US3528826A

US3528826A - Processing products in flexible containers

Info

Publication number: US3528826A
Application number: US772321A
Authority: US
Inventors: Donald C Wilson
Original assignee: FMC Corp
Current assignee: FMC Corp
Priority date: 1968-10-31
Filing date: 1968-10-31
Publication date: 1970-09-15
Anticipated expiration: 1987-09-15
Also published as: GB1280517A; BE741035A; DE1954282A1; FR2022037A1

Description

PROCESSING PRODUCTS IN FLEXIBLE CONTAINERS Filed Oct. 51, 1968 Sept. 15, 1970 0. c. WILSON 4 Sheets-Sheet f3 INVENTOR. DONALD 0. WILSON JCU aavrgo ATTORNEYS Sept. 15, 1970 D. 0. WILSON 3,

PROCESSING PRODUCTS IN FLEXIBLE CONTAINERS Filed Oct. 51, 1968 4 Sheets-Sheet 5 F 'IEi El II-TENSION 55 as E 2 so 2.2. a4 L 24 24 V' WATER LEVEL ONE-WAY VALVE B8 EXTERNAL INTERNAL PRESSURES PRESSURES HEAD SPACE nomm fifi u BY W 4% 7 PRODUCT \f.

ATTORNEYS D. c. WILSON 3,528,826

PROCESSING PRODUCTS IN FLEXIBLE CONTAINERS Sept. 15, 1970 4 Sheets-Sheet 4 Filed 001). 31, 1968 INVENTOR. DONAILD C. WILSON Cl). C" 6. 7w

ATTORNEYS United States Patent 3,528,826 PROCESSING PRODUCTS IN FLEXIBLE CONTAINERS Donald C. Wilson, San Jose, Calif., assignor to FMC Corporation, San Jose, Calif., a corporation of Delaware Filed Oct. 31, 1968, Ser. No. 772,321 Int. Cl. A231 3/02 U.S. Cl. 99-185 29 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for purging air from and collapsing the headspace of a filled flexible container which forms semi-rigid Wrinkles in its walls when the headspace is collapsed. A first method includes providing a one-Way valve in the container and then repeatedly lowering and raising the container in hot liquid to progressively collapse and pump gas out of the container. A second method includes alternately lowering the containers into a plurality of hot and cold waterbaths whereby a steam-air mixture forms and a portion thereof escapes during immersion in hot water, and the steam remaining in the container condenses during submergence in cold water thus progressively collapsing the wrinkled container.

CROSS REFERENCE TO RELATED APPLICATIONS The method and apparatus of the present invention defines an improvement over the method disclosed in my copending application Ser. No. 693,330 which was filed on Dec. 26, 1967, which issued as Pat. No. 3,501,318 on Mar. 17, 1970 and is assigned to the assignee of the present invention. This copending application covers the concept of forming a one-way valve in a flexible container and causing gases to discharge therefrom in response to the application of hydrostatic pressure acting on the external surfaces of the container. These containers were either heated in steam, water, or both, causing steam to form in the headspace of each container. The containers were then immersed, partially or fully, in water which applied a hydrostatic pressure to the outer surfaces of the containers thus collapsing the headspace of each container and forcing the air and cooking gases through the one-way valve.

BACKGROUND OF THE INVENTION Flexible containers, which are commonly referred to as pouches, are only partially filled with the product being packaged and have potentially large headspaces within which air and other non-condensible gases may form. The air that is present in the containers is in the form of headspace air, air dissolved in the packaging medium or included in the product, and interstitial air which is air that is present Within the interstices of the product. This air must be evacuated from the container before sealing in order to prevent oxidation of the product if the product is a food product such as fruits, vegetables, meats, and powdered or granular materials.

It has been discovered that the flexible pouches sometimes become semi-rigid when large pieces of a food product, for example, are placed in pouches that are relatively small; or when relatively dry product with only a small quantity of liquid in the interstitial space is packaged. The semi-rigidness is caused by reinforcing wrinkles that form in the pouch film between the comers of the pouch and the food product in the pouch. When such wrinkles occur, a single application of Water pressure acting on the external surfaces of each submerged pouch is not suflicient to overcome the internal pressure plus the rigidity added by the wrinkles to fully collapse the headspace in the pouch and, accordingly, a considerable quantity of air remains in the pouch which causes oxidation of food products.

