Method and apparatus for reducing the temperature of articles

A method of freezing animal carcasses comprises spraying the carcass with liquid nitrogen to produce a chilled outer layer thereby to seal the moisture within the carcass for the dual purpose of maintaining the quality of the meat and preventing the frosting or icing up of the heat exchange coils of a forced draught cooling system utilized subsequently to bring the entirety of the carcass to a desired chilled or frozen condition. Also disclosed is a freezing room including means for liberating a cryogenic liquid into the air stream from the fans of a forced draught cooling system for rapid pull-down of the room temperature.

FIELD OF THE INVENTION 
The invention provides a method and apparatus for reducing the temperature 
of articles, more particularly foodstuffs containing moisture such as 
animal carcasses, for short or long term storage thereof. 
SUMMARY OF THE PRIOR ART 
A presently used method for cooling and freezing food articles of small 
size, for example less than 5 kg in weight, utilises a tunnel through 
which the articles are passed and in which they are immersed in a bath of 
cryogenic liquid or subjected to spray jets of a cryogenic liquid. The 
cryogenic liquid customarily used is liquid nitrogen or liquid carbon 
dioxide. Such arrangements however have not proven to be economically 
viable for large articles for example, sides of beef, which are 
considerably more than 5 kg in weight. 
A further known method for cooling and freezing articles up to 5 kg weight 
comprises the step of immersing the articles in a bath of refrigerated 
water/glycol mixture to pre-chill them prior to placement in a cold room 
where they are subjected to a blast of cold air produced by fans blowing 
the air through a heat exchanger, usually the evaporator of a mechanical 
refrigeration plant, which absorbs heat from the air. 
Alternatively articles of weight considerably greater than 5 kg may be 
placed in a cold room with forced draught cooling equipment so as to bring 
down the temperature of the articles over a relatively long term as the 
room temperature is pulled down. In such instances the air velocity within 
the room requires careful selection as the air is a fluid heat transfer 
medium and sufficient of it must be circulated to carry the heat from the 
product to be cooled to the heat exchanger. 
In general, air velocities of from 2 to 10 meters per second are normal 
and, if the articles are unpackaged or not well packaged, significant 
moisture losses occur. This moisture is transported by the circulating air 
until it is deposited on the surfaces of the heat exchanger where it turns 
to ice and progressively impairs the efficiency of the exchanger and 
therefore of the refrigeration plant as a whole which as a consequence 
must be operated for periods of greater length than if icing up of the 
heat exchanger did not occur. 
The invention relates particularly to the cooling, chilling and freezing of 
freshly slaughtered animals such as cattle, sheep, pigs or portions of the 
carcasses of same and poultry, such as turkeys, for eventual human 
consumption. Carcass chilling or freezing minimises meat spoilage by 
bacterial growth and is therefore a necessary step in processing the meat. 
It is desirable to extend the storage life of meat but the chilling 
methods previously used result in an undesirable loss of moisture in the 
meat tissue by evaporation. 
Batch chilling is the method adopted in most abattoirs. Typically a cold 
room is filled with hot carcasses or sides of meat at approximately 
37.degree.-40.degree. C. over a loading period of two to three hours while 
cold air is circulated around the room by forced draught cooling units. 
The air circulation is continued for the next twenty hours or so until the 
chilled carcasses are removed for further processing (at approximately 
10.degree. C.). 
In a well run and well designed cold room approximately 2% of the initial 
carcass weight is lost due to evaporation of moisture from the carcass 
surfaces. This weight loss is considered to be excessive and of 
considerable economic importance to the meat industry. 
Of even more economic significance is the fact that the moisture derived 
from the carcasses is deposited as ice or frost on the exposed surfaces of 
the heat exchangers of the mechanical refrigeration plants utilised to 
refrigerate the carcasses with consequent reduction in efficiency thereof. 
That reduction in efficiency not only increases the energy requirements to 
run the plant but also lengthens the duty cycle and so reduces the plant 
utilisation factor. 
A prior attempt to overcome that difficulty is described in U.S. Pat. No. 
4,028,774 where carcasses at body temperature for ultimate chill room 
hanging are pre-conditioned by exposure in a chilling tunnel to air at a 
temperature of from -30.degree. F. to -10.degree. F. for the purpose of 
producing a frozen crust on the carcass to prevent the subsequent release 
of moisture therefrom. That expedient is not altogether satisfactory 
because of the expensive nature of the large mechanically refrigerated 
chilling tunnel utilised and the fact that icing-up of the heat exchangers 
in that tunnel still occurs. Furthermore, there is still appreciable loss 
of carcass weight in the early stages of its progress through the tunnel. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a method and apparatus which 
prevents or at least greatly reduces moisture loss from food articles to 
be refrigerated said articles having a high moisture content, usually in 
excess of 50% by weight. 
