EP0731319A1

EP0731319A1 - Cooking oven provided with rapid chilling arrangement using cryogenic gas

Info

Publication number: EP0731319A1
Application number: EP96102219A
Authority: EP
Inventors: Franco Tassan Mangina
Original assignee: Zanussi Grandi Impianti SpA
Current assignee: Electrolux Zanussi Grandi Impianti SpA
Priority date: 1995-03-07
Filing date: 1996-02-15
Publication date: 1996-09-11
Also published as: ITPN950014A1; IT1282412B1; ITPN950014A0

Abstract

Food cooking oven comprising a cooking cavity, one or more heating elements for heating up said cavity, at least a motor-driven fan adapted to mix up the atmosphere existing in said cavity, and provided also with a conduit coming in from the outside and introduced in said cooking cavity and terminating with a nozzle ejecting into said cavity, wherein said conduit is adapted to inject into said cavity a flow of cryogenic gas supplied by a reservoir situated outside the oven. In the motor-driven fan there is provided at least a suction opening for taking in the gas contained in the cooking cavity, while the ejection nozzle is arranged close to and oriented toward said suction opening. In a preferred manner said cryogenic gas delivery conduit is provided with a valve arrangement adapted to enable the inflow of cryogenic gas into said cavity to be shut off and adjusted.

Description

The present invention refers to a food cooking oven adapted to perform one or more cooking processes using generally known methods and techniques, such as for instance, and without any limiting purpose, both cooking by microwaves and cooking by heating the cavity through the combustion of fuel gases and/or through the energization of resistance-type electric heating elements appropriately arranged within the cooking cavity, or even cooking by a combination of both these methods performed either simultaneously or in sequence so as to create special food cooking conditions and effects, said cooking methods being further capable of being performed jointly with a so-called "steaming" process, ie. with an injection of steam into the cooking cavity.
In the following description, reference will be made particularly to a food cooking oven of the type generally used in food-service or catering applications, although it will be appreciated that what is herein described and claimed equally applies to any type whatsoever of food cooking ovens.
It is generally known that food cooking in an oven is performed in different manners, and under different conditions, in accordance with the special results and effects that have to be obtained, and the peculiarities of such different cooking manners and conditions from such viewpoints as rapidity of cooking, cleanliness, safety, energy usage and evenness are well known in the art, so that they shall not be dealt with any longer here.
The need is also widely known in the art, particularly in the commercial foodservice operations, to make provisions so that, after cooking, the food can be removed from the oven to be transferred as quickly as possible into appropriate quick-chilling containers, generally known in the art by the name of "quick chillers" or some other similar name, which are adapted to quickly remove heat from the food by means of a mechanically circulated flow of refrigerated air.
The purpose of this practice is twofold, ie. enabling the oven to be as quick as possible ready for a subsequent cooking process and, at the same time, making it possible for the just cooked food to be preserved for a period of two to three days before being picked up again for regeneration, ie. being put in the oven again for reheating to serving temperature.
However, the above described cooking-storage-regeneration process has a number of operational drawbacks that limit the scope of its application and make it quite expensive, complicated and labour-intensive.
Such drawbacks are substantially determined by the costs of purchasing and servicing, including cleaning, a quick-chilling apparatus that which additionally requires a definite space, which is not always so easy to find at an appropriate location near the oven, for its installation. Furthermore, transferring the food from the oven into the quich-chilling apparatus and vice-versa causes kitchen personnel to be generally kept busy with such a task exactly in the moments in which the same personnel is most required for other pressing tasks. Another drawback is brought about by the relatively complicated procedure required to correctly and efficiently programme the various operations in the manner in which they are carried out presently, ie.:

the cooking operation,
the chilling operation,
the preservation under as-chilled conditions,
the reheating/regeneration operation.

