WO2016038039A1

WO2016038039A1 - Controlling a cooking process of food

Info

Publication number: WO2016038039A1
Application number: PCT/EP2015/070502
Authority: WO
Inventors: Wei Li; Bin Yin; Mo Li; George LUO
Original assignee: Koninklijke Philips N.V.
Priority date: 2014-09-11
Filing date: 2015-09-08
Publication date: 2016-03-17

Abstract

The embodiments of the present invention are related to cooking control process. A method for controlling a cooking process of food is disclosed. The method comprises steps of obtaining a protein status in the food in the course of heating the food; determining a doneness level of the food at least partially based on the protein status; and controlling the cooking process of the food at least partially based on the determined doneness level. Corresponding apparatus is also disclosed.

Description

CONTROLLING A COOKING PROCESS OF FOOD

FIELD OF THE INVENTION

The present technology relates to the field of cooking control, particularly to a method for controlling a cooking process of food at least based on detecting the doneness level of the food. The technology also relates to an apparatus, a cooking device and a computer readable storage medium for performing the method.

BACKGROUND OF THE INVENTION

Currently, home cooking control either relies on manual control by the user during cooking or preset parameters input by the user before cooking, such as food type, cooking time, temperature, etc. In the first case, mistakes of user may 'destroy' the food, e.g. overcooked. In the second case, manual input brings inconvenience and is still experience dependent, and furthermore a non optimal cooking result is often encountered due to a significant discrepancy between the actual food and the 'average' food model used by a cooking appliance.

Food doneness is largely associated with its core temperature. Currently, this is monitored invasively during cooking by inserting a needle shaped thermometer into the food. The method of detecting food doneness is destructive and moreover only provides temperature information of a particular part of the food which can not accurately represent the overall temperature in the food. Furthermore, the needle in the cooking machine will make the cooking machine difficult to clean. Meanwhile, in order to avoid damage the food seriously, it is often that a very thin needle is used. Such needle is so liable to broke or bend as to impact its usage. Also, the machine structure will be complicated with the added needle, which will also increase the product cost of the cooking machine.

SUMMARY OF THE INVENTION

It is an object of the present disclosure to solve or alleviate at least one of the problems mentioned above.

A first aspect of the present disclosure is a method for controlling a cooking process of food. The method comprising obtaining a protein status in the food in the course of heating the food; determining a doneness level of the food at least partially based on the protein status; and controlling the cooking process of the food at least partially based on the determined doneness level.

Protein is a good indicator representing the actual status of the food along a cooking process, because it is an important ingredient in the food (e.g., meat), meanwhile the protein status of the food is highly related to the food doneness during the cooking process. The actual indicator for doneness level is protein denaturation, i.e. the chemical status of the protein, which can provide more direct and precise information of the status of food based on established relation between the doneness level and the protein denaturation extent.

The advantages of the method are embodied in the following aspects. In the first aspect, the proposed method offers an automatic cooking solution in comparison with traditional methods that need user's input about target time/temperature. In this method, the user is only required to set a target doneness level of the food without inputting other cooking parameters such as temperature, cooking time etc., which is not easily grasped by an average user. As a result, it minimizes user intervention during cooking. In the second aspect, precise cooking control is enabled due to the direct indication of protein status during cooking. Temperature is a traditional indicator for cooking process. It is the cause of ingredient status change, but it is not the direct indicator of food status. In some cases, with salt, with different meat composition, with different personal preferences, and with different meat types, the temperature cannot give precise doneness information. By contrast, in this method, protein status is proposed as the indicator of food doneness, which facilitates to detect the food doneness more timely and accurately.

Optionally, the method may emit a plurality of radio frequency signals into the food noninvasively and receive a plurality of reflection signals or transmission signals of the radio frequency signals from the food. The reflection signals is a part of the radio frequency signals that reflect from the food, and the transmission signals is a part of the radio frequency signals that transmit through the food. Then, the method may obtain the protein status based on the plurality of radio frequency signals and the plurality of reflection signals or transmission signals.

By involving the penetrative signal such as radio frequency signal in obtaining the protein status of the food, the food doneness can be determined in a non-invasive way. In this way, the integrity of the food will not be destroyed, thereby improving the visual experience when tasting the food. Optionally, the plurality of radio frequency signals may have the same frequency. As such, the method may emit the plurality of radio frequency signals into the food at different points of time in the course of heating the food; obtain the protein status based on dielectric properties of the food, the dielectric properties are determined based on the phases or amplitudes of the radio frequency signals and the plurality of reflection signals or transmission signals; and determine the doneness level of the food based on the dielectric properties over time.

The change of dielectric property in food is featured by staged drop and rise associated with food doneness levels, which makes the determination of the doneness level of the food independent of the absolute measurement value, thereby protecting the

determination of the doneness level against disturbing factors such as initial status of the food, composition variance in the food. This is an apparently advantage by comparison with measuring temperature (monotonically increasing) or moisture loss (monotonically decreasing).

Optionally, the plurality of radio frequency signals may have at least two frequencies. As such, the method may emit the plurality of radio frequency signals into the food; extract parameters indicating the protein status in the food based on the plurality of radio frequency signals and the plurality of reflection signals or transmission signals; and determine the doneness level of the food based on the extracted parameters.

The introduction of multi-frequency information makes the sensing more robust against various disturbing factors including measurement error, electronic noise and food variation. Therefore, the food doneness can be determined accurately.

The different frequencies may also be used for obtaining a doneness level for particular respective depths, and the method then comprises combining the different doneness levels to derive an overall doneness level. The extracted parameters in this case may comprise a dielectric attenuation parameter for each depth, and the method may then comprise converting the dielectric attenuation parameters into respective doneness levels using calibration information.

A second aspect of the present disclosure is an apparatus configured to control a cooking process of food. The apparatus comprises an obtaining unit, a determining unit and a controlling unit. The obtaining unit is adapted to obtain a protein status in the food in the course of heating the food; The determining unit adapted to determine a doneness level of the food at least partially based on the protein status; and the controlling unit adapted to control the cooking process of the food at least partially based on the determined doneness level. A third aspect of the present disclosure is a cooking device. The cooking device comprises an apparatus configured to detect doneness of food as described above.

