CA2016939C - Processing of poultry - Google Patents

Abstract

Scalded, defeathered and eviscerated poultry is exposed to a cryogen atmosphere at a temperature of about -30°F. or below, by moving the poultry for about 5 minutes through an atmosphere created by expanding liquid cryogen to create a blizzard of cryogen snow and vapor.
The skin and a part of the meat immediately therebeneath is chilled to form a soft outer crust, and the crusted poultry is equilibrated in a cold zone until the carcass reaches 40°F. or below.
The crust may be created while the carcasses move along an endless belt in a freezer enclosure while fans and liquid cryogen spray nozzles create the blizzard of snow. The crusted poultry may be sprayed with water during equilibration to preserve an attractive appearance of the outer skin, or alternatively, the crusted poultry may be moved through an ice-water bath. Evaporative air chilling may also be used to initially lower the temperature of the poultry prior to the formation of the soft outer crust.

Description

201~939 PROCESSING OF POULTRY

This invention concerns the processing of poultry and more specifically the treatment of freshly slaughtered poultry to rapidly lower the body temperature to acceptable levels for further processing and/or shipment to consumers.
Heretofore in the United States, U.S.D.A.
regulations have allowed processors of poultry to chill whole carcasses in mechanically refrigerated or ice-cooled water baths, sometimes referred to as the communal bath method, inasmuch as carcasses enter one end of an elongated bath and slowly move to the opposite end as their body temperature is lowered from an entrance temperature of about 100F. to an exit temperature of about 40F. or below. Chickens are then segregated by weight, and often packed in ice at 32-34F. or mechanically refrigerated at about 28F. Whereas, this has been an accepted and widespread practice throughout the United States, it is not without disadvantages.
Poultry chilled by the communal bath takes up a large amount of water, e.g., 10 to 12 weight percent, a major portion of which subsequently drains from the bird as weepage, thus preventing the immediate packaging of the poultry following chilling lest the weepage subsequently form an unattractive puddle or pool within the transparent package. During the time when the carcass is in the water bath, generally from about 45 minutes to one hour, a substantial percentage of protein, body fluids and fat are leached from the bird, resulting in a less flavorful final product. Further disadvantages result from the growing shortages in the amount of available water for such processing throughout the country, resulting in (1) the encountering of occasional shutdowns in poultry processing plants because of the 20169;~9 unavailability or rationing of water, (2) the rising cost of potable water and/or (3) increasing sewer charges for the eventual discharges from the plant.
In Europe, for example, the use of the communal bath method for chilling has been supplanted by other methods, such as mechanically cooled air-blast chilling and water-spray chilling. More recently, the development of an evaporative air chilling process has proved a feasible alternative, as described in the December 1980 issue of Broiler Industry, pp. 42-48. In such an evaporative air chiller, the carcasses are hung by one leg from a conveyor mechanism and are periodically sprayed with potable water in order to keep the surface of the product wet during the entire procedure. As a result, a high rate of evaporation is achieved without removing water from the internal part of the bird and while achieving a high heat flux from the bird.
Oftentimes, a carcass will be sprayed between 5 and 7 times from the time it enters the chiller until it exits, while a mechanically cooled average air temperature of about 43F. is maintained. The evaporative air chilling process utilizes substantially less water than the communal bath; however, it is able to reduce the temperature of the poultry only to about 54 to 50F., a final temperature which is substantially above the storage and shipment temperature required by the U.S.D.A.
BRIEF STATEMENT OF THE INVENTION
By exposing scalded, defeathered and eviscerated poultry to a cryogen atmosphere at a temperature of about -30F. or below and by moving the poultry through such an atmosphere which is created by expanding liquid cryogen in a manner to create a blizzard of cryogen snow for at least about 5 minutes, the skin and a part of the meat immediately therebeneath is chilled to form a soft outer crust in the low 30F. degrees range. Thereafter, the crusted poultry is equilibrated in a temperature zone below ambient until the the carcass reaches 40F. or below substantially therethroughout.
The crust may be created while the carcasses move along an endless belt in a freezer enclosure while fans and liquid cryogen spray nozzles are used to create the blizzard of snow. The crusted poultry may be sprayed with water during the equilibration step so as to preserve an attractive appearance of the outer skin, or preferably, the crusted poultry may be moved through and ice-water bath.
Another possible alternative employs an evaporative air chilling step to initially lower the temperature of the poultry prior to the formation of the soft outer crust in the cold cryogen atmosphere.
In summary of the above, the present invention may be considered a providing a process for treating freshly slaughtered chicken carcasses, which process comprises the steps of defeathering and eviscerating the chicken carcass, exposing the eviscerated chicken carcass to a zone having a cryogen atmosphere at a temperature of about -30 F. or lower, maintaining the chicken carcass in motion through the cryogen atmosphere zone while maintaining the temperature at about -30O F. or lower, continuing the exposure to the cryogen for at least about 5 minutes in the zone so that the skin of the chicken carcass is frozen and an outer soft crust is formed beneath the skin, and equilibrating the crusted chicken carcass below ambient temperature until the chicken carcass reaches a temperature of 40 F. or below substantia~lly therethroughout.

