WO1990004928A1

WO1990004928A1 - A method and an apparatus for cooking packaged food

Info

Publication number: WO1990004928A1
Application number: PCT/US1989/005010
Authority: WO
Inventors: Max Pierre Beauvais
Original assignee: Culinary Brands, Inc.
Priority date: 1988-11-09
Filing date: 1989-11-07
Publication date: 1990-05-17
Also published as: CA2002452A1

Abstract

The present invention is an apparatus and a method for cooking food at 60°C for later sale, reheating and consumption. The invention provides uniform heating of food items - regardless of type, thickness, orientation to the heat source (103, 104), or position on the assembly line (105, 106). Most importantly, the appealing characteristics of the food are preserved.

Description

A METHOD AND AN APPARATUS FOR COOKING PACKAGED FOOD

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to the cooking of packaged food; and more particularly to the cooking of food sealed in pouches for later sale, reheating and consumption.

Description of the Prior Art

The present invention is particularly useful for the cooking of more elaborately prepared dishes, the so-called gourmet foods. With gourmet foods, a most exacting standard of food quality is demanded. In this regard, the cooking method must do more than simply assure good health. The precooked food must retain the taste, texture and color of freshly prepared, superior cuisine.

All of the known "precooking" methods for gourmet foods suffer from one or more serious drawbacks, the most important of which are: l) the method is destructive to the quality of the food, 2) the cooking method fails to completely eliminate microorganisms, 3) the cooking method fails to accommodate differences in size and thickness of identical food items, and/or 4) the cooking method is impractical for large scale commercialization. Complete sterilization of food requires temperatures around 121°C over a period of time. Unfortunately, such a temperature is highly destructive to the appealing characteristics of superior cuisine; food that is cooked in this manner loses its texture, color, fragrance and taste. Use of a lower temperature, however, entails the risk that viable microorganisms remain after cooking. With the recognition that sterilization temperatures are unsuitable, a temperature for cooking must be determined that is safe and yet non¬ destructive. Second, a machine design must be selected that can deliver and maintain this temperature continuously and consistently. Both of these problems are further complicated by the fact that successful commercialization of precooked gourmet food requires large scale cooking. Thus, the temperature must assure, in a reproducible manner, high quality product throughout an entire batch and the machine must accommodate high volume processing.

Even where methods have been devised to attempt to accommodate variability, prior art methods have not been able to balance these relationships for large scale commercialization. Two machine designs have been primarily employed: 1) an immersion bath cooker, and 2) a steam-heated, air chamber cooker. In the case of the immersion bath cooker, food is immersed in a bath or pool of hot water. The immersion is thought to provide a uniform heating environment. It is observed, however, that because of food packaging, heating is not uniform.

Food to be cooked in an immersion bath is first placed in a package. Unpackaged food would come in direct contact with water and would either fall apart (e.g. fish, stuffed game) or become dispersed (e.g. peas, rice) . Packaged foods, however, are not suited to immersion type designs because the extent to which the package will become immersed will depend on the amount of air in the package, the size of the package, and the weight of its contents. It is not practical on an industrial scale to control all of these variables for all food items. Steam-heated, air chamber cookers consist of chambers where the air temperature is maintained by injection of steam. It is thought that, through the process of vapor distribution and equilibrium, the chamber provides a uniform heat. It is observed, however, that heating is not uniform. The correct cooking temperature is maintained by frequent injections of steam through the ports directly into the chamber body. These injections create local areas of much higher temperature. The processes of vapor distribution and equilibrium alone are not sufficient to prevent these local areas of higher temperature. A means must be provided to thoroughly and continuously mix the heated air. Introducing food into the chamber disturbs this mixing and can create local areas of lower temperature. Such chambers are, therefore, best suited to static processing. That is, the food must be placed in the chamber, the chamber closed, and the chamber left undisturbed until the cooking is complete. At that time the chamber must be completely emptied of cooked food before cooking of the next batch can begin. Such a method is not efficient and is, therefore, highly impractical for large scale commercialization.

