/or or adsorbing the surfactant thereonto. Preferably, the treatment compound 10 thus comprises a treatment powder, and in a highly preferred embodiment, the treatment powder comprises a porous rhyolitic material, in combination with from about 33 to about 75 wt. % water. In a most preferred embodiment, a food compatible acid is also employed along !5 with a porous rhyolitic carrier.

In accordance with another embodiment of the method of the present invention the step of continuously treating the recirculating cooking fluid comprises contacting the treatment powder with the cooking fluid ²⁰ for a predetermined period of time, preferably less than about two minutes, and most preferably less than about one minute.

In accordance with another embodiment of the method of the present invention, the method includes ²^ passing the cooking fluid through a filtering medium, applying the treatment powder to the filtering medium, and then removing the filtering medium with the treatment powder thereon from the cooking fluid.

In accordance with a preferred embodiment of

30 the method of the present invention, the cooking fluid is an oil, such as a triglyceride, and the treatment compound is capable of selectively reducing the content of the surfactants in the cooking fluid or oil as reflected by the presence of ACM's therein to below about ό 2.4, and preferably to below about 1.3. Brief Description- of Drawing

The following detailed description of the present invention can be more fully appreciated with reference to the Figure, in which: FIG. 1 is a schematic representation of a continuous process in accordance with the method of the present invention. Best Mode of Carrying Out Invention

As has been discussed above, and as is described in U.S. Patent No. 4,349,353, the presence of alkaline contaminant materials (ACM's) has been employed as a yardstick in determining the quality of fats and oils. Thus, the specific test for evaluating the presence of such ACM's as set forth in U.S. Patent No. 4 ,349 _r353 is incorporated herein by reference thereto. The applicants have now discovered,- however, that the complexities inherent in these organic systems, which are constantly changing during use, have particular application and yield particularly surprising results in connection with continuous processes. That is, by continuous processes it is meant those systems, generally at the wholesale level, where large quantities of food product are continuously processed in relatively large amounts of fats and oils.

As is described above, the principal use of various filter aids as treatment powders in the past has been in conjunction with the various batch-type systems in common commercial use at the retail level. Thus, the standard practice has been to determine the degree of degradation of the oil, by various means, and to then treat the entire batch of oil in a single step, after which the oil can hopefully be returned to service. The need for such treatment basically arises from an appreciation of the fact that the oils generally exhibit three stages: an initial stage with new oil which has not yet been "broken-in," and which does not cook well; an operative stage in which the slightly used oil results in fried food products with a well-cooked interior, as well as a crisp exterior and minimal oil soakage; and a degraded oil stage in which the food is not cooked completely in the interior, but develops an excessively hard exterior and severe oil soakage. In these batch-type systems it was thus conventional to observe various parameters in order to evaluate these stages. These have included the degree of color variation, the presence of free fatty acids, the presence of ACM's, the presence of polymeric materials, etc.

In the case of continuous food processing, many of the assumptions generated in connection with the batch processes discussed above were merely carried over. Thus, the general procedure used has been to remove .and treat the used oil on a batch basis. Applicants have now discovered, however, that highly unexpected advantages occur by the continuous treatment procedures of the present invention. This discovery initially arose from the applicants' realization that the generation of ACM's in such systems arises from more than one source. Thus, although it was previously known that such materials were formed due to the introduction of food impurities into the frying oil, and their interaction with various degradation products therein, they now understand that even without the introduction of such impurities, the simple heating of these oils causes the generation of such ACM's, and that the combined effect of both of these sources of ACM's must be considered in an overall evaluation of any system for improving the used oil.

Furthermore, even in connection with the generation of ACM's purely on the basis of the introduction of food impurities into the frying oil, it has always been believed that the major amount of these materials arose from the water ejected from the food in its first entry into the hot oil. It has now been discovered, however, that this is not the case, but that instead in a continuous process there is a continuous build-up of ACM materials, and thus in a given system an ACM gradient is established as these materials continue to build up from one end of a continuous system to the other. This is the case even in those systems which are continuously being stirred, and recirculated for the removal of crumb and other such solid materials therefrom. Although the specific system developed by the applicants based upon this discovery is discussed in more detail below, the principal unexpected result which can now be realized arises from the applicants' discovery that continuous treatment of recirculating fat or oil in such continuous systems result in a surprising reduction in the overall generation of ACM materials throughout the system, and in turn yields highly unexpected results in terms of the maintenance of the overall quality of the fat or oil being used therein, and this most dramatically exhibits itself in terms of the overall life span of the oil. Indeed, there is almost a doubling of the useful life thereof.