Poultry, such as chickens, turkeys and the like, needs to be chilled as rapidly as possible following slaughter to slow the growth of microorganisms. Poultry normally has a fairly high body temperature, i.e., a degree or two above 100F. The birds are stunned, have their throats cut or are decapitated, and are then scalded prior to going through the usual defeathering VLS:ld .

- 3a -operation. Generally, the birds are vacuum-eviscerated following defeathering, and it was at this point that the birds heretofore were rinsed and then chilled in the communal water bath. The birds would enter one end of an ice-filled water bath, maintained at about 32F, and after about an hour's time in the bath, the temperature of the eviscerated birds would have dropped to below 40F, the criterion set by U.S.D.A.
Instead of being chilled in an ice-water bath, the birds are loaded onto the conveyor of a cryogen freezer which moves the birds through a cryogen atmosphere at a temperature below -30F within an enclosure or zone wherein they are preferably subjected to a blizzard of cryogen snow. Various suitable cryogenic freezers may be employed; for example, a straight-line tunnel freezer, such as that shown in U.S. Patent No. 3,815,377, issued June 11, 1974 to Lewis VLS:ld Tyree, Jr., may be used. Alternatively, a freezer using a spiral conveyer, such as that shown in U.S. Patent No.
3,733,848, might be employed.
As mentioned above, once the bird is killed, it is important that its body temperature be reduced as rapidly as possible in order to slow the growth of microorganisms. The primary region subject to microorganism growth is the outer skin of the birds because the interior is substantially sterile, and the cryogenic freezer is particularly effective in combatting microorganism growth at the region of the skim surface.
Carbon dioxide is the preferred cryogen because it has been found that microbes and bacteria, which grow and contribute to spoilage, are particularly susceptible to the influence of carbon dioxide. Growth of many of these microorganisms is completely inhibited in the presence of a carbon dioxide atmosphere. Carbon dioxide will also dissolve in any fat present at the surface of the carcass and create an environment that is antagonistic to the growth of bacteria. The cell structure of other microorganisms will rupture when dropped below 32F. in about 2 minutes or less. Thus, in the preferred embodiment, a tunnel freezer or a large cabinet freezer of the types to which reference has been made will be filled with a substantially completely cryogen atmosphere that will exert a very significant retardation effect upon bacteria growth and potential spoilage. In addition to carbon dioxide, nitrogen has been found to be an effective cryogen for poultry processing, and freezers filled with a substantially completely nitrogen atmosphere will exert a significant retardation effect upon bacteria growth as well. Other cryogens are also believed suitable for such processing.
The movement of the birds along a conveyor path within a cryogen atmosphere of at least about -30F., will result in the initial soft freezing of the skin and of the flesh of the bird immediately adjacent thereto.

