Abstract:
The invention relates to a method of producing a plurality of portions of a precooked food wherein the food is initially cooked at temperatures above 80° C. and prepared, the food is then cooled in a cooling phase within a maximum time of 120 min passing through the temperature range of 55° C. to 8° C. to a final temperature in the range of 8° C. to 0° C., and stored for a few days at the final temperature. The food is poured into an agitator vessel ( 22 ) during the cooling phase wherein the food is simultaneously thoroughly mixed and cooled during the cooling phase by an agitator ( 01, 26 ) constructed as a heat exchanger according to the invention.

Description:
FIELD OF THE INVENTION 
   The invention pertains to a method for producing a plurality of portions of a precooked food wherein the food is initially cooked at temperatures above 55° C. and prepared ready for consumption, with the food then being cooled in a cooling phase from the preparation tempurature to a final temperature. 
   The invention further pertains to an agitator for arrangement in an agitator vessel wherein intermixable mass contained in the agitator vessel can be thoroughly mixed by driving the agitator, and wherein the agitator is constructed in the fashion of a heat exchanger and a cooling and/or heating medium can flow through the agitator at least in sections, and wherein the agitator has an agitator head, at least one agitating vane and cross-pieces connecting the agitator head and the agitating vanes. 
   BACKGROUND OF THE INVENTION 
   In many community care institutions, for example canteens of large companies or in hospitals, there is a need for food to be distributed seven days a week. If this food is freshly prepared each time seven days a week, high costs are incurred because kitchen staff can only be employed over the weekend if corresponding extra charges are paid. Thus, a method described in the specialist circles as “cook and chill” is used in many cases. In this method the food is only prepared on weekdays with the portions required for the weekend being precooked at this time. After the precooked quantity of food has been prepared, this is chilled to a temperature below 8° C. and stored at a suitable cool temperature. In this case, the temperature should briefly fall below 3° C. at least once. The food mass can then be heated for consumption at the weekend in its entirety or in portions. 
   A problem with the “cook and chill” method is that hygiene problems can occur as a result of the storage of the food before its heating. In this case, it is not so much the storage at a temperature below 8° C. that is critical since micro-organisms such as bacteria and fungi barely multiply at these temperatures. Rather it is the cooling phase which is to be regarded as the critical stage during which the food passes through a temperature range from 55° C. to the final temperature below 8° C. In this temperature band micro-organisms in the pre-cooked food find optimum conditions for multiplication and thus multiply especially vigorously during the cooling phase. 
   In order to keep the multiplication of micro-organisms below a tolerable level during the cooling phase, it is necessary for the precooked food to be cooled to the final temperature within the shortest possible time. In order to reliably reduce the multiplication of micro-organisms during the cooling phase, it is essential that not only parts of the food have reached the final temperature within a sufficiently short time but that the food mass from the edge as far as the core has been continuously cooled to the final temperature. 
   If the food is cooled merely starting from the edge, for example, by placing a container containing the food mass in a refrigerator, the time before the core of the food mass has reached the end temperature depends on the volume of the food mass relative to its edge surface at which cooling can take place. In order to keep the cooling phase during passage through the critical temperature range until the final temperature is reached in the core of the food mass to a tolerable level in the range of less than 120 minutes, especially shorter than 90 minutes, it is thus known that flat containers can be filled with the pre-portioned food and these flat containers can then be cooled individually. However, this pre portioning in smaller containers again incurs higher costs. 
   DE 40 09 157 C2 describes a method for pre-treating rice wherein the rice is precooked in accordance with a specific temperature process and then dried. 
   EP 0 338 282 BI discloses a method for sterile precooking of noodle products which can then be packaged ready for consumption after cooking. 
   DE 37 27 594 A1, DE-OS 1 926 704 and DE 32 00 1.65 A1 each describe agitators wherein the agitator is constructed in the fashion of a heat exchanger and can have a cooling or heating medium flowing through it. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is to propose a new method for cooling a plurality of portions of a precooked food without the need to pre-portion this before the cooling process. 
   It is a further object of the invention to propose an agitator that is especially suitable for implementing the method according to the invention. 
   An advantage of the method according to the invention is especially that during the cooling phase the food is cooled and at the sane time thoroughly mixed by using an agitator. As a result of the thorough mixing of the food mass which later yields a plurality of individual food portions, rapid temperature equalization can be achieved between the various temperature regions in the agitator vessel. In addition, by using an agitator constructed as a heat exchanger through which flows a gaseous or a liquid coolant, the cooling surface in contact with the food is enlarged considerably. As a result, the cooling phase for passing through the critical temperature range between 55° C. and 8° C. can be shortened considerably by these measures. 