Turning to the Figure, a continuous process is shown in that Figure which includes a primary heated fryer tank 1, which includes a continuous conveyor 3 recirculating therein from an inlet end 5 to an outlet end 7 in the direction shown by the arrows thereon. The heated fryer tank 1, which is heated by conventional means which are not shown in the Figure, will thus include oil maintained at a level 9 so as to fully immerse the conveyor 5 thereunder. Thus the food treatment process realized by the use of this system includes heating the oil within the fryer tank 1, and application of the food product onto the conveyor 3 at the inlet end 5 so that the food then travels down the length of the conveyor 3 while it continues to cook, to the outlet end 7, at which point.the fully fried food can be removed.

The oil recirculation system used in this system includes a central drain 11 in the heated fryer tank 1. The used oil thus recirculates through recirculation line 13 with the assistance of a recirculation pump 15 therein. The oil itself is thus returned to return point 17 at the outlet end of the recirculation line 13. At that point an oil collection tank 20 is located. This oil collection tank 20 can basically have a square or rectangular configuration, but is separated into an oil collection compartment 21 and a separate waste collection compartment 22, which two compartments are divided by wall member 23 therebetween. Within the oil collection department 21 a conveyor 25 is mounted. This conveyor 25 again generally runs from an entry end 24 to an exit end 26 on a continuous basis. Furthermore, in conjunction with conveyor 25 a continuous supply of filter paper is supplied from filter paper roll 26 and is fed along with the moving belt of the conveyor 25. Then, the conveyor 25 and the filter paper travel together through the oil collection compartment, and then the conveyor 25 begins its return leg back to entry end 24, the filter paper then passes through an opening in the wall member 23 into the waste collection compartment 2 of the oil collection tank 20. Thus, the used oil including contaminants, which include in addition to the above-noted items various other materials, including crumb and other solid contaminants, etc., exits from the exit end 17 of recirculation pipe 13 onto the upper surface of the filter paper above conveyor 25 as shown in the Figure. It should also be noted that at this point the oil is retained substantially in its heated condition. Mounted above the oil collection tank 20 is a dispenser 30. The treatment material or treatment powder, such as the preferred LIFE powder (LIFE is a registered trademark of MirOil Products Company, Inc.). is thus contained in the dispenser 30, and is continuously applied to the upper surface of the filter paper 26 in relatively small amounts, as it passes across conveyor 25 adjacent to the point of entry of the used hot oil.

The oil itself, after passing through the filter paper 26, and entering into the oil collection compartment 21 of the oil collection tank 20, now has not only been purified in terms of the removal of crumb and other solid material, which then exits with the filter paper 26 as it passes through the opening in the wall member 23 into the waste collection tank portion 22 of the oil collection tank 20, but has now also been treated in accordance with the critical treatment procedure of the present invention so as to reduce the ACM materials therein. The fresh filtered oil can then be reintroduced into the heated fryer tank 1 through return line 32 under the control of return valve 34.

The critical use of a specified treatment material in dispenser 30 as applied to the recirculating oil, and namely a material which is capable of selectively reducing the ACM or surfactant content of the oil is crucial to the attainment of the improved results of this invention. Most particularly, the preferred material is an active filter aid designated LIFE, which comprises a non-alkaline, non-dusting, non-irritating powder material designed to remove or control the surfactants formed -during use of frying oils. Not wishing to be bound by any theory, it is believed that this powder material slows the degradation of heated oils by apparently slowing down the hydrolysis and rate of oxidation of the oil along with the subsequent development of surfactant species therein. Furthermore, subsequent to use of this material and absorption and/or adsorption of these surfactant materials from the oil, this material is removed and leaves no other residue in the oil. The highly unexpected nature of this invention is thus exemplified by the fact that the use of other known filter aids which are not capable of doing so does not yield the improved results, including the extended oil life, of the present invention. Nothing in the prior art would have predicted that this would be the case.

