WO2001091621A1

WO2001091621A1 - Heating devices for self heated food packages

Info

Publication number: WO2001091621A1
Application number: PCT/GB2001/002295
Authority: WO
Inventors: Matthew John Searle
Original assignee: Thermotic Developments Limited
Priority date: 2000-05-30
Filing date: 2001-05-23
Publication date: 2001-12-06
Also published as: AU2001258609A1

Abstract

The heating regime of an exothermic reaction-type heating device is set by choosing different ratios of a first fluid reactant to a second reactant. In one device, high temperatures are provided by a substantially stochiometric amount of the first reactant and in another device the first reactant is provided in greater quantities so that it boils and limits the device temperature.

Description

HEATING DEVICES FOR SELF HEATED FOOD PACKAGES

The present invention relates to a method of making a heating device for providing a desired quantity of heat to a food package, a method of producing a self- heated food package and a set of heating devices for heating food packages.

The prior art is replete with self-heating food and beverage containers. Most use an exothermic chemical reaction to provide the heat, most commonly between quicklime and water. For brevity, the following discussion refers to quicklime and water but it is envisaged that the invention is applicable to other materials and combinations of materials which act exothermically together.

It is further envisaged that materials additional to quicklime and water could be used, for example a material such as oil may be added.

It has long been appreciated that the overall quality of heat which can be provided by given amount of quicklime can be estimated to a reasonable accuracy. Provided the quantity of water is at least equal to the stochiometric quantity, and provided a distribution of water is such that a complete reaction takes place, the quantity of heat produced is clearly defined. However, the applicant has appreciated the fact that the temperature which is reached by a vessel containing the reaction materials may not be appropriate to properly heat food.

Firstly, certain foods may be best heated using a dry, relatively high- temperature source. Examples of such foods are pizzas. Other foods are best heated using latent heat from steam, examples being rice and noodles. Yet other foods are best heated by an initial burst of steam which causes the temperature to rise relatively rapidly, followed by dry high temperature heat to provide, or restore crispness.

Prior art self-heating containers provide only a single heating regime. One prior art device, US Patent 5295475 provides a device in which high temperature steam passes up into food to be heated so that the latent heat of vaporisation is added to the conducted heat from the exothermic reaction. This would not be suitable for foods that should be crisp.

Another prior art document, US Patent 5628304 discloses a self-heating container having a first vessel for containing food or a beverage to be heated surrounded by an outer reaction chamber. The reaction chamber is initially divided into two parts, one containing quicklime and the other water, the two being separated by a frangible wall. A cutting device is provided to allow the two reactive materials to come together. Heat transfer is by direct conduction through the barrier between the reaction chamber and the food or beverage-containing vessel. This container is suitable for beverages, but would not allow for heating of crisp foods nor of foods such as rice.

A third prior art device is disclosed in US Patent 3871357. This discloses a self-heating pouch which is disposed in the bottom of a container, the container having a tray disposed within it for food to be heated. Upon activation of the pouch heat is released which passes by convection and conduction into the tray. This device relies on food transfer of heat through the food.

It is accordingly an object of the present invention to at least partially mitigate the limitations of the prior art.

According to a first aspect of the invention there is provided a set of heating devices for heating a food package, each of said heating devices having a casing containing a predetermined quantity of first material and further containing a second material for reacting endothermically with the first material, said second material having a first boiling point, said set of heating devices comprising a first heating device for providing heat at a temperature in excess of said first boiling point and a second heating device for providing second material vapour at a temperature of substantially said first boiling point.

Preferably, the casing of at least said second heating device has a pressure vent device for exit from said casing of said vapour.

Preferably again, the first heating device contains substantially the stochiometric quantity of second material for the predetermined quantity of first material.

Preferably, the second heating device contains a quantity of second material greater than said stochiometric quantity by an amount which restricts the casing temperature to substantially said first boiling point. Advantageously, the quantity of second material loads the exothermic reaction sufficiently to cause the casing temperature to rise to said first boiling point, and immediately thereafter to start to fall below said first boiling point. Advantageously again, the quantity of second material is selected to limit the casing temperature to rise to said first boiling point for a first time period thereby to provide output vapour for said first time period, thereafter allowing the casing temperature to rise above said first boiling point. Preferably the second material includes water, whereby said vapour is steam, and said boiling point is substantially 100 deg C.

Conveniently, the first material includes calcium oxide. Advantageously each device contains substantially the same quantity of first material. Conveniently the casings are of metal.

Conveniently again the casings of each device are substantially identical. Conveniently, the casing of the first heating device has a width and a height, and the width dimension is greater than the height dimension.