Because these are the regions most susceptible to bacteria growth, soon after the bird enters the cryogenic freezer, bacteria growth at these potential trouble spots is very substantially reduced.
S Preferably, the atmosphere within the cryogenic freezer is maintained at a temperature of about -90 to -100F., and a blizzard of cryogen snow (at a temperature of -110F.) is created therewithin by the expansion of high pressure liquid cryogen through appropriate nozzles. Mechanical fans or blowers are employed within the enclosure to maintain a constant circulation of the cryogen atmosphere and to preferably create vapor flow paths which are either countercurrent to or crosscurrent to the path of the birds as they move along the conveyer. The constant motion of the conveyers, coupled with the movement of the atmosphere as directed by the fans, efficiently and effectively creates the outer soft crust.
The provision of refrigeration within the enclosure by the expansion of liquid cryogen through spray nozzles results in the creation of cold cryogen vapor plus fine particles of cryogen snow. Coupled with the atmospheric movement created by the fans, this combination creates a blizzard of cryogen snow throughout the enclosure that is particularly effective in building up a soft crust upon the birds in a relatively short period of time. Using a cryogen tunnel, such as that shown in the Tyree patent, such a frozen outer crust can be created in about five minutes. The use of a spiral conveyer within a large cabinet freezer, although more efficient overall, requires a generally longer time of exposure, i.e., between about 10 and about 15 minutes within the suitably cold cryogen atmosphere.
When the birds emerge or exit from the cryogenic freezer, the outer crust will be at a temperature below 32F.; however, the internal part of the bird, while at a lower temperature than that at which it entered, will be substantially above 32F. As a result, a period of equilibration is necessary so that the entire bird is below the specified maximum temperature of 40F. to meet the U.S.D.A. standards, and equilibration.
Equilibration may be effected in various different ways, for example by disposing the crusted birds in a cold room maintained at some temperature below 40F., e.g., about 35F., or by moving them along a surge conveyer through a tunnel or the like wherein an atmosphere below 40F. is maintained. A time period of from about 30 to about 45 minutes should be sufficient to effect equilibration, and at the end of equilibration, the birds are ready for either immediate packaging or for cutting into pieces followed by packaging of the pieces in desired quantities. The ability to package the birds, either whole or in parts, within five to fifteen minutes following completion of equilibration is a decided advantage over the communal bath chilling method, where it was necessary to wait for a substantial drainage period or else face the problem of unattractive weepage within the completed partially transparent package.
The taste of a bird chilled in the above-specified manner is improved significantly over that chilled by the traditional communal water-ice bath wherein leaching of the flavoring and fat occurs;
however, the appearance of the bird may be slightly darker than normal because the skin is much firmer than the relatively pliable, waterlogged skin to which the U.S. public has become accustomed. It has been found that by exposing the crusted birds to a water mist upon exiting from the cryogenic freezer, a thin glaze of water-ice is formed over the entire skin of the bird.
During the subsequent equilibration, the heat within the bird travels outward to the soft frozen crust, eventually thawing both the crust and the thin glaze of water-ice.
The presence of the water at the skin at the time of thawing gives the thawed skin a pliable, juicy appearance that is substantially indistinguishable from that with which the consuming public has become accustomed as a result of the communal bath chilling. Accordingly, the use of a water mist to provide a glaze of ice, usually in an amount not more than about 10 grams of water per pound of poultry, provides a bird exhibiting advantages of both chilling processes: the resultant bird has the locked-in flavor of the cryogen-chilled bird and has the attractive appearance of a water-chilled bird.
As a possible alternative to the misting and glazing, a somewhat hybrid process can be used to achieve the equilibration by using existing equipment formerly employed for the total communal bath chilling. Once the crusting of the birds has been achieved in the cryogenic freezer so that the skin is soft frozen, and the under-lying layers beneath the skin are also soft frozen, preferably to a depth of at least about 0.1 inch, it is found that equilibration can be carried out in a water-ice bath without the undesirable take-up of water and leaching of flavor and fat which previously occurred. Because the water-ice bath is at about 32F., there is substantially no tendency for the frozen skin to melt because of its contact with the 32F. water. As a result, equilibration can take place in about 30 minutes or less during passage through such an ice-water bath, with a water pickup of less than 5% and with the birds being removed from the exit end of the bath at about the time that the heat from the center of the birds has migrated outward and substantially accomplished the thawing of the frozen crust. As a result, existing equipment can be used to carry out the equilibrating to obtain the attractive appearance of a totally water-chilled bird and yet retain the locked-in flavor of a cryogen-chilled bird.
One further alternative to the aforementioned processes lies in the initial treatment of the bird following eviscerating and rinsing. At this point the birds can be subjected to evaporative air chilling by spraying them with water while subjecting them to circulating cold air at a temperature of about 40 to 50F. for a time sufficient to lower the temperature of the bird to below about 60F. Generally, this can be accomplished in about 20 minutes, and in about 25 to 30 minutes the temperature of the birds approaches about 54F. The birds are then removed from this chiller and are crusted using the cryogenic food freezer in the manner hereinbe~ore described; however, a relatively shorter period of time is required inasmuch as the entering temperature of the birds is substantially below that of the scalded, just-eviscerated bird.
Consequently; a somewhat lower amount of cryogen is expended per bird resulting in some cost saving, which of course is counterbalanced by the cost of operating the mechanical refrigeration equipment to maintain the desired air temperatures in the evaporative air-chilling section. Inasmuch as the total time expended between evisceration and exit from the cryogenic chiller would be somewhat greater in this instance, a substantially lesser period of equilibration is necessary to reduce the overall temperature of the bird to or below the maximum 40F. temperature.
It is felt that the use of cryogen chilling has a number of advantages over the traditional communal water bath heretofore employed in the United States. In addition to eliminating the waste which results from the leaching of the fat and the water-soluble proteins from the birds, which has a negative effect on flavor, it simultaneously reduces the need to treat the effluent and clean up these leached components before discharge to a receiving stream in order to meet existing pollution standards. It of course significantly lowers the water requirements for a poultry processing plant and can thus contribute to alleviating the shortages which many community water systems are experiencing during times of ;~016939 _g high water usage. The elimination of the communal bath also serves to prevent potential cross-contamination of healthy, clean birds by one which might be in some way infected, and in this respect it also minimizes or S eliminates the need for including relatively large amounts of chlorine that is now required in such an ice-water bath in order to guard against such infection.
As a result, there is a total absence of chlorine from the bird and improvement in flavor in this regard, in addition to the significant improvement in flavor which results from the locking-in of the fat and soluble proteins that have been traditionally lost. More efficient use of floor space in a poultry processing plant can also be achieved, and packaging may take place immediately following the conclusion of the equilibration step without danger of subjecting the resultant packages to unattractive weepage.
Although the invention has been described in terms of the presently preferred embodiments, it should be understood that various changes and modifications as would be obvious to one having the ordinary skill in this art may be made to the described processes without departing from the scope of the invention which is defined by the appended claims. Various features of the invention are emphasized in the claims which follow.

