US3759722A - Method for evacuating packages - Google Patents

Abstract

AN IMPROVED METHOD FOR VACUUM PACKAGING AN UNCURED RED MEAT ARTICLE IS PROVIDED, IN WHICH A SHRINKABLE PLASTIC FILM BAG CONTAINING THE MEAT ARTICLE AND HAVING AN OPEN TOP IS PROGRESSIVLEY SUBJECTED TO A PERIPHERAL PRESSURE EXERTED BY A FLUID AT A TEMPERATURE NOT SO COLD AS TO STIFFEN THE FILM BUT NOT WARM ENOUGH TO DETRIMENTALLY AFFECT THE SURFACE OF THE MEAT OR TO SHRINK THE FILM. THE OPEN TOP OF THE BAG IS MAINTAINED IN COMMUNICATION WITH THE ATMOSPHERE. THE AIR IN THE BAG IS EXPELLED RAPIDLY THROUGH THE OPEN TOP UNDER THE PRESSURE OF THE FLUID ONTO THE BAG. THE BAG IS THEN CLOSED AND, IF DESIRED, HEAT SHRUNK.

Description

Sept. 18, S|MON METHOD FOR EVACUATING PACKAGES 2 Sheets-Sheet 1 Filed March 31, 1970 INVENTOR SELWYN SIMON ATTORNEY Sept. 18, 1973 5 S|MQN METHOD FOR EVAGUATING PACKAGES Filed March 31, 1970 2 Sheets-Sheet 2 FIG. 3

/ ATTORNEY United States Patent Office 3,759,722 Patented Sept. 18, 1973 3,759,722 METHOD FOR EVACUATIN G PACKAGES Selwyn Simon, Glencoe, Ill., assignor to Union Carbide Corporation, New York, NY. Filed Mar. 31, 1970, Ser. No. 24,187 Int. Cl. B6511 25/06 US. Cl. 99-174 13 Claims ABSTRACT OF THE DISCLOSURE An improved method for vacuum packaging an uncured red meat article is provided, in which a shrinkable plastic film bag containing the meat article and having an open top is progressively subjected to a peripheral pressure exerted by a fluid at a temperature not so cold as to stiffen the film but not warm enough to detrimentally affect the surface of the meat or to shrink the film. The open top of the bag is maintained in communication with the atmosphere. The air in the bag is expelled rapidly through the open top under the pressure of the fluid onto the bag. The bag is then closed and, if desired, heat shrunk.

The present invention relates to the packaging of articles in plastic film, more particularly in bags made from such film and in the evacuation of air from said bags during the packaging operation.

It is important to remove air from tight fitting plastic film packages, particularly from those containing food articles such as meat, poultry and the like. Evacuation of the air prevents bridging of the film between protruding parts of food articles when they have irregular shapes such as between the wings and thighs of poultry or between bones of a red meat cut, for example, and it generally promotes a better shrink and cling of the film to the surface of the product which prevents or at least retards oxidation and deterioration of the meat. Also, evacuation reduces expansion of air inside the packaging film if the food product is subsequently cooked in the package.

Heretofore, evacuation of plastic film packages has been effected in various manners. According to a well known method described in British Pat. No. 554,048 and in US. Pat. No. 2,876,112, a food article is placed in a plastic film bag or pouch, the pouch is then lowered and dipped into a heated liquid bath. Under the action of the hot liquid, the pouch shrinks about the enclosed article and air contained in the pouch is forced out through an open portion in the top of the pouch, the open portion being kept out of the hot bath. If desired, the bath is heated to temperatures above the heat sealing temperature of the plastic film from which the pouch is made, which permits sealing of the open top portion of the pouch at the end of the dipping operation. The attractive simplicity of this method, however, is offset by several disadvantages. It is difi'icult to control the combined evacuation and shrinking operation: when the liquid bath is heated to temperatures high enough to make the film shrink, shrinkage frequently takes place before satisfactory level of evacuation has taken place which results in undesirable pockets of air entrapped in the package, particularly in the case of irregularly shaped articles. If immersion in the heated bath is extended beyond about 5 seconds to try to obtain a better evacuation of the air, the surface of the enclosed food article (meat) is cooked which is unacceptable in fresh meat packaging. In the packaging of uncured, red meat articles, not only cooking but simple discoloration of the surface of the red meat is unacceptable. Furthermore, since the meat packing houses are usually maintained at cool or cold temperatures, vaporization of liquid from the hot bath inevitably takes place, and the resulting condensation and dripping of liquid from the ceiling and walls of the room may become unacceptable from a sanitary point of view and dangerous from a safety point of view.