SUMMARY OF THE INVENTION In accordance with the present invention a product such as a bulky, non-flowable food product to be sterilized is placed in and partially fills a pouch having three edges sealed and one edge, or mouth, open. The pouch is then gripped so as to apply a stretching force across the pouch at a point slightly below the mouth thereby providing a one-Way valve which permits gases to escape but prevents fluids from entering the pouch. The pouch is then repeatedly moved downwardly and upwardly in a heated liquid bath.

When the pouch initially enters the heated liquid, the hydrostatic pressure acting on the external surface of the pouch partially collapses the headspace thereby forcing some of the headspace gases through the one-way valve. Continued downward movement of the pouch causes the pressure acting on the external surfaces of the pouch to exceed the pressure within the pouch thereby partially collapsing the headspace and forming the aforementioned reinforcing wrinkles therein. Each time the containers move upwardly through the liquid bath, the gas within the containers headspace expands but the wrinkles in the container have caused a relatively large reduction in pouch volume and have thus compressed the gas in the pouch. However, upon reduction of external pressure on the pouch, the compressed internal gas finds it easier to escape the pouch via its mouth than to increase the volume of the pouch by straightening out the Wrinkles formed therein and overcoming the pressure acting on the walls of the pouch. Thus, repeated variations in hydrostatic pressure acting on the surfaces of the pouch due to its up and down movement through the heated liquid in effect, pumps a mixture of steam and air from the pouch with the gases escaping each time the pouch moves upwardly in the liquid. In this way the air is gradually pumped out of the pouch and the walls of the pouch gradually collapse around the product even though wrinkles are present in the pouch walls.

It will be understood that if wrinkles do not form in the container walls, vertical up and down movement when the container is completely submerged in hot water is ineffective since the headspace of each flexible container will merely contract during downward movement and return to its original size during upward movement.

In the second embodiment of the invention the containers are alternately moved through hot water and cold Water. When in the hot water, a steam-air mixture is formed in the headspace of each container and a portion of the steam-air mixture flows out of the container through the one-way valve. When the container is immersed in cold water, the remaining steam in the headspace is condensed forming a suction force inside the container which artially collapses the container. Thus, by alternately heating and cooling the containers in water baths, which baths apply a hydrostatic pressure to the outer surfaces of the containers, the air is gradually purged therefrom and the container walls are gradually collapsed even though wrinkles are formed in the outer surfaces thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic vertical section taken through a first embodiment of the invention illustrating an atmospheric cooker and cooler, certain parts of the cooking chamber being broken away.

FIG. 2 is an enlargedtransverse section taken along 3 lines 2-2 of FIG. 1 showing several carriers each adapted to support several containers.

FIG. 3 is a front elevation of a fragment of a carrier having a filled flexible container clamped thereto with three edges sealed and the upper end open, said view illustrating the manner of tensioning the upper portion of the container to provide a one-way valve.

FIG. 4 is a side view of the filled container illustrating the shape of the filled container prior to being immersed in a liquid.

FIG. 5 is a diagrammatic vertical sectional view of a container after the container has been immersed up to its mouth in a liquid, said view diagrammatically illustrating hte internal and external pressures acting upon the container walls immediately after the container has been immersed.

FIG. 6 is a perspective of a container illustrating wrinkles therein as they appear after the container has completed one cycle downwardly and upwardly through the liquid and has thereafter been sealed.

FIG. 6A is a section taken at a reduced scale along lines 6A6A of FIG. 6 showing the wrinkles therein, the thickness of the walls of the container being greatly exaggerated.

FIG. 6B is a section taken along lines 6B-6B of FIG. 6, illustrating the initial shape of a corner wrinkle, the thickness of the walls of the container being greatly exaggerated.

FIG. 7 is a perspective of a container after it has completed two cycles through the liquid and has been sealed in accordance with the present invention.

FIG. 7A is a section similar to FIG. 6A but taken along lines 7A7A of FIG. 7 and indicating the shape of the container and wrinkles when the container is further collapsed.

FIG. 7B is a section similar to FIG. 6B taken along lines 7B7B of FIG. 7 illustrating a sharper corner wrinkle.

FIG. 8 is a perspective of a sealed container after it has completed several cycles through the apparatus.

FIG. 8A is a section similar to FIGS. 6A and 7A but taken along line 8A8A of FIG. 8 and indicating the shape of the container and wrinkles after substantially all of the air has been purged therefrom.

FIG. 8B is a section taken along lines 8B8B of FIG. 8 illustrating the shape of a final corner wrinkle.

