in fig1 , a cross section through an egg assembly adapted to be prepared in a conventional microwave oven is shown . the egg 1 has a yolk 2 , albumin 3 , and a shell 4 . enclosing the shell , the egg is provided with a packaging which in this embodiment consists of a single layer 5 which completely enfolds the egg 1 . this layer 5 is here in a firm thermal contact with the shell 4 . in order to prevent an egg from exploding while subjected to microwave radiation , and at the same time allowing swift preparation of an egg , it was found that the layer which is in contact with the egg shell should have a dielectric constant with an imaginary part , ε ″, in a certain range , explained below . in an embodiment , the layer 5 can comprise a layer of water - retaining matrix material . an example of such a matrix material is a fibrous layer capable of absorbing water . other examples of such matrix material are a hydrogel , for instance . the layer 5 is such that when soaked with water it results in a layer with the thickness of about 1 - 5 mm . in an embodiment , such a layer is soaked with water with 0 . 4 - 0 . 5 m nacl . in an alternative embodiment , the layer comprises a water - retaining matrix material holding a salt , for instance nacl , in a substantially solid form . in a layer of between 1 - 5 mm of water - retaining material , about 1 gr of salt will generally be present . in an embodiment , the salt will be uniformly distributed . before use , an egg with such a layer is first brought into contact with some water which it will soak . next , it is placed in a microwave oven and prepared . the matrix material or any material enclosing it should be such that the layer thickness remains almost the same during the boiling process . in order to maintain the properties of layer 5 , the packaging can comprise a further , outer layer ( not shown in the drawing ). to that end , the outer layer can have one of the following properties . it can be designed to retain the thickness of the layer 5 during boiling of the egg . if the layer 5 comprises a water retaining matrix material , it can also be a watertight layer in order to prevent the water to escape during boiling of the egg . in an embodiment , the outer layer is a plastic material enfolding the layer 5 and having a thickness of less than 2 mm . alternatively or additionally , in order to diminish influences of the first layer on the egg , for instance its taste , a contact layer can be present between the egg shell and the first layer . via this contact layer , the first layer is in heat exchanging contact with the egg shell . the contact layer prevents the first layer , or ( salt ) water or other components in the first layer , to come into direct contact the egg shell . the contact layer in an embodiment is an elastomeric layer following the shape of the egg it encloses . it thus allows thermal contact between the first layer and the egg shell . in fig2 and 3 , an alternative way of providing a layer around an egg , which allows preparation of an egg using microwave radiation , is shown . this embodiment provides a packaging for an egg . in this embodiment , the packaging provides a layer 6 of material . this layer 6 is shaped to have an inner surface following the contour of the shell 4 of the egg . this surface is at a distance from the eggshell of the egg . thus , it allows the provision of a cavity 8 around the shell 4 of the egg . in order to provide a uniform cavity , i . e . to make the distance between the inner surface of the layer 6 and the outer surface of the shell 4 of the egg as uniform as possible , the packaging is provided with spacers 7 on the layer 6 . these spacers 7 keep an egg substantially centred in the packaging , thus providing a substantially uniform cavity 8 around the shell 4 of the egg . in use , the cavity can be filled with a material which has the properties defined above . in an embodiment , the packaging has two parts which are connected via a hinge 9 . thus , the packaging can be hinged open , an egg can be placed in the packaging , and the packaging can be closed around the egg . part 10 indicated a filling opening 10 . in an embodiment , a closed rim 11 ( fig3 ) provides a liquid - tight closure of the packaging . in a further embodiment , a part of the closing rim 11 can provide a sealable conduit 10 for filling the cavity 8 with a liquid having the properties , in particular the imaginary dielectric constant , described above . in an embodiment , the packaging is substantially made from a polymer material having a softening temperature of at least 130 degrees celsius . an example of such a polymer material is pet , polyethylene terephthalate . in such an embodiment , the packaging can be formed from a sheet of this polymer material in a deep - drawing process . the latter process as such is well known in the art , and will not be explained further in this description . in such an embodiment , a hinge may be formed as a thinned line of material , allowing two parts to hinge . it thus forms a living hinge . in a particular embodiment , the spacers 7 may be formed as parts of the layer of polymer material which bulges inward . in operation , such a packaging is opened , an egg is placed inside , and the packaging is closed again . next , via a sealable filling opening the cavity 8 is filled with a liquid material having the properties described in this document . in an embodiment , the distance between the inner surface of the layer and the egg shell 4 , i . e . the width of the cavity , is between about 2 - 4 mm , in particular about 3 mm . this cavity can be filled with a liquid having a dielectric constant with the imaginary part mentioned above . as an example , it can be filled with water having about 0 . 