In order to avoid these disadvantages, another method has been more commonly used in which evacuation is effected by placing a food article in a bag, or a pouch, of plastic film, introducing an evacuating nozzle into the bag and drawing a vacuum on the bag, and closing the evacuated bag at a point adjacent to the packaged food article while maintaining a vacuum on the opening of the bag. The main disadvantage of this procedure is that it is diflicult to prevent random tensioning of the film around the food article before evacuation is complated, which results in the formation of undesirable pockets of entrapped air in the bag. Another disadvantage is the risk of premature necking of the film at the mouth portion of the bag with concomitant interruption of the necessary free path for the air flowing out of the bag. Premature tensioning and necking of the film can only be prevented or overcome by time-consuming additional manipulations of the bag and/ or of the evacuating nozzle.

It is an object of this invention, therefore, to provide a method for packaging a food article in a plastic film bag which eliminates the risks of cooking or discoloring the surface of a red meat article, of premature tensioning and necking of the plastic film during evacuation of the bag and the concomitant formation of pockets of entrapped air in the resulting package.

It is another object of this invention to provide a method for progressively and smoothly evacuating a plastic film bag containing a food article which avoids excessive manipulations of the packaged article and prevents reentry of air into the evacuated package.

The objects of the invention are achieved by progressively subjecting a shrinkable plastic film bag containing a red meat article and having an open mouth to a peripheral pressure exerted by a fluid at a temperature well below the shrinkage temperature of the film and expelling air from the bag through its open mouth. The fluid pressure is progressively applied onto the bag from the bottom up. The bag is thereafter closed and may, if desired, be subjected to a conventional heat treatment'to shrink the film.

The method of the invention will now be more particularly described with reference to the accompanying drawing wherein:

FIGS. 1 and 2 are schematic perspective views of a plastic film bag containing a red meat article showing progressive steps of evacuation of the air in the bag according to an embodiment of the invention, wherein the fluid employed is water;

FIG. 3 is a cross-section view of an apparatus for evacuating the air from a plastic film bag containing a red meat article according to another embodiment of the invention wherein the fluid employed is air;

FIG. 4 is a cross-section view of another apparatus for evacuating the air from a plastic film bag containing a red meat article wherein the fluid employed is also air; and

FIG. 5 is a view similar to that of FIG. 4 showing the bag in the apparatus at the end of the evacuation step.

For the packaging of primal cuts of red meat, the plastic film from which the bag: is made should preferably be substantially impervious to oxygen to insure satisfactory preservation of the meat. The film may be made from polyesters or other polymers such as vinylidene chloride polymers or copolymers, from mixtures of at least 50% by weight vinylidene chloride polymers and/ or copolymers with other polymeric resins well known to those skilled in the art, as long as the film obtained from these mixtures is soft, flexible and impervious to air and oxygen. Laminates may also be used, such as vinylidene chloride film laminated with polyethylene film,

or polyethylene film coated with a vinylidene chloride composition. Polyvinylidene chloride film is preferred for use in the invention. The film may be between 1 mil and 5 mils and preferably between 1.5 to 2.5 mils thick. The bag should be of a size larger than is required to accommodate the article, i.e., of a size sufficient to conform narrowly to the countour of the article, preferably at least larger to allow for shrinkage of the film. On the other hand, if the bag is of a size much too large for the article, it is difiicult to obtain an effective vacuum because air may remain entrapped in folds of excess film. It has been found generally that a satisfactory vacuum may be attained with bags of a size up to- 45% larger than is required to accommodate the article.