The LIFE powder material itself consists of an expanded, rhyolitic, obsidian perlite material with an amorphous silicate structure. Furthermore, the powder compositions employed in the dispenser 30 comprise the porous rhyolite carrier and water, and preferably sufficient water so that when contacted with hot fats and oils above the boiling point of water the water steams and disperses the composition throughout the oil. Thus, the composition preferably contains from about 33 to about 75 wt. % water. In a preferred embodiment the composition comprises the porous carrier, water, and a food compatible acid, such as citric acid, tartariσ acid, acetic acid, phosphoric acid, malic acid and mixtures thereof, with the preferred food compatible acid being citric acid. The overall composition preferably contains between about 2 and 10 wt. % of the food compatible acid, and more preferably between about 4 and 6 wt. % thereof. The rhyolitic materials themselves are rendered "expanded" or porous by methods well known in the art, such as by heat expansion. Thus, these rhyolitic materials are initially heated to remove substantially all of the free moisture content, and the dried material is then directed to a "popper" where it is exposed to the flame of a gas jet at temperatures-generally in the range of about 1480°C. The rhyolite material is then allowed to expand to produce the porous rhyolite carrier material used in this invention, which generally has a low density and a spherical shape. Preferably, the material has sizes in the ranges of from about 8 to about 120 mesh, more preferably from about 20 to about 80 mesh, and most preferably from about 40 to about 60 mesh. The porous spheres act as carriers both for the water and, when used, the food compatible acid such as the citric acid into the hot fryer oil. An average analysis of this inorganic material includes a compositional analysis on a percentage basis as follows:

Silica 75.62%

Alumina 12.02

Ferric oxide 2.36

Calcium oxide 0.83

Magnesium oxide 0.40

Sodium oxide 1.56 Potassium oxide 6.10

Loss on Ignition 0.91

There are a considerable number of other treatment powders which are being employed as filter aids in this industry. These include diatomaceous earth, which primarily comprises a silica powder material, and which is obtainable from various sources; a zeolitic mineral base, FRYLIGHT, a product of Kaiser Aluminum Co.; a calcium and magnesium hydroxide material fused with diatomaceous earth, which is sold under the name MICROSWEET, a product of Manville Corporation; and a magnesium silicate material sold under the name MAGNESOL, a product of Reagent Chemical and Research Inc. As has been discovered by applicants, however, from among these materials only the above-described rhyolitic material can successfully selectively reduce the ACM or surfactant content of the oil when used in accordance with the method of the present invention, and thus achieve the unexpected superior results hereof. in order to demonstrate this, a hydrogenated and winterized (liquid) soybean oil was used to cook breaded vegetable and protein foods and french fries until it was ready for discard. The used oil was diluted to the original fryer volume with fresh oil. This brought it to a concentration of 27% total polar materials, as measured by the IUPAC-AOAC column chro atography method. This base oil (unfiltered and containing about 5% by weight of large and fine crumb) was the starting point for testing the properties and efficacy of a number of treatment powders. The properties of the powders are shown in Table 1 below, and results obtained by using each treatment on aliquots of the oil are shown in Table II below. Table I

Amounts ; of Powders Added to Oils

Density Powder (gm) % Powder

Powder g/cc 180g Oil (w/w)

Diatomaceous Earth 0.35 0.90 0.50

MICROSWEET 0.23 0.90 0.50

Bone - 2.00 1.11

LIFE 0.24 0.75 0.42

Silica Gel

(Merck 60A) 0.49 0.90 0.50

FRYLIGHT 0.53 2.25 1.25

MAGNESOL 0.41 2.45 1.36

Table II

Lovibond

PCM FFA ACM Red Yellow Blue

Fresh Oil 1.0 0.02% 1.1 0.1 0.9 0

A Unfiltered 3.1 4.21 2.5 15.0 >79.9 4.4

B Paper 3.0 4.14 2.4 11.2 _.72.1 0

C 1 Micron 3.0 4.16 2.4 10.4 72.0 0

A Diatomaceous

Earth 3.0 4.17 3.0+ 10.4 71.0 0

B 1 Micron 3.0 - 3.0 10.3 70.1 0

A Silica Gel 3.0 4.20 2.8 11.0 79.3 0.2

B 1 Micron 2.9 - 2.8 9.8 70.0 0

A LIFE 3.1 4.25 1.3 11.0 78.0 0

B 1 Micron 3.0 - 1.2 10.0 72.0 - 0

Lovibond

PCM FFA% ACM Red Yellow Blue

A FRYLIGHT 2.8 4.15 3.3 9.5 73.0 0

B 1 Micron 2.8 - 3.2 8.7 70.0 0

A MAGNESOL 2.7 3.99 4.3 9.5 74.2 0

B 1 Micron 2.7 - 4.3 8.6 70.0 0

The method which was employed to conduct this evaluation included withdrawal of samples of the base oil from a five gallon polypropylene carboy. The treatment powders were applied to aliquots of well-mixed, but untreated oil which was then passed through a 1.0 micron teflon mesh using pressure from a heated hand-held large syringe.