FIG. 9 is a diagrammatic vertical section with parts broken away illustrating a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT An atmospheric cooking and cooling apparatus 20 (FIG. 1) is provided to continuously package bulky products, preferably food products, filled in flexible containers or pouches 22 (FIGS. 2 to 8).

The physical characteristics of the pouches must meet certain criteria to be useful in the present invention. For lack of a better term, the pouch material will be referred to as a crinkly material. 'Under this invention, the crinkly material is deformable enough to partially conform to the shape of a bulky product under external liquid pressure, but in so confining to the product it also gathers into reinforcing ribs or wrinkles along the conforming sections. The material is relatively inextensi ble thus once it has been gathered as described above, it will resist straightening out into its initial form. By way of example, a crinkly pouch material found suitable for practicing the present invention is a heat scalable, laminated film having an outerlayer formed of a polyester resin film sold under the trade name of Mylar, a central layer of thin aluminum, and an inner layer of polyethylene.

Prior to being filled, the lower edge 24 and side edges 26 and 28 of

side walls

30 and 32 of the container or pouch are hermetically sealed by application of heat nd pressure to provide a flat container having an unsealed or open upper end portion 34 which defines the mouth 36 of the container. A one-way valve 38 is formed in the mouth 36 of the container as will be described hereinafter.

The atmospheric cooking and cooling apparatus 20 (FIGS. 1 and 2) comprises a housing 40 defined by

side walls

42 and 44,

end walls

46 and 48, a roof 50, and a floor 52 all secured together in fluid tight relationshi as by Welding. An inlet opening 53 is formed in the end wall 46, and a discharge opening 54 is formed in the end wall 48 to permit an endless conveyor 55 to pass therethrough. The housing 40 is divided into a deep air purging chamber PC and a cooking chamber C by a wall 46a. The lower portion of chambers PC and C are filled with water to the levels indicated, and the water is heated to approximately its boiling point at 212 F. by steam from

manifold

56 and 56a. In addition to the water W in the cooking chamber C, saturated steam at 212 is also introduced into the chamber C from conduit 56]) and serves as an additional cooking medium.

After the containers pass through the heated water in the housing 40, the mouths thereof are hermetically sealed by a sealing mechanism 57 as fully described in my c0- pending application, which mechanism applies heat and pressure to the container mouths. The sealed containers are then moved under cooling water sprayed from a cooling system 58 disposed above the housing 40. A trough 59 is formed on the roof of the housing and collects the cooling water for recirculation or discharge by means not shown.

As shown in FIGS. 1 and 2, the endless. conveyor comprises a pair of parallel endless chains 60 and 62 (FIG. 2) trained through tracks (not shown) above the trough 59, and around pairs of sprockets 68 keyed to stub shafts 70 journaled within the housing 40, and around other sprockets 72 journaled outside of the housing. The sprockets 68 are arranged to move the conveyor along a vertical zigzag path through the hot water in the cooker. The vertical runs of each of these paths is preferably be tween about three to ten feet long, and there are preferably about 4 to 10 vertical runs of the conveyor. The conveyor is driven in the direction indicated by the arrows in FIG. 1 by a motor M which is connected to a shaft 76 by a chain drive 78. The shaft 76 has two of the sprockets 72 keyed thereto and extends the full width of the housing thereby simultaneously driving both

chains

60 and 62.

In order to transport flexible containers through the atmospheric cooking and cooling apparatus 20, each

chain

60 and 62 of the conveyor 55 has a plurality of pins 80 (FIG. 2) projecting inwardly therefrom with the pins on one chain being in axial alignment with the pins on the other chain.

A plurality of evenly spaced carriers 82 (FIG. 2) are removably mounted on each pair of axially aligned pins 80. Each carrier 82 includes an elongated transversely extending base 84 having upwardly extending arms 85 secured thereto and connected as by hooked ends to the associated ends to the associated pair of pins. Each base 84 has a plurality of pairs of spring steel arms 86 projecting upwardly therefrom with the arms 86 of each pair being resiliently stressed so that their upper ends are resiliently urged away from each other. Clamps 88 are secured to the arms 86 near the upper ends thereof and are connected to the side edges 26 and 28 of the associated container 22 to apply a tensioning force across the mouth 36 of the container 22 as indicated in FIG. 3. This tensioning force provides the aforementioned oneway valve in the container mouth which permits gases to escape from the container and prevents fluids from entering the container. A third clamp 90 is associated with each pair of arms 86 and is secured to the base 84 in position to grip the lower edge 24 of the flexible container 22 thereby preventing flotation of the lower end of the container.