The present invention represents another design approach to the problem. The apparatus of the present invention has been found to assure a more reproducible and reliable means of producing the uniform heating of packaged food cooked on an industrial scale.

This resolution of the uniformity problem has important market consequences. From a manufacturing standpoint, the improvement means greater flexibility. Larger batches can be prepared for high volume customers (conference centers, banquet halls, etc.) without fear that the quality of identical items will vary between each item and each batch. From a consumption standpoint, low volume customers (gourmet delicatessens, specialty shops, etc.) will be more likely to buy the product when it is clear that the product, while produced on a large scale, satisfies the demanding quality standards for gourmet cuisine.

SUMMARY OF THE INVENTION The present invention relates to an apparatus and a method for cooking packaged food for later sale, reheating and consumption. The invention provides uniform heating of food items—regardless of type, thickness, orientation to the heat source, or position on the assembly line. Most importantly, the appealing characteristics of the food are preserved.

The apparatus comprises a conveyor for moving packaged food into a cooking area. The packaged food is impinged on one side thereof with a continuous flow of heated liquid. A substantially constant temperature is provided on the other side of the -packaged ^"food. The temperature of the heated liquid is controlled to within 0.25° of 60°C. The speed of the conveyor is regulated to control the amount of time the packaged food is in the cooking area.

Food, once cooked, can thereafter be cooled in the same device. A cold liquid rain chamber and its complementary cold liquid reservoir is partially separated from the hot liquid rain chamber and its complementary hot liquid reservoir. Food, cooked within the hot liquid rain chamber, moves via the support belt into the cold liquid rain chamber. The continuous and uniform cold liquid shower cools the food as it exits the device. The parallel support belts can move at different speeds with respect to one another, allowing for the cooking and cooling of food items at different times.

DESCRIPTION OF THE DRAWINGS Figure 1 is a graphic representation of the relative heat sensitivities of a number of common, food-related, vegetative bacteria at non- sterilization temperatures.

Figure 2 is a graphic representation of the impact of a fixed cooking time where the external cooking temperature is 70°C.

Figure 3 is a graphic representation of the impact of a ten minute difference in the time to reach the internal cooking temperature of 70°C due to variability in size and thickness of two identical food items.

Figure 4 is a graphic representation of the impact of a ten minute difference in the time to reach the internal cooking temperature of 65°C due to variability in size and thickness of two identical food items.

Figure 5 is a graphic representation of the impact of a ten minute difference in the time to reach the internal cooking temperature of 60°C due to variability in size and thickness of two identical food items.

Figure 6 shows a perspective view of the apparatus of the present invention.

Figure 7 is a cutaway perspective showing the rain chamber and temperature control portion of the apparatus of the present invention.

Figure 8 is an enlarged view of the rain chamber flow-through plate showing the spacing and dimensions of the shower pores. Figure 9 is an end view cutaway along the lines 4-4 shown in Figure 6.

Figure 10 is a side view cutaway showing one embodiment of the apparatus of the present invention having only one rain chamber on each side.

Figure 11 is a side view cutaway showing another embodiment of the apparatus of the present invention having one hot liquid rain chamber and its complementary hot liquid reservoir separated from one cold liquid rain chamber and its complementary cold liquid reservoir on each side of the apparatus.

DESCRIPTION OF THE INVENTION

The invention is specifically designed to cook and/or cool food packaged by the "sous-vide" method, developed in France. In the "sous-vide" method food is prepared, vacuum-packaged and sealed in pouches. The sealed package food is then heated in the pouch, sealing in all the natural juices and flavors. The pouches are then chilled until ready to reheat and serve. This cooking method allows food to retain its freshness and flavor to an extent unachieved by other methods. Almost any type of food, regardless of the extent or nature of its preparation, is suitable for this method. As noted earlier, the cooking of gourmet food for commercialization necessarily involves cooking at a temperature lower than sterilization temperature. Indeed, for gourmet food even the temperature for boiling water is too destructive. Choosing the appropriate temperature requires consideration of both the optimum cooking temperature for the particular food and general principles of microorganism biology. Heat Sensitivity of Food The heat sensitivity of food is determined by the heat sensitivity of the elements of its composition. Food is composed of proteins, fats, polysaccharides and other complex molecules. The particular composition depends on the particular food. Thus, the heat sensitivity of a particular food depends on its particular composition.