A fourth aspect of the present disclosure is a computer readable storage medium storing instructions. When executed on an apparatus, the instructions cause the apparatus to perform the steps of the method as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The technology will now be described, by way of example, based on embodiments with reference to the accompanying drawings, wherein:

Fig. 1 schematically illustrates a flowchart of a method for controlling a cooking process of the food in accordance with an embodiment;

Fig. 2 schematically illustrates a flowchart of a method for controlling a cooking process of the food in accordance with an embodiment;

Fig. 3 is an exemplary diagram schematically illustrating the temperature dependence of dielectric property of the food;

Fig. 4 is an exemplary diagram schematically illustrating the repeatability that the dielectric property of the food has dependence on the temperature;

Fig. 5 is an exemplary diagram schematically illustrating the determination of the food doneness with the derivative scheme;

Fig. 6 is a block diagram of an apparatus configured to control a cooking process of food in accordance with an embodiment;

Fig. 7 schematically illustrates a block diagram of an apparatus configured to control a cooking process of food in accordance with an embodiment;

Fig. 8 schematically illustrates the arrangements of the array of radio frequency sensing probes in accordance with an embodiment;

Fig. 9 schematically illustrates an example of setting weighting efficient for the array of RF sensing probes in determining the doneness level of the food;

Fig. 10 schematically illustrates the arrangements of the RF sensing probe in the cooking device in accordance with an embodiment;

Fig. 1 1 schematically illustrates how a food item can be characterized by a set of layers;

Fig. 12 schematically illustrates how a reflected signal is affected by the dielectric property of multiple layers; and Fig. 13 schematically shows test results which demonstrate the relationship between depth and frequency.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments herein will be described more fully hereinafter with reference to the accompanying drawings. The embodiments herein may, however, be embodied in many different forms and should not be construed as limiting the scope of the appended claims. The elements of the drawings are not necessarily to scale relative to each other. Like numbers refer to like elements throughout.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" "comprising," "includes" and/or "including" when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The present technology is described below with reference to block diagrams and/or flowchart illustrations of methods, apparatus (systems) and/or computer program according to the present embodiments. It is understood that blocks of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, may be implemented by computer program instructions. These computer program instructions may be provided to a processor, controller or controlling unit of a general purpose computer, special purpose computer, and/or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer and/or other programmable data processing apparatus, create means for implementing the functions/acts specified in the block diagrams and/or flowchart block or blocks. Accordingly, the present technology may be embodied in hardware and/or in software (including firmware, resident software, micro-code, etc.). Furthermore, the present technology may take the form of a computer program on a computer-usable or computer- readable storage medium having computer-usable or computer-readable program code embodied in the medium for use by or in connection with an instruction execution system. In the context of this document, a computer-usable or computer-readable storage medium may be any medium that may contain, store, or is adapted to communicate the program for use by or in connection with the instruction execution system, apparatus, or device.

Embodiments herein will be described below with reference to the drawings. Taking beef steak cooking as example, the core temperature is usually used as the indicator of beef steak doneness. As illustrated in the table below, the doneness of the beef steak is divided into a plurality of doneness levels. The individual doneness levels correspond to the respective temperature ranges.

However, it is recognized that the temperature is only a physical indicator of the food in cooking, and the actual indicator for doneness extent is protein denaturation, i.e. the chemical status of the protein, which can provide more direct and precise information of the status of food based on established relation between doneness level and protein denaturation extent, also referred to as the protein status.

Fig. 1 schematically illustrates a flowchart of a method for controlling a cooking process of the food in accordance with one embodiment.

In step 1 10, the method obtains the protein status in the food in the course of heating the food. Here, the food refers to any kind of food that has protein as one of the dominant ingredients, such as beef, pork, egg, and the like. For purpose of explanation, the beef steak will be used to describe the embodiments herein by way of example.

There are four distinct levels of protein structure. In the tertiary structure, spatial arrangement is attained when a linear protein chain with secondary structure segments folds further into a compact three dimension (3D) form. Protein curls up on itself so that hydrophobic elements of the protein are buried deep inside the structure and hydrophilic elements end up on the outside. Some water molecules in food are bounded on the surface of protein by hydrophilic elements, e.g. hydrogen bonding. In the course of heating the food, the protein denaturation happens. In particular, the tertiary structure disrupts, leading to hydrophilic bonding breaks, and the bound water becomes free water. Also, the denaturation is accompanied by the release of calcium and magnesium ions.

As seen, during the protein denaturation, the bound water becomes free water, and ions are released. These two factors both largely change the dielectric property of the food. The protein denaturation process can be detected by measuring food dielectric property change. In other words, the protein status can be indicated by the dielectric behavior in the food.

In one embodiment, the method may invasively cut food samples from the food during heating the food, and put the food samples into a separate protein status analyzer, which is responsible for analyzing the protein status of the food samples. As such, the method may take the protein status of the food sample as the protein status of the food. In another embodiment, the protein status of the food can be obtained in a non-invasive way. In particular, the method may emit a penetrative signal such as radio frequency (RF) signal to the food, which penetrative signal can penetrate into the food at a sufficient depth (e.g.

centimeters) to detect the status of protein. The protein status of the food can be obtained by measuring the RF frequency absorption indicating the dielectric behavior in the food, which will be described in detail later.

In step 120, the method determines a doneness level of the food at least partially based on the protein status. Specifically, the doneness level of the food can be determined based on established relation between doneness level and the protein status. Herein, the protein status can be indicated in various ways, such as by the dielectric property change pattern, the spectrum characteristics of the RF signals suggesting the dielectric property in the food, as will be discussed later. For example, the method may search the database for the doneness level corresponding to the dielectric property change pattern (e.g. a curve shape) that indicates the protein status. For another example, the method may utilize the spectrum characteristics of the RF signals suggesting the dielectric property in the food to predict the doneness level of the food. The implementation of these embodiments will be discussed in detail later.

