Patent Application
20050153022
This application claims the benefit of priority under 35 U.S.C. § 119 of German Application DE 10 2004 001 525.2 filed Jan. 10, 2004, the entire contents of which are incorporated herein by reference.
The present invention pertains to a process for deep-flying material to be deep-fried in a heat transfer fluid, especially fat. Furthermore, the present invention pertains to a device for deep-frying material to be deep-fried in a heat transfer fluid, especially fat, which can be heated by means of a heating means, is recycled by means of a pump, and is brought into contact with the material to be deep-fried in a deep-flying container.
Cooking foods to make the raw products contained in them fit for consumption and/or more tasty belongs to the cultural techniques acquired by mankind a long time ago. Besides hygienic and organoleptic reasons, nutrition physiological aspects, such as the denaturing of protein or the swelling of starch, play a role as well. Baking or deep-frying with fat in a pan or deep fryer improves the taste of foods. In addition, both cooking methods enjoy particular popularity because of their rapidity.
The deep-frying process is currently carried out, as a rule, with the use of conventional dipping type deep fryers, in which case a small quantity of material to be deep-fried is immersed into a relatively large quantity of deep-frying fat and is thus deep-fried. The quantity ratios are due, on the one hand, to the circumstance that a lowering of the temperature of the fat during the introduction of the material to be deep-fried shall be prevented from occurring as much as possible for rapid and uniform cooking, and, on the other hand, it shall be possible to carry out a continuous deep-frying process. As an improvement, continuously operating deep fryers are known, for example, from WO 01/21051 A1. In such deep fryers, deep-frying fat is heated in a fat reservoir, and a quantity of deep-frying fat, which is small compared to the quantity of the material to be deep-fried, is subsequently introduced into a deep-frying container. The deep-frying fat introduced is heated further extremely rapidly but in such a way that its quality is prevented from deteriorating in a separate heating zone with a large contact surface, and is returned into the reservoir via an overflow after the end of the deep-frying operation. Deep-frying fat is absorbed by the material to be deep-fried during the deep-frying operation, so that the loss must be compensated by adding fresh deep-frying fat as needed.
A large number of scientific studies have recently demonstrated that acrylamide, which is currently classified as hazardous to health for the human body because this substance is considered to be a possible carcinogen, is formed during any kind of deep-frying process. It was, furthermore, shown that the formation of acrylamide is affected mainly by the material composition of the material to be deep-fried, the deep-frying temperature during the deep-frying process, the deep-frying time as well as the quality of the deep-frying fat. In addition, it is considered to be a scientifically proven fact that the formation of acrylamide during deep-flying can be reduced by lowering the deep-frying temperature, selecting the shortest possible deep-frying time and by modifying the composition of the deep-frying fats used.
The above-mentioned factors can be affected only to an insufficient extent at best in the prior-art deep-frying processes and devices, so that such processes are associated with an increased risk for damage to health due to acrylamide during the consumption of foods prepared in this manner.
The basic object of the present invention is to improve a process and a device of the type described in the introduction such that the acrylamide content in the deep-fried product can be kept as low as possible.
The object is accomplished in a process of the type described in the introduction by the material to be deep-fried being cooked at successively decreasing temperature of the heat transfer fluid.
To accomplish the object, provisions are made in a device of the type described in the introduction that a series of deep-frying chambers with different temperatures of the heat transfer fluid is provided for cooking the material to be deep-fried.
The deep-frying temperatures and residence times of the material to be deep-fried in the heat transfer fluid, especially fat, can thus be controlled according to the present invention in a simple, flexible and reliable manner, so that a considerable reduction of the acrylamide content in the cooked food can be achieved.
According to a preferred variant of the process according to the present invention, provisions are made for the temperature to be ≧170° C. and preferably 185° C. at the beginning of the cooking operation. Improved crust formation of pores is obtained on the surface of the material to be deep-fried due to an increased temperature at the beginning of the deep-frying operation, which leads to reduced evaporation of the moisture contained in the material to be deep-fried. This is especially advantageous concerning the formation of acrylamide, because scientific studies prove that an increased moisture content in the food is associated with an improved tendency towards the formation of acrylamide.
In addition, provisions are made in a variant of the process according to the present invention for the temperature to be <170° C. at the end of the cooking operation. According to scientific studies, a temperature of 170° C. can be considered to be a critical temperature concerning the formation of acrylamide, especially during the preparation of potatoes by deep-frying (French fries). Cooking at temperatures below this critical temperature of 170° C. ensures a further reduction of the acrylamide content.
