Method for cooling carcasses

A method for chilling carcasses which comprises the steps of introducing a cryogenic fluid into a rotatable drum of a meat tumbler, the drum having inner walls which are cooled by the cryogenic fluid; placing carcasses to be chilled inside the drum; and rotating the drum so that the carcasses contact each other and the inner walls until they are chilled to a sufficient degree. The cryogenic fluid cools the drum to a temperature of approximately 32 .degree. F. A small quantity of water may be introduced into the drum of the tumbler either immediately before or immediately after the introduction of the cryogenic fluid. The water forms an ice layer on the inner walls to prevent the carcasses from sticking to the inner walls. The primary chilling of the carcasses takes place between the tumbling carcasses and the cold inner walls and/or ice layer. The carcasses may also be tumbled in the drum in an inert gas or vacuum atmosphere to massage surface moisture back into the carcasses.

BACKGROUND OF THE INVENTION 
This invention relates generally to a method for chilling carcasses and 
more specifically to a method for chilling poultry carcasses utilizing a 
tumbling process, which process results in chilled poultry carcasses which 
are at an ideal storage and transportation temperature with minimum 
product deterioration. 
SUMMARY OF THE PRIOR ART 
Various processes are available for the production of fresh poultry 
carcasses. The term "fresh" in this disclosure is used to denote carcasses 
which are not frozen but which are at a temperature sufficiently low 
enough to substantially prevent deterioration of the meat. The temperature 
of a "fresh" carcass is in the region of 28.degree. F.-34.degree. F. 
After slaughtering, carcasses must be cooled fairly rapidly to a 
temperature which is low enough to substantially prevent bacterial growth, 
i.e. to around 32.degree. F.-34.degree. F. Conventional air chiller 
systems have been used in the past to effect this cooling. In these 
systems, carcasses are disposed on a conveyer or on shackle line and 
passed through a 32.degree. F.-35.degree. F. air cooled chamber, where 
after some 90-120 minutes, or longer for larger size carcasses, they 
emerge at a temperature of between 34.degree. F.-35.degree. F. Exposure to 
the air for this length of time causes a loss of some of the original 
fluids due to evaporation. 
To overcome this problem, methods of processing have been developed which 
include a brief period of rapid freezing of the exterior surface of the 
carcasses. This substantially prevents moisture loss from the carcasses 
during later processing. U.S. Pat. No. 4,028,774, granted to Allan et al 
on Jun. 14, 1977, discloses that this exterior freezing is achieved by 
blowing cold air on the carcasses. U.S. Pat. No. 4,325,221, granted to 
Grewar on Apr. 20, 1982, discloses the use of a cryogenic fluid sprayed on 
the carcasses. A method of crust freezing the outermost layers of the 
carcass by immersing the same in a cryogenic fluid bath is taught by U.S. 
Pat. No. 4,367,630, granted to Bernard et al on Jan. 11, 1983. 
In essentially all of the above processes, temperatures well below 
32.degree. F. are used to freeze the exterior surface of the carcasses or 
a layer of moisture surrounding the exterior surface of the carcasses. The 
moisture retained by the carcasses is either in the form of natural 
fluids, or moisture added by means of subjecting the carcasses to water 
sprays or immersion in water chillers. 
Equilibration tunnels or extended shackle lines are included in the 
processing area to allow the temperature of these chilled carcasses to 
equalize, or equilibrate, after they exit the freezer area. This requires 
a substantial outlay of capital on the part of the processor. For 
chickens, for example, the volume of carcasses processed, (up to 8,000 
birds per hour or more), the length of the conveyor or shackle line 
involved, and the cost of the area for chilling the carcasses become major 
hurdles to processors installing this type of system. An 8,000 bird per 
hour line requiring 120 minutes of chilling would require 8,040' of 
shackle lines, (based on each carcass requiring 6" of space), plus the 
associated refrigeration system, considerable space to install the same, 
and the required capital investment. 
Once the carcasses are subjected to temperatures above 32.degree. F. during 
subsequent storage, transportation and retailing, the moisture retained by 
the abovementioned processes tends to be lost, and is generally found as 
free water, usually reddish in colour, in the packaging of the product. 