In step 130, the method controls the cooking process of the food at least partially based on the determined doneness level. For example, if the determined doneness level is equal to the target doneness level, the method may terminate the cooking process, and audibly or visually signal the user to remove the food from the cooking device. If the determined doneness level is approaching to the target one, the method may tune the cooking parameters of the cooking device, including the heating power level, the duty cycle and the cooking time, so as to eventually reach the target doneness level without over-cooking.

The advantages of the method are embodied in the following aspects. In the first aspect, the proposed method offers an automatic cooking solution in comparison with traditional methods that need user's input about target time/temperature. In this method, the user is only required to set a target doneness level of the food without inputting other cooking parameters such as temperature, cooking time etc, which is not easily grasped by an average user. As a result, it minimizes user intervention during cooking. In the second aspect, precise cooking control is enabled due to the direct indication of protein status during cooking. Temperature is a traditional indicator for cooking process. It is the cause of ingredient status change, but it is not the direct indicator of food status. In some cases, with salt, with different meat composition, with different personal preferences, and with different meat types, the temperature cannot give precise doneness information. By contrast, in this method, protein status is proposed as the indicator of food doneness, which facilitates to detect the food doneness more timely and accurately.

Furthermore, conductive food heating, such as frying, baking and grilling, involves a process of the heat transferring from the food surface to inside, which results in a negative temperature gradient to the center of the food. Thus, traditionally the core temperature of the food is used to indicate the food doneness. In order to acquire the core temperature of the food, it is often that the temperature probe (e.g. thermocouple or thermal resistor) is inserted into food to measure the core temperature. It is an invasive sensing technique, which can destroy the integrity of the food. Hence, it is desirable that the food doneness can be determined in a non-invasive way, which is made possible by involving the penetrative signal such as radio frequency signal in obtaining the protein status of the food.

As mentioned above, the protein status of the food in the course of heating the food can be indicated by the dielectric behavior in the food. The food dielectric behavior is dominated by several dielectric mechanisms. For radio frequencies, dipole orientation and ionic conduction are the main mechanisms. At the low RF frequencies, ionic conduction is the main effect. At the high radio frequencies, dipole orientation, which means that a polar molecule can adjust its direction according to an external electric field, contributes more. In the middle of RF frequencies, both of the two mechanisms are playing a part. The frequency relevance of food dielectric property is the basis of sensing the protein status of the food by radio frequency signals. Now, the process to obtain the protein status by RF signal, and thereby determine the food doneness in a non-invasive way, will be set forth with reference to Fig. 2.

In Fig. 2, the method may emit a plurality of radio frequency signals into the food noninvasively continuously or discretely during heating the food at step 101, and receive a plurality of reflection signals or transmission signals of the radio frequency signals from the food at step 105. The reflection signals is a part of the radio frequency signals that reflect from inside of the food. The transmission signals is a part of the radio frequency signals that transmit through the food. Optionally, the reflection signals can be reflected from different depths of the food. As such, the reflections signals can indicate the energy absorption of RF signals at different depth of the food, which will help obtain the protein status of the food more accurately. Then, the method may obtain the protein status based on the plurality of radio frequency signals and the plurality of reflection signals or transmission signals at step 1 10. Specifically, the method can be implemented in the following ways:

Implementation I

The method may emit a plurality of radio frequency signals into the food at different points of time in the course of heating the food and receive the respective reflection signals or transmission signals. These radio frequency signals have the same frequency. The reason for emitting the plurality of radio frequency signals at different points of time in the course of heating is explained as below.

During the protein denaturation, the bound water becomes free water, and ions are released. These two factors both largely change the dielectric property of food. Hence, the protein denaturation process can be detected by measuring food dielectric property change. Specifically, in the initial stage of cooking (before protein denaturation), the increase in ionic mobility with temperature increase can lead to the increase in energy absorption of radio frequency. During protein denaturation, the increasing amount of free water and released ions largely accelerate the energy absorption of RF. At the later stage of denaturation, the water evaporation decreases the amount of free water and therefore decreases the ionic mobility, which results in decrease of RF energy absorption. As such, the dielectric property change in the food can be suggested by the change of the RF energy absorption during heating the food. In other words, the dielectric property of the food can be represented by the RF energy absorption, which can be quantized by scattering parameters such as Sn and S₁₂, dielectric constant or loss factor.

Since the protein status can be indicated by the dielectric behavior, i.e. the dielectric property change during heating the food, in order to obtain the protein status, the method may calculate the dielectric properties over time based on the phases and/or amplitudes of the emitted radio frequency signals and the plurality of reflection signals or transmission signals at step 1 10. For example, the dielectric property can be represented by Sn, which is calculated as the ratio of the phase and/or amplitude of the emitted RF signal and the phase and/or amplitude of the corresponding reflection RF signal. For another example, the dielectric property can be represented by S₁₂, which is calculated as the ratio of the phase and/or amplitude of the emitted RF signal and the phase and/or amplitude of the corresponding transmission RF signal.

Subsequently, the method may determine the doneness level of the food based on the obtained dielectric properties at step 120. For example, the method may use the obtained dielectric properties to form a curve which illustrates the change of the dielectric property over time, and then match the shape of the curve with those predetermined curves indicating the individual doneness level to obtain the doneness level indicated by the curve.

The mapping between the predetermined curves and the individual doneness are illustrated in Fig. 3. Fig. 3 is an exemplary diagram schematically illustrating the temperature dependence of dielectric property of the beef steak. As shown, the horizontal axis is the temperature in Celsius, the vertical axis is the amplitude of Sn in decibel. Two frequencies are selected representing of low frequency and high frequency cases. The upper curve is for 1 MHz, and the lower curve is for 0.5 GHz. The change of dielectric property in the beef steak can be divided into three stages. In the stage I (18-40 °C), the drop in Sn is mainly due to the increase in ionic mobility which increases with temperature. In the stage II (40-55 °C), the temperature reaches the denaturation zone, and Sn largely decreases because bound water changes into free water and myosin denaturation has been accompanied by the release of calcium and magnesium ions. In the stage III (55-70 °C), Sn rebounds because the ionic mobility decreases due to water evaporation. As indicated, the shape of the curve indicating the dielectric property change has a dependency on the temperature, meanwhile the doneness levels for a beef steak corresponds to the respective temperature ranges. For example, 'medium rare' falls in 55-60 °C, 'medium' falls in 60-65 °C, and 'medium well' falls in 65-69 °C. Hence, the mappings between the shape of the curve indicating the dielectric property change and the doneness level is established.

