FIELD OF THE INVENTION

The present invention generally relate to a cooking device utilizing the ohmic heat generated by applying electric power to food materials directly.

BACKGROUND OF THE INVENTION

Ohmic cooking (also called Joule cooking) is a cooking method utilizing the ohmic heat generated by the electrical resistance of the food when electric current passes through food materials to be cooked. Unlike other traditional heating methods, e.g.

microwave or heat plate, the heat is generated directly by the current passing through each part of the food materials with less heat transfer by convention and conduction, so the heating efficiency and evenness are improved.

In a basic model, an ohmic cooking device comprises a container and two electrode plates connected to a power supply. In cooking operation, the electrode plates are placed within the container opposite to each other with a distance therebetween to form a cooking chamber. Food materials to be cooked are placed in the cooking chamber with contacting to both electrode plates. An electrical power is applied to the food materials and a current is generated and passes through the food, so as to heat the materials.

Ohmic heating has been proved to be a fast and good method to cook dough food, but in another aspect some problems exist. While utilizing ohmic cooking device to cook dough food, the dough surface directly contacting with electrodes has a higher temperature than other portions of the dough. This phenomenon may be brought by the fact that the resistance in the surface area of dough contacting with the electrode is higher than that of the other parts of the electrical circuit. Since the dough, the contacting surface and the electrode plates are serial in the circuit, a higher electrical resistance will generates more heat. As a result, the contacting surface area of the dough loses water faster than other portions of the dough. Especially, when the temperature reaches 100°C, the moisture in the dough continuously evaporates, and the surface becomes hard and dry. This may disconnect the electrical connection between the dough and the electrodes, resulting in a bad cooking result. SUMMARY OF THE INVENTION

In view of the foregoing, there is a need in the art for a solution capable of utilizing ohmic heating device to cook dough food, but avoiding the fast water loss in the surface area of dough which directly contacts with the electrode plates and the resulting electrical disconnection between the dough surface and the electrode plates. This object is achieved by providing a cooking device comprising:

a pair of electrode plates comprising a contact surface that is used to contact food materials, which is adapted to be connected to an electrical power supply; and

a container adapted to form a cooking chamber for accommodating the pair of electrode plates and food materials to be cooked;

when the pair of electrode plates are arranged in the cooking chamber, the contact surfaces face to each other and keep a distance therebetween;

wherein the contact surface comprises a water preservation layer.

The water preservation layer could keep some extra moistures around the contacting surface area of the dough. Although the temperature on the contacting surface is still higher than other portions and the moisture keeps evaporating, the extra moistures will prevent the contacting surface of the dough from becoming dry and hard. The electrical connection between the dough surface and the electrode plates can be maintained, so that the ohmic heating can be continued until the cooking is completed.

In an example of the embodiments, the water preservation layer comprises a mesh adapted to preserve water. Here mesh means a plate-like structure comprising many holes. No matter how the mesh or hole is formed, by weaving or etching, and no matter the plate is plane or curved, it should be within the scope of this invention. Not all meshes are suitable to be used to preserve water. The capability of water preservation of a mesh depends on the nature of material as well as the dimension of the holes. For the meshes made of materials that do not absorb water, such as metal, with the holes dimension decreases, a better water preservation capability is obtained. A skilled person can obtain the necessary specific parameters by experiments for each kind of material. For the meshes made of materials that absorb water, such as cotton, the holes dimension is no longer the primary factor influencing the water preservation capability.

Before cooking operation, the mesh can be for example dipped into or poured with water. The holes on the mesh can keep some extra moistures around the contacting surface area. During heating, this kept extra water can continuously compensate the water evaporation resulted by the high temperature. So that the contacting surface of the dough will not become dry and hard before the cooking is completed.

This mesh could be made of conductive materials like metal, carbon, graphite, or insulative materials like plastic, fibre, or their combinations. Conductive mesh can help to apply the electrical power to the dough. Insulative mesh should be used together with a conductive surface. Since dough is very soft, it can penetrate the holes of the mesh and contact the conductive surface to receive electrical power.

A mesh made by fibre can usually absorb more water than other materials.

This provides a higher freedom in the design of the mesh. In a specific example, the mesh comprises gauze. Gauze is a cheap, clean and convenient material having been widely used in normal people's daily lives. Being made of fibre, gauze has a better property in absorbing and keeping water compared with metal or plastic.

Stainless steel is a common materials used in kitchen appliance. When the water preservation layer comprises a stainless steel mesh, in order to obtain a better water preservation property of the mesh, it is preferable that the holes have a dimension smaller than 60 mesh. A more preferable scope is smaller than 80 mesh.

It is possible for the cooking device to comprise a water channel connecting the water preservation layer to a water source. Preferably, the water channel is arranged behind the water preservation layer. No matter how the water preservation layer is designed, the water preservation property cannot be unlimited. The kept extra water could be dried out if heating lasts for a long enough time. A water channel can supplement more water when the kept water is dried out. This can ensure a good cooking result in a wider application scope. In addition, with supplementary water supply, the requirements on the water preservation property can be decreased. There provides a higher freedom in the design of the water preservation layer.