This presents an unsatisfactory product from an appearance point of view, 
and the customer also buys the wasted fluids at the price of the poultry 
meat. 
In addition to the above, various parts of the carcasses, especially the 
wings in the case of poultry, tend to freeze during processing. This 
results in the necessity for a long equilibration time to allow the frozen 
parts to thaw so that they can be manipulated in machines designed to 
either cut and/or package the same. Freezing of the exterior surface and 
any subsequent storage of poultry carcasses especially, tends to dehydrate 
and discolour the skin, making the end product less saleable. 
SUMMARY OF THE INVENTION 
The present invention is a method for chilling carcasses which 
substantially overcomes the disadvantages of previously used systems. 
It is an object of the present invention to provide a method for lowering 
carcass temperature as rapidly as possible to slow down bacterial growth; 
It is a further object of the present invention to provide a method for 
chilling carcasses which substantially prevents the natural fluids from 
dripping out of the carcasses during processing; 
It is a further object of the present invention to provide a method for 
chilling carcasses which tends to reduce the capital cost required for 
processing carcasses to produce fresh meat. 
It is a further object of the present invention to provide a method for 
chilling carcasses which produces more easily manipulatable carcasses at 
the end of the chilling process. 
The method of chilling carcasses as disclosed in the present invention 
comprises the steps of: 
a) introducing a cryogenic fluid into a rotatable drum of a meat tumbler, 
the drum having inner walls which are cooled by the cryogenic fluid; 
b) placing carcasses to be chilled inside the drum; 
c) rotating said drum so that said carcasses contact each other and said 
inner walls until they are chilled to a sufficient degree. 
In the preferred embodiment of the invention the cryogenic fluid is either 
carbon dioxide gas or nitrogen gas. The cryogenic fluid cools the drum to 
a temperature of between 32.degree. F. and 38.degree. F., and preferably 
to a temperature of 32.degree. F. Additional cryogenic fluid may be added 
during rotation of the drum to maintain the temperature of the drum at the 
desired level. 
A small quantity of water may be introduced into the drum of the tumbler 
either immediately before or immediately after the introduction of the 
cryogenic fluid. The water is sufficiently cooled by contacting the inner 
walls of the drum to form a thin ice layer thereupon, thereby 
substantially preventing the carcasses from sticking to the inner walls of 
the drum. The primary chilling of the carcasses takes place between the 
tumbling carcasses and the ice layer. Additional quantities of water may 
be added during rotation of the drum to maintain the ice layer on the 
inner walls. 
The carcasses are exposed in the drum to a temperature sufficiently low 
enough to rapidly chill the exterior surfaces of the carcasses. The drum 
temperature is, however, not set at a temperature below 32.degree. F. The 
carcasses are tumbled in the drum for around 60 minutes during which time 
the carcasses may be subjected to a vacuum or inert gas atmosphere to 
allow moisture disposed on the exterior surfaces of the carcasses to be 
reabsorbed into the carcasses to bind with the protein of the meat.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
After evisceration, or evisceration and exposure to a conventional water 
chiller, the carcasses are introduced into a meat massager or tumbler. 
Massagers are rotating drums which are presently used in the meat 
processing industry to break down meat fibres and tenderize the meat. The 
massager or tumbler used in the present invention is the MARATHON 
SUPERTUMBLER.TM. produced by HMC Heller Meat Systems Consulting GmBH of 
Augustdorf, West Germany, however, any other suitable tumbler may be used. 
In the preferred embodiment of the present invention, a cryogenic fluid, 
carbon dioxide or nitrogen gas for example, is sprayed into the drum. The 
cryogenic fluid is sprayed via exteriorly disposed piping through the 
drum's open door and into the interior of the drum. A tumbler may, 
however, be modified to spray the cryogenic fluid through interiorly 
disposed piping. 
The cryogenic fluid cools the inner walls of the drum and the temperature 
of the drum is set at between 32.degree. F. and 38.degree. F., and 
preferably at 32.degree. F. A very light mist of a small quantity of clean 
water is sprayed onto the inner wall of the drum. The water may be sprayed 
into the drum either immediately before or immediately after the 
introduction of the cryogenic fluid. The water is cooled by contacting the 
inner walls and forms a thin ice layer upon the inner walls. This ice 
layer prevents carcasses from sticking to the inner wall and tearing the 
skin. 
