Patent Application
20170285597
The present invention relates to a method for controlling the cooking process in ovens for food use.
The invention is particularly, but not exclusively, relevant to the technical field of methods for controlling the cooking processes in ovens for food use, where the cooking processes take place in convection ovens or combined (air and steam) ovens.
One of the problems encountered in this field is that of providing the best possible uniformity of cooking. In these ovens, the concept of uniformity of cooking is related to various aspects concerned with the size of pieces of food to be cooked and their distribution in the cooking chamber. A certain number of baking trays containing food may be placed in an oven of this type, and a plurality of pieces of food for cooking may be placed in each baking tray. An example of this is seen in ovens for pastry products, in the baking of sweet pastries placed in a certain number on a plurality of baking trays housed simultaneously in the cooking chamber of the oven.
With reference to this example, assuming that the same type of food, characterized by the same shape, weight, composition (percentage of water, sugars, fats, protein, etc.), structure and surface appearance (also denoted by the term “texture”) is to be cooked, and if these pieces of food are placed in the same number and arrangement in each baking tray, two kinds of non-uniformity of cooking may occur.
A first kind of non-uniformity is the non-uniformity of cooking between one baking tray and another, and depends primarily on the geometry of the oven, the distribution of the air speeds in the vertical direction (from the lowest to the highest part of the cooking chamber), and the position and geometry of the heating elements. The problems of this kind of non-uniformity are not expressly tackled by the present invention.
However, a second type of non-uniformity concerns a specific baking tray placed at a specific point in the cooking chamber. In the following text, therefore, the expression “uniformity of cooking” of food is considered to relate to a specific baking tray placed at a specific level in the oven, and to a specific batch of food characterized by the same quality, shape, weight, composition and arrangement.
On this basis, the degree of uniformity of cooking is difficult to evaluate by objective methods, because it depends on the color, the surface structure (texture), and the organoleptic characteristics of each individual piece of food on the baking tray in question. Typically, after the definition of the food and a standard cooking program, the evaluation is carried out by a number of persons, on the basis of a sensory analysis or, more simply, the color and shape of the cooked food. This evaluation may be made more objective by awarding grades which may, for example, relate to an evaluation scale (providing an evaluation assessment from 1 to 10, for example).
In all cases, however, the non-uniformity of cooking among pieces of food on the same baking tray depends on:
The temperature (surface and internal) of the food depends on its initial temperature and on conditions b) and c), and obviously varies over time.
The speed of the air and/or steam depends on the geometry of the oven, the type of fan, its rotation speed and the number and position of baking trays in the oven. Clearly, it also depends on the point on the baking tray that is examined, since the position and shape of the food on the baking tray have a substantial effect on the fluid dynamics at different points. In the following text, reference will always be made to a given fan or fan system (there may be a plurality of fans), a given geometry (of the cooking chamber, the baking tray supports, the casing, etc.) and a specified arrangement of the food on the baking tray, so that the only remaining variable is the number of baking trays. Evidently, if there is a change in the number of baking trays and their position in the oven, there is also a change in the fluid dynamics of the air and steam, and consequently in the speed affecting the food at individual points on the baking tray.
The temperature of the air and/or steam also depends greatly on the point on the baking tray that is examined. Indeed, if cooking takes place at a specified temperature (180° C., for example), it is necessary to consider where this temperature is measured, and kept as constant as possible, by the oven control system. In most cases, the temperature is measured near the wall of the cooking chamber, in a delivery area of the oven fan. Consequently, the air coming into contact with the food, which comes from outside the baking tray, is at a temperature practically equal to the specified temperature (also called the set point temperature, equal to 180° C. in this example). As the air enters the baking tray and exchanges heat with the food, it is cooled. It will be readily understood that the air leaving the baking tray near the intake area of the fan may be at a much lower temperature than the set point (as much as 20° C. lower, for example).
Usually, at the start of the cooking process, if the set point temperature (Tset) is kept constant, it is found that the temperature difference (DT) between the average temperature (Tin) of the air and/or steam entering the baking tray (typically from three sides, that is to say from the opposite lateral walls and from the front) and the mean temperature (Tout) at the exit from the baking tray (typically from the said nearest to the fan) is much greater than the temperature difference found at the end of cooking. This phenomenon causes the pieces of food positioned at the edges of the baking tray to be contacted by hotter air and/or steam than the pieces located in the center of the baking tray and/or near the fan intake, resulting in non-uniformity of cooking.