Since the

clamps

88 and 90 and the carriers 82 are fully disclosed in my aforementioned application, if a more detailed description of the same is desired reference may be had to said copending application.

In operation of the atmospheric cooking and cooling apparatus 20, flexible containers are partially filled with the product to be processed leaving a relatively large headspace therein as indicated in FIG. 5. It will be assumed that the product is of the type, or size, mentioned above which causes reinforcing wrinkles to form in the walls of the flexible containers. The containers are then attached to the carriers 82 by the associated clamps 88 and 90, and the carriers are connected to the conveyor 55 at a feed station F (FIG. 1). The free hanging carriers and containers clamped thereto are then moved into the purging chamber PC and are moved downwardly into the water W therein which is maintained at about 212 F. As each container initially enters the hot water some of the headspace air is forced out of the container by hydraulic pressure acting on the external surfaces of the container and steam is formed within each container and mixed with the remaining air therein to form a steamair mixture causing the headspace to expand somewhat as indicated in FIG. 5. Further downward movement in the hot water causes the external pressure acting on each container to increase thereby partially collapsing the containers forming the aforementioned wrinkles therein. During this time the gases do not escape through the one way valve since the pressure inside the container is substantially equal to that acting on the external surfaces of the one-way valve. However, the increased external pressure and resulting partial collapse of the headspace causes the internal pressure to increase.

During upward movement of each container through the hot water in the housing, the external pressure acting on the container gradually reduces while the relatively high internal pressure causes the headspace to expand somewhat. Because of the presence of wrinkles in the walls of the container, the container headspace will not expand to its original size during upward movement and accordingly the internal pressure will become greater than the external pressure and will cause some of the air trapped within the headspace and wrinkles to expand and escape through the one-way valve as the container moves upwardly in the hot water. If sealed after completion of this first cycle, a container with a half pear therein would appear somewhat as shown in FIGS. 6, 6A and 6B.

At the beginning of the next downward movement in the liquid bath, the steam-air mixture within the headspace includes less air than was present in the headspace during previous downward movement through the hot water because the headspace has reduced in size.

Each partially collapsed container is again moved downwardly and then upwardly in the hot water to force additional portions of the steam-air mixture out of the container through the one-wa valve. At this time the walls of the container, if sealed, would appear as illustrated in FIGS. 7, 7A and 7B. The above procedure is repeated for each downward and upward movement through the hot water thereby progressively diminishing the size of the headspace and reducing the amount of air, as well as gases formed during the cooking process, in the headspace so that the headspace of each container is filled with substantially pure water vapor or steam when the container is moved into the cooking chamber C. During this time the containers are moving along a vertical zig-zag path with the containers being heated by atmospheric steam in the chamber C and being periodically immersed in hot water so that the hydrostatic pressure acting on the external walls of the containers will cause cooking gases to be purged therefrom. After the containers are moved out of the cooking chamber C, each container is hermetically sealed by the application of heat and pressure from the sealing device 57 with the appearance of the container being similar to that illustrated in FIGS. 8, 8A

and 8B. The sealed containers are then cooled as they are moved through cooling water sprayed from conduit 58. The cooled and sealed containers are then removed from the conveyor 55 at discharge station D, and other containers to be processed are placed on the conveyor 55 at feed station F.

In accordance with the above described preferred embodiment of the invention it is recognized that the hydrostatic pressure acting on the external surfaces of each container compresses the gases within the headspace causing the headspace to reduce somewhat in volume due to pure compression even if all the gas in the headspace was noncondcnsible. However, most of the gas in the headspace is a condensible gas and much of this gas condenses due to the above mentioned hydrostatic pressure acting on the container walls thereby causing further collapse of the container headspace. Although both of these headspace reducing forces cooperate to collapse the container and reduce the headspace size, a much greater proportion of the size reduction of the headspace is attributed to the pressure induced condensation than is attributed to the pure compression of gases without condensation. Since a considerable amount of the steam in the container has been condensed by the increased pressure at the lower end of its downward stroke in the purging chamber PC, the steam-air mixture within the container is rich in air at this point. During the initial portion of the next upward stroke, the reduced pressure acting on the external surfaces of the container will allow a gas that is rich in air to escape from the container through the one-way valve.