The fluid may be a liquid, such as a water bath or a salt water bath, or a stream of air at high velocity. It must be maintained at a temperature above that at which the film stiffens but below that at which the film shrinks. When a bath is used, it must be kept at a temperature below the shrinkage temperature of the film, but not cold enough to stiffen the film and to prevent its collapse against the article. In the packaging of uncured red meat, it is essential to avoid discoloration of the surface of the red meat article by heat. Discolored meat is commercially unacceptable and the meat article must be trimmed of all the discolored portions before sale to the consumer, which is very costly. A noticeable increase of the temperature of the surface of the red meat article, which might very easily occur before discoloration takes place, should also be avoided because it could affect the quality of the meat on storage. Thus, the bath should not only be at a temperature below the shrinkage temperature of the film, but also at a temperature which will not detrimentally affect the surface of the meat article. It has been found that satisfactory results are obtained when the bath is maintained at a temperature within a range of from 40 F. to 100 F. and preferably from 55 F. to 85 F., with a vinylidene chloride film bag. The same temperature ranges may be used when air is employed as the fluid.

Other requirements for optimumoperation are the rate and time of exposure to the fluid of the bag containing thearticle. In order to produce an effective evacuation of the air, the bag is subjected to the peripheral pressure exerted by the fluid to permit progressive and full wiping action of the fluid upon the bag during collapsing of the film against the article. In this manner, the film conforms narrowly to the contour of the meat article and the formation of undesirable pockets of air entrapped between protruding portions of the meat article or between folds in the bag is prevented. The rate of progressive exposure to the pressure from the fluid should preferably be no greater than 1 foot per second. When using a bath, it has been found that a time of immersion as short as 2 seconds, is generally suflicient to produce an effective vacuum in the bag. But it should be understood that a time of up to 5 seconds or more might be necessary, depending on the size and shape of the red meat article and on the size of the bag. During the immersion, the meat article is maintained entirely below the surface of the bath, while the open top portion or mouth of the bag is kept outside of the bath in communication with the atmosphere to permit egress of the air expelled from the bag by fluid pressure.

Referring to the drawing, FIGS. 1 and 2 illustrate schematically a preferred practice of the method of the invention. A plastic film bag 10, containing a red meat article 12, and having an open mouth 14, is progressively lowered into a Water bath 16 contained in a tank 18. An operator, with one hand, holds the meat and bag in the water in such a manner that the meat article 12 is entirely below the surface of the bath, and with the other hand holds the open mouth 14 of the bag outside of the bath. Under the pressure of the water, the bag is collapsed and forced to conform to the shape of the meat article, and the air is expelled from the bag 10 through its open mouth. After evacuation, the bag is closed below the surface of the water, such as by gathering the neck portion of the bag and closing it with a metal clip, for example. After the clipping operation, as it is called, the bag is removed from the bath. In this manner, air is prevented from re-entering the bag. The closed bag may, if desired, be thereafter subjected to a conventional heat shrinking operation. For example, the bag may be contacted with a stream of hot air, or sprayed with, or dipped in, a hot liquid such as hot water. :If desired, only the portion of the bag closed with a clip may be heat shrunk, to provide a more hermetic closure.

As above-mentioned, instead of evacuating the air contained in the bag by progressively immersing it into a water bath, evacuation may be effected by subjecting the bag to a stream of high velocity air peripherally directed at the bag and progressively applied, beginning with the bottom of the bag and terminating with its top portion. This other embodiment of the method of the invention is illustrated in FIGS. 2 to 4 which show two alternative apparatuses, respectively, for carrying it out.