It is a further object of the invention to reduce the accumulation of frost 
or ice on the exposed surfaces of the heat absorbing heat exchangers of 
mechanical refrigeration plant's forced draught cooling units in cold 
rooms utilised to refrigerate such articles thereby improving their 
continuing efficiency. 
The invention consists in a method of refrigerating a moist article 
comprising the steps of quick chilling a thin outer layer of the article 
to seal the moisture therein by contacting it with a cryogenic liquid and 
subsequently cooling the article throughout by placing it in a 
mechanically refrigerated cold room under conditions which ensure that the 
previously chilled outer layer does not thaw. 
According to preferred embodiments, the cold room is furnished with forced 
draught cooling units and cryogenic liquid is liberated in the air stream 
emerging from the fans of those units for a relatively short period after 
the articles have been placed in the cold room to ensure that the surface 
layer on each article does not thaw as a result of heat flow from the 
interior of the article to the surface until the temperature in the cold 
room has been pulled down to a sufficiently low figure to obviate that 
possibility. Of course the release of cryogenic liquid in this way 
shortens the total time which the articles have to spend in the cold room 
to reach the desired fully frozen condition. 
The term "cryogenic liquid" as used herein refers to a liquid having a 
boiling point at normal atmospheric pressures of less than -50.degree. C. 
Liquid nitrogen and liquid carbon dioxide are typical examples thereof. 
The term "cold room" as used herein refers to a refrigerated space in which 
articles may be placed for the reduction in temperature thereof and with 
which is associated an exteriorly adjacently located mechanical 
refrigeration plant supplying refrigerating medium to a heat exchanger of 
at least one forced draught cooling (FDC) unit within the cold room. 
From the foregoing it will be seen that the present invention contemplates 
transporting freshly slaughtered carcasses, for example suspended from an 
overhead gantry, through a suitable space wherein the carcass will be 
subjected to direct contact with a cryogenic liquid and the cold gas 
evolved therefrom. The amount of cryogenic liquid directed at the carcass 
is sufficient temporarily to freeze and thus seal the surface membranes to 
prevent the egress of moisture from the carcass. The carcass is then 
transported directly into a cold room where it is subjected to 
refrigeration by the FDC unit or units therein until the deep butt 
temperature reaches approximately 10.degree. C. At that time some or all 
of the carcasses may be removed from the cold room for butchering 
operations such as de-boning, quartering or the like. 
If the carcasses removed for butchering are required to be frozen for 
storage they may be returned to the cold room or alternatively and more 
preferably to another cold room together with carcasses and other food 
articles to be frozen taken directly from the first mentioned cold room. 
That other cold room preferably is provided with a source of cryogenic 
liquid externally of the room and directed by a conduit to discharge by 
open ended pipeline or spray nozzle adjacent to the fans of the FDC units 
in the room. When the chilled articles to be frozen are installed in the 
cold room the fans of the FDC units are turned on and a supply of 
cryogenic liquid commenced so that the gas evolved by the evaporation of 
the liquid is circulated throughout the cold room and into contact with 
the carcasses. The supply of cryogenic liquid is terminated after 
approximately one hour when the mechanical refrigeration plant may be 
brought into action. The cold atmosphere will be circulated by the fans of 
the FDC units bringing the atmosphere into contact with the cooling coils 
of the units thereby further reducing the temperature of the room and 
contents within it. Under such circumstances and unlike the operation in 
conventional freezer rooms, no moisture is lost from the carcasses, etc. 
and therefore the atmosphere within the room remains dry with the heat 
exchanger coils or the like of the FDC units remaining ice-free so that 
they perform to their maximum designed capacity. As a consequence 
carcasses will become frozen and the temperature will equilibrate through 
the meat in approximately half the time previously required. Thus the 
carcasses not only retain their moisture content but the utilisation of 
the cold rooms is greatly improved by the reduction in time required to 
reach the required level of refrigeration of the article.

Referring now to FIGS. 1 and 2, following killing of the beast in a 
slaughter house the carcass is taken to a preparation room 3 for 
preparation prior to chilling. The carcass indicated at 5 is suspended 
from an overhead gantry 7 along which it is transferred to a pre-chilling 
station 9 which is a heat insulated room located preferably adjacent to 
the preparation room 3 and a chiller room 11. 