A plurality of poultry carcasses are placed into the drum. Cryogenic fluid 
may be sprayed onto the carcasses themselves to begin the chilling 
process, or during processing to maintain the temperature within the drum 
at about 32.degree. F. Water may also be sprayed periodically, or 
continuously, into the drum to maintain the ice layer on the inner walls. 
The drum is rotated and the carcasses tumble into contact with each other 
and with the cold inner walls of the drum. The chilling of the carcasses 
takes place primarily between the cold inner walls of the drum, or the ice 
layer, and the tumbling carcasses. As any specific parts of the carcasses 
are not continuously in contact with the cold inner wall of the drum, or 
the ice layer, freezing of the carcasses, especially the wings for 
example, is substantially prevented. 
The carcasses are tumbled in the drum at a temperature which is 
sufficiently low enough to rapidly chill the exterior surfaces of the 
carcasses, but not at a temperature below 32.degree. F. The carcasses are 
preferably tumbled in the drum at a temperature of 32.degree. F. for about 
60 minutes, producing uniformly chilled carcasses, which have 
substantially no frozen portions and which are a substantially fresh 
state. The carcasses in the tumbler do not substantially undergo freezing 
and thawing. 
This tumbling process results in carcasses which are chilled throughout to 
a substantially uniform temperature of between 32.degree. F. and 
34.degree. F. Because the carcasses have spent time in the tumbler, and 
because the temperature is uniform, when the carcasses exit the tumbler 
they are easier to manipulate and can be more easily cut up and packaged 
than carcasses processed in other ways. 
During this tumbling process, the carcasses may also be subjected to an 
inert gas or vacuum atmosphere for a period of 10 to 30 minutes during the 
60 minutes of tumbling. This allows any surface moisture or water on the 
exterior surfaces of the carcasses to be massaged back into the meat 
protein. The carcasses are preferably tumbled at a temperature of 
32.degree. F. as the binding property of protein is maximized at this 
temperature, even though some binding will still occur at 38.degree. F. 
The meat and water or moisture on the surface of the carcasses must be 
maintained above the freezing point in order to get the surface moisture 
reabsorbed into the skinned carcass. Moisture in the order of 
approximately 2-4% of carcass weight can be reintroduced into the 
carcasses in this manner. The inert gas or vacuum atmosphere is required 
to substantially prevent smearing of the meat. 
If the carcasses have been passed through a conventional water chiller 
prior to being placed in the tumbler, each carcass has moisture or water 
of between 4% and 16% of carcass weight disposed on its exterior surface. 
Much of this surface moisture or water must be drained off before the 
carcasses reach 32.degree. F. This can be accomplished by placing the 
carcasses in a non-refrigerated tumbler prior to introducing them into the 
refrigerated tumbler and processing them as described above. 
After this process the carcasses can be stored at 32.degree. F. without 
excessive moisture loss, as the moisture has been reintroduced into the 
protein of the skin and carcass, and is not merely surface moisture. For 
extended shelf life, the carcasses could be stored at 28.degree. 
F.-32.degree. F. Once the moisture is bound with the protein in the 
carcass, it tends to stay in the meat, thus maintaining the water to 
protein ratio of fresh poultry throughout processing. A product chilled in 
this manner is more likely to be juicy when cooked than one which has been 
processed in another manner which permits dehydration of the carcass to 
occur. Any moisture reabsorbed by the protein also tends to retard 
dehydration and discoloration (barking or browning) of the skin should the 
carcasses be subjected to the long term drying effect of refrigerated 
storage. 
Using a tumbler to accomplish the chilling and equilibration steps in the 
processing of carcasses tends to save on both space required in processing 
plants for these steps and in labour costs. 
While the invention has been described in conjunction with specific 
embodiments thereof, it is evident that many alternatives, modifications, 
and variations will be apparent to those skilled in the art in the light 
of the foregoing description. Accordingly, it is intended to embrace all 
such alternatives, modifications and variations, as fall within the spirit 
and broad scope of the appended claims.