The filter aid/treatment powders were stirred slowly into the oil to avoid the spattering or entraining of air. The oil was heated to 180* + l'C with constant slow stirring in a beaker on a hot plate, the powder added, and the oil/powder system was allowed to cool to 130^βC (5 to 10 minutes) . The oil was then gravity filtered through S&S filter paper at 80^βC in an oven (20 to 30 minutes) .

The particular values shown in Table II can be interpreted with reference to Table III below.

Table III

Test Scale Color % Polars

PCM 1 blue 0-12

2 It. blue 12-21

3 green-blue 22-27

4 green >27

Test Scale Color ppm Soao

ACM 1 yellow 0- 6

2 It. green 7-10

3 green ca. 35

4 blue ca. 65

5 purple 150 % FFA as Oleic Acid by AOCS titration method

Lovibond Color: Blue is equivalent to haze and is to be subtracted from red. The red plus the yellow corresponds to the color of the oil seen in a cell 1" deep. A light oil is red = 1.0 + yellow = 10.0. A dark oil is red = 10.0 + yellow = 70.0 in this system.

The filtration media used to clarify the oils were paper and one-micron mesh teflon disks. Particles finer than 1.0 micron in diameter did not influence color readings. Filtering through a bed of diatomaceous earth one-eighth inch in depth on paper was equivalent to the effect of filtering through a one-micron filter disk. An analysis of the results set forth above in terms of color bodies indicated that visible color bodies in the oil only constituted a small fraction in the oil to begin with, and that the various alkaline treatments did not remove most of the color body in the oil. In any event, most significantly it was established that only the LIFE product selectively decreased the ACM or surfactant content in the oil.

The following specific example of a continuous process in accordance with the present invention will further illustrate the improved results obtainable in accordance with the present invention, without limiting same.

A conveyorized, gas-fired fryer with an oil capacity of 3200 lbs. was operated at 375'F for the continuous frying of 1.5 oz. (per unit) breaded chicken patties (a fabricated food) . The oil was a heavy-duty frying oil (hydrogenated and winterized soybean oil from

Humko-Kraft) normally used at the factory. A special design of the frying system was that three large oil holding tanks were employed to hold already used, but oil having a low percentage of free fatty acids obtained from prior frying runs. When the fresh charge of oil in the fryer had degraded to about the 1% level, oil was drained into the fryer from the holding tanks to make up for oil removed from the fryer on fried food.

Two runs were carried out, one with no treatment, and one with the treatment powder (LIFE) being continuously added to an isolated stream of the fryer's recirculating oil, with the powder being removed on a continuous-roll filter in a system similar to that shown in the Figure. The results are shown in Tables IV, V and I below. a^Table IV

NO TREATMENT

Breaded Chicken § 12,000 1 1/2 oz. units/hr.

(1,125 lbs. ./hr.)

Total

Hours IUPAC IUPAC AOCS

Oil Samole Used % Polars % Polvmer % FFA

Fresh Ό 5.0 0.9 0.02

Used 3 11.7 4.8 0.88

Reheated to temp & overnite 4 15.4 6.4 0.96

Continued in use 8 16.4 8.1 2.96

Continued in use 8* 16.0 7.3 1.23

Continued in use 11 20.1 . 7.7 3.42

*Just after dilution 15.8 6.6 0.90 with holding tank Oil

WITB [ TREATMENT

Breaded Chicken § 12,000 1 1/2 oz. units/hr. (1,125 Ibs./hr.)

Total

Hours IUPAC IUPAC AOCS

Oil Sample Used % Polars % Polvmer % FFA

Fresh 0 5.0 0.9 0.02

Used 1 6.2 1.8 0.10 Reheated to temp & overnite 4 7.6 2.2 0.36 Continued in use 8 16.9 7.1 0.83 Continued in use 8* 9,7 3.3 0.57 Continued in use 11 15.4 5.0 1.95 *j_ust after dilution 6.6 1.4 0.13 with holding tank oil Table V

NO TREATMENT

1/2" Lovibond Cell Visible

Red Yellow Blue Color

0.2 0.7 0.2 It. yellow

3.2 15.0 1.6 dk. yellow

5.2 24.0 5.0 dk. yellow

11.0 60.0 14.0 dk. yellow

12.2 65.0 6.0 amber

10.0 50.0 10.1 yellow

WITH TREATMENT

1/2" Lovibond Cell Visible

Red Yellow Blue Color

0.2 0.7 0.2 It. yellow

1.0 2.4 0.8 It. yellow

4.1 10.4 4.1 yellow

2.0 7.6 0.7 yellow

4.1 21.0 1.3 yellow

Table VI % Fatty Acid Profile (FAME) of Factory Frying Oils

No Treatment:

Total Carbon #

Hours 12:0 14:0 16:0" 18:0 18:1 18.2 18:3 20:0

Fresh 0 0.07 0.13 10.92 3.42 61.64 22.61 0.09 0.11

3 0.12 0.16 11.05 3.48 61.58 22.80 0.09 0.14

4 0.14 0.15 10.57 3.56 61.61 21.59 0.38 0.51 8* 0.16 0.17 11.24 3.58 62.55 21.14 0.11 0.19 11 0.21 0.24 13.26 3.30 59.73 23.05 0.00 0.08 holding tank 0.13 0.15 10.71 3.64 60.72 21.70 0.46 0.65 With Treatment:

Total Carbon #

Hours 12:0 14:0 16:0 18:0 18:1 18.2 18:3 20:0

Fresh 0 0.07 0.13 10.92 3.42 61.64 22.61 0.09 0.11

1 0.05 0.11 9.87 5.27 59.87 22.30 0.11 0.24

4 0.05 0.12 16.75 6.91 55.83 19.37 0.00 0.11

8* 0.06 0.44 14.77 5.54 58.36 19.81 0.00 0.13

11 0.11 0.19 15.05 5.46 58.45 19.69 0.04 0.13 holding tank 0.07 0.11 10.12 5.06 59.21 23.38 0.00 0.16

As shown in Tables IV and V, use of the method of the present invention, even after accounting for slight differences in make-up oils used, resulted in a reduction in the build-up in total polar materials in the oil as well as polymer, color and free fatty acid sub¬ components of the total polar materials present therein. It was thus observed that, on a general basis, the overall use of the process of the present invention resulted in the ability to reduce the use of oil from about 0.071 lbs. of oil per unit of product down to about one-half that value or about 0.035 lbs. of oil per unit of product. Furthermore, Table VI shows an analysis of the methyl esters of the fatty acids in the two runs carried out herewith. It has therefore been observed that by employing the method of the present invention it is now not only possible to improve the quality of the fats and oils used, and to lengthen their life, but the results obtained demonstrate a reduced tendency for the oil to soak into the frying food products, which in turn causes these products to lose less water, demonstrate reduced rates at which polymers form in the oil, demonstrate reduced rates of hydrolysis to fatty acids, demonstrate reduced rates of conversions of fatty acids to oxidized and other degradation products, and show an overall reduced rate of accumulation of total polar materials in the oil. Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. Industrial Applicability

The method of the present invention is useful for carrying out commercial continuous food frying processes over extended periods of time.

Claims

1. A method for controlling the quality of a cooking fluid used in a food frying process in which degradation products including surfactants are produced during said frying process which comprises continuously recirculating said cooking fluid through a cooking zone and a recirculation zone, and continuously treating said recirculating cooking fluid with a treatment compound so as to selectively reduce said surfactants in said cooking fluid below the level of said surfactants normally produced during said frying process whereby the useful life of said cooking fluid is substantially increased.

2. The method of claim 1 wherein said treatment compound is capable of selectively sorbing said surfactants thereonto.

3. The method of claim 2 wherein said treatment compound comprises a treatment powder.

4. The method of claim 3 wherein said step of continuously treating said recirculating cooking fluid comprises contacting said treatment powder with said cooking fluid for a predetermined period of time.

5. The method of claim 4 wherein said predetermined period of time is less than about two minutes.

6. The method of claim 2 including passing said oil through a filtering medium, and including applying said treatment powder to said filtering medium, and removing said filtering medium with said treatment powder thereon from said oil.

7. The method of claim 1 wherein said treatment powder comprises a porous rhyolitic material.

8. The method of claim 1 wherein said porous rhyolitic material includes between about 33 and about 75 wt. % water.

9. The method of claim 7 wherein said treatment powder includes a food-compatible acid.

10. The method of claim 8 wherein said food- compatible acid comprises citric acid.

11. The method of claim 1 wherein said continuous treatment of said recirculating cooking fluid takes place in said recirculation zone.

12. The method of claim 1 wherein said cooking fluid comprises an oil.

13. The method of claim 12 wherein said oil comprises a triglyceride.

14. The method of claim 1 wherein said treatment compound is capable of selectively reducing the content of said surfactants in said cooking fluid as reflected by the presence of ACM's therein to below about 2.4.

15. The method of claim 1 wherein said treatment compound is capable of selectively reducing the content of said surfactants in said cooking fluid as reflected by the presence of ACM's therein to below about 1.3.