In FIG. 2, there is shown an air ring, similar to the air rings commonly used in the extrusion of tubular thermoplastic films, and generally indicated at 20. The air ring 20 comprises a cup-shaped chamber 22 communicating with compressed air conduits 24. The air conduits 24 are connected to a source of compressed air (not shown). The lower part of the chamber 22 has an upper wall 26, an inner, cylindrical wall 28, and a bottom wall 30. An annular slot opening 27 is provided in the wall 26 for exit of high compressed air from the chamber 22. A disc 32 having a central circular open ing 34 is disposed in spaced parallel relationship with the upper wall 26 of the chamber 22 to define 'an annular distributing passage 36 for the compressed air from the chamber 22 through the annular opening 27. The circular opening of the disc 32 and the inner, cylindrical wall 28 form a cylindrical passage 38 for a plastic film bag 10 containing a meat article 12. The opening 34 is preferably chamfered to direct the compressed air flowing through the passage 36 obliquely and upwardly toward the centerline of the air ring 20. The bag 10 containing the meat item 12 is progressively lowered through the passage 38 at a rate of less than 1 foot per minute, the bottom of the bag being supported by any convenient means, such as a downwardly moving forked platform, for example (not shown). Under the pressure of the air flowing at high velocity from the annular distributing passage 36 and peripherally impinging onto the Wall of the bag 10, the air in the bag is progressively expelled, as the wall of the bag is forced to collapse and is progressively wiped against the meat item.

A further embodiment of the method of the invention, wherein air evacuation is effected by progressively lowering a bag containing meat item into a chamber while a plurality of streams of high velocity air are didirected at the bag, as illustrated in FIGS. 4 and 5. A double-wall chamber 40 is mounted on a frame 42. The chamber 40 has an inner side wall 44 and an outer side wall 46 defining a passage 45 for compressed air. The outer side wall 46 is connected to an air conduit 48 communicating with a source of compressed air (not shown). The inner side wall 44 of the chamber 40 is provided with a plurality of vertically spaced-apart air nozzles 50 obliquely directed towards a central opening 52 in the top wall 54 of the chamber. The opening 52 has a periphery larger than the periphery of the bag 10 containing the meat article 12.

A platform 56 is provided to support and lower the bag 10 with the meat article 12 from the opening 52 down to the bottom part of the chamber 40 at a predetermined controlled rate of less than 1 foot per minute. The platform 56 is preferably made of a screen or of a foraminous material to permit free passage therethrough of the upwardly directed compressed air around and about the bag. The shape of the platform is not critical; it may be fiat or forked, for example. It depends on the shape of the bagged article. Means are provided for raising and lowering the platform 56, such as a screw thread 58 cooperating with a threaded bushing 60 and a roller chain drive 62 actuated by a gear-motor 64 fastened to the frame 42. The platform 56 may be adapted to be rotated as it is lowered and may also be restrained from rotation. Other means may also be used for lowering and raising the platform, such as a pneumatic cylinder, for example.

The operation of the apparatus shown in FIGS. 4 and 5 is very simple. High velocity streams of air flow into the chamber 40 from the upwardly directed nozzles 50. They peripherally impingle onto the wall of the bag beginning with the bottom, as the bag is progressively lowered through the chamber. The open mouth 14 of the bag is maintained outside of the chamber in communication with the atmosphere. As in the preceding embodiments, the bag is progressively collapsed against the meat article and forced to conform to the shape of the article under the pressure of the high velocity streams of air, and the air contained in the bag is progressively expelled through the open mouth of the bag. When the desired degree of evacuation has been attained, the bag is closed, such as with a metal clip, before being removed from the chamber to prevent re-entry of air into the bag. The closed bag may, if desired, be thereafter heat shrunk in conventional manner.

In the embodiments of FIGS. 3 to 5, the velocity of the compressed air streams may easily be determined by those skilled in the art. It has been found that with an air ring of 4 inches in diameter and a bag containing an article of about 3.5 inches in diameter, a velocity of about 2400 feet per minute was satisfactory. It depends on the size of the bags to be evacuated and on the shape of the meat articles in the bags.

Although the air ring of FIG. 3 and the air chamber of FIGS. 4 and 5 are disposed to permit passage therethrough of the bag along a vertical line, they could be disposed so as to permit passage of the bag along a horizontal, or an oblique, line if desired.

