The invention relates to a method for preparing dough products, such as loaves, the method comprising the steps of preparing dough and forming a dough product therefrom and heating the dough product with the aid of microwave radiation. From practice, it is known to use microwave radiation for manufacturing dough products, such as loaves. The dough product may be made to rise or be cooked with the aid of, for instance, microwave radiation, by exposing the dough products, simultaneously or not simultaneously, to conventional baking methods, such as hot air. Using microwave radiation for manufacturing dough products is particularly favourable with respect to using only conventional baking methods, such a hot air and the like, since microwave radiation provides that the process of manufacturing the products is considerably shorter and more energy efficient. The fact is that microwave rays cause a high-frequency alternating electric field having direct interaction with polar molecules in the dough, such as water molecules. Through the frictional heat effected by the molecules having been set into vibration, the dough is heated from the inside outwards. The microwave radiation is completely absorbed by the dough products so that the energy efficiency is high. However, as the energy conversion takes place within the dough products, it is difficult to perceive when such a dough product has risen and/or is cooked, so that the final dough product may not have the desired quality.

Therefore, the invention aims to provide a method for manufacturing dough products, such as for instance loaves, wherein the method is efficient and wherein the heating process of the dough products can be controlled well so that good quality dough products can be obtained. To that end, the invention provides a method of the type mentioned in the opening paragraph, characterized in that the microwave radiation is controlled depending on a calibration line representing a relation between a core temperature of the dough product and a surface temperature of the dough product in order to have the dough product rise and/or cook. Such a method provides that the core temperature does not become too high in relation to the surface temperature. What is thus prevented is that the core of the dough product has a relatively high temperature and an outside of the core product has a relatively low temperature so that the dough product does not heat in a desired manner. As the surface temperature of a dough product is controlled during the heating process and as the calibration line, representing the relation between the core temperature and the surface temperature, couples a particular core temperature to a surface temperature, the core temperature too can be controlled well. When the surface temperature is measured, the value of the core temperature at this surface temperature is known with the aid of the calibration line and, based thereon, the microwave radiation can be controlled in a desired manner so that the process is controllable. Hence, the core temperature is controllable which provides that the leavening action in the dough product can be controlled. This method for preparing dough products results in dough products with a fine structure. According to a further elaboration of the invention, the surface temperature of the dough product is measured during the preparation of the dough product and based thereon a power, a frequency and/or radiation time of the microwave radiation is set. An advantage of controlling the frequency of the microwave radiation is that as a result, so called hotspots in the dough product can be prevented. According to a further elaboration of the invention, the power can be varied over time in a pulsating or continuous manner. In a further elaboration of the invention, the calibration line represents a relation between the core temperature and the surface temperature in association with a particular course of the power of the microwave radiation over time. Through heating the dough product by means of the microwave radiation with the aid of the calibration line, the leavening action in the respective dough product can be controlled, as it were. By carefully regulating the temperature in the dough product, the leavening process can be started and stopped at a desired moment. At a temperature of 5O ⁰ C for instance, the yeast cells lose their activity so that rising slows down and eventually stops. This enhances a well controllable and reproducible process for heating dough products so that they rise and/or cook in a desired manner, and/or at a desired point in time and/or such that a desired volume of the dough products is achieved.

The invention further relates to a method for determining an above- described calibration line, this determination comprising measuring a core temperature and an associated surface temperature of a dough product with a particular composition during heating of the dough product, wherein the temperatures are measured in association with a particular course of the power of microwave radiation over time. By measuring of at least one dough product, kneaded from dough having a particular composition, in a particular preparation unit, the core temperature and the surface temperature during the heating time of the dough product in association with a particular course of the power, a relation between the core temperature and the surface temperature over time in association with this course of the power can be determined.

According to a further elaboration of the invention, the calibration line can be made more reliable by having the measuring of the core temperature and the surface temperature take place on a number of dough products of a same composition, while average values of the temperatures over time associated with the particular course of power are determined. As a result, variations in the temperatures and hence in the calibration line are somewhat levelled off.

According to a further elaboration of the invention, it is preferred that the core temperature is measured with the aid of a core temperature meter which is inserted into the dough product and which measures the core temperature of the dough product during heating. Such a core temperature meter is suitable for use in microwave radiation and can determine the core temperature of the dough product highly accurately.

Preferably, the surface temperature is measured with the aid of a surface temperature meter, such as, for instance, a pyrometer.