Further, in order to prove the repeatability of the dielectric property change having dependency on temperature, three different types of beef steak were prepared and heated. The results are shown in Fig. 4. In order to compare the curves precisely, the curves were normalized to [0, 1 ] . The upper figure shows the results at 1 MHz, and the lower one shows that at 0.5 GHz. The similar profiles are shown (i.e. stage I-III), and it is shown that the curves have obvious repeatability.

As indicated, the shape of the curve indicating the change of dielectric property in food is featured by staged drop and rise associated with food doneness levels, which makes the determination of the doneness level of the food independent of the absolute measurement value, thereby protecting the determination of the doneness level against disturbing factors such as initial status of the food, composition variance in the food. This is an apparently advantage by comparison with measuring temperature (monotonically increasing) or moisture loss (monotonically decreasing).

Implementation II

After obtaining the dielectric properties as described in Implementation I, the method may also set up a function, denoted as f(t), based on the obtained dielectric properties. The f(t) is a function of the dielectric properties with respect to time. A derivative is taken for the f(t), and then normalized with respect to the f(t), whereby a function g(t) is derived, which can be formulated as:

/(

As such, the method may calculate the value of g(t) at the current point of time, and then compare the calculated value with the predetermined threshold ranges indicating the individual doneness levels. In this way, the doneness level indicated by the calculated value can be determined.

Now, the process to establish the predetermined threshold ranges indicating the individual doneness levels will be introduced with reference to Fig. 5. Taking the beef steak as example, a plurality of beef steak samples are used in training the threshold values. These beef steaks vary in kind, quality, size, and thickness. For each of the beef steaks, the change of the dielectric property during the heating is recorded, whereby the corresponding f(t) and thereby the g(t) can be recorded as illustrated in Fig. 5. Meanwhile, the doneness level will be marked along the curve g(t), which doneness level can be measured by invasive method (e.g. thermocouple) or provided by a professional chef. In this way, the threshold ranges indicating the individual doneness levels are identified for this sample. For example, the threshold range for doneness level i can be denoted as

THi_iUpper]. As such, the resulting threshold range for the doneness level i can be calculated by averaging the identified threshold range for this doneness level of these samples.

Implementation HI

The inventors of the present invention also recognize that the doneness level of the food can be predicted by the spectrum characteristics of the RF signals at multiple frequencies. In particular, the spectrum characteristics of the RF signals at multiple frequencies obtained at a specific point of time can be used in combination to predict the doneness level of the food at the specific time point.

In an embodiment, in order to determine the doneness level of the food at the current point of time, the method may emit a plurality of radio frequency signals into the food. These RF signals have at least two frequencies, which can be emitted concurrently or successively in a short time interval near the current point of time.

Then, the method may receive the respective reflection signals or transmission signals and extract parameters indicating the protein status in the food based on the plurality of emitted radio frequency signals and the plurality of reflection signals or transmission signals. The parameters refer to the spectrum characteristics of the RF signals, including, but not limited to, the magnitude and/or phase of the emitted radio frequency signals at different frequencies; the magnitude and/or phase of the reflection signals or transmission signals at different frequencies; the scattering parameters of the emitted radio frequency signals such as Sii and S₁₂; the derivation information of the emitted RF signals, the reflection signals or transmission signals; the morphological information of these RF signals at multiple frequencies, for example, the ratio of the magnitudes/energies of the RF signals at the high frequency and the low frequency.

After extracting the parameters, the method may determine the doneness level of the food based on the extracted parameters. For example, the method may input the parameters as predicting variables into a doneness predictive model, and the predictive model can predict the doneness level based on the predicting variables. Here, the predictive model can be set up using data mining techniques, which includes Bayesian network, decision tree/random forest, neural network, k-Nearest Neighbor (k-NN) algorithm, and the like. For example, a large number of samples pairing the parameters (or features) extracted from the emitted RF signals, the reflection signals, or the transmission signals (denoted by

x— x X X \

i i ' 2' · · · ^{« J} ) and the doneness level (denoted by Q will be trained using the k-NN algorithm to build up the doneness predictive model.

Fig. 6 is a block diagram of an apparatus configured to control a cooking process of food in accordance with one embodiment. As shown in Fig. 6, the apparatus 600 includes an obtaining unit 610, a determining unit 620 and a controlling unit 630. The apparatus 600 can work separately. It also can be partially or completely integrated into a cooking device. Now the functions of these elements will be described with reference to Fig. 6.

The obtaining unit 610 in the apparatus 600 obtains the protein status in the food in the course of heating the food. Here, the food refers to any kind of food that has protein as one of the dominant ingredients, such as beef, pork, egg, and the like.

In one embodiment, the obtaining unit 610 may invasively cut food samples from the food during heating the food, and put the food samples into a separate protein status analyzer, which is responsible for analyzing the protein status of the food samples. As such, the obtaining unit 610 may take the protein status of the food sample as the protein status of the food. In another embodiment, the protein status of the food can be obtained in a noninvasive way. In particular, the apparatus 600 may emit a penetrative signal such as radio frequency wave to the food, which penetrative signal can penetrate into the food at a sufficient depth (e.g. centimeters) to detect the status of protein. Therefore, the obtaining unit 610 can obtain the protein status of the food can by measuring the RF frequency absorption reflecting the dielectric behavior in the food, which will be described in detail later.

The determining unit 620 in the apparatus 600 determines a doneness level of the food at least partially based on the protein status. Specifically, the doneness level of the food can be determined based on established relation between doneness level and the protein status. Herein, the protein status can be indicated in various ways, such as by the dielectric property change pattern, the spectrum characteristics of the RF signals suggesting the dielectric property in the food, as will be discussed later. For example, the determining unit 620 may search the database for the doneness level corresponding to the dielectric property change pattern (e.g. a curve line) that indicates the protein status. For another example, the determining unit 620 may utilize the spectrum characteristics of the RF signals suggesting the dielectric property in the food to predict the doneness level of the food. The implementation of these embodiments will be discussed in detail later.