According to a second aspect of the invention there is provided a method of making a plurality of heating devices for providing a desired quantity of heat to a food package, the heating devices using the exothermic reaction of quicklime with water to provide said heat, the method comprising selecting a quantity of quicklime in accordance with the desired quantity of heat; determining, in dependence on the quantity of quicklime, a first quantity of water and a second quantity of water, the first quantity being substantially the stochiometric quantity needed to react with the quantity of quicklime and the second quantity being greater than the first quantity by a predetermined amount, said predetermined amount being sufficient to generate steam from said exothermic reaction and to thereby limit the casing temperature to substantially 100 deg C; providing a plurality of casings; a quicklime disposing step comprising disposing said selected quantity of quicklime in said casings; disposing one of said first quantity and said second quantity of water in at least one of said casings; disposing the other of said first quantity and said second quantity of water in at least one of said casings. Preferably said predetermined amount is substantially 30% of said first quantity. Advantageously, after said quicklime disposing step, the method comprises securing a barrier to said casing, said barrier being effective to form a chamber in said casing whereby said chamber contains said quicklime and hermetically seals said quicklime in said chamber.

Alternatively, said quicklime disposing step comprises providing an hermetically sealed container containing said quicklime, and disposing said container in said casing.

According to a third aspect the invention proposes a method of producing a self- heated food package comprising providing a plurality of heating devices, each of said heating devices having an external envelope, the envelope including a first container containing a fluid and a second container containing a predetermined quantity of first material, wherein the fluid is provided for reacting endothermically with the first material, the heating devices including a first heating device adapted to have an envelope temperature in excess of 100 deg C and a second heating device adapted to provide steam at a temperature of substantially 100 deg C; selecting between the first and second heating devices in accordance with a nature of food to be heated in said package; and installing the selected one of the first and second heating devices in said package. Preferably said fluid comprises water and the first material comprises calcium oxide.

Advantageously each of the heating devices contains substantially the same predetermined quantity of the first material.

Conveniently the casings of each of the heating devices are externally substantially identical.

Advantageously the providing step comprises hermetically sealing at least the second container of each device, whereby said water and water from the atmosphere is prevented from reaching the first material.

An exemplary and non limiting embodiment of the invention will now be described with reference to the accompanying drawings in which:- Figure 1 discloses a first heating device for heating a food package useful in understanding the present invention;

Figure 2 discloses a second heating device for heating a food package useful in understanding the present invention and

Figure 3 discloses a release valve for use with the heating devices of figures 1 and 2.

In the various figures like reference numerals refer to like parts.

Referring first to figure 1, a heating device 1 consists of an outer casing having a cylindrical wall 2 with a circular base wall 3. Walls 2 and 3 are of metal. A foil circular top wall 4 closes the container which generally resembles a conventional can. An outer lid 5 engages the top edge of the cylindrical wall 2. Within the heating device 1 there is disposed a frangible wall 6 which divides the device into a first lower container 10 and a second upper container 11. The lower container 10 contains a quantity of anhydrous calcium oxide 20. The quantity of calcium oxide (quicklime) is determined to provide a desired heat output when slaked with an adequate amount of water. The quicklime may be provided as a powder, or in any other desired form. In one embodiment, the quicklime may be mixed with a granular material, for example plastics granules, to facilitate mixing with water. In another embodiment the quicklime may be mixed with, or be associated with a material which changes state when heated in the temperature range 30-100 deg C. A suitable material is paraffin wax. The effect of the state change is to absorb heat from the exothermic reaction, and then to release it when the state change reverses, thus prolonging the heating regime.

The second container 11 contains a quantity of water 21 and a piercing device 30. In the exemplary heating device shown in figure 1, the piercing device 30 is formed of plastics material as a generally nail-formed member having an enlarged generally planar head portion 31 in close proximity to the foil top 4 and a downwardly- depending piercing portion 32 which has an end region that rests on the partition wall portion 6. Also shown in figure 1 is a valve 40 which will be described more fully with respect to figure 3. The valve of this embodiment is operated by overpressure in the lower container due to exothermic reaction between the water and quicklime. In other embodiments the valve may be disposed in a wall of the second container.

While the valve of the presently described embodiment remains in the closed position the quicklime is in an hermetically-sealed container. This prevents slaking due to atmospheric moisture and give a long shelf life to the heating device.

The device of figure 1 is designed to provide heat from conduction, convention and/or radiation so as to heat food which should be kept dry. Thus the device of figure 1 has a quantity of water 21 which is selected to slake the quantity of lime 20 substantially without the production of steam. In the device of figure 1, as little or no steam is produced, the pressure conditions in the heating device one may be such that no valve 40 is required.

To determine the quantity of water that is required, it is first necessary to determine the quantity of lime that will be needed. The heat which is required to warm a given type of food is well understood and this quantity will determine the amount of lime needed. To allow for incomplete penetration of the water, a quantity of quicklime around 20% greater than the quantity that would be needed for perfect mixing of water is used.