When the cooking device further comprises a control unit and a sensor unit that is adapted to sense a parameter reflecting the humidity nearby the water preservation layer or the contacting surface area, the water channel can supply water automatically when the humidity is lower than a threshold.

The sensor unit can comprise a temperature sensor, a current sensor and/or a humidity sensor. As explained before, the local temperature around the contacting surface area of the dough is critical to the water evaporation. Thus, by monitoring the local temperature, the humidity change around the contacting surface can be estimated. The current sensor can predict the potential risk of a current cut-off originating from the dry and hard contacting surface of the dough by monitoring the changes of the current through the circuit.

In a preferable embodiment, the water preservation layer is detachable. This enables a better convenience for cleaning. Especially when gauze is used as the water preservation layer, a new piece of gauze could be used for each cooking. This can totally save the time for cleaning.

The electrical power applied to the electrode plates could be alternating current with voltage gradient higher than 1 V/cm during fermentation and higher than 5 V/cm during cooking. Preferably, the voltage gradient could be higher than 3V/cm during fermentation and higher than 10 V/cm during cooking.

In an example of the embodiments, the cooking device can use a pair of electrode plates that at least a part of the electrode plates is in the form of an electrical mesh. In this embodiment, the electrical mesh can function as a water preservation layer and an electrode plate simultaneously.

Other features and advantages of embodiments of the present invention will also be understood from the following description of exemplary embodiments when read in conjunction with the accompanying drawings, which illustrate, by way of example, spirit and principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

Figs. 1A and IB show a basic model of a cooking device according to this invention, wherein in Fig. IB the electrode plates are placed within the container;

Fig. 2 shows an example of the electrode plates used in the cooking device shown in Fig. 1;

Figs. 3A and 3B show another example of the electrode plates that could be used in a cooking device in accordance with the invention, wherein Fig. 3B shows a cross sectional view along line N-N in Fig. 3A; and

Fig. 4 shows another embodiment of the cooking device according to this invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will now be discussed with reference to several example embodiments. It should be understood that these embodiments are discussed only for the purpose of enabling those skilled persons in the art to better understand and thus implement the subject matter described herein, rather than suggesting any limitation on the scope of the subject matter.

Referring to Figs. 1A and IB, a basic model of a cooking device according to this invention is shown. Fig. IB shows that the electrode plates are placed within the container. Figs. 1 A and IB are only sketches helping to understand the principles of this invention, so they show a very simple structure.

Basically, the cooking device 10 comprises a container 11 and a pair of electrode plates 15a, 15b. The container 11 in the drawings looks like a cuboid box. Its side walls enclose and form a cooking chamber 13 for accommodating the food materials to be cooked. Other auxiliary parts of the cooking device 10, like a cover or a user interface, are not shown, but it can be envisaged that these auxiliary parts can be added to the shown embodiment without any difficulty.

Fig. 2 shows an example of the electrode plates used in a cooking device in accordance with this invention. The electrode plates 15a, 15b are made of a piece of metal mesh. There are arrays of holes 17 on the mesh which are used to preserve water. These holes could be formed by punching or etching. While, it could be easily envisaged that the electrode plates could also be formed by weaving. By adapting the width of and the space between the metal strands or strips, as well as other parameters of weaving, holes of different dimensions can be formed.

In this embodiment, since the whole electrode plates 15 a, 15b are in the form of a metal mesh, the water preservation property is closely relevant with the dimensions of the holes of the mesh. If the dimensions of the holes are too big, the surface tension of the water layer cannot sustain and the water layer will get broken.

A group of standard stainless steel sieves with holes of different dimensions (40, 60, 80 and 100 meshes) are tested by immersing them into water for 10 seconds, and then getting them out. The capability of the holes of the sieves for holding water is shown in the below table. Experiment results show that the dimensions of the holes are smaller, the water preservation property of the mesh is better. Test Dimension Result

1 40 meshes the water layer in the holes will 'break' quickly after getting out of the water solution

2 60 meshes the water layer in the holes can be hold > lmin

3 80 meshes the water layer in the holes can be hold > 5min

4 100 meshes the water layer in the holes can be hold > 5min

Based on the experiment results, for a mesh made of materials that do not absorb water, like metal, in order to ensure a good enough water preservation property, it is better the dimensions of the holes 17 are smaller than 60 mesh. Dimension scope of smaller than 80 mesh is further preferable.

In another experiment, an ohmic cooking device in accordance with this embodiment is used to make buns. It utilizes a pair of standard stainless steel sieves with holes of 100 meshes as electrode plates. An alternating current is applied to the electrode plates and to the dough to be cooked. During fermentation, the electrical power is 3 V/cm lasting for 30 minutes, and during cooking, the electrical power is 11 V/cm lasting for 25 minutes. By observation, it is found that the buns are well cooked.