Provisions may, furthermore, be made according to the present invention for the material to be deep-fried to pass consecutively through a number of deep-frying chambers, beginning from the first deep-frying chamber, in which chambers the heat transfer fluid has a reduced temperature compared to the particular preceding deep-frying chamber. A deep-frying temperature decreasing over time can thus be obtained in a simple manner.
The heat transfer fluid is advantageously recycled according to the present invention by a pumping means, and it is preferably heated by a heating means and subsequently fed into a first deep-frying chamber. In a preferred variant of the process according to the present invention, the heat transfer fluid is heated as a function of parameters of the material to be deep-fried present in the deep-frying chambers, especially the weight and/or the moisture content of the material to be deep-fried in the first deep-frying chamber. The temperature of the heat transfer fluid decreases when the material to be deep-fried is introduced into it mainly because of the weight and the moisture content (percentage of water) in the material to be deep-fried, because a certain quantity of heat is needed to heat the material to be deep-fried and especially to evaporate moisture (water) present in the material to be deep-fried. To make it possible to cook the material to be deep-fried in such a way that the cooking is essentially harmless for health, provisions are consequently made in the course of a preferred improvement of the process according to the present invention for the heating of the heat transfer fluid to take place such that the temperature of the heat transfer fluid is essentially 170° C. or lower in the deep-frying chambers following the first deep-frying chamber.
Since, as was already mentioned, the quality of the heat transfer fluid is also decisive for the formation or the lack of formation of acrylamide during the deep-frying process, provisions may, furthermore, be made according to the present invention for the heat transfer fluid to be filtered after it has flown through the deep-frying chambers. Furthermore, quality features of the heat transfer fluid, such as the radiation absorption behavior, viscosity and the like, may also be subjected to continuous monitoring by means of sensors, in which case the process according to the present invention is continued, the heat transfer fluid is fully or partially replaced, additives are added to the heat transfer fluid, or the process is interrupted, preferably as a function of the measured values supplied by the sensors. It can thus be ensured that the cooking operation is not carried out or continued at any time with heat transfer fluid of an inferior quality, so that the formation of acrylamide can be effectively reduced in this way as well.
In an improvement of the device according to the present invention, provisions are made for the deep-frying chambers to be arranged in a series one after another, so that the material to be deep-fried can be transferred from a deep-frying chamber into an adjacent deep-frying chamber in which the temperature of the heat transfer fluid is lower. The cooking proposed in the course of a process according to the present invention at consecutively decreasing temperatures can thus be carried out technically with a simple design.
The deep-frying chambers are expediently formed by receiving means for the material to be deep-fried. The receiving means may have a basket-like design and preferably have at least one wall that is essentially impermeable for the flow of the heat transfer fluid. Provisions may also be made in addition or as an alternative for the wall that is essentially impermeable to the flow of the heat transfer fluid to be arranged in the deep-frying container. The flow of the heat transfer fluid can be affected by means of the impermeable walls and/or partitions such that the material to be deep-fried is brought optimally into contact with the heat transfer fluid in each deep-frying chamber and the heat transfer fluid preferably flows through it in order to achieve an acceleration of the cooking process and, associated with this, a reduction in the formation of acrylamide.
Provisions are made in an extremely preferred variant of the device according to the present invention for the receiving means to be mounted tiltably for transferring the material to be deep-fried, in which case especially a rotatable mounting around an axis is provided for the tilting. The material to be deep-fried is correspondingly transferred from one deep-frying chamber into the next one in a simple manner by tilting the receiving means, which may be performed manually or automatically.
The deep-frying container of a device according to the present invention may have an inlet [for the heat transfer fluid] in the area of the first deep-frying chamber and an outlet for the heat transfer fluid in the area of the last deep-frying chamber. In addition, a temperature sensor may be provided at least in the inlet area of the deep-frying container, so that the inlet temperature of the heat transfer fluid can be regulated as a function of at least one measured signal of the temperature sensor. It is ensured in this manner that the temperature profile of about 185° C. decreasing to a value of ≦170° C., as was outlined above, can be obtained in the deep-frying container, i.e., in the individual deep-frying chambers, at any time.
In a variant, the device according to the present invention may have an additional heating means for the fine regulation of the inlet temperature. As an alternative or in addition, the same purpose is served by a mixing device for mixing quantities of the heat transfer fluid with different temperatures before the heat transfer fluid flows into the deep-frying container.