All these operations must in fact be carried out under strictly coordinated conditions, so that errors can be made quite frequently and easily when trying to programme them correctly.
Last, but not least, there is another important point to be considered, ie. the hygienic aspect. As a matter of fact, cooked food can easily get exposed to contamination by just handling it from the oven to the chiller and vice-versa. Furthermore, keeping the cooked food stored for periods of up to 2 or 3 days in the chillers under ambient air conditions, even if at a relatively low temperature, undoubtedly contributes to an increased risk of contamination and spoilage due to the presence of a wide variety of contaminating substances and bacteria in the air.
Combined apparatuses are already known which are capable of performing both the cooking functions and the chilling and reheating ones in the same single cavity. Such apparatuses, however, perform their chilling function by using the traditional technique based on the cyclic compression of refrigerant media, ie. a technique that is generally known to put heavy weight and volume penalties on the design of such apparatuses, as well as considerable constructional complications. Furthermore, such a technique is generally entirely inadequate in enabling the temperature of rather large amounts of food to be pulled down with due rapidity from such high values as 100°C or even more.
A method is also known, for instance from the disclosure in the French patent specification no. 80 07982, which makes use of a cryogenic medium for quick-freezing a mass of fresh fruit to be subsequently processed after being partially thawed.
However, such a method refers solely to such products as fresh fruit which are neither heated up to any high temperature value nor cooked. Furthermore, such products are actually deep-frozen so as to be able to be preserved as such for very long periods of time, whereas in catering or foodservice operations cooked food is desirably preserved for periods that should possibly not exceed two or three days at most, so that a much higher conditioning temperature is required, although a really considerable useful refrigeration capacity must anyway be available in view of the possibility of pulling down the temperature of the cooked food with the required rapidity from values that may be in excess of 100°C.
The need therefore arises to provide a food cooking oven which is also capable of performing intensive temperature pull-down phases for chilling the just cooked and still very hot food, and which is further adapted to keep a cold temperature to the level required for preserving the same food inside the same cavity, by using readily available techniques and without increasing the manufacturing and operating costs of the oven to any significant extent.
These and other advantages, which will become apparent in the course of the following description, are reached in a type of cooking ovens having the characteristics as substantially described with particular reference to the single accompanying Figure which is a cross-sectional view of an oven and a cryogenic-gas reservoir according to the present invention.
Referring to this Figure, this is shown to illustrate a vertical cross-sectional view of the interior of a food cooking cavity 1, comprising a motor-driven fan 2 arranged on the rear side of said cooking cavity, and appropriate arrangements for generating and propagating the heat inside said cavity, said arrangements being illustrated here by way of non-limiting example in the form of sections of circular resistance-type electric heating elements 3 surrounding the fan 2.
A plurality of pans 4 containing the food to be cooked are shown to be arranged one above the other inside said cooking cavity, where also the suction opening 5 of the fan 2 is arranged, said fan blowing the air taken in from the interior of said cavity 1 toward the outer annular portion 6 thereof, from which the air is then blown again into the cavity through conduits and apertures that are not shown here since they are already well-known in the art. An appropriately insulated reservoir 7 containing cryogenic liquid, in particular liquid nitrogen, carbon dioxide, liquid air or the like.
A conduit 8 branches off said reservoir, which after running along an appropriately provided path, duly supported all along said path, terminates with an ejecting nozzle 9 that is arranged inside the cooking cavity. In a preferred manner, said nozzle 9 is situated in front of the suction opening 5 of the fan and is oriented in such a manner in relation therewith that the flow of gas ejected therefrom is immediately taken in by the fan and brought to impinge against the blades of the same fan. Said conduit 8 is additionally provided with a valve-like element 10 which is preferably arranged within the oven casing for reasons that will be readily apparent.
The operation of such an oven-chiller arrangement is basically as follows: upon conclusion of a normal cooking cycle according one of the known methods, ie. by electric heating and forced convection, gas heating with burners that may be associated with or separated from the cooking cavity, microwaves, steam or the like, the heat generation process is ended and the temperature pull-down phase is immediately started, such a phase consisting essentially in opening the valve means 10 so that the cryogenic gas contained in the reservoir 7 can start to flow spontaneously into the conduit 8 and from here, through the open valve means 10, into the cooking cavity of the oven.
The result of such an operation is that the cryogenic medium gets mixed up with the much hotter atmosphere prevailing in the cooking cavity, thereby causing the cryogenic medium itself to almost instantaneously evaporate under extraction of heat from the interior of the cooking cavity. As a consequence, an adequate amount of frigories, which can be easily adjusted by controlling the valve means 10 accordingly, is in this way rapidly contributed to the atmosphere prevailing in the cooking cavity, said contribution of frigories determining a quick fall in the temperature of the cooked food.
In order to ensure a quicker and more uniform diffusion of the cryogenic medium in the oven cavity, the nozzle 9 of the conduit 8 should most appropriately be arranged in proximity of or close to the suction opening of the fan and so oriented in relation therewith that the cryogenic medium, forced by the action of the fan, is caused to immediately spread all over the interior of the cavity. When the temperature inside the cooking cavity has been lowered to the desired value, the above described chilling phase is terminated through the closure of the valve means 10, while the food itself is ready for preservation at a storage temperature that is slightly above 0°C. To this purpose, the chilled food may be transferred into a traditional refrigerator cabinet or the same oven may be used asa refrigerator by adjusting the temperature of the cavity correspondingly through the valve means 10.
The entire above-described process can advantageously be automated if the oven is provided of thermostat means 11 adapted to enter and register a pre-setting of the temperature inside the cavity and signal any possible deviation of the measured temperature from the pre-set one to an appropriately provided control means 13, said control means 13 being adapted to adjust the setting of the valve means 10 according to the signals conveyed by said thermostat means 11.
The whole complex formed by said thermostat means, control unit and valve means is arranged and adapted so as to ensure that the food preservation temperature is effectively and safely held at its pre-set value through a fully automatic control function. However, such a technique is within the capabilities of anyone skilled in the art, so that it shall not be explained here any further.
In an advantageous manner, such an oven is provided with a vent 14, which is equally adjustable and is adapted to open or close in view of anabling exhausted cryogenic gas (ie. cryogenic gas that has heated up to no longer useful temperature values) to escape from the cavity.
The oven is of course provided with a number of other devices and arrangements which, not being relevant to the purposes of the present invention, shall however be omitted here.
Although the present invention has been described on the basis of the example of a preferred embodiment thereof and using a generally known terminology, it should by no means be regarded as being limited by this, since anyone skilled in the art is able to use such a teaching to bring a number of modifications and variations thereto in terms of either shape or construction thereof.