Figs. 3A and 3B show another example of the electrode plates 25a, 25b that could be used in a cooking device in accordance with this invention. Fig. 3A shows the contacting surface of the electrode plates 25a, 25b and Fig. 3B shows a cross sectional view along line N-N in Fig. 3A.

With reference to Fig. 3B, the details of the electrode plates 25a, 25b are clearly shown. The electrode plates 25 a, 25b comprise an electrical substrate 30 and a water preservation layer 29. The electrical substrate 30 could be made of metal, carbon or graphite and could supply electrical power to the food materials. The water preservation layer 29 could be made of conductive materials, too, or of insulative materials like plastic or cotton cloth. When the water preservation layer 29 is made of insulative materials, its dimensions should be designed that the soft dough could penetrate the holes 27 on the water preservation layer 29 and contact the electrical substrate 30 to build up the electrical circuit. Meanwhile, the water kept in the holes can also help to maintain the circuit.

In an embodiment, the water preservation layer 29 is gauze, which is detachably fixed to the electrical substrate 30. Compared with metal or plastic, gauze has a better property in absorbing and keeping water, so the freedom in the dimensions of the holes could be very large. Because of the detachable arrangement, the gauze can be removed from the device for washing. Or, the users can use a new piece of gauze for each cooking because gauze is very cheap and easy to acquire from market.

Behind the electrical substrate 30, two sets of water channels 31, 32 are arranged. Fig. 3 A clearly shows an example of the configurations of these water channels 31, 32 with dashed lines. These water channels 31, 32 could be connected to a water supply (not shown) through a water inlet 33 and/or a water outlet 34. The water is supplied to at least a part of the holes 27 for supplementing new water to the water preservation layer 29. While it can be easily envisaged that the water channels can also be arranged in other methods.

Fig. 4 shows another embodiment of the cooking device 40 in accordance with this invention. In this embodiment, the cooking device 40 comprises a control unit 41, a power supply unit 36, a water supply unit 43, a user interface 42 and a sensor unit 35 as well as two electrode plates 25a, 25b and two sets of water channels 31, 32.

A user can input through the user interface 42, choosing the food type or materials to be cooked, amount of food, personal preferences, etc. The Power supply unit 36 is connected to the electrode plates 25a, 25b to apply alternative current to the food materials.

The sensor unit 35 may comprises a humidity sensor on the contacting surface of each electrode plate 25a, 25b. The sensed results will be sent to the control unit 41 for a comparison with a pre-decided threshold, so as to determine whether the humidity of the contact surface of the dough is too low and a risk of circuit cut-off exists. In some

embodiments, a temperature sensor or a current sensor can be used independently or together with the humidity sensor for predicting the risk. Since the temperature is closely relevant with the water evaporation, a coordination can be obtained between temperature and humidity. While a current sensor can monitor the changes of the current through the circuit, it can predict the potential risk of a current cut-off originating from the dry and hard contacting surface of the dough.

When the control unit 41 finds the risk, it can control the water supply unit 43 to supplement more water to the water preservation layer of the electrode plate 25 a, 25b through the water channels 31, 32. This is very helpful to ensure a good cooking result especially when the cooking lasts for a long time and a large amount of food materials are cooked.

Now the cooking process will be explained in simple words with reference to the previous explanations on the cooking devices in accordance to this invention.

Before cooking starts, the electrode plates 15a, 15b, 25a and 25b could be first dipped into water or washed with water for several seconds. When the water preservation layers are detachable, like for example a layer of gauze, the gauze can be fixed to the electrode plates after this step. Now the holes and/or the fibres in the water preservation layers can keep or absorb an amount of water.

Then the electrode plates 15a, 15b, 25a and 25b can be assembled into the cooking chamber with the contact surfaces facing to each other. A prepared dough can be placed into the cooking chamber with good contacting to both electrode plates. Sometimes, the electrode plates need to be adjusted thereafter to ensure the good contacting.

After cooking starts, electrical power is supplied to the dough through the electrode plates. Preferably, it is an alternating current with voltage gradient higher than lV/cm, which is suitable for dough cooking. With the heating continues, the temperature around the contact surface of the dough becomes higher than the other parts and consequently the local water evaporation becomes faster. However, since the holes 17, 27 and/or the fibres in the water preservation layers 19, 29 of the electrode plates have kept or absorbed an amount of water, this water will compensate the faster local water evaporation, so that the contact surface of the dough is prevented from being dry or hard.

If the heating lasts for a long time and the kept water is almost dried out, the control unit 41 will detect this risk by monitoring the sensed results from the humidity sensor or temperature sensor or current sensor in the sensor unit 35. Then the control unit 41 will control the water supply unit 43 to supply more water to the water preservation layers 19, 29 so as to refill the holes 17, 27 and the fibres.

Various modifications, adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. Any and all modifications will still fall within the scope of the non-limiting and exemplary

embodiments of this invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Any reference signs in the claims should not be construed as limiting the scope.