The invention further relates to a preparation unit for heating dough products, such as loaves, the preparation unit comprising at least one microwave radiation source for heating the dough products with the aid of microwave radiation in order to have the dough products rise and/or cook, the unit further comprising a control in which a dough product specific calibration line can be programmed on the basis of which the control can control the at least one microwave radiation source, and a dough product manufacturing apparatus provided with such a preparation unit. Such a preparation unit and dough product manufacturing apparatus provide advantages and effects similar to those mentioned with the above-mentioned method.

Further elaborations of the invention are described in the subclaims and will be further elucidated in the following with reference to the drawings.

Fig. 1 shows a schematic cross sectional view of a dough product manufacturing apparatus for preparing dough products;

Fig. 2 shows a schematic diagram in which the steps of the method for manufacturing dough products are represented; and Fig. 3 shows a schematic diagram in which the steps of the method for determining a calibration line are represented.

In Fig. 1, an apparatus 1 for manufacturing dough products P, such as loaves, is shown. The apparatus 1 is provided with a preparation unit 2. In another embodiment of the invention, the preparation unit 2 can also be provided as at least two separate modules provided one behind the other, for instance a separate module for having the dough products P rise, and a separate module for cooking the dough products P. The preparation unit 2 of Fig. 1 is provided with a conveyor belt 3 with which dough product P are conveyed in baking tins 4 in a conveying direction Rt. In a different embodiment of the invention, the preparation unit 2 can be provided without a conveyor belt 3. The baking tins 4 in which the dough products P are provided are preferably synthetic baking tins 4 provided with small openings, conducting the microwave radiation S well. However, the baking tins 4 can also be, for instance, of a metal.

The preparation unit 4 is further provided with a number of microwave radiation sources 5 which may be provided above as well as below the conveyor belt. The microwave sources 5 are positioned such that the microwave radiation S reaches the dough products P in a simple manner. Naturally, the number of microwave sources 5 in the preparation unit 2 can vary, as well as the location of the sources 5 in the internal space 7 of the preparation unit 2. Additionally, the preparation unit 2 is provided with microwave reflection elements 6. These elements 6 prevent the microwave radiation S from reflecting back into the sources 5, which may be harmful to the sources 5. The microwave reflection elements 6 can for instance be ventilators that distribute the radiation in an internal space 7 of the preparation unit 2. In the internal space 7 of the preparation unit 2, pyrometers 8 are disposed which, in use, measure an outermost surface temperature of the dough products P. The manufacturing apparatus 1 further comprises a control 9 for controlling the microwave radiation sources 5. The pyrometers 8 are connected to the control 9 for passing on temperature measurements of the outermost surface temperature of the different products P to the control 9. In the control 9, a calibration line is programmed on the basis of which the preparation unit 2, at least the microwave radiation sources S and/or the conveyor belt 3, is controlled in order to have the dough products P rise and/or cook in a desired manner, at a desired time and/or to a desired volume so that the dough products P with a desired quality are obtained. The cooked loaves have no crust or only a very thin one. By providing a browning unit 2 downstream of the preparation unit 2 in the apparatus 1, a crunchy, colored crust can be provided on the dough product P after the product P has been cooked. Such a browning unit can for instance be a bandoven or comprise an infrared radiation source. In this exemplary embodiment, the preparation unit 2 comprises at the infeed 2a and outfeed 2b thereof radiation protectors 11 which stop the microwave radiation S to prevent this radiation S from, for instance, coming into contact with a user of the preparation unit 2. Advantages of such an apparatus 1 according to the invention are that this apparatus 1 can have dough products rise and cook in a low-energy manner. A saving of approximately 70% compared to conventional apparatuses can be achieved with the apparatus 1 according to the invention. Further, owing to the relatively brief rising time and cooking time, the apparatus can be relatively small and have a relatively small floor surface for manufacturing large quantities of dough products P. In another embodiment of the invention, the apparatus 1 can be provided with a varying number of microwave radiation sources 5 which may be controlled independently of each other. This is favourable when different types of dough products P are prepared in the preparation unit 2.

With the apparatus 1 described hereinabove, a dough product P can be manufactured according to the method of the invention. Prior to clarifying the method further, first, the method for determining a calibration line for a dough product P with a particular composition intended for a specific preparation unit 2 will be described with reference to Figs. 1 and 2.

Method for determining the calibration line

In Fig. 2, a diagram is shown in which the different steps for determining the calibration line are represented. The calibration line is specific to a dough product P with a specific composition and volume and specific to a particular preparation unit 2 (see Fig. 1). The composition of the dough depends, inter alia, on the raw materials used upon preparation of the dough.