The quality of cooked meat is dependent on its color, juiciness, softness and taste. Color is due not only to the pigment (the different stages of the myoglobin) , but also to the condition of the tissue surface. Myoglobin is fixed at the heart of the muscular fiber on the myofibrilla protein. Red color appears by transparency through the sarcoplasm. One of the components of the sarcoplasm is albumin.

When the meat is raw, the albumin is transparent. Heat or acid denatures the sarcoplasmic proteins and particularly the albumin. The coagulation of albumin produces a translucent white screen around the myofibrilla proteins and of the myoglobin that modifies the appearance of the red color and becomes dark gray. This passage from rare to cooked corresponds to the denaturation of albumin, which occurs at approximately 62°C.

The juiciness of the meat depends on the water retention power of the myofibrilla proteins. It is a very complex phenomenon depending not only on the final temperature but also the length of time to reach the final temperature.

As for the cooking of fish, the best result is obtained when it is cooked at the center at approximately 56°C. However, its organoleptic quality can only be kept for a short period of time because this low temperature does not denature the internal proteolytic enzymes, and the storage time is comparable to a raw product.

Microorganism Sensitivity To Heat Different microorganisms have different susceptibilities to heat. Moreover, the inactivation of a population of a particular microorganism is not instantaneous, regardless of the temperature used. With the concentration of the microorganism a constant, the particular temperature employed will have the greatest impact on the length of time needed for inactivation.

One convenient means of characterizing heat inactivation of bacteria is to measure the time at which a percent of the bacterial population is killed. For example, a decimal reduction (D) equals the number of minutes to destroy 90% of the organisms. (Of course, it is important to specify whether spores or vegetative organisms are sought to be destroyed; the difference between sterilization temperatures and non-sterilization temperatures in terms of D values is enormous.) When D is plotted against temperature, the number of degrees (in °C or °F) to traverse a log cycle is defined as the slope (Z) . Z is, thus, a measure of the relative heat sensitivity of a particular organism.

Figure 1 shows the relative heat sensitivities of a number of common food-related, vegetative bacteria at non-sterilization temperatures. The time for a standard amount of bacterial destruction (in minutes) is plotted against temperature. It is evident that from the slopes (Z values) that each species (solid lines) has its own, unique heat sensitivity. From these different slopes an average slope (Z) has been calculated to be 6.66 (dashed line) . From the average slope line (dashed line) it is clear that, in general, the same level of destruction of vegetative bacteria is achieved at 70°C in one minute as is achieved at 60°C in 31.7 minutes.

Normally, more than one decimal reduction is necessary to achieve an acceptable level of bacterial reduction. For convenience, F is defined as the number of minutes to destroy a given number of organisms at a given temperature. Regardless of what this given number happens to be in the particular case, F values provide a standard means of assessing relative bacterial destruction at different temperatures and different times_..

Figure 1 can be evaluated in terms of F values. The average slope (Z) was determined to be 6.66. This slope can be adopted in the general formula for F:

F = (t)10^x, where x = T-T¹

such that: F = (t) 10^x, where x = T-T' 6.66

In this formula, T'is the temperature with which all other temperatures (T) are to be compared, and t is the time assessed at T. For convenience, we can always assess T at one minute. Then t = 1 and can be disregarded. Importantly, we can arbitrarily adopt any T', depending on what relative difference we are interested in assessing. For example, where T'= 60:

^•F = (l)10^x, where x = T-60

6.66

Note now that if T'= 60 and T = 60, F = 1. On the other hand if T' = 60 and T = 70, F = 31.7. From this last calculation, the relationship between F values and the slope should be clear. The same level of bacterial destruction is achieved at 70°C in 1 minute as is achieved at 60°C in 31.7 minutes. Expressed in F values, 70°C at 1 minute yields an F value of 31.7 as compared to 60°C at 1 minute.