To make it possible to completely remove the heat transfer fluid from the deep-frying container, for example, for cleaning purposes, a device according to the present invention has, according to another embodiment, a reservoir for the heat transfer fluid from the deep-frying container. To determine quality features of the heat transfer fluid, such as the radiation absorption behavior, viscosity or the like, a sensor means may be arranged in the reservoir. Furthermore, a device according to the present invention preferably has a filter means for the heat transfer fluid to preserve the quality of the heat transfer fluid by removing suspended matter. Feed means for replacement heat transfer fluid and/or additives, which have a container for the medium to be fed as well as a pumping means in the preferred embodiment, may also be present for the same reason.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.
Other properties and advantages of the present invention will appear from the following description of exemplary embodiments on the basis of the drawings. In the drawings,
Referring to the drawings in particular,
The device 1 according to the present invention has, first, a deep-frying container 3, which is filled with a heat transfer fluid 4, here deep-frying fat, for cooking the material to be deep-fried 2. The filling level of the deep-frying container 3 is marked by a broken (level) line P. The deep-frying container 3 has an inlet 3.1 and an outlet 3.2 for the heat transfer fluid 4, which is circulated (arrow R) through the deep-frying container 3 by means of an oil pump 5 in the area of the outlet 3.2. Temperature sensors S1, S2 for determining the temperature θI, θO of the heat transfer fluid 4, which are connected with a control means 6 of the device 1 via lines indicated by broken lines, are arranged in the inlet area 3.1 and in the outlet area 3.2 of the deep-frying container 3.
A heating chamber 3.3, through which the heat transfer fluid 4 can likewise flow and which is separated from the deep-frying container proper by a bulkhead partition 3.3a, is located upstream of the inlet 3.1 of the deep-frying container 3, and a heating means 7 for the heat transfer fluid 4, here a tubular heating element, which may have a series of PCT resistor heating elements (not shown), for example, within a jacket tube, is arranged in the heating chamber 3.3. Furthermore, an additional temperature sensor S3 for determining the temperature of the heat transfer fluid 4, which said sensor is likewise in functional connection with the control means 6 (broken line), is arranged in the heating chamber 3.3.
Moreover, according to
As was explicitly shown for the sensors S1-S4, all other components of the device according to the present invention, which can be actuated mechanically and/or electrically, i.e., the pump 5, the tubular heating element 7, the pumping means 9.2, 9.2′ as well as the drain means 10 are in connection with the control means 6 of the device 1 according to the present invention via corresponding connections, but this is not shown in
A series of deep-frying chambers K1-K4 are formed within the deep-frying container 3 of the device 1 according to the present invention. In general, a number n of deep-frying chambers Kn may be provided. A number of vertical partitions 3.4a, 3.4b, 3.4c, whose vertical extension h ends below a level P of the heat transfer fluid 4 in the deep-frying container 3, are provided within the deep-frying container 3 to create the deep-frying chambers K1-K4. Receiving means 11, 11′, 11″, 11(3) in the form of deep-frying baskets are arranged in the deep-frying chambers K1-K4. The deep-frying baskets have a cross section of an essentially circular segment-shaped form, which corresponds especially to a square in the exemplary embodiment being shown. The deep-frying baskets 11-11(3) are made essentially permeable to the heat transfer fluid 4, as it is suggested by the broken limiting lines of the deep-frying baskets and the arrows S, which latter indicate the direction of flow of the heat transfer fluid 4 within the deep-frying chambers K1-K4 and hence through the deep-frying baskets 11-11(3) and the material to be deep-fried 2. In their lower area, which is the rear area in relation to the flow S, the receiving means 11-11(3) have a wall 11.1, 11.1′, 11.1″, 11.1(3), which is essentially impermeable to the heat transfer fluid 4 and ensures, together with the partitions 3.4a-c already described, a defined flow S in the deep-frying chambers K1-K4. It becomes clear from the graphic representation that the flow behavior S shown can also be achieved alternatively in a similar manner without the partitions 3.4a-c, so that these may be eliminated in the course of an alternative embodiment of the device 1 according to the present invention, in which case their task is assumed solely by the impermeable wall 11.1-11.1(3) of the deep-frying baskets.