Claims (8)

1. A process for treating freshly slaughtered chicken carcasses, which process comprises the steps of defeathering and eviscerating the chicken carcass, exposing said eviscerated chicken carcass to a zone having a cryogen atmosphere at a temperature of about -30° F. or lower, maintaining said chicken carcass in motion through said cryogen atmosphere zone while main-taining said temperature at about -30° F. or lower, continuing said exposure to said cryogen for at least about 5 minutes in said zone so that the skin of said chicken carcass is frozen and an outer soft crust is formed beneath the skin, and equilibrating said crusted chicken carcass below ambient temperature until said chicken carcass reaches a temperature of 40° F. or below substantially therethroughout.

2. A process in accordance with Claim 1 wherein said cryogen comprises carbon dioxide.

3. A process in accordance with Claim 1 wherein said cryogen comprises nitrogen.

4. A process in accordance with Claim 1 wherein CO2 snow is circulated by blowers in said zone to create a blizzard of CO2 snow.

5. A process in accordance with Claim 1 wherein said chicken carcass is exposed to water spray during said equilibration step.

6. A process in accordance with Claim 3 wherein said chicken carcass is packaged for retail sale within 15 minutes following the conclusion of said equilibration.

7. A process in accordance with Claim 1 wherein said equilibration is carried out in an ice water bath for up to 30 minutes without taking up 5 percent or more water.

8. A process in accordance with Claim 1 wherein said temperature of said eviscerated chicken carcass is reduced to below about 60°F. in an evapo-rative air chiller prior to said exposure to said cryogen atmosphere.