Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
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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.
DETAILED DE8CRIPTION OF THE PREFERRED EMBODIMENT8
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
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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
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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.
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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
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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
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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
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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
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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.