The controlling unit 630 in the apparatus 600 controls the cooking process of the food at least partially based on the determined doneness level. For example, if the determined doneness level is equal to the target doneness level, the controlling unit 630 may terminate the cooking process, and audibly or visually signal the user to remove the food from the cooking device. If the determined doneness level is approaching to the target one, the controlling unit 630 may tune the cooking parameters of the cooking device, including the heating power level, the duty cycle and the cooking time, so as to eventually reach the target doneness level without over-cooking.

The advantages of the embodiment are embodied in the following aspects. In the first aspect, it offers an automatic cooking solution in comparison with traditional methods that need user's input about target time/temperature. In this embodiment, the user is only required to set a target doneness level of the food without inputting other cooking parameters such as temperature, cooking time etc, which is not easily grasped by an average user. As a result, it minimizes user intervention during cooking. In the second aspect, precise cooking control is enabled due to the direct indication of protein status during cooking.

Temperature is a traditional indicator for cooking process. It is the cause of ingredient status change, but it is not the direct indicator of food status. In some cases, with salt, with different meat composition, with different personal preferences, and with different meat types, the temperature cannot give precise doneness information. By contrast, in this embodiment, protein status is proposed as the indicator of food doneness, which facilitates to detect the food doneness more timely and accurately.

In order to achieve this object, the apparatus 600 may further comprise an emitting unit 601 and a receiving unit 605 as illustrated in Fig. 7.

The emitting unit 601 in the apparatus 600 may emit a plurality of radio frequency signals into the food noninvasively. For example, the emitting unit 601 can be an open-ended coaxial probe. The probe may keep touch with the food when emitting the RF signal. Alternatively, the probe may don't contact with the food while emitting the RF signal, as long as the emitted RF signal can penetrate into the food up to a depth sufficient to detect the protein status.

The receiving unit 605 may accordingly receive a plurality of reflection signals or transmission signals of the radio frequency signals from the food. The reflection signals is a part of the radio frequency signals that reflect from inside of the food. The transmission signals is a part of the radio frequency signals that transmit through the food. Optionally, the reflection signals can be reflected from different depths of the food. As such, the reflections signals can indicate the energy absorption of RF signals at different depth of the food, which will help obtain the protein status of the food more accurately.

When the receiving unit 605 is configured to receive the reflection signals, it can be placed on the same side of the food. In this case, the receiving unit 605 and the obtaining unit 601 can be integrated together as a single element. Additionally or

alternatively, when the receiving unit 605 is configured to receive the transmission signal, it will be placed on the other side of the food in opposition to the emitting unit 601.

Subsequently, the obtaining unit 610may obtain the protein status based on the plurality of radio frequency signals emitted by the emitting unit 601 and the plurality of reflection signals or transmission signals received by the receiving unit 605.

These units in the apparatus 600 may collaborate in the following ways to determine the doneness level of the food:

Implementation I

The emitting unit 601 may emit a plurality of radio frequency signals into the food at different points of time in the course of heating the food and the receiving unit 605 may receive the respective reflection signals or transmission signals. These RF signals have the same frequency. The RF signals can be emitted and received continuously or discretely during heating the food.

In order to obtain the protein status, the obtaining unit 610 may calculate the dielectric properties over time based on the phases and/or amplitudes of the emitted radio frequency signals and the plurality of reflection signals or transmission signals. For example, the dielectric property can be represented by Sn, which is calculated as the ratio of the phase and/or amplitude of the emitted RF signal and the phase and/or amplitude of the

corresponding reflection RF signal. For another example, the dielectric property can be represented by S₁₂, which is calculated as the ratio of the phase and/or amplitude of the emitted RF signal and the phase and/or amplitude of the corresponding transmission RF signal.

The determining unit 620 may determine the doneness level of the food based on the obtained dielectric properties. For example, the method may use the obtained dielectric properties to form a curve which illustrates the change of the dielectric property over time, and then match the shape of the curve with those predetermined curves indicating the individual doneness level to obtain the doneness level indicated by the curve.

As mentioned above, the shape of the curve indicating the change of dielectric property in food is featured by staged drop and rise associated with food doneness levels, which makes the determination of the doneness level of the food independent of the absolute measurement value, thereby protecting the determination of the doneness level against disturbing factors.

Implementation II

After obtaining the dielectric properties as described in Implementation I, the obtaining unit 610 may also set up a function, denoted as f(t), based on the obtained dielectric properties. The f(t) is a function of the dielectric properties with respect to time. A derivative is taken for the f(t), and then normalized with respect to the f(t), whereby a function g(t) is derived, which can be formulated as:

/(

As such, the obtaining unit may calculate the value of g(t) at the current point of time, and then the determining unit may compare the calculated value with the predetermined threshold ranges indicating the individual doneness levels. In this way, the doneness level indicated by the calculated value can be determined.

Implementation HI

The emitting unit 601 may emit a plurality of radio frequency signals into the food. These RF signals have at least two frequencies, which can be multiple separated frequency points, a frequency band, or combination thereof. They can be emitted

concurrently or successively in a short time interval. Then, the receiving unit 605 may receive the respective reflection signals or transmission signals.

The obtaining unit 610 may extract parameters indicating the protein status in the food based on the plurality of emitted radio frequency signals and the plurality of reflection signals or transmission signals. The parameters refer to the spectrum characteristics of the dielectric property in the food, including, but not limited to, the magnitude and/or phase of the emitted radio frequency signals at different frequencies; the magnitude and/or phase of the reflection signals or transmission signals at different frequencies; the scattering parameters of the emitted radio frequency signals such as Sn and S₁₂; the derivation information of the emitted RF signals, the reflection signals or transmission signals; and the morphological information of these RF signals at multiple frequencies, for example, the ratio of the magnitudes/energies of the RF signals at the high frequency and the low frequency.