During the progressive collapsing of the container headspace as above described, the internal temperature of the product within the container will gradually increase. Such gradual increase in temperature causes the steam-air mixture within the headspace of the container at the beginning of a downward cycle of .movement in the hot liquid to include less air in proportion to steam than was present therein at the beginning of the previous downward movement through the hot water.

It will also be understood that in accordance with the preferred embodiment of the present invention the liquid within the container will approach. but will never reach its boiling point and accordingly the product will not foam. It will further be understood that the one-way valve will not permit a pressure within the container to exceed the pressure acting on the external surfaces of the container by more than about one-third of an ounce per square inch.

In the preferred embodiment of the invention as above described, the water in the chamber PC is heated to a temperature near its boiling point so as to partially cook the product and so as to fill the headspace with a steamair mixture that is relatively high in steam. Because of this high ratio of steam to air, the hydrostatic pressure applied to the container at the lower point in each of its cycles through the chamber PC will rapidly collapse the headspace due to the fact that a considerable amount of the vapor or steam condenses. It will be understood, however, that if the water in the chamber PC is not heated, the headspace will be collapsed as above described but that the container must be moved through more vertical cycles to provide the same degree of collapse since the steam-air mixture within the container will be much lower in steam content and accordingly, less steam or water vapor will condense during each cycle.

As illustrated in FIG. 9 a second embodiment of an atmospheric cooking and cooling apparatus is provided. Since many parts of the apparatus 100 are the same as those of the apparatus 20, parts of the apparatus 100 that are equivalent to those of the apparatus 20 will be assigned the same numerals followed by the letter a, and only those parts of the apparatus 100 which differ from apparatus 20 will be described in detail.

The apparatus 100 (FIG. 9) includes an endless conveyor 55a which moves carriers 82a having flexible containers or pouches clamped thereto from feed station Fa along a zig-zag path through a housing 40a to a discharge station Da. A plurality of spaced, water filled troughs 10-2 and 104 are mounted in the housing 40a. Each trough 102 is filled with hot water maintained at substantially its boiling point by steam supply conduits 106, and each trough 104 is filled with cold water from conduits 108. The

troughs

102 and 104 are arranged so that the containers are alternately introduced into a hot water trough 102 and then a cold water trough 104. After moving out of the cold water in the final cooling trough 104, the containers are moved through an elongated cooking trough 110 filled with hot water and maintained at the desired cooking temperature by steam from conduit 111. The cooking trough 110 is of sufficient length to cook the particular product being processed. The flexible containers with the cooked products therein are then sealed by the sealing device 57a and are subsequently cooled by water sprayed from conduit 58a.

When operating the cooking and cooling apparatus 100 with containers which are filled with a product that causes reinforcing wrinkles to occur in the walls of the container, it has been discovered that dipping the flexible containers first in hot Water at about 212 F. for to seconds will cause the headspace to fill with a steamair mixture, and that some of the air in the steam-air mixture will be expelled through the one-way valve of each container due to the hydrostatic pressure acting on the external surfaces of the container and due to the expansion of the heated non-condensible air. The containers are then dipped into cold water for about 15 to 30 seconds which causes the steam in the headspace of each container to condense and, because the one-way valve will not permit air to enter the container, will cause the container to partially collapse thereby forming reinforcing wrinkles in the walls thereof. The partially collapsed containers are again immersed in hot water Which causes the air in the headspace of each container to expand and a steam-air mixture to again form in the headspace and in the wrinkles of the partially collapsed container. During this heating period an additional quantity of air and steam flows from the container through the one-way valve. The container is again dipped into cold water which condenses the steam therein and further collapses the container.

It has been determined that three to five hot-cold cycles are sufiicient to collapse the containers sufliciently to expel substantially all the air from the containers. The collapsed containers are then moved through the hot water in the elongated cooking trough 110 for a period suflicient to cook the contents of the containers. After the containers have been cooked, they are sealed by the device 57a. The sealed containers are then cooled by water sprayed from conduits 58a, and the sealed and cooled containers are subsequently remove-d from the conveyor a at discharge station Da.

From the foregoing description it is apparent that a method and apparatus is provided for expelling air from flexible containers which are filled in such a manner as to cause reinforcing wrinkles to occur in the Walls thereof. In accordance with the first embodiment of the invention the wrinkled containers are progressively collapsed and air is removed therefrom by repeatedly moving the containers downwardly and upwardly through a hot water bath. In accordance with the second embodiment of the invention the containers are collapsed and air is expelled therefrom by alternately heating and cooling the containers in hot and cold water baths.