   It is fundamentally possible to cool the food merely by using the agitator constructed as a heat exchanger. However, the cooling power can be increased considerably if the agitator vessel is also cooled during the cooling phase. Conventional agitator vessels constructed as doublewalled and through which flows a coolant such as iced water, ice slush or a glycolwater mixture can be used for this purpose. 
   In order to carry out the method according to the invention, a new type of agitator is required which is suitable for thoroughly mixing the food in conjunction with the agitator vessel. The agitator is generally constructed in the fashion of a heat exchanger and can have a cooling medium flowing through it so that thermal energy can be removed from the food mass as a result. In order to be able to achieve an adequate flow cross-section in the agitator head, as is especially required when using ice slush as coolant, the agitator head in the agitator according to the invention is formed of a fixedly arranged lid and tank which is rotatable with the agitator, wherein the lid can be attached to the tank in a sealing fashion. 
   The use of the agitator according to the invention is not limited to the usage for cooling pre-cooked food. If a heating medium, for example, hot water or hot steam, flows through the agitator instead of a cooling medium, it is naturally also possible to heat the food mass mixed thoroughly by the agitator. As a result, the duration of the heating phase during the preparation of the food can be shortened appreciably since larger quantities of heat can be coupled into the food mass in a shorter time. 
   The agitator according to the invention is also not limited to the area of usage for food preparation but can be used in all cases where intermixable masses must be heated or cooled as uniformly as possible. Intennixable masses in the sense of this invention are all substances or substance mixtures whose state of aggregation at least allows slight intermixing. These especially include highly viscous masses such as mashed potato for example, or mixtures of liquid constituents and solid constituents such as a stew, for example. 
   For example, it is feasible to use the agitator according to the invention in the chemical industry in order to thoroughly mix various reagents and at the same time to cool or heat them. The dimensioning of the agitator according to the invention depends on the particular usage. Dimensions having diameters in the centimeter range for laboratory equipment as far as diameters of a few meters in the chemical industry are feasible. When the agitator according to the invention is used for the preparation of food, its dimensions are substantially determined by the dimensions or the maximum capacity of the vessels in which the food is accommodated. Depending on the cooling or heating power required, the cooling or heating surface presented by the agitator can be adapted in a simple manner for example by increasing the number of agitating vanes. The outer dimensions of the agitator can remain unchanged in this case. 
   All gaseous or liquid media, for example, iced water, a glycol-water mixture, liquid nitrogen, hot water or hot steam can be used as cooling and/or heating medium since the cooling or heating medium merely removes thermal energy from the mass to be thoroughly mixed or couples it therein, but there is no direct exchange of material. In the food area iced water, hot water and hot steam are especially suited for use in the agitator according to the invention, since these media are already present in many cases in large kitchens and in addition, in the event of faults, that is if the medium unintentionally escapes from the agitator, for example, as a result of leakages, there is no health hazard. 
   The design of the agitator is fundamentally arbitrary as long as at the outer surfaces of the agitator which come into contact with the mass to be intermixed, it is made possible for sufficient heat exchange between the mass to be intermixed and the cooling or heating medium flowing through the agitator. It is especially advantageous if the agitator has an agitator head and one or a plurality of agitating vanes wherein the agitator head and the various agitating vanes are interconnected by means of cross-pieces. The agitator vanes and cross-pieces should be constructed as double-walled and thereby form individual pipe sections. By means of a suitably sealing join between the agitating vanes, the cross-pieces and the agitator head, for example, by welding the individual parts, a closed pipe is formed whose inlet and return open into the agitator head. An inlet and an outlet for the cooling or heating medium are provided on the agitator head itself. As a result, the cooling or heating medium flows into the agitator head and from there flows through the individual agitating vanes and the cross-pieces connecting the agitating vanes. The medium cooled or heated as a result of the heat exchange in the cross-pieces or agitating vanes then flows out via the agitator head and is removed via the outlet. In this case, it is especially advantageous if the cooling or heating medium is guided in a cooling or heating circuit by a cooler or a heating device. Naturally, it is also possible for a plurality of pipes running parallel to one another to run from the agitator head through the individual agitating vanes and crosspieces such that cooling or heating medium can flow through the agitator along a plurality of pipes running parallel one to the other. 
   In order to prevent intermixing of the cooling or heating medium at the inlet or return in the agitator head, the agitator head can have two separate chambers. The first chamber forms the inlet of the pipe through the agitator and can be connected to the inlet for the cooling or heating medium. The second chamber then forms the return of the pipe through the agitator and can be connected to the outlet for the cooling or heating medium. Intermixing of the fresh cooling or heating medium at the inlet with the already heated or cooled cooling or heating medium at the return is eliminated by the dividing wall between the two chambers. 