The method of the invention will now be illustrated in the following examples.

EXAMPLE I Four primal beef top round cuts of approximately the same size were placed in identical polyvinylidene chloride film bags having a length of 32 in. and a flat width of 18 in. The film had a thickness of 1.9 mil. The bags were of a size about 20% larger than required to accommodate the beef cuts. Four water baths at different temperatures were placed in a refrigerated room at 30 F. Each bag containing a beef cut was progressively immersed in one of the four baths at a rate of 1 foot per second and then kept in the water with the meat fully submerged for 2 seconds to evacuate the air contained in the bags. After 2 seconds immersion, the bags were conventionally closed with a metal clip fastened around the top portion of the bags in the water. The distance from the clip to the top edge of each bag was kept the same as much as possible. The clip is generally placed at such a distance that it will be close to the meat out after the bag has been shrunk. In this Example and in the following ones, the clips were fastened about 3 inches above the meat.

The vacuum in each closed bag was measured as follows: Each bag was placed in a chamber provided with a vacuum pump. The chamber containing the bag was evacuated until the appearance of the bag was the same as before immersion in the bath, i.e., the film around the artiele was loose, which meant that the pressure in the bag and in the chamber was approximately the same. The pres- TABLE I Internal absolute pressure (inches Hg) in the bags after evacuation Water bath (temp. F.)

5O: 'lilie bags tended to stiffen at temperatures below about Five primal beef short loin cuts of approximately the same size were placed in the same type of polyvinylidene chloride film bags 18 inches wide and 32 inches long. The film had a thickness of 1.9 mils. The bags were of a size about 25% larger than required to accommodate the beef cuts in a snug fit.

The bags containing the meat cuts were then hydrostatically evaculated, closed and shrunk by following exactly the same procedure as described above. The results of the tests appear in Table II below:

TABLE II Internal absolute pressure (inches Hg) in the bags Water bath (temp. F.) after evacuation 44 15 50 'lIhe bags tended to stiffen at temperatures below about EXAMPLE II Tests were carried out with commercially available bags made from polyvinylidene chloride film of various thicknesses. Eighteen primal beef short loin cuts as identical as possible in size and weight were placed in polyvinylidene chloride film bags 18 inches wide and 32 inches long. The only difference between the bags was the thickness of the films which was respectively 1.9 mils (Bags No. 1), 2.15 mils (Bags No. 2), and 1.5 mils (Bags No. 3). There were 6 bags of each film thickness. All the bags containing the meat cuts were hydrostatically evacuated and closed, following the procedure described in Example I and using water baths at various temperatures. In all the bags, the closing clip was positioned at a distance of 22 inches from the bottom seal of the bags. The internal absolute pressure in each bag was measured before shrinking the bags, following the procedure described in Example I.

The results of these tests are shown in Table III below:

TABLE III Before shrinking-internal absolute This example shows that hydrostatic evacuation according to the method of the invention may be satisfactorily carried out with bags made from polyvinylidene chloride vacuum, by allowing the entrapped air to bleed from the film of various thicknesses indicated by the same degree air pockets. of efiectiveness. It is advantageous to use heavier gauge EXAMPLE 1v film to protect the heavy primal cuts of beef.

EXAMPLE HI 5 Storage tests were effected with beef primal cuts packages in polyvinylidene chloride film bags according to the The following tests were made in order to illustrate method of the invention and according to the conventhe advantages of the method of the invention over contional nozzle evacuation, respectively, followed by shrinkventional evacuation methods. ing in hot water.