The receiving means 11-11(3) can be pivoted or tilted in their rear, upper area about an axis A extending in parallel to the surface O of the heat transfer fluid 4 in the deep-frying container 3 essentially in the direction of the flow loop S; for reasons of clarity, the axis A is shown explicitly for the receiving means 11′ in the deep-frying chamber K2 only, but an identical axis is also present in each of the other deep-frying chambers K1, K3, K4. Any drive means as may be present (not shown) for tilting the receiving means 11-11(3) around the axes A are likewise connected with the control means 6 of the device 1 and can thus be controlled by same.
A direction of extension of the deep-frying container 3 is designated by “x” in
The deep-frying process according to the present invention takes place as follows with the use of the deep-frying device shown in
The temperature of the deep-frying fat decreases continuously in the direction of extension x of the deep-frying container 3 from one chamber to the next because of heat losses to the material to be deep-fried 2 and the environment (due to radiation, convection and heat conduction), i.e., the temperature of the deep-frying fat is higher in chamber K2 than the temperature of the deep-frying fat in the deep-frying chamber K3, which in turn is higher than the temperature in the deep-frying chamber K4 (Kn), which is <170° C. according to the present invention. By pivoting the deep-frying baskets 11-11(3) around their respective axis A—either manually or in an automated manner via drive means and control—and by tilting the material to be deep-fried 2 farther into the respective subsequent receiving means 11′-11(3), which is brought about as a result, the cooking process is thus continued according to the present invention with consecutively decreasing deep-frying temperature. This is detected continuously by means of the temperature sensors S1-S3 and adjusted by controlling the heating output of the tubular heating element 7 such that the increased inlet temperature will prevail within the first deep-frying chamber K1 and a final temperature of <170° C. will prevail in the last deep-frying chamber K4 (Kn). The energy supply is correspondingly regulated by heating as a function of the temperature gradient of the deep-frying fat in the deep-frying container 3 and the quantity of material to be deep-fried 2 introduced. In addition, the energy supply can also be additionally affected by a suitable regulation of the velocity of flow of the heat transfer fluid 4 by correspondingly actuating the pump 5.
The transfer of the material to be deep-fried from one chamber to the next by tilting the baskets is also advantageous especially in case of relatively soft material to be deep-fried because the material to be deep-fried will thus not stick. By contrast, continuous delivery, which is not shown here explicitly, is also possible in case of relatively solid materials to be deep-fried.
The temperature profile in the deep-frying container 3, which was characterized above, is shown in
The great reduction of the deep-frying temperature in chamber K1 is explained above all by the loss of moisture from the material to be deep-fried due to the evaporation of water during heating. This fact shall be illustrated below by a calculation example:
After inserting the numerical values indicated, an energy demand of E=145.7 kJ is obtained, of which 113 kJ account for the energy of evaporation Ev=mW′·ev alone, so that the energy demand is determined especially by the evaporation of the water contained in the material to be deep-fried.
The energy E calculated above is extracted from the heat transfer fluid in the process according to the present invention and in the device according to the present invention, which leads to a reduction of the temperature of the heat transfer fluid depending on the weight of the heat transfer fluid. With cF1=1.67 J/(g·K) for the specific heat capacity of the fluid and according to what was stated above,
Δθ=E/(cF1·mF1),
so that a 1/mF1 dependence of the temperature reduction Δθ on the weight of the fluid present is obtained. The reduction Δθ of the temperature of the deep-frying fat delays the cooking process and leads to the increased formation of acrylamide, and the energy E removed is therefore steadily compensated by the heat supply regulated according to the present invention. According to the view in
As a general rule, the amount of energy must be supplied within a defined period of time as a function of the energy demand in order to optimize the cooking process.
If, as in the above calculation example, 146 kJ are needed to evaporate the moisture contained in 160 g of material to be deep-fried, it may, furthermore, be assumed that up to 75% of the water will have already evaporated after 30-50 sec, depending on the nature of the material to be deep-fried, and 75% of the rest of the energy demand (110 kJ) is also needed.
The following equation is obtained at a hypothetical temperature difference of Δθ=185° C.−170° C.=15° C. (corresponding to 15 K):
It follows from this that at least 4.4 kg of deep-frying fat with 185° C. must be fed in in 30 sec in order to prevent the deep-frying temperature from dropping, on average, below 170° C.