   In order to construct the connections for the inlet and outlet of the cooling or heating medium simply, for example, in the fashion of plug couplings to which suitable hoses can be connected, it is advantageous if the agitator head has one fixed part and one part which can be rotated together with the agitating vanes. The connections for the inlet or outlet of the cooling or heating medium are then arranged in the fixed part whereas the rotatably mounted part of the agitator head forms the inlet or outlet into the pipe through the agitator. 
   In order that the agitating vane according to the invention can be used in different agitating vessels, it is advantageous if different adapter elements can be affixed to the agitator head as desired, and can each be brought into engagement with different drive shafts. As a result, it can thereby be achieved that the agitator with the agitator head, the agitating vanes and the cross-pieces can be produced in standard product series and can be adapted to different drive shafts by attaching different adapter elements. 
   Alternatively to driving the agitator by means of a drive motor and a drive shaft which transmits the rotational motion, the flow energy of the cooling or heating medium flowing in at the inlet can also be used to drive the agitator. For example, known flow lamellae can be arranged for this purpose in the agitator head, which convert the flow energy of the inflowing medium into a rotational movement. 
   The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
       FIG. 1  shows a side view of an agitator; 
       FIG. 2  shows a first perspective view of the agitator from  FIG. 1 ; 
       FIG. 3  shows a second perspective view of the agitator from  FIG. 1 ; 
       FIG. 4  shows a wire frame model of an agitator head; 
       FIG. 5  shows a schematic cross-sectional view of an agitator head; 
       FIG. 6  shows a perspective view of an agitator vessel with agitator; 
       FIG. 7  shows a top view of the agitator vessel with agitator from  FIG. 6 ; 
       FIG. 8  shows a side view of a second embodiment of an agitator; 
       FIG. 9  shows a first perspective view of the agitator from  FIG. 8 ; 
       FIG. 10  shows a cross-section through the agitator head of the agitator from FIG.  8 ; 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawings in particular,  FIG. 1  shows an agitator  01  which can be used in a vessel for preparing food and is used to thoroughly mix and heat or cool the food. 
   The agitator  01  is manufactured as a welded part and is substantially constructed of an agitator head  02 , eight agitating vanes  03  and crosspieces  04 ,  05 ,  06 ,  07  and  08  which connect the agitating vanes  03  or the agitator head  02 . The agitating vanes  03  and the cross-pieces  04  to  08  are constructed as double-walled and are connected to form a closed pipe so that a cooling or heating medium flowing in at the agitator head  02  flows through the agitator  01  along this pipe and can remove thermal energy or couple in thermal energy. 
   The agitating vanes  03  are inclined at an angle of around 20° with respect to their horizontal plane of movement so that when the agitator  01  is rotationally driven about its central axis the mass flowing past the agitating vanes  03  is deflected upwards or downwards so that the mass is continuously intermixed and no stationary zones are formed. 
   The agitator  01  is driven using a drive shaft, not shown, which is provided in the agitator vessel and which extends from the base of the agitator vessel upwards and can be brought into engagement in a receptacle on the agitator head  02 . So that the drive shaft does not collide with the agitator  01 , the cross-piece  07  is constructed in the fashion of a ring conduit so that the drive shaft can penetrate through the agitator  01  in the region of the cross-piece  07 . 
   Attached to each of two of the cross-pieces  05  and to the two lower agitating vanes  03  are skimming elements  09  which are guided along the component wall of the agitator vessel during the rotational drive movement of the agitator  01 , so that no stationary zones form in the boundary region between the mass and the component wall, but optimal intermixing is also achieved in this region. In order that the agitator can be used in agitator vessels of different dimensions, the skimming elements  09  are adjustably attached to the agitator  01  so that the sizes can be compensated. 
     FIGS. 2 and 3  show the agitator  01  in two different perspective views. 
   In  FIG. 4  the agitator head  02  is shown in enlarged view as a wire frame model. The cover of the agitator head  02  with the connections for the inlet and outlet of the cooling or heating medium is not shown in this wire frame model. The agitator head has two concentrically arranged chambers  10  and  11  which are separated from one another by a dividing wall  12 . The cross-pieces  04  both open into the inner chamber  11  whereas the cross-pieces  08  open into the outer chamber  10 . By this means it is achieved that the fresh cooling or heating medium can flow into the agitator  01  via the outer chamber  10  and the cross-pieces  08  and is separated by the dividing wall  12  from the already heated or cooled cooling or heating medium that flows back via the cross-pieces  04  into the chamber  11  of the agitator head  02 . 