Optimum Cooking Time It has been empirically observed that, within a large group of identical food items, the speed at which food reaches the cooking temperature will differ significantly due to small differences in food size and thickness. Thus, different thicknesses (cuts) of the same food require different cooking times.

The fact that different cuts of the identical food require different cooking times means that, for a large quantity of identical food items cooked at a fixed temperature, the cooking time must be adjusted so that the cuts that are slow to reach the cooking temperature have time to do so. On the other hand, the cooking time must not be so long that the cuts first to reach the cooking temperature are overcooked.

The problem is best illustrated by example. Assume an oven temperature of 70°C, and three fish fillets of one, one and one-half, and two inches in thickness. The center of the one inch thick fillet may reach the desired cooking temperature in thirty minutes. On the other hand, the one and one-half inch piece of fish in the same oven may take thirty five minutes and the two inch piece of fish may take forty minutes to reach the desired temperature. If, in order to accommodate the thicker pieces, the cooking time is selected to be forty minutes, the one inch thick piece will continue to cook for ten minutes after it has reached the selected internal cooking temperature. In a 70°C oven, with a desired internal cooking temperature of 61°C, five additional minutes may be sufficient to raise the internal temperature as much as 3°C or more (Figure 2). Ten minutes may be sufficient to raise the internal temperature as much as 6°C or more. When taking into consideration rising from 53°C to the internal temperature, holding for five minutes and cooling during the cooking process, this difference in internal temperature will result in large differences in F values (Figure 2) . Most importantly, this difference will result in a different (and inedible) taste and texture. One aspect of the present invention is, therefore, the recognition that the external cooking temperature (i.e. the oven temperature) must be the same as the desired internal temperature.

Optimum Cooking Temperature While keeping the external cooking temperature the same temperature as the desired internal cooking temperature avoids variability in internal cooking temperature, it does not do away with the problems created by variability in food size and thickness. Furthermore, it says nothing about what the internal cooking temperature should be. Figure 3 shows the impact of a ten minute difference in the time to reach the internal cooking temperature of 70°C due to variability in size and thickness of two identical food items. As discussed above, the cooking of food involves three components: 1) rising, 2) holding, and 3) cooling. Since heating of solids is achieved by conduction rather than convection, the rising is a slow process; the rising from 53°C to 70°C in Figure 3 is shown to be approximately twenty eight minutes for the smaller piece and approximately thirty-five for the larger, thicker piece. There is then a fifteen minute holding period, followed by a cooling period of between twenty-seven and thirty-two minutes.

In Figure 3, the slope determined from Figure 1 (Z=6.66) has been presumed. With this slope, Figure 1 shows that only one minute is required at 70°C to achieve the proper level of bacterial destruction. Nonetheless, because of the requirements of the three components of cooking, Figure 3 shows that much more time is actually needed to achieve an internal temperature of 70°C. Thus, the Figure 1 calculation of one minute has little meaning in practice.

The impact of the ten minute rising difference and subsequent holding and cooling periods in Figure 3 is expressed in terms of F values. As discussed earlier, F values are arbitrary standard units for the analysis of relative amounts of bacterial destruction. The F value achieved for the thinner piece with an internal temperature of 70°C (assuming the calculated average slope (Z=6.66)) is calculated by adding the individual values for the rising phase (315.64), holding phase (475.85), and cooling phase (152.02). This value is 943.51. It is clear that, because of the longer time that is actually needed, F values are achieved in Figure 3 that are much higher than needed. In addition, the F values for the two pieces are found to differ significantly from one another.

Figure 4 shows the impact of a ten minute difference in the time to reach the internal cooking temperature of 65°C due to variability in size and thickness of two identical food items. As in Figure 3, Figure 4 shows the three phases of the cooking process: 1) rising, 2) holding, and 3) cooling. Again, the rising is a slow process; the rising from 53°C to 65°C in Figure 4 is shown to be approximately twenty-four for the smaller piece and approximately thirty-one minutes for the larger, thicker piece. There is then a fifteen minute holding period, followed by a cooling period of between twenty-two and twenty-eight minutes. In Figure 4, the slope determined from Figure 1 (Z=6.66) has again been presumed. With this slope, Figure 1 shows that 5.6 minutes is required at 65°C to achieve the proper level of bacterial destruction. We see in Figure 4, however, that, from the practical requirements of the three components of cooking, much more time is required.