The determining unit 620 may determine the doneness level of the food based on the extracted parameters. For example, the determining unit 620may input the parameters as predicting variables into a doneness predictive model, and the predictive model can predict the doneness level based on the predicting variables. Here, the predictive model can be set up using data mining techniques as described above.

In addition, as known, conductive food heating involves a process of the heat transferring from the food surface to inside. Hence, it may occur that when the core reaches a desired doneness level, the other parts, especially those at corners and close to edge, are overcooked. The extent of overcooking increases with the size and thickness of a beef steak. Undercooking happens with an irregular food shape or uneven food composition distribution. In these cases, although the core is cooked to a proper doneness level, over- or undercooking at other parts may affect on overall taste and mouth-feel (stiff, less juicy etc). Thus, it is desirable that the overall doneness level of the food can be determined by taking into account its spatial unevenness.

In order to achieve this object, the apparatus 600 may comprise a plurality of pairs of the emitting unit 601 and the receiving unit 605, each of which may emit a plurality of radio frequency signals into different parts of the food and receive the respective reflection signals or transmission signals therefrom. For example, the plurality of pairs of the emitting unit 601 and the receiving unit 605 are an array of open-ended coaxial probes. The probes can be arranged inside one plane or following a specific curvature, as illustrated in Fig. 8. If the probes keep touch with the food in operation, a curved surface may lead to better contact and therefore improved signal to noise ratio (SNR) of detection. The probes can be equidistantly placed or arranged in a specific pattern as desired.

The obtaining unit 610 may obtain protein statuses in the different parts of the food based on the radio frequency signals and the plurality of reflection signals or transmission signals for the individual parts.

Then the determining unit 630 may determine doneness levels of the different parts of the food based on the respective protein statuses, and calculate the doneness level of the food by weighing the doneness levels of the different parts of the food. The overall doneness level of the food can be generally described by a function as below:

DL_mma = f(PL_i,DL_i,..DL_N)

where ^oveml1 represents the overall doneness level, and DLi(i=l,2, .

represents the doneness level for individual parts of the food.

By way of example, the ^ ^a can be calculated by the formula as

^DLoverall = ^Τ°^ά (∑ W^L, )

(1)

where ^W' is the weighing factor of the doneness level , ^roun^(^x) [_s to take an integer closest to ^x . Take beef steak frying as an example, in order to be mathematically operational, the doneness level is assigned with integer numbers from 1 to 5 that are defined by { l='rare', 2='medium rare', 3='medium', 4='medium well', 5='well done'} .

Setting of the weighing factor ^W' is based on the relevance of a local doneness level to the overall one. The doneness of the core is most important, as it is used traditionally as a defining criterion, so the weighing factor can be set the highest. In common sense, the doneness degree gets less important when moving away from the core towards corners and edges. Thew^ therefore can be set in a descending order accordingly.

An example of the weighing factor value setting is given in Fig. 4. Assuming the doneness levels detected by the nine probes are

Central probe: 'medium'=3;

Edge probe: 'medium well'=4;

Corner probe: 'well done' =5.

Then the overall doneness calculated according to formula (1) is

DL_ovemll = rounds A * 3 + 4 * 0.1 * 4 + 4 * 0.05 * 5) = 4

i.e. medium well. This example shows that the overall doneness is better determined as 'medium well' despite 'medium' at the center, taking into account the actual doneness degree of the four relatively large edge areas.

Doneness levels from individual probes can be given fractional values in order to allow a higher doneness 'resolution' in the intermediate calculation, for instance, 3.5 for a status between 'medium' and 'medium well'.

The present disclosure also proposes a cooking device comprising the apparatus configured to control a cooking process of food as described above. The emitting unit and the receiving unit in the apparatus can be arranged into the cooking device as appropriate, such as on lid of the cooking device, at bottom of the cooking device, etc.

By way of example, the arrangements of the emitting unit and the receiving unit in the cooking device are illustrated in Fig. 10.

In Fig. 10(a), both the emitting unit and the receiving unit are placed on lid of the cooking device. The receiving unit may receive the reflection signals. They don't have contact with the food in operation. In Fig. 10(b), both the emitting unit and the receiving unit are placed at the bottom of the cooking device, i.e. under the food. They have contact with the food in operation. In Fig. 10(c), one of the emitting unit and the receiving unit is placed at the bottom of the cooking device, the other one is placed on lid of the cooking device. The receiving unit may receive the transmission signals. In Fig. 10(d), the arrangement is similar to Fig. 10 (c) except that both the emitting unit and the receiving unit have contact with the food in operation.

In Fig. 10(e), the emitting unit and the receiving unit are placed at the bottom of the side wall of the cooking device in opposition to each other. As such, the food is placed between the emitting unit and the receiving unit. The emitting unit emits the RF signals into the food from a side of the food, and the receiving unit receives the transmission RF signals propagating through the food from another side of the food. Alternatively, the emitting unit and the receiving unit can be placed in the middle of the side wall of the cooking device in opposition to each other as illustrated in Fig. 10(f). In this case, the RF signals emitted by the emitting unit will graze through the food, and the scattered signals will be received by the receiving unit. This is especially applicable for the food that is too thick to be transmitted by the RF signals.

It is explained above that the determining unit 630 may determine doneness levels of the different parts of the food based on the respective protein statuses, and calculate the doneness level of the food by combining the doneness levels of the different parts of the food with different (mathematical) weights. As explained above, the overall doneness level of the food can be generally described by a function as below:

DL_mma = f(PL_i,DL_i,..DL_N)

When multiple frequencies are used, each frequency enables information about the protein status to be obtained up to a certain depth. The individual doneness levels may thus each relate to a particular depth within the food item. The doneness level for different depths is thus combined to derive an overall doneness level.

The signal generator may for example generate multi-frequency RF signals ranging from a few MHz to a few GHz.

As explained above, an antenna can function as both an emitter and receiver.

The RF signal emitted by the antenna interacts with the food through the air and the reflectance is received by the antenna. The S 1 1 reflection coefficient is associated with the dielectric property of the food. The RF penetration depth d_p can be defined as the distance at which the power drops to 1/e (=37%) of its value at the surface of the material, and for food (which is assumed to be nonmagnetic), can be expressed as:

2nf 2S> [ -1]

In this formula, the dielectric constant ε' and loss factor ε" are both a function of the RF frequency f. Thus, d_p is dependent on the frequency f.