It should also be noted that, in most cases, ovens are pre-heated to a temperature higher than Tset so that, when the batch of food is placed in the oven, the resulting temperature decrease is not too great, enabling the oven to regain its temperature rapidly, thereby ensuring that the temperature of the air entering the baking tray (Tin) is practically equal to Tset. Thus the phenomenon described above, which leads to non-uniformity of cooking, is strengthened.
A principal object of the present invention is to provide a method for controlling the cooking process in ovens for food use, designed to overcome the drawbacks of the cited prior art, and intended, in particular, to reduce the non-uniformity of cooking.
This and other objects, which will be more fully apparent from the following text, are achieved by the invention by means of a method for controlling the cooking process, devised in accordance with the appended claims.
Other features and advantages of the invention will become clearer from the following detailed description of a preferred exemplary embodiment thereof, illustrated, for guidance and in a non-limiting way, with reference to the attached drawings, in which:
With reference to the aforementioned figures, the method according to the invention is designed to control the cooking process in an oven for food use, having a conventional structure, designed for cooking food according to a predetermined cooking program. The oven is designed to receive at least one baking tray in the cooking chamber, on which tray the food is arranged with a predetermined quality, quantity, piece size and distribution.
Cooking ovens suitable for the use of the method according to the invention may be convection (air) ovens or combined (air and steam) ovens, which can cook food in baking trays, the number of which may vary from 1 to n.
Supports 7 are provided inside the cooking area of the chamber 2, on each of the opposite lateral walls 2b, 2c of the chamber, and are designed to support a plurality of baking trays 8 to contain the food to be cooked. The baking trays 8 may be accommodated in the chamber by being stacked vertically one above the other, while being spaced apart.
In the following text, it is assumed that the described method is applied with reference to a specific baking tray (tray 8 in the example), placed at a specific level in the oven, and to a specific batch of food characterized by the same quality, shape, weight, composition, piece size and arrangement. The number 10 indicates the pieces of food, shown schematically, arranged on the baking tray 8.
In the aforesaid conditions the invention aims to reduce as far as possible the degree of non-uniformity of cooking among the pieces of food 10 subjected to a predetermined cooking program.
According to the method, a first temperature sensor 11 is provided, and is placed inside the cooking chamber 2 in the delivery area of the fan 4 (being supported on one of the lateral walls 2b, 2c of the chamber, for example). Said sensor 11 is then provided to measure the temperature of the air (Tin) which comes into contact with the food from outside the baking tray 8, and which is then directed towards the intake area of the fan, as shown in
Also, according to the method, at least a second temperature sensor, indicated by 12, is provided, this sensor being placed in the intake area (indicated by 9 in the drawings) of the fan, for example by fastening it to the casing 6, and being used to measure the temperature (Tout) of the air leaving the baking tray 8 near the intake area of the fan 4, after it has exchanged heat with the food placed in the baking tray.
For cooking the food, provision is made for the preliminary identification of a cooking program which can define the way in which the temperature value indicated by Tset (also called the set point temperature) is to vary with time. The symbol tset denotes the cooking time, that is to say the period of time between the initial instant (t=0) and the final instant (t=tset) at the end of cooking.
To simplify the description, the curve of variation of the temperature Tset (shown in solid lines and indicated by C in
Assuming that the air coming from outside the baking tray 8 and striking the pieces of food 10 is at a temperature substantially equal to the specified set point (T=Tset), the air tends to be cooled as it enters the baking tray and exchanges heat with the food. Clearly, the air leaving the baking tray near the intake area of the fan is then at a much lower temperature than the temperature Tset. In most cases, at the start of the cooking process, if the set point (Tset) is kept constant, it is found that the temperature difference DT between the temperature Tin of the air and/or steam entering the baking tray (typically from three sides; see
The aim of the method according to the invention is to keep the temperature difference DT between suitable optimal values from the start to the end of cooking.
For this purpose, the method provides for the calculation of the difference DT between the values of the temperatures Tin and Tout measured by the sensors 11, 12, by subtracting the value of said temperature Tout at the intake from the temperature value Tin in the delivery area:
DT=Tin−Tout
On the basis of the calculated difference DT, the method provides for the setting of a predetermined difference DT′ between the temperatures which is less than the calculated temperature difference DT, but is such that it does not cause an increase in the cooking time tset beyond a predetermined percentage of the cooking time in order to complete the cooking process. Accordingly, the heating means and the fan 4 are controlled by the oven control unit during the cooking stage in such a way that the temperature difference in the cooking chamber is kept substantially constant and equal to the predetermined value DT′ during the cooking time tset.