The impact of the ten minute rising difference and subsequent holding and cooling periods in Figure 4 is expressed in terms of F values. The F value achieved for the thinner piece with an internal temperature of 65°C (assuming the calculated average slope (Z=6.66)) is calculated by adding the individual values for the rising phase (60.81), holding phase (84.49), and cooling phase (21.70). This value is 167. It is clear that, because of the longer time that is actually needed, F values are achieved in Figure 4 that are much higher than needed. In addition, the F values for the two pieces are found to differ significantly from one another. Figure 5 shows the impact of a ten minute difference in the time to reach the internal cooking temperature of 60°C due to variability in size and thickness of two identical food items. As in Figures 3 and 4, Figure 5 shows the three phases of the cooking process. Again, the rising is a slow process; the rising from 53°C to 60°C in Figure 5 is shown to be approximately twenty minutes for the smaller piece and approximately twenty-five minutes for the larger, thicker piece. There is then a twenty minute holding period, followed by a cooling period of between twenty-two and twenty-eight minutes.

In Figure 5, the slope determined from Figure 1 (Z=6.66) has again been presumed. With this slope, Figure 1 shows that thirty-one minutes is required at 60°C to achieve the proper level of bacterial destruction. We see in Figure 3, however, that, from the practical requirements of the three components of cooking, less time is required at 60°C (the holding period) . This is true even where the rising differs by ten minutes.

An even better appreciation of this feature of cooking at 60°C comes from the F values of Figure 5. The F value achieved for the thinner piece with an internal temperature of 60°C (assuming the calculated average slope (Z=6.66)) is calculated by adding the individual values for the rising phase (8.82), holding phase (25.0), and cooling phase (3.4). This value is 37.2 With a holding period of only twenty- five minutes, F values are achieved in Figure 5 that are almost exactly what are needed. Importantly, the difference in size and thickness accommodated by the holding period accounts for only a small difference between F values for the two pieces. Given the above considerations, the present invention provides that the food is cooked until its internal temperature reaches 60°C. Heating at 60 "C, so called "pasteurization" after Louis Pasteur, is successful because all pathogenic vegetative bacteria are killed at that temperature after a given amount of time (determined by the bacterial concentration) . Pasteurization, while killing vegetative microorganisms, cannot destroy the endospores. The food must, therefore, be refrigerated after cooking. Pasteurization temperatures, however, achieve this reduction in vegetative microorganisms without the accompanying loss of food taste and, as seen above, achieve this reduction within a practical time period for industrial cooking. Indeed, 60°C is the only temperature that will cause the destruction of vegetative bacteria with no damage from overcooking even when the holding period is sixty minutes or more.

Apparatus Design From the above it is clear that the cooker/cooler must provide a uniform temperature of

60°C that is constant to within plus or minus 0.25°C. The selection of the optimum cooking temperature of 60°C, together with the level of uniformity demanded, necessitates a particular apparatus design. The most important design consideration in this regard is that the apparatus be continuous.

One embodiment of an apparatus particularly suited to carry out the present invention is shown in Fig. 6. Figure 6 shows a perspective view of one embodiment of a cooker/cooler apparatus (100) of the present invention. The apparatus (100) consists of a frame (101) , supporting a hood (102) above parallel rain chambers (103,104) (shown in Fig. 9), parallel support belts (105,106), and parallel reservoirs (107,108) (shown in Fig. 9). The frame (101) allows for the connection of external liquid inlet pipes (109 (not shown) , 110) via inlet ports (111 (not shown) , 112) as well as the connection of external liquid outlet pipes (113 (not shown) , 114) via outlet ports (115,116) (shown schematically in Fig. 9). The hood (102) consists of a roof (117) and numerous access panels (118) that slidably fit into the frame (101) . Each of the access panels (118) can be removed quickly and easily by pulling outwardly on the panel handles (119) . The reservoirs (107,108) are supported by the frame (101) below the hood (102) . Each reservoir consists of two end panels (120A, 120B (not shown)), two side panels (121A,121B) (shown in Fig. 7) and a bottom panel (122B) , and is opened at the top. Each reservoir accommodates an internal collection pipe (123 (not shown),124) that is in turn connected via outlet ports (115,116) to external liquid outlet pipes (113 (not shown),114). The external liquid outlet pipes (113 (not shown),114) connect via pipe joints (125 (not shown),126) to the external liquid inlet pipes (109 (not shown),110), allowing for recirculation of the liquid.