   The schematic structure and the function of the agitator head  02  can be seen from the schematic cross-section shown in FIG.  5 . The two chambers  10  and  11  are separated one from the other by the dividing wall  12 . Both chambers  10  and  11  are bounded towards the outside by a fixedly arranged cover  13  and a tank  14  which is rotatably mounted together with the agitator. The dividing wall  12  is securely welded to the base of the tank  14  in a liquid-tight fashion. 
   The cooling or heating medium flows into the chamber  10  via the inlet  15  and from there into the cross-pieces  08  which form the inlet into the pipe through the agitator  01 . After the cooling or heating medium has flowed through all the cross-pieces  04  to  08  and the agitating vanes  03 , it flows back into the chamber  11  of the agitator head  02  via the crosspieces  04  forming the return, from where it can be removed via the outlet  16 . In order to seal the chambers  10  and  11 , shaft sealing rings  17  are arranged in the sealing gaps between the stationary lid  13  and the tank  14  rotating together with the agitating vanes or the dividing wall  12 . 
   In addition to the inlet  15  and the outlet  16 , also provided in the lid  13  is a compressed air connection  18  to which a compressed air pipe can be connected. Compressed air can be pressed into the chamber  10  via the compressed air connection  18  so that the heating or cooling medium in the agitator  01  can be displaced outwards via the chamber  11  and the outlet  16 . 
   The center of the tank  14  is constructed as a polyhedral toothed structure  19  into which the end of a drive shaft  20  shaped in a complementary fashion can be brought into engagement so that a torque can be transmitted from the drive shaft  20  to the tank  14 . Attached to the lid  13  is a tamper prevention element  21 , shown by the broken line, to prevent any tampering with the driven agitator  01  from outside. 
     FIG. 6  shows the agitator  01  as can it can be arranged in an agitator vessel  22  constructed as a cooking vessel. 
     FIG. 7  shows the agitator  01  and the agitator vessel  22  viewed from above. The agitator vessel  22  is for its part also constructed as doublewalled and can have the same cooling or heating medium flowing through it as the agitator  01  so that the food arranged in the agitator vessel  22  can be heated or cooled in a shorter time. 
     FIG. 8  shows a second embodiment of an agitator according to the invention viewed from the side. As in the agitator  01  there are provided double-walled cross-pieces  03 ,  04 ,  05 ,  06 ,  07  and  08  through which a suitable coolant such as ice slush can flow. The ends of the cross-pieces  04  and  08  each open into the agitator head  23  which is formed from a lid  24  and a tank  25 . 
   In order to be able to transmit the drive power of the drive motor to the agitator  26  there is provided a receptacle which is formed of two vertical cross-pieces  34  and  35  and three inner polyhedral elements  31 ,  32  and  33  (see  FIG. 9 ) affixed thereto. The drive shaft not shown in  FIG. 8 , which extends vertically upwards in the agitator vessel engages in a formlocking fashion in the inner polyhedral elements  31  to  33  in order to transmit the driving moment to the agitator  26 . A particular advantage here is that the agitator  26  can be simply placed on the drive shaft from above especially without the need to dismantle the agitator head  23 . 
     FIG. 9  shows a perspective view of the agitator  26  wherein in particular the agitating vanes  09  can be identified. 
     FIG. 10  shows a cross-sectional view of the structure of the agitator head  23 . The agitator head  23  is substantially formed from a circular ring shaped tank  25  and a lid  24  rotatably mounted thereon. In order to achieve the rotatable mounting of the lid  24  on the tank  25  there is provided a securing element  29  and a bearing element  30  constructed in the fashion of a roller bearing. The securing ring  29  is rotatably mounted on the inner ring  27  of the tank  25  by means of the bearing element  30 . In order to fix the lid  24  to the tank  25 , fixing screws are inserted through corresponding recesses in the lid  24  and screwed into the fixing ring  29  from above, as indicated by the dot-dash line in FIG.  10 . As a result, the lid  24  is thereby rotatably mounted on the tank  25  so that it is only necessary to affix the inlet  15  and the outlet  16  to assemble or dismantle the agitator  23  in an agitator vessel. 
   As a result of the circular ring-shaped structure of the tank  25 , an inlet chamber  10  laterally bounded by the inner ring  27  is formed at the center of the tank  25 . The outlet chamber  11  is bounded by the component wall of the tank  25  and the securing ring  29 . The two chambers  10  and  11  are sealed in a liquid-tight fashion by the various sealing rings  17  so that during operation of the agitator  26  the coolant cannot escape from the chambers  10  and  11  through the sealing gaps. As a result of the arrangement of the chamber  10  at the center of the tank  25 , a very compact agitator head can be formed whereby the compressive forces acting on the various components of the agitator head  23  do not exceed a tolerable level even at high internal pressures such as occur especially when ice slush is used as coolant. 
   While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.