In general, an RF signal at a lower frequency has a larger penetration depth. For example, the value of d_p of an RF wave of different frequencies in a beef meatball is listed below:

27 MHz 40 MHz 915 MHz 1800 MHz

Penetration depth (mm) 61.7 51.1 17.0 1 1.9

The penetration depth at a certain frequency relates to the RF decaying rate in the food. The reflected signal provides information relating to the protein status (and thus the doneness level along the signal travelling path), as shown in Fig. 1 1.

In Fig. 1 1, each frequency f_x is associated with a penetration depth. For example, the penetration depth at 40 MHz (51.1 mm) is larger than that at 915 MHz

(17.0cm), which means the RF wave at 40 MHz can detect information concerning the food item deeper than that at 915 MHz.

In Fig. l l, fi>->f,>f(,₊i)>-.

To make use of different depth information, the determining unit 620 receives the S 1 1 reflection signals, which relate to the dielectric property of the food, as inputs from a multi-frequency sensor probe and it determines the overall (i.e. volumetric) doneness level over the thickness direction, i.e., doneness levels corresponding to different layers of the food.

The food is characterized as divided into n layers perpendicular to the thickness direction according to the penetration depths dp at selected frequencies.

In the equation:

DL_ovemll = f(DL_x,DL₂,...DL_N) DLi (ϊ=1 ,·· ·,Ν) then represents the doneness level at the i-th layer (i < N), as shown in Fig. 1 1.

The S 1 1 reflection parameter takes account of the dielectric properties up to the penetration depth. Thus:

S_i = g(DL₁, DL₂ DL ) (3) where S_r represents the S I 1 signal parameter at the i-th frequency (i-th depth), and the function g() indicates that the value S_r is dependent on the doneness information along the signal path up to the final penetration depth for that signal, i.e. for each layer up to the i-th layer.

As explained above, DL_r can be assigned with integer numbers from 1 to 5 that are defined by { l='rare', 2=' medium rare', 3='medium', 4=' medium well', 5='well done' } . Of course, a different number of discrete values can instead be used.

A possible model of overall (volumetric) doneness can be derived using the approach explained with reference to Fig. 12.

The RF wave decays as an exponential function along the propagation path, thus defined by e^""² according to Maxwell's equations, where a represents the dielectric property of the food, which is related to the doneness level, and z represents the propagation path.

The signal Si at fi received as a result of the RF wave propagating through the first layer is denoted as:

Note the 2d term as the signal passes through the layer twice as a result of the reflection. The signal (S₂ at f₂) received as a result of the RF wave propagating through the first layer and the second layer, is denoted as:

S₂ = 5_{o e}-(«i+a₂)2d (₅)

Then, (Xi can be denoted as: ^ai ~ 2d ¾=1 " (6) where a_r indicates the dielectric property of i-th layer, which is related to the volumetric doneness level DL,.

What this means is that by processing the signals for successive depths, the dielectric attenuation parameter a for each layer can be obtained in an iterative manner.

The frequencies can be selected so that the food item is divided into layers approximately 0.5cm thick. Thus, the system may operate with approximately 10 different frequencies in order to penetrate to a depth of 5 cm (for a total food item thickness of 10cm).

A higher number of different frequencies enables either a finer resolution between layers or a greater penetration depth. By way of example, there may be between 4 and 20 different frequencies, selected to give a maximum penetration depth (as defined above as the 1/e power drop) of between 5 and 20cm.

Once each value of a has been obtained, the relationship between o and DL_r can be determined by a predictive method based on calibration information. This calibration information can be obtained based on system training using samples of food items, and by measuring the actual doneness levels by an invasive method, such as temperature probes or chemical analysis of the samples, or analysis by a chef. This training method is described above in connection with obtaining threshold values. In this way, dielectric attenuation parameters are converted into respective doneness levels using calibration information.

The controlling unit 630 receives the overall (volumetric) doneness level determined by the determining unit (by combining the doneness levels for the different depths), and compares this with a value derived from the user's specified desired doneness level. There is a doneness distribution along the thickness direction in the cooked food, especially when using conduction heating. When the user defines a desired overall doneness level, a target volumetric doneness level DLoveraii can be determined based on a pre-set program which maps between a user's seting and a corresponding value of the overall doneness level DLoveraii.

The cooking control can be based on a single overall doneness level. Thus, the user's selection is converted to an overall doneness level DLoveraii and the cooking is controlled until this doneness level is reached. However, the cooking process may instead be based on doneness levels for multiple depths, to provide more intelligent functionality. For example, target doneness levels may be set for multiple depths. During cooking, a difference ADL_r will exist between the measured doneness level DLi for a particular depth i and a target doneness level to that depth

which is given by: ADL_i = \DL_i - DL_i>target \ (7)

A cooking strategy can be determined based on one or more values of ADL_r. For example:

When all values of ADL_r are equal to 0, which means the food is cooked to the target doneness at each depth, terminate the cooking process, and signal the user to remove the food from the cooking device, for instance with audio or light;

When ADLr for a surface portion of the food is significantly below ADL_r in the core portion, which means the surface portion of food is cooked too quickly compared to the core portion, turn the power down (in the case of continuous heating) or increase the period of cooking pulse (in the case of pulse heating) to make the heating function more evenly;

When ADLi on the opposite sides of the food are significantly different, which means the doneness of two sides is not even, flip the food. This may be suitable for cooking in a pan (more than cooking in an oven).

Fig. 13 shows how the magnitude of a normalized S I 1 signal varies during cooking (i.e. as a function of time) for different frequencies. This is based on a test during which a piece of beef was cooked in a frying pan with an induction cooker. A probe placed on the top side of the beef provided and measured RF signals at 0.2GHz, 0.7 GHz, 1.2 GHz, and 2GHz.