4 - 0 . 5 m nacl . this packaging thus prepared can be placed in an ordinary household microwave oven . next for preparing a soft - boiled egg , this is subjected to a program for instance of 70 seconds at 800 watt and about 20 seconds at 560 watt . thus , it is possible to prepare a soft - boiled egg in about 80 seconds . in the current invention , it was found that in order to prepare an egg in microwave radiation , it requires a packaging comprising a first layer having certain well defined properties . it was found that the right properties of this layer prevent the egg from exploding in a microwave oven . in fact , it was found that the relation between layer thickness and ε ″, the imaginary part of the dielectric constant , is of importance . fig4 shows the results of calculations giving the upper range and lower range of the relationship between ε ″ and layer thickness for which it is possible to prepare an egg using microwave radiation . please note that the value of ε ″ in the graph is defined at 2 . 45 ghz . in fact , the area between these curves is the area in which ε ″ and layer thickness d should be in order to allow a chicken egg of between about 45 gr and 75 gr to be prepared within 120 seconds . within this area , for instance a material with a certain ε ″ can be linked to a layer thickness . in fact , the lower limit relates to the combinations of ε ″ and layer thickness which is close to the properties which allow a 45 chicken gr egg to be hard - boiled in about 100 seconds . the upper limit relates to the combinations of ε ″ and layer thickness which little above to the properties which allow a 75 gr chicken egg to be soft - boiled in about 120 seconds . in equations , the lower limit can be represented by ε ″( d )= 229 · d − 1 . 168 and the upper limit can be represented by ε ″( d )= 2989 · d − 2 . 237 . the area is further limited by , ε ″( d )= 300 . in fact , it was found that a 45 gr egg , for instance a small chicken egg , can be soft - boiled in about 80 seconds when layer 5 has a layer thickness d and ε ″ selected from an area with a lower limit ε ″( d )= 380 · d − 1 . 25 and the upper limit can be represented by ε ″( d )= 1600 · d − 2 . in this range , ε ″( d )& lt ; 300 . on the other hand , a 75 gr egg , for instance a large chicken egg , can be soft - boiled in about 120 seconds when the layer thickness d and ε ″ selected from an area with a lower limit ε ″( d )= 1600 · d − 2 and the upper limit can be represented by ε ″( d )= 2989 · d − 2 . 237 . in this range , ε ″( d )= 300 again limits the area . fig5 shows a curve indicating the relationship between temperature , ε ″ and molarity of salt or saline water , i . e . water having the indicated molarity of nacl . it shows that the relationship between temperature , ε ″ and molarity is complex and non - linear . it thus illustrates that it is not straight forward to transfer one molarity into another . in practice , when providing egg assemblies according to the invention to the consumer , the effectiveness of the assembly may be further improved by a proper matching between size ( or better yet , weight ) of the egg , ε ″ of the material provided in the packaging , and layer thickness of the packaging . furthermore , the layer thickness should vary less than 30 %. in that way , it can be possible to provide egg assemblies which can be “ boiled ” in for instance a microwave oven in a reproducibly way . fig6 shows a schematic drawing of an apparatus for cooking or boiling or preparing an egg . the apparatus 21 has a housing 22 which has a cavity 23 . in this cavity 23 a holder 24 is provided . this holder 24 has at least one cavity 25 in the shape of an egg . in this embodiment , there are two cavities 25 . in an apparatus there can be as many as 4 cavities 25 for preparing eggs . the holder 24 provides the layer described above . the apparatus 21 further has a controller 26 which is operationally coupled to a weight sensor 27 in each of the cavities 25 for determining if an egg is placed in the cavity 25 . in particular if an egg is placed in the cavity 25 , it allows for determining its weight . alternatively , one weight sensor 27 can be provided weighting increase in the weight of the holder 24 . as the eggs have about the same weight , it allows determination of the number of eggs in the holder 24 . providing a weight sensor 27 for each cavity 25 has an additional advantage in that it allows detection of which cavity 25 holds an egg . the controller is in a further embodiment operationally coupled to a temperature sensor 28 in each of the cavities 25 . the temperature sensor 28 first is a safety for preventing overheating of the egg ( s ). furthermore , it provides temperature information to the controller 26 during the preparation process