In the first step 30 of the method, dough products P are kneaded from a dough with a particular composition and placed in a baking tin 4.

Then, in a number of dough products P a core temperature meter 10 (see Fig. 1) is placed (step 31). The core temperature meter 10 is resistant to microwave radiation S and is, for instance, of a glass fiber with a tip of ceramic material. Such a core temperature meter 10 can measure the core temperature accurately to 0.1 of a degree.

The separate dough products P are then fed one behind the other through the preparation unit 2 (step 32) in which the dough products P are heated. During heating, both the core temperature and the surface temperature, which is measured with the aid of the pyrometers 8, of each dough product P are measured and recorded over time. These temperatures, in turn, relate to a particular course of the power of the microwave radiation sources 5 of the preparation unit 2.

The core temperature and the surface temperature of each of the heated dough products are stored and, preferably, average values thereof are determined (step 33). The average values of the core temperatures of the different dough products P and the average values of the surface temperatures of the different dough products P represent, in association with a particular course of the power, a particular relation over time, which forms the calibration line (step 34). Since various process factors influence the calibration line, the calibration line is specific to a particular preparation unit 2. Process factors such as the distance from the microwave radiation sources 5 to the dough product P, the location of the microwave radiation sources 5 relative to the dough product P, the power range of the microwave radiation source 5, a frequency range of the microwave radiation source 5 and/or a conveying speed of the dough products P through the preparation unit 2 can influence the course of the calibration line related to a course of the power of the microwave radiation sources 5 over time. For a description of the method for preparing a dough product P, reference is made to Fig. 3, with the calibration line from step 34 serving as starting point.

Method for preparing a dough product In Fig. 3, a diagram is shown in which the different steps for preparing a dough product P are represented. Before the dough products P can be prepared, the calibration line, which is preferably determined with the above-described method, is entered into the control 9 of the manufacturing apparatus 1, at least of the preparation unit 2 (step 40). The dough products P are manufactured on the basis of the same recipe as the dough products P used in the method for determining the calibration line. The dough products P therefore have the same composition and are prepared from the same raw materials. The dough products P are placed in baking tins 4 and then positioned on a conveyor belt 3 (step 41). The conveyor belt 3 is set in motion in order to move the dough products P in a conveying direction Rt for, successively, feeding them to an infeed 2a of the preparation unit 2 (step 42), conveying them through the preparation unit 2 and then, via an outlet 2b, having them leave the preparation unit 2 as a dough product P ready for consumption. With the preparation unit 2, a dough product P can be made to rise (step 43) and/or be cooked (step 44). The rising time according to the method of the invention has a duration of approximately one third of the duration of the leavening process according to the state of the art, with a dough product P of a weight of approximately 750 grams. Cooking according to the method of the invention can be faster by approximately one fifth of the required cooking time according to the state of the art, with a dough product P with a weight of approximately 750 grams.

By means of the microwave radiation S ₅ the leavening action in the dough product P is controlled, while the temperature of the product P preferably does not exceed 35°C, so that the quality of leavening remains high. Owing to the microwave radiation S, the processes that take place in the dough product P take place simultaneously throughout the entire dough product P. As the microwave radiation S controls the leavening action, CO2 is formed so that an airy dough is created. By measuring the surface temperature during the leavening process, the core temperature of the dough product P can be accurately determined, while the microwave radiation S is controlled depending on the calibration line. On the basis of the calibration line, the power, the frequency and/or the radiation time of the microwave radiation S is controlled. After approximately 20 minutes, the leavening process has finished. In order to stop the leavening process through control of the microwave radiation, the temperature can be brought above 50 ⁰ C, so that yeast cells lose their activity whereby the leavening process slows down and eventually stops. Then, the dough products P can be further heated in order to cook the dough products (step 44).

When the leavening process has stopped, the power of the microwave radiation S can be increased so that eventually, the temperature of the dough products reaches 95°C-98°C. With these temperatures, the formation of steam is prevented which is favourable to prevent moisture from ending up in the containers in which the dough products P are conveyed. During cooking, the surface temperature of the dough products P is measured and, on the basis of the calibration line, the microwave radiation is controlled. Cooking has a duration of at most 6 minutes. When the dough product P is cooked, it can be taken from the baking tin 4. Then, the dough product P does not have a crunchy, colored crust (step 46). It is also possible that the dough product P is post-browned in, for instance, a bandoven or with the aid of infrared radiation S (step 45).

It will be clear that the invention is not limited to the exemplary embodiment described but that various modifications are possible within the framework of the invention as outlined by the claims.