Figure 7 is a cutaway view showing the rain chambers (104) in relation to the reservoirs (108) . Each rain chamber (104) consists of a flow-through plate (127) having numerous shower pores (128) . The spacing and relative dimensions of the shower pores are illustrated in Figure 8. While various spacing and dimensions might be used, it has been found that pores of 0.159 cm in diameter spaced 2.54 cm apart provide the best results. Each flow-through plate (127) has two solid side panels (129,130) and is open at the top to receive liquid. While various dimensions of the flow-through plate are possible, it has been found that side walls 10 cm in height provide sufficient containment of liquid for proper flow rate out the shower pores of the above-named spacing and dimensions. The external liquid inlet pipes (109 (not shown),110) connect via liquid inlet ports (111 (not shown),112) to the internal liquid dispensing pipes (131,132) . Each internal liquid dispensing pipe has numerous dispensing pores (133) for dispensing liquid into the rain chamber (104) flow-through plate (127) . In operation, packaged food is conveyed by each belt (106) into the frame (100) . A uniform shower of liquid passes from the internal dispensing pipe (132) through the rain chamber (104) and impinges said packaged food. This creates a cooking environment of uniform vapor density and temperature, and has found to provide superior heat penetration of the packaged food. The reservoir (108) , furthermore, provides a stable thermal mass for the rain chamber (104) , allowing for a substantially constant temperature on the other side of the packaged food. The amount of time of cooking is controlled by the speed of the support belt (106) .

The containment of rain chamber (104) by the hood (102) , the collection of the liquid in the reservoir (108) , and the recirculation of the liquid back through the rain chamber (104) allows for a stable, uniform temperature of 60°C plus or minus 0.25°C. This stability, unlike prior art designs, is achieved under conditions where food is continuously entering, moving through, and exiting the chamber.

Figure 9 is an end view cutaway and best illustrates the mirror image design of the apparatus. The left-hand rain chamber (103) , the left-hand support belt (105) and the left-hand reservoir (107) are separated from the right-hand rain chamber (104) , the right hand support belt (106) and right-hand reservoir (108) by a system dividing panel (134) that extends from the hood (102) to the bottom of the frame. The mirror image design provides two parallel cooking systems that may be run separately and independently.

The support belts (105,106) consist of hard plastic and are designed as open screens, having more open area than support area. The support belts are themselves supported by fixed internal support plates (135,136). The support belts are engaged by superior rollers at the loading end (Fig. 10) (137,138 (not shown) ) and the recovery end (Fig. 11) (139 (not shown),140). Inferior rollers (139A (not shown),140A) may be used at the recovery end in addition as shown in Figure 11. Each superior roller has numerous protruding catches (141) to pull the support belts and prevent lateral movement.

Figure 10 is a side view cutaway showing one embodiment of the apparatus having only one rain chamber (103) on each side. In such a case only one reservoir (107) and only one internal liquid dispensing pipe (131) is needed on each side of the apparatus. Figure 11 is a side view cutaway showing another embodiment of the apparatus having one hot liquid rain chamber (103A) and its complementary hot liquid reservoir (107A) separated from one cold liquid rain chamber (103B) and its complementary cold liquid reservoir (107B) by a side dividing system (142) . With such a design, separate cold and hot internal liquid dispensing systems are used. Each consists of an external inlet pipe connected via liquid inlet ports to internal dispensing pipes (131A,131B). While many types of liquids will work with this design, best results are achieved when the hot liquid is water and the cold liquid is 25% (by volume) ethylene glycol in water.