Overhead gantry 7 of the preparation room may consist of many similar rails 
throughout the preparation room which may interconnect as desired to 
enable versatility of gantry connecting with a similar gantry in the 
pre-chilling station 9 and with a similar series of gantry rails in 
chiller room 11. The gantry throughout the diagram for simplicity is shown 
as one rail numbered 7. 
Located in pre-chiller station 9 is a means of supplying a cryogenic liquid 
to impinge upon the carcass 5 as it proceeds through the pre-chiller 9 
thence to chiller room 11. The means by which the cryogenic liquid is 
supplied may be a conduit or a series of interconnected conduits 13 
forming a spray header from which a number of sprays 15 of liquid may 
emanate to impinge on the carcass 5. Conduit 13 connects with a source 30 
of cryogenic liquid. The supply of cryogenic liquid to spray header 
conduit 13 and sprays 15 will be dependent upon the size of the carcass 
and the frequency with which a carcass is supplied to the pre-chiller 
station. Suitable valves, temperature controllers, sequence timers and the 
like are provided in order to ensure adequate supply of cryogenic liquid 
to chill the skin of the carcass whilst being economical in the usage of 
the cryogenic liquid. 
For preference the effect of the liquid spray is enhanced by providing a 
circulating fan 31 or fans in the pre-chiller station to provide a gas 
velocity therein of at least 2 meters per second. 
Further, the gas produced by evaporation of the liquid which requires to be 
vented from the pre-chiller station may with advantage be fed to a cold 
room currently in use for refrigerating articles or storing previously 
refrigerated articles. 
Following the pre-chill in station 9 the carcass is transported into 
chiller room 11 as for example along gantry 7 or otherwise as the 
installation requires. 
In order to conserve the cold emitted by the cryogenic liquid supplied to 
pre-chiller station 9 the entrance to the pre-chiller from preparation 
room 3 preferably comprises curtains 32 which permit the transport 
therethrough of a carcass but return to the closed condition without 
assistance. Similar curtains 33 may be supplied prior to entry into the 
chiller room 11 of the diagram if the installation is an interconnected 
one as shown. As an alternative air curtains may be installed at the 
entrance and exit of the pre-chiller station. 
Chiller room 11 may comprise an insulated walled room in which is installed 
a number of forced draught cooling units 17 connected to an externally 
located mechanical refrigeration plant (not shown). The room is fitted 
with an insulated door to isolate the interior of the room once it is 
filled with articles to be chilled. During the filling procedure the fans 
of the FDC units may be operated to ensure adequate circulation of 
atmosphere around the articles therein. 
Although the preceding description refers to carcasses other large items 
may be passed through the pre-chiller station in baskets, trolleys or the 
like and stored in the chiller room for treatment. 
When the chiller room is filled the door is securely closed and the 
mechanical refrigeration plant brought into action to bring the contents 
of the room to the desired temperature. When this situation is achieved 
those articles which are to be further prepared such as by butchering or 
de-boning are transported to a suitable treatment room. The chilled 
articles which are to be frozen together with the further prepared 
articles if they too are to be frozen are then transferred to a cold room 
operated as a freezer room. 
Conveniently the cold room 11 illustrated in FIGS. 1 and 2 may also provide 
the facilities of a freezer room, an example of which is shown in FIG. 3. 
A freezer room is indicated in FIG. 3 by numeral 4. It has an insulated 
outer wall 6, FDC units 8 a door 10 and a gantry rail 12. 
FDC units 8 are connected to a mechanical refrigeration plant (not shown) 
which supplies a refrigeration medium to the heat exchanger coils 14 of 
FDC units over and about which the atmosphere of the freezer room is 
circulated by fans 16 thereby to transfer the heat of the room atmosphere 
to the refrigeration plant. 
To enable a cold room to be utilised as the freezer room of preferred 
embodiments of the present invention it is provided with an externally 
located source of cryogenic liquid 18 which by appropriate valving and 
insulated pipeline 20 cryogenic liquid is supplied to a conduit 22 which 
terminates in open ended pipeline or has spray nozzles 24 to direct the 
cryogenic liquid and the gas evolved therefrom at the fans 16 of the FDC 
units 8. 
To compensate for the increased volume of atmosphere within the freezer 
room due to the gas evolved from the cryogenic liquid, room 4 is fitted 
with an exhaust port 26 and an extractor fan 28 which will be brought into 
operation during the period of supply of cryogenic liquid to conduit 22.