Claims

Food cooking oven, in particular for large catering or commercial foodservice operations, comprising a cooking cavity (1), one or more heating elements (3) for heating up said cavity, possibly provided also with an arrangement adapted to convey steam from an outside steam generation apparatus into the interior of said cooking cavity, characterized in that there is provided a conduit (8) coming from the outside and leading into said cooking cavity, wherein said conduit terminates with a nozzle (9) ejecting into said cavity, said conduit being adapted to inject a flow of cryogenic gas into said cavity.
Food cooking oven according to claim 1, comprising further at least a motor-driven fan (2) adapted to mix up the atmosphere existing in said cavity, characterized in that said conduit is supplied with cryogenic gas from a reservoir (7) situated outside the oven.
Food cooking oven according to claim 1 or 2, characterized in that in said at least a motor-driven fan arrangement (2) there is provided at least a suction opening (5) for taking in the gas contained in the cooking cavity, wherein said ejection nozzle is arranged close to and orientated toward said suction opening.
Food cooking oven according to any of the preceding claims, characterized in that cryogenic gas delivery conduit is provided with a valve arrangement (10) adapted to enable the inflow of cryogenic gas into said cavity to be shut off and adjusted.
Food cooking oven according to claim 4, characterized in that it is provided with thermostat means (11) adapted to measure the temperature inside the cooking cavity, to be pre-set so as to detect a predetermined temperature and send a corresponding signal, when such a pre-set temperature is reached, to control means (13) adapted to receive a signal representative of said temperature from said thermostat means, wherein said thermostat means (11), control means (13) and valve arrangement (10) are on their whole adapted to enable a pre-defined temperature value to be automatically reached and held within the cooking temperature.
Food cooking oven according to any of the preceding claims, characterized in that it is provided with a vent arrangement (14) adapted to enable spent cryogenic gas, ie. cryogenic gas that heats up to no longer useful temperatures, to escape from the cooking cavity, wherein said vent is capable of being selectively shut or openend even partially.