The theoretical amount of water which is required to slake the quicklime - the stochiometric amount - is 32%. If this amount, or slightly less than this amount is provided then the result is a hot reaction in which all steam will ultimately be consumed. The temperature of the outer walls of the device will rise to well in excess of 100°C, typically around 200°C. It will be clear that the device shown in figure 1 could, if suitably configured, be provided to heat up various different types of food for which steam heating would be inappropriate. A typical example is a pizza, in which case a suitable configuration would be a heating device having a width dimension much greater than the height dimension. The generally can-shaped device shown in figure 1 is applicable to heating food disposed about the casing, especially food which had previously been baked or fried. In use, the protective cover 5 is removed from the top of the device and some pressure is exerted on the central region of the upper foil 4. This causes the generally pointed region of the piercing portion 32 of the piercing device 30 to break frangible wall 60 so that water 12 flows down onto the quicklime to slake it. As the water reaches the top surface of the quicklime 20, slaking starts, with a rapid rising temperature of the surface region. This will cause some of the water to boil and form steam, but the steam will condense on the inside of the device and run down to continue the slaking process. As the quantity of water is slightly less than the stochiometric quantity all of the water will be consumed in the slaking process without substantial increase of pressure.

The device of figure 2 is chosen where the food can be heated with steam with either no ill-effects, or to advantage. In this device the quantity of water 121 is selected to be around 100% more than that shown in the embodiment of figure 1. The same quantity of quicklime is used.

In this case, when the pressure is exerted on the piercing member 30 the water runs down into the lower container 10 and begins to slake the quicklime 20. Whereas in the first embodiment the temperatures of the casing of the heating device is able to rise to around 200°C due to all of the energy being converted into a high temperature of the quicklime, in the second device, the energy which is released by the exothermic reaction is partially converted into the latent heat of evaporation of the water. Thus, the extra water forms a load on the exothermic reaction so as to limit the temperature to substantially 100°C. The steam generated leaves via the valve 40 and is useable to heat food such as rice due to the latent heat of condensation of the steam.

The quantity of water 121 may be determined by experimentation, bearing in mind the wide variations in properties of quicklime, to be such as to prevent the temperature of the casing ever rising beyond 100°C, in which case substantially all of the heating effect is obtained from the condensation of steam. Alternatively, it is possible to determine a quantity of water which is such as to provide an initial burst of steam followed by a rise in temperature of the casing to around 200°C.

The device of figure 1 is designed to provide a high temperature environment of around 200 C casing temperature for perhaps thirty minutes whereas the device of figure 2 provides a steam output at 100°C for three minutes. Both of the devices use the same quantity of quicklime.

As noted above, quicklime varies widely in its properties, depending on kiln conditions, degree of granularity and presence of impurities. The variations may mean that more of one type of quicklime is needed to provide a desired heat output than of another type. Equally, the ratio of water to quicklime needed for full reaction, or for "full steam" may vary.

However, as a guide, typical ratios are around 3 parts quicklime to 1 part water to provide a dry heat regime, and 3 parts quicklime to 2 parts water for full steam followed by casing temperature fall. Between these ratios, steam will be provided for part of the time, followed by temperature rise. Less water than about 3: 1 will leave unslaked lime, and substantially more than 3:2 may be used to prevent steam generation. Referring now to figure 3 an exemplary pressure release valve is shown. The pressure release valve forty consists of a resilient stopper member 41 which sealingly engages with a circular aperture in the cylindrical wall 2. In the valve shown in figure 3, the stopper member 41 is generally conical and extends from a spring portion 42 which is elongate and secured to the outer surface of the wall 2. The device shown includes a breakable barrier disposed between the two containers ten and eleven. It will, however, be clear to those skilled in the art that other forms of device could be provided in which an ejectable lid, twist cap or any other form of temporary seal could be used to separate the two reagents. The device could also be provided with a hydrophilic material to absorb condensate. Many different devices may be used for tearing or piercing a breakable barrier where provided.

The applicant envisages providing a range of heating devices which can provide a heating regime appropriate to the food involved. Such a range might include a group of devices all containing substantially the same amount of quicklime, so as to be capable of the same heat output. However, each performance, ranging from dry heat to steam heat via devices having varying proportions of steam and dry heat. It is also envisages that the group could contain members having water in excess of the amount enabling steam production, thus having a casing temperature that does not reach 100°C. Such members are useable where it is essential for the food or beverage not to reach 100 deg C. One situation is where the food/ beverage itself would suffer from over- heating and another is where the user needs to be protected against high temperatures - for example where baby food is being heated. Other sets of devices may have members which contain differing amounts of quicklime, and quantities of water selected to give the desired performance. Many different shapes are envisaged according to the food type.