The necessary energy of 146 kJ is available over the entire cooking time at a temperature difference of Δθ=15° C. in a deep-frying amount of deep-frying fat of about 6 kg. Consequently, about 6 kg of deep-frying fat with 185° C. are added within 30 sec in case of continuous production to guarantee the deep-frying temperature of 170° C. at the end of the process. The hypothetical cooking time is about 120 sec; if a plurality of portions are being cooked simultaneously, the energy demand per unit of time increases correspondingly. A change in the parameter Δθ affects the necessary deep-frying amount of deep-frying fat per time.
In general, it can be stated that the amount of energy needed for deep-frying per g of material to be deep-fried is about 0.9 kJ, which corresponds to about 0.036 kg of deep-frying oil with Δθ=15° C. in case of a material to be deep-fried, containing
The deep-frying temperature in chamber K1 decreases in the manner outlined in
To evaluate the quality of the deep-frying fat, parameters of the deep-frying fat, which are determined by means of the sensor S4 shown in
The necessary data are sent by the sensor S4 and transmitted to the control means 6 of the device 1. Via control connections, not shown, the device can subsequently actuate either the pumping means 9.2, 9.2′ for feeding additives or fresh fat, or initiate the complete replacement of the heat transfer fluid 4 by actuating the drain means 10. To interrupt the deep-frying operation, the circulating pump 5 can be stopped and the tubular heating element 7 can be switched off by means of suitable control signals of the control means 6.
In functional connection with the axes A of the receiving means 11-11(3), the device according to the present invention may have, as was said, suitable drive means, not shown, for the automatic tilting of the receiving means, which can preferably also be actuated via the control means 6 according to a predetermined flow chart, so that the deep-frying operation according to the present invention can take place possibly independently from a human operator operating the device. The suitable additives include, in principle, all the additives known to the person skilled in the art especially for improving the heat transfer to the material to be deep-fried or as stabilizers, for example, citric acid, ascorbic acid, curcuma oil, rosemary oil and emulsifying agents. However, the use of silicone (E900) is preferably deliberately avoided in light of the acrylamide problem mentioned.
Instead of the heating chamber 3.3 (
The heat transfer fluid 4 is heated on its way in the direction of an inlet 3.1 of the deep-frying container 3 by means of a heating means 7 which is arranged along a fluid line 13 and optionally surrounds same. The heating means 7 is complemented by another heating means 7′ in the immediate vicinity of the inlet 3.1, which acts as a dynamic heater and thus makes possible the more accurate (fine) metering of the thermal energy being fed.
As was already indicated in
The subject of
As in
By positioning the smallest possible quantity of material to be deep-fried (portion sizes of approx. 100-200 g; cf. the above calculation example), it is guaranteed according to the present invention that the deep-frying fat, which is caused to flow, can flow better through the material to be deep-fried than in prior-art conventional deep-frying processes, in which relatively large quantities of material to be deep-fried are deep-fried during a cooking operation. By introducing only a small quantity of material to be deep-fried of a certain temperature into heated deep-frying fat of a different, higher temperature, the cooling Δθ of the deep-frying fat decreases because of the relationships explained in detail above, which are also described by a formula. Together with the elevated inlet temperature θ1 proposed for the deep-frying fat, this leads to better crust formation of the pores on the surface of the material to be deep-fried at the beginning of the deep-frying operation compared to conventional deep-frying processes. As a result, the diffusion of fat molecules into the core area of the material to be deep-fried will subsequently decrease, so that the material to be deep-fried will have, as a result, a correspondingly lower percentage of fat. What is decisive here is not the absolute weight of the material to be deep-fried but the amount of energy needed to heat the material to be deep-fried. If the material to be deep-fried has a high water content and especially a relatively large surface compared to its volume (e.g., cut material to be deep-fried), energy is removed from the deep-frying fat very rapidly, especially at the beginning of the deep-frying operation, and correspondingly smaller quantities are to be introduced. However, if the material to be deep-fried is in the form of complete pieces, e.g., chicken legs or pastry products with a relatively high percentage of water, the energy demand for heating will be distributed over a relatively long period of time and/or it is, on the whole, not so high, so that it is also possible to introduce larger quantities.
Moreover, a reduction of the overall deep-frying time is achieved due to the rapid and uniform heating of the material to be deep-fried, which is achieved according to the present invention. As a result and especially also because of the temperature profile provided according to the present invention, the formation of acrylamide, which is undesirable because it is hazardous to health, is reduced to a basically unavoidable minimum.
While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 001 525.2 | Jan 2004 | DE | national |