Several kinds of primal cuts of beef were placed in The meat cuts were beef top rounds and beef shoulder polyvinylidene chloride film bags 16 to 18 inches wide clods. The size of the cuts Was kept as constant as posand 32 inches long. The bags were of a size between sible. The beef top rounds were packaged in bags having and 30% larger than required to accommodate the beef 8- flat Width of 18 inches, a length of 32 inches and of cuts in a snug fit. The film had a thickness of 1.9 mils. a S ze 15 to 20% larger than required to accommodate A first set of these bags containing the meat cuts was 1 the cuts in a snug fit. The beef shoulder clods were packevacuated according to the method of the invention by aged in bags having a flat width of 16 inches, a length immersion in a water bath at 55 F, for a time of 2 sec- Of 32 inches and Of a $126 t0 larger than required onds at an immersion rate slightly below 1 foot per to accommodate the cuts. The meat cut packages prosecond, following the procedure described in Example I. duced according to the method of the invention were The top portion of each evacuated bag was closed, below 20 obtained following the procedure of Example I. The meat the surface of the bath, with a conventional metal clip. cut packages conventionally produced were obtained by The closed bags were thereafter dipped into water at the following procedure: the open end of each bag was 195 F. for 1 second and conventionally heat shrunk. connected to a vacuum nozzle for a time between 20 and A second set of these bags, respectively containing the 30 seconds. The bags were thereafter closed with convensame meat cuts as the first set, was evacuated and shrunk 25 tional metal clips and then dipped into water at 195 F. simultaneously by immersion in a water bath at 195 F. for about 2 seconds and shrunk.

The evacuated and shrunk bags were then closed in con- The packages were then stored in a refrigerated room ventional manner, maintained at a temperature 0f from 30 F. to 32 F.

The vacuum (in Hg absolute pressure) in the bags of and for periods of 1, 2 or 3 weeks, respectively, and the the two sets was measured following the procedure de- 30 appearance of the meat cuts was observed. The results scribed in Example I, with the exception that it was measof the storage tests are shown in Table V below:

TABLE V Beef top rounds Beet shoulder clods stored at 3032 F. stored at 30-32 F. Primal beef out conventionally conventionally storage Evacuated by evacuated with Evacuated by evacuated with period the method of a vacuum the method of a vacuum Experimental measurement (Weeks) the invention nozzle the invention nozzle 11 s 11 9. Initial internal bag pressure (inches Hg) a 6 10 Excess trim (percent) after storage 1 0 Tied/brown. Exposed meat color after storage allowing for rebloom 2 Re Red e Red Red Gray/red Gray/red.

l The weight percent of meat surface darkened during storage and which had to be trimmed off the meat cuts before they were sold to the consumer. 2 Rebloom takes place upon removal of the red meat out from the oxygen-impermeable bag. When the beef is exposed to the oxygen in the air, oxymyoglobin is formed which gives the meat its red color.

ured after the bags had been heat shrunk. The results As can be seen from the above results, the appearance appear in Table IV below: of the meat cuts was substantially the same, irrespective TABLE IVrCOMPARISON OF VACUUM LEVELS IN PLAS of the method employed to evacuate the bags. It strikingly T10 BAGS EVACUATED BY THE METHOD OF THE illustrates the advantage of speed achieved by the method VEN'IION AND CONVENTIONALLY of the invention, wherein the number of meat articles B f ut 1 H 2 B f ut I1 packaged per minute is at least 6 times greater than that of meat articles packaged by the conventional vacuum Beef top rounds 11 14 Beef top rounds if) g nozzle method.

3 12 1g EXAMPLE V 8 20 n 17 Two sets of four primal beef rib cuts of approximately Beef shoulder clods.-- 11 18 Beef ribs 1 7 the Same size were placed in identical polyvinylidene t8 3 chloride film bags having a length of 32 in. and a flat 10 18 12 24 width of 18 in. The film had a thickness of 1.9 mil. The bags were of a size about 20% larger than required to 1 Evacuated according to theinvention using hydrostatic pressure with ac o odat the beef cut in a nu fit, Th air ontained a O t k Y rgteiat I. (2 sec. immersion followed by shrin age in atcr at m the g were evacuated y blowmg Streams of g 1 Evacuated conventionally using hydrostatic pressure with water 65 v l it i f an i i heated at 95 (5 sec'lmmersmm'. Each bag Was progressively lowered through the cen- In addition to having a vacuum level inferior to that tral passage in the air ring at a rate of less than 1 foot of the bags evacuated according to the invention, the bags per minute. The compressed air was at room temperature, in the second set were not commercially acceptable bei.e., about 'F. and the bags were subjected to the flow cause, in each instance, the meat was discolored and 70 of air for a time of between 2 and 5 seconds. The only pockets of entrapped air appeared in all the bags. The difference in the conditions of the tests for the first and air pockets were indicated by spot bridging of the film second set of bags, respectively, was that the air was in the samples, i.e., portions of the films were stretched flowing at a velocity of 3000 feet per minute for the evacbetween protruding parts of the cuts. The immersion time nation of the first, and at a velocity of 4000 feet per of 5 seconds was selected in order to obtain maximum minute for the evacuation of the second set. The bags were then closed and the vacuum in the closed bags was measured following the procedure of Example I. The internal absolute pressure in the closed bags was found to be between about 18 and inches Hg, respectively.