The side dividing system (142) consists of upper side dividing panel system (143) and lower side dividing panel system (144) , as well as upper flexible dividers (145, 146) and lower flexible dividers (147,148). This side dividing design allows for separate cooking and cooling within the same apparatus. In the operation of the cooking/cooling apparatus (100) , the superior rollers are connected to a controllable motor (Fig. 1) (149) which is, in turn, connected to a motor control means (150) (commercially available from Boston Gear) . The controllable motor is such that the parallel support belts can move a different speeds with respect to one another, allowing for the cooking and cooling of food for different times. Flexible sealing panels (151,152), attached to the hood (102) at each end of the apparatus, rest on the support belts, sealing in the heat and vapor even when the belts are in motion.

In the operation of the cooking/cooling apparatus (100) , the external liquid inlet pipes (109 (not shown) ,110) are connected to a liquid supply

(not shown) and a vapor supply (not shown) . With the contemplated injection system (shown schematically as- 153 in Fig. 7) , vapor is not injected directly into the apparatus. Vapor is injected into the liquid provided by the liquid supply to control the temperature of the inlet liquid which is measured by a temperature sensor (154) . An automated controller means (155) (commercially available from Taylor Co.) adjusts the vapor injection according to the temperature measured for the inlet liquid. The vapor injection is achieved by movement of the vapor plunger (156) .

The sealed pouch containing the food is heated in the apparatus to 60°C. Higher temperatures, while possible, will have an adverse impact on the taste and texture of the food. These conditions have been - found to be the best mode of achieving reproducible quality.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for cooking packaged food comprising: a) means for conveying said packaged food into a cooking area; b) means for impinging said packaged food on one side thereof in said cooking area with a continuous flow of heated liquid; c) means for providing a substantially constant temperature on the other side of said packaged food; d) means for controlling the temperature of said heated liquid; and e) means for regulating the speed of said conveying means, to control the amount of time said packaged food is in said cooking area.

2. An apparatus for cooking packaged food as in claim 1 further comprising means for cooling said packaged food.

3. An apparatus for cooking packaged food as in claim 1 wherein said conveying means is comprised of one or more support belts.

4. An apparatus for cooking packaged food as in claim 1 wherein said impinging means is comprised of one or more rain chambers.

5. An apparatus for cooking packaged food as described in claim 4 wherein said rain chamber is comprised of a flow-through plate having uniformly spaced shower pores of uniform dimension.

6. An apparatus for cooking packaged food as described in claim 1 wherein said constant temperature providing means is comprised of one or more reservoirs.

7. An apparatus for cooking packaged food as described in claim 7 wherein said reservoir accommodates an internal liquid collection pipe.

8. An apparatus for cooking packaged food as described in claim 5 wherein said impinging means is further comprised of internal liquid dispensing pipes.

9. An apparatus for cooking packaged food as described in claim 8 wherein said internal liquid dispensing pipes have uniformly spaced dispensing pores of uniform dimension.

10. An apparatus for cooking packaged food as described in claim 9 wherein said internal liquid dispensing pipes are suspended above said rain chamber flow-through plate.

11. A method for cooking packaged food comprising the steps of: a) conveying said packaged food into a cooking area; b) impinging said packaged food on one side thereof in said cooking area with a continuous flow of heated liquid; c) providing a substantially constant temperature on the other side of said packaged food; d) controlling the temperature of said heated liquid; and

. e) regulating the speed of said conveying means to control the amount of time said packaged food is in said cooking area.

12. A method for cooking packaged food as in claim 11 further comprising the step of cooling said packaged food.

13. A method for cooking packaged food as in claim 11 wherein said heated liquid is maintained at 60°C.

14. A method for cooking packaged food as in claim 11 further comprising the step of recirculating said heated liquid.

15. A method of cooking and pasteurizing packaged food, comprising the steps of : heating said packaged food at a substantially constant temperature of 60°C; and varying the amount of time said packaged food is heated at said constant temperature until the packaged food is cooked and pasteurized.

16. The method of Claim 15 further comprising the step of: immediately cooling said packaged food once the amount of time of said packaged food is reached.