The devices may be used in containers supporting the food and restricting the air flow to the food, so as to speed the heating process. Beverages may be heated, either by steam or by dry heat. The steam may be used to treat the food or drink, for example to 'froth' milk for coffee.

Claims

1 A set of heating devices for heating a food package, each of said heating devices having a casing containing a predetermined quantity of first material and further containing a second material for reacting endothermically with the first material, said second material having a first boiling point, said set of heating devices comprising a first heating device for providing heat at a temperature in excess of said first boiling point and a second heating device for providing second material vapour at a temperature of substantially said first boiling point.

2. The set of heating devices of claim 1 wherein the casing of at least said second heating device has a pressure vent device for exit from said casing of said vapour.

3. The set of heating devices of claim 1 or 2, wherein the first heating device contains substantially the stochiometric quantity of second material for the predetermined quantity of first material.

4. The set of heating devices of any preceding claim, wherein the second heating device contains a quantity of second material greater than said stochiometric quantity by an amount which restricts the casing temperature to substantially said first boiling point.

5. The set of heating devices of claim 4, wherein the quantity of second material loads the exothermic reaction sufficiently to cause the casing temperature to rise to said first boiling point, and immediately thereafter to start to fall below said first boiling point.

6 The set of heating devices of claim 4, wherein the quantity of second material is selected to limit the casing temperature to rise to said first boiling point for a first time period thereby to provide output vapour for said first time period, thereafter allowing the casing temperature to rise above said first boiling point.

7 The set of heating devices of any preceding claim, wherein the second material includes water, whereby said vapour is steam, and said boiling point is substantially 100 deg C.

8 The set of heating devices of any preceding claim, wherein the first material includes calcium oxide.

9 The set of heating devices of any preceding claim, wherein each device contains substantially the same quantity of first material.

10 The set of heating devices of any preceding claim, wherein the casings are of metal.

11 The set of heating devices of any preceding claim, wherein the casings of each device are substantially identical.

12 The set of heating devices of any of claims 1-11, wherein the casing of the first heating device has a width and a height, and the width dimension is greater than the height dimension.

13 The set of any preceding claim and further comprising a further heating device for producing a casing temperature which does not reach said boiling point.

14 A method of making a plurality of heating devices for providing a desired quantity of heat to a food package, the heating devices using the exothermic reaction of quicklime with water to provide said heat, the method comprising selecting a quantity of quicklime in accordance with the desired quantity of heat; determining, in dependence on the quantity of quicklime, a first quantity of water and a second quantity of water, the first quantity being substantially the stochiometric quantity needed to react with the quantity of quicklime and the second quantity being greater than the first quantity by a predetermined amount, said predetermined amount being sufficient to generate steam from said exothermic reaction and to thereby limit the casing temperature to substantially 100 deg C; providing a plurality of casings; a quicklime disposing step comprising disposing said selected quantity of quicklime in said casings; disposing one of said first quantity and said second quantity of water in at least one of said casings; disposing the other of said first quantity and said second quantity of water in at least one of said casings.

15 The method of claim 14 wherein said predetermined amount is substantially one-third of said first quantity.

16 The method of claim 14 wherein said predetermined amount is substantially two-thirds of said first quantity.

17 The method of claim 14 wherein said predetermined amount is substantially greater than one third and substantially less than two-thirds of said first quantity.

18. The method of any of claims 14 to 17, and further comprising, after said quicklime disposing step, securing a barrier to said casing, said barrier being effective to form a chamber in said casing whereby said chamber contains said quicklime and hermetically seals said quicklime in said chamber.

19 The method of any of claims 14 to 17, and wherein said quicklime disposing step comprises providing an hermetically sealed container containing said quicklime, and disposing said container in said casing.

20. The method of any of claims 14 to 19, wherein said quicklime disposing step further comprises disposing paraffin wax in association with said quicklime

21. A method of producing a self-heated food package comprising providing a plurality of heating devices, each of said heating devices having an external envelope, the envelope including a first container containing a fluid and a second container containing a predetermined quantity of first material, wherein the fluid is provided for reacting endothermically with the first material, the heating devices including a first heating device adapted to have an envelope temperature in excess of 100 deg C and a second heating device adapted to provide steam at a temperature of substantially 100 deg C; selecting between the first and second heating devices in accordance with a nature of food to be heated in said package; and installing the selected one of the first and second heating devices in said package.

22. The method of claim 21 wherein said fluid comprises water and the first material comprises calcium oxide.

23 The method of claim 21 or 22 wherein each of the heating devices contains substantially the same predetermined quantity of the first material.

24 The method of claim 21 , 22 or 23 , wherein the casings of each of the heating devices are externally substantially identical.

25 The method of any of claims 21 -24 wherein the providing step comprises hermetically sealing at least the second container of each device, whereby said water and water from the atmosphere is prevented from reaching the first material.