Although the method of the invention has been particularly described with reference to the evacuation of plastic film bags containing red meat articles, it should be well understood that it may be used to evacuate plastic film bags containing red meat articles, it should be well understood that it may be used to evacuate plastic film bags containing other articles as well, such as other kinds of meat products and food articles and not even necessarily food articles, but all irregularly shaped, solid articles which have to be packaged in evacuated, flexible bags.

What is claimed is:

1. In a method for packaging an uncured red meat article by providing a bag of shrinkable plastic film, said bag having an open mouth and being of a size slightly larger than is required to accommodate the article, placing said article in said bag, evacuating air contained in the bag, and closing the bag, the improvement which comprises:

providing a bag of a size at least 10% larger than is required to accommodate the article,

providing a fluid at a temperature above that at which the film stiflens but below that at which the film shrinks,

progressively subjecting the bag containing the article,

to a peripheral pressure exerted by the fluid, from the bottom of the bag up, while maintaining the open mouth of said bag in communication with the atmosphere,

progressively collapsing the film against the article and expelling the air from said bag through said open mouth,

the temperature of the fluid and the time of exposure of the bag to said fluid being such as to prevent detrimental changes to at least the surface of the meat.

2. A method claimed in claim 1, in which the fluid is maintained at a temperature between 40 F. and 100 F.

3. A method as claimed in claim 1, in which the bag containing the articleis subjected to the fluid pressure for a time of at least 2 seconds.

4. A method as claimed in claim 1, in which the fluid 10 is a stream of air at a velocity of more than 2000 feet per minute.

5. A method as claimed in claim 1, in which the closed bag is heat shrunk.

6. A method as claimed in claim 1, in which the shrinkable plastic film is impervious to oxygen.

7. A method as claimed in claim 1, in which the shrinkable plastic film is selected from the group consisting of a polyester and a vinylidene chloride polymer film.

8. A method as claimed in claim 1, in which the bag has a size up to 45% larger than is required to accommodate the article.

9. A method as claimed in claim 1, in which the fluid is a water bath, the bag containing the article is progressively immersed in the bath until the meat article is entirely below the surface of said bath, and the bag is closed before removing it from said bath to prevent ingress of air thereinto.

10. A method as claimed in claim 9, in which the water bath is maintained at a temperature of from F. to F.

11. A method as claimed in claim 9, in which the article is immersed in the bath for a time up to 5 seconds.

12. A method as claimed in claim 9, in which the bag is closed by clipping a top portion thereof under the surface of the bath.

'13. A method as claimed in claim 12, in which the tied top portion of the bag is thereafter subjected to heat and shrunk.

References Cited UNITED STATES PATENTS 2,071,300 2/ 1937 'Gammeter 99-474 2,376,583 5/1945 De Poix 99--174 X 2,830,909 4/1958 Hagen 99'174 2,876,112.- 3/1959 Vail 99--174 X 2,966,4 14 12/1960 Fuster 99--174 FOREIGN PATENTS 498,923 12/ 1953 Canada 99l74 FRANK W. IJUTIER, Primary Examiner -R. HALPER, Assistant Examiner US. Cl. X.R. 53-22

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