for controlling the preparation process . finally , it measures the temperature of an egg before it is going to be prepared . in that way , the process can be controlled better . the temperature sensor 28 in an embodiment is positioned to contact an egg placed in the cavity 25 . in an embodiment , the apparatus 21 has an inlet 29 for water . in an embodiment , this inlet 29 is attached to a water mains . the inlet 29 in this embodiment is provided with a controllable valve 30 which is operationally coupled to the controller 26 . in that way , the controller 26 can arrange for the provision of water in the holder 24 . in an embodiment , a further temperature sensor 32 is provided in the inlet 29 for measuring the temperature of incoming water . this water can for instance also be used for cooling an egg after the cooking process . in a further embodiment , the apparatus 21 has an outlet 31 for water . in an embodiment , this outlet 31 is coupled to a drain . the outlet 31 in this embodiment is provided with a controllable valve 38 which is operationally coupled to the controller 26 . in that way , the controller 26 can arrange for removal from holder 24 of the water after use . in an embodiment , the apparatus further has a input part 33 through which the desired state of preparation of the egg can be entered . this input part 33 is operationally coupled to the controller 26 . for instance , a selection switch 35 , knob , or push button 35 can be provided which has several settings , for instance three settings for selecting a soft , medium or hardboiled egg . display 34 is operationally coupled to the controller 26 and can display for instance settings of selector means 35 , but also remaining preparation time . furthermore , the apparatus can sound an alarm when the eggs are ready . in the embodiment , the housing has hinges 36 for a lid 37 , enabling opening of the microwave cavity 23 . the holder 24 in this embodiment has two parts thus allowing access to the cavities 25 in order to place or remove eggs . based on the weight , measured temperatures and selection on the input part 33 , the controller sets the amount of microwave energy needed to prepare egg in the desired way . controller 26 may also calculate a preparation time . furthermore , the apparatus 21 can have display 34 showing for instance the remaining time for preparing the one or more eggs in the holder 4 . in operation , lid 37 is opened providing access to the holder 24 . for instance hinging the two parts of holder 24 apart provides access to the cavities 25 . next , eggs can be placed in the cavities 25 . the holder 24 and the lid 37 are closed , and a user operates selection switch 35 in order to set the way the eggs need to be boiled . the controller 26 operates the valve 30 to allow water via inlet 29 to access the holder 24 . the holder 24 is further provided with for instance salt in a matrix in order to be mixed into the water to provide the first layer having the parameters required . it will be clear that said first layer being in heat exchanging contact also means that a thin layer of material which is transparent to microwave radiation , or almost transparent to microwave radiation , can be present between the first layer and the egg shell . thus , holder 4 can be a hollow material having a space which provides , when filled with salt water as defined above , the firsts layer inside holder 4 , enveloping or enfolding the egg , and in heat exchanging contact with said egg . alternatively , in order to diminish influences on the egg which may influence taste , a contact layer , also discussed above , can be present between the egg shell and the first layer . via this contact layer , the first layer is in heat exchanging contact with the egg shell . the contact layer prevents the first layer , or ( salt ) water from the first layer , to contact the egg shell . after or while filling the cavity 25 in the holder 24 with water , controller 26 determines the size of the eggs present , the desired cooking selection , the temperature of the eggs and the temperature of the water . from these parameters controller 26 can be able to calculate the required microwave power and cooking time . controller 26 starts the cooking process , in an embodiment meanwhile monitoring the temperature of the eggs in order to prevent overheating and to follow the process . if required , and in an embodiment , controller 26 can adjust the power of cooking time depending on measured parameters . thus , it may be possible to use eggs that are less strictly selected . alternatively , demands on the layer around the eggs can be less strict . controller 26 can also display the remaining time on display 34 . using the apparatus , eggs may be prepared in about 60 - 180 seconds . it was found that a selection of m - class eggs would be enough to result in a good preparation result . m - class eggs are selected eggs having a weight of between about 53 - 63 grams . thus , the apparatus would allow for instance a range of eggs to be prepared in a reproducible way , even by ordinary consumers . thus , the apparatus can be designed for preparing m - class eggs . fig7 shows an embodiment of a holder 24 capable of holding at least one egg in the apparatus 21 . the holder 24 in