It can be seen that the turning points of the S 1 1 signal (minimas) associated with different stages of protein denaturation appear later for higher frequencies. The lower side of the meat cooks first, and this corresponds to a deeper penetration depth for the probe mounted on top of the meat. Thus, in this test, the degree of doneness decreases from the bottom to the top side of the meat due to the upward heat transfer. The test demonstrates that a lower frequency RF signal carries doneness information from a deeper portion of the meat.

While the embodiments have been illustrated and described herein, it will be understood by those skilled in the art that various changes and modifications may be made, any equivalents may be substituted for elements thereof without departing from the true scope of the present technology. In addition, many modifications may be made to adapt to a particular situation and the teaching herein without departing from its central scope. Therefore it is intended that the present embodiments not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the present technology, but that the present embodiments include all embodiments falling within the scope of the appended claims.

Claims

CLAIMS:

1. A method (100) for controlling a cooking process of food, comprising steps of:

obtaining (1 10) a protein status in the food in the course of heating the food; determining (120) a doneness level of the food at least partially based on the protein status; and

controlling (130) the cooking process of the food at least partially based on the determined doneness level.

2. The method of claim 1, the method (100) further comprises:

emitting (101) a plurality of radio frequency signals into the food noninvasively;

receiving (105) a plurality of reflection signals or transmission signals of the radio frequency signals from the food, wherein the reflection signals being a part of the radio frequency signals that reflect from the food, and the transmission signals being a part of the radio frequency signals that transmit through the food; and

wherein the obtaining step (1 10) comprises obtaining the protein status based on the plurality of radio frequency signals and the plurality of reflection signals or

transmission signals.

3. The method of claim 2, wherein the plurality of radio frequency signals have the same frequency, the emitting step (101) comprises emitting the plurality of radio frequency signals into the food at different points of time in the course of heating the food;

the obtaining step (1 10) comprises obtaining the protein status based on dielectric properties of the food, the dielectric properties are determined based on the phases or amplitudes of the radio frequency signals and the plurality of reflection signals or transmission signals; and

the determining step (120) comprises determining the doneness level of the food based on the dielectric properties.

4. The method of claim 3, wherein the determining step (120) comprises determining the doneness level corresponding to a change of the dielectric properties, for example a change in scattering parameter, dielectric constant or loss factor.

5. The method of claim 2, wherein the plurality of radio frequency signals have at least two frequencies;

the emitting step (101) comprises emitting the plurality of radio frequency signals into the food;

the obtaining step (1 10) comprises extracting parameters indicating the protein status in the food based on the plurality of radio frequency signals and the plurality of reflection signals or transmission signals;

the determining step (120) comprises determining the doneness level of the food based on the extracted parameters.

6. The method of claim 5, wherein each different frequency is for obtaining a doneness level for a particular depth, and the method comprises combining the different doneness levels to derive an overall doneness level.

7. The method of claim 6, wherein the extracted parameters comprise a dielectric attenuation parameter for each depth, and wherein the method comprises converting the dielectric attenuation parameters into respective doneness levels using calibration

information.

8. An apparatus (600) configured to control a cooking process of food, comprising:

an obtaining unit (610) adapted to obtain a protein status in the food in the course of heating the food;

a determining unit (620) adapted to determine a doneness level of the food at least partially based on the protein status; and

a controlling unit (630) adapted to control the cooking process of the food at least partially based on the determined doneness level.

9. The apparatus of claim 8, the apparatus (600) further comprises:

a emitting unit (601) adapted to emit a plurality of radio frequency, radio frequency, signals into the food noninvasively;

a receiving unit (605) adapted to receive a plurality of reflection signals or transmission signals of the radio frequency signals from the food, wherein the reflection signals being a part of the radio frequency signals that reflect from the food, and the transmission signals being a part of the radio frequency signals that transmit through the food; and

wherein the obtaining unit (610) is adapted to obtain the protein status based on the plurality of radio frequency signals and the plurality of reflection signals or transmission signals.

10. The apparatus of claim 9, wherein the plurality of radio frequency signals have the same frequency, the emitting unit (601) is adapted to emit the plurality of radio frequency signals into the food at different points of time in the course of heating the food;

the obtaining unit (610) is adapted to obtain the protein status based on dielectric properties of the food, the dielectric properties are determined based on the phases or amplitudes of the radio frequency signals and the plurality of reflection signals or transmission signals; and

the determining unit (630) is adapted to determine the doneness level of the food based on the dielectric properties.

1 1. The apparatus of claim 9, wherein the plurality of radio frequency signals have at least two frequencies;

the emitting unit (601) is adapted to emit the plurality of radio frequency signal into the food;

the obtaining unit (610) is adapted to extract parameters indicating the protein status in the food based on the plurality of radio frequency signals and the plurality of reflection signals or transmission signals;

the determining unit (630) is adapted to determine the doneness level of the food based on the extracted parameters.

12. The apparatus of claim 1 1, wherein

the determining unit (630) is adapted to obtaining a doneness level for a particular depth from each different frequency, and to combine the different doneness levels to derive a volumetric doneness level, and wherein the obtaining unit is adapted to extract parameters which comprise a dielectric attenuation parameter for each depth, and

wherein the determining unit (630) is adapted to convert the dielectric attenuation parameters into respective doneness levels using calibration information.

13. The apparatus of claim 9, wherein the apparatus (600) comprises a plurality of pairs of the emitting unit (601) and the receiving unit (605), the plurality of emitting units (601) are adapted to emit a plurality of radio frequency signals into different parts of the food;

the obtaining unit (610) is adapted to obtain protein statuses in the different parts of the food based on the radio frequency signals and the plurality of reflection signals or transmission signals for the individual parts;

the determining unit (630) is adapted to determine doneness levels of the different parts of the food based on the respective protein statuses, and calculating the doneness level of the food by weighing the doneness levels of the different parts of the food.

14. A cooking device, comprising an apparatus (600) configured to control a cooking process of food according to any one of the claims 9-13, wherein the emitting unit (601) and the receiving unit (605) of the apparatus are placed on lid of the cooking device or at bottom of the cooking device.

15. A computer readable storage medium storing instructions which, when executed on an apparatus, cause the apparatus to perform the steps of the method according to any one of the claims 1-7.