In fact, the temperature difference DT cannot be reduced at will, since a decrease in this difference usually increases the cooking time; a condition of compromise (optimization) is therefore established, between a small difference DT (corresponding to high uniformity of cooking) and an acceptable cooking time. Tests conducted by the applicant have shown that, for a large number of foods, an increase in cooking time up to 100% may be readily accepted, if it is accompanied by a consistent increase in the uniformity of cooking.
As regards the identification of the temperature difference DT′ (DT′<DT), this difference is preferably selected to be within the range between DT−1° C. and DT=3° C., if DT−1° C.>1° C., or DT=2° C. for values of DT−1° C. less than or equal to 1° C., the temperature difference (DT) being calculated in the initial stages of the cooking process on the basis of the temperatures (Tin, Tout) measured by the respective sensors 11, 12 in the cooking chamber.
The correct measurement of the temperature Tout at the fan intake may prove to be rather difficult, since the temperature may be very different in different areas of the intake section, since at some points the air will have passed through the baking tray, thereby being considerably cooled and therefore showing a large difference DT, while at other points the air temperature will be only slightly below the temperature Tin, thus exhibiting a small difference DT. According to the invention, this problem is overcome by providing for the use of a plurality of temperature sensors in the intake area of the fan, and preferably by using the highest value of the calculated difference DT. If this choice is made, the phenomenon of non-uniformity of cooking can be controlled more effectively.
In a preferred example, provision is made to arrange the sensors 12 of the plurality of sensors in the intake area in alignment with each other and spaced apart along a vertical direction (which intersects the horizontal direction of the axis of rotation of the fan). This is because the aforesaid phenomenon is most strongly influenced in this vertical direction.
To measure the temperature in the intake area of the fan 4, provision may also be made, as an alternative to the preceding example, for the use of a multipoint core sensor which is typically provided with a plurality of temperature measurement points. The multipoint core sensor may therefore be conveniently used for this type of cooking in which it is desirable to improve the uniformity of cooking by operating with small temperature differences DT.
On the other hand,
Another advantage that may be obtained with this method is that it has an effect both on the energy used for cooking and on the cooking times, and also that pre-heating may be eliminated and cooking may be started even if the oven is at ambient temperature, or in any case is at a temperature of less than Tset. This is because, if the cooking is governed by the difference DT, the oven will start to cook at low values of the temperature Tin to keep DT at the predetermined value. The temperature Tin will then increase with the passage of time until it reaches the value of Tset at a time which may be either more or less than the time tset (
Purely by way of example, to indicate an order of magnitude of the parameters present in the application of the method according to the invention, assuming that, for a given food, the corresponding cooking program provides for a temperature Tset of 180° C., and, assuming that the difference DT, calculated on the basis of the values Tin and Tout measured by the sensors, is equal to 20° C. at the start of the cooking process, it is likely that the value of the difference DT′ will be set, for example, at 10° C. The heating and fan means are therefore controlled by the oven control system with the aim of keeping the temperature difference in the cooking chamber equal to the value of the difference DT′ (for example by modulating the thermal power supplied by the oven). The difference DT in the cooking chamber is calculated on the basis of the temperature measurements made by the sensors 11, 12 with a certain measurement frequency, for example with measurements made every 0.5 second.
Any increase in cooking time (beyond tset), required because the oven is operating with a lower temperature difference DT and therefore with a lower average temperature of the air and/or steam, is then selected to complete the cooking process. This increase is then correlated with the set temperature difference DT′, and may vary according to the type of food being cooked. Usually, an increase in cooking time limited to not more than 100% of the cooking time tset is reasonably acceptable, given the improved uniformity of cooking achieved. Indeed, there are some industries, such as the bakery industry, where uniformity of cooking may be much more important than cooking time. The increase in cooking time may then be pre-selected on the basis of preferred values found experimentally and correlated both with the type of food and with the temperature differences used. In a first exemplary embodiment, the increase in cooking time may then be selected and set manually by the operator.
Alternatively, the increase in cooking time may be identified and set by an automatic system, being for example calculated by correction methods implemented in the control logic of the oven, for example of the type described in the co-pending Italian patent application no. 102015000015162 in the name of the present applicant, the description of which is considered to be entirely incorporated herein by reference within the limits of the purpose of the present invention.
Thus the invention achieves the proposed objects while achieving the stated advantages by comparison with the cited known solutions.
A principal advantage of the method according to the invention is that it improves and increases the uniformity of the cooking process (for a plurality of pieces of food contained in the same baking tray), by correcting the temperature profile in the cooking chamber and the actual cooking time for a pre-selected cooking program, on the basis of the difference between the temperatures measured by respective sensors at the entry to and the exit from the baking tray during the cooking process.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102016000034750 | Apr 2016 | IT | national |