this embodiment has a first half 24 ′ and a second half 24 ″, allowing access to the egg cavity 25 . it is clear that other provisions are possible to allow access to the egg cavity 25 . the egg cavity 25 in this embodiment has an ell enclosing layer assembly comprising in this embodiment naturally the first layer 5 . the layer assembly further comprises a contact layer 40 to be positioned between the first layer 5 and the egg . the layer assembly can further comprise an outer layer 41 . in this embodiment , the layer assembly is positioned in the egg cavity 25 in such a way that a space 42 remains between the outer layer 41 and the inner wall of the holder 24 defining the egg cavity 25 . surrounding the egg cavity 25 in order to seal it , a sealing ring 43 can be provided . the layer assembly in the egg cavity 25 can be permanently connected to the holder 24 . in an embodiment , it is replaceable . thus , it can be used many times , or alternatively a disposable layer assembly can be used . the material of the holder 24 is permeable to microwave radiation and absorbes as little microwave radiation as possible . it can be largely made from a plastic material . the layer assembly is held inside the egg cavity 25 . egg cavity 25 is shaped in such a way that every shape of egg in a certain weight class of eggs fitted with the layer assembly fits within said egg cavity 25 , preferably with little space remaining . in the drawing , the remaining space 42 is represented larger than it will usually be . contact layer 40 is flexible , in order to be able to follow the shape of different eggs . in particular , it is rubbery or an elastomeric material . thus , enclosure of air between the egg shell and the contact layer should be prevented as much as possible . the contact layer 40 prevents liquids from the first layer 5 from contacting an egg held in the layer assembly . the contact layer 40 further allows a heat exchanging contact between the first layer 5 and an egg shell of an egg . in order to be able to withstand the temperatures of cooking or preparing an egg , the contact layer should be heat stable up to a temperature of about 130 ° c . in an embodiment , the contact layer is a silicone polymer layer , or an alternative elastomeric material . the outer layer in an embodiment is flexible , preferably even elastomeric , though it may be a little more ridged than the contact layer 40 . it too like the contact layer 40 is transparent to microwave radiation . it also is stable up to a temperature of about 130 ° c . in an embodiment , the first layer 5 provided between the contact layer 40 and the outer layer 41 is a layer of salt water described above . alternatively , it is a hydrogel or another material having the properties mentioned earlier in this description . in an embodiment , the first layer 5 is in contact with the water supply or inlet described above . in an embodiment , via the inlet 29 and using the controllable valve 30 , it is possible to add more or less water and thus to modify properties of the first layer . it is , for instance , possible to modify the layer thickness for instance by providing more or less water . it is even possible to modify in that way the ε ″ of the first layer . thus , using measure weight of each egg , the controller can modify the first layer properties to allow preparation of an egg within the short time defined above . it will also be clear that the above description and drawings are included to illustrate some embodiments of the invention , and not to limit the scope of protection . starting from this disclosure , many more embodiments will be evident to a skilled person , which are within the scope of protection , and the essence of this invention and which are obvious combinations of prior art techniques and the disclosure of this patent .
the invention relates to an apparatus for boiling an egg , said apparatus comprising a device for providing microwave radiation in a confined space , said space further comprising a holder provided with at least one cavity adapted to the shape of an egg with an eggshell , said cavity provided with a first layer surrounding the eggshell , said first layer :— is in heat exchanging contact with the shell of the egg ;— has a dielectric constant with an imaginary part , ε ″, between 20 - 500 at a temperature between 0 ° c .- 100 ° c . and at a microwave frequency of 2 . 45 ghz , and — having a layer thickness d of 1 - 6 millimetre and varying less than 30 % over the egg , or said holder for holding at least one egg assembly adapted for cooking an egg using microwave radiation , said egg assembly comprising an egg having an eggshell which is provided with an packaging surrounding the eggshell , said packaging comprising a first layer which :— enfolds the shell of the egg and is in heat exchanging contact with the eggshell ;— has a dielectric constant with an imaginary part , ε ″, between 20 - 500 at a temperature between 0 ° c .- 100 ° c . and at a microwave frequency of 2 . 45 ghz , and — has a layer thickness d of 1 - 6 millimetre and which varies less than 30 %, and — said packaging designed to retain the layer thickness of the first layer while said egg assembly is subjected to said microwave radiation to turn said egg into a boiled egg .