Although the best mode contemplated for carrying out the present invention has been herein shown and described the subject matter which is regarded as the invention is set forth in the appended claims.

I claim:

1. A method of reducing the headspace of and purging air from a partially filled flexible container that is sealed on three edges and has an unsealed mouth and which forms reinforcing wrinkles in its walls when the headspace is being collapsed about a large product in the container; comprising the steps of closing the mouth of the container to provide a one-way valve which allows gases to flow out of the container and prevents fluids from entering the container; moving the container along a vertical path downwardly and upwardly through at least one liquid bath; and heating the liquid in said one liquid bath substantially to its boiling point thereby forming a steam-air mixture within the headspace of the container; the hydrostatic force acting on the external surfaces of the container during at least a portion of the downward movement of the container in said path causing reinforcing wrinkles to form in the container walls, causing a portion of the steamair mixture to escape from the headspace through the one-way Valve, and causing the headspace to reduce in size.

2. A method according to claim 1 wherein the container is repeatedly moved along a vertical zig-zag path, wherein the container is fully submerged in the heated liquid, and wherein each downward movement of the submerged container is of suflicient length to provide a pressure change in excess of about 1 /2 p.s.i.g. acting on the external surfaces of the container thereby causing reinforcing wrinkles to form in the external surfaces thereof.

3. A method according to claim 2 wherein the expansion resisting strength of the reinforcing wrinkles and the gradual reduction of hydrostatic pressure acting on the external surfaces of the container during upward movement of the container causes the pressure of the steamair mixture within the container to exceed the pressure required to open said one-way valve thereby causing an additional quantity of the steam-air mixture to escape from the container through the one-way valve.

4. A method according to claim 3 wherein each vertical upward and downward cycle of the container in the liquid expells a portion of the air from the container headspace thereby progressively reducing the proportion of air to steam for each pass through the heated liquid.

5. A method according to claim 1 wherein a plurality of liquid baths are provided, heating the liquid in certain of said baths to about 212 F., cooling the liquid in others of said baths, and moving the containers along a vertical zig-zag path so that the container is alternately immersed in the hot liquid and in the cool liquid for first forming a steam-air mixture in the container and expelling a portion of the mixture through said one-way valve while immersed in the heated liquid, and for thereafter condensing the steam remaining in the container to create a vacuum which partially collapses the container while immersed in the cool liquid thereby forming reinforcing ribs in the container walls.

6. A method according to claim 5 wherein each immersion in hot liquid causes the steam-air mixture to form in the container and wherein the ratio of steam to air pr0- gressively increases and the headspace volume progressively decreases after each immersion in hot liquid.

7. A method of packaging a bulky non-flowable product in a flexible open mouth pouch of a crinkly material, comprising the steps of closing the mouth of the partially filled pouch to provide a one-way valve which allows gases to flow out of the pouch but precludes the flow of fluids into the pouch, moving the pouch downwardly through a liquid for partially collapsing the pouch about the product and simultaneously forming wrinkles in the pouch for resisting expansion of its walls and compressing the gases therein, raising the partially collapsed pouch in the liquid until the unit gas pressure in the pouch exceeds the unit pressure on the external surfaces of the pouch, the pressure required to open the one-way valve being less than that required to re-expand the partially collapsed pouch against the external pressure acting thereon so that gases within the pouch will escape from the mouth of the pouch through the one-way valve rather than re-expanding the pouch by unfolding the wrinkles formed therein during immersion.

8. A method according to claim 7 wherein the pouch is repeatedly moved downwardly and upwardly through said liquid for progressively increasing the stiifness of the wrinkles and progressively decreasing the volume of the headspace of the pouch.

9. A method according to claim 8 wherein the liquid is a heated liquid and the product includes sufl'icient moisture to cause vapor to form within the pouch, which vapor mixes with the other gases within the pouch to progressively purge substantially all of the other gases from the pouch.

10. A method according to claim 7 wherein the liquid is hot water that is heated substantially to its boiling point.

11. A method according to claim 9 wherein the liquid is hot water heated substantially to its boiling point, and wherein the pouch is moved downwardly through the liquid for a distance sutficient to provide a pressure change acting on the external surfaces of the pouch of at least about 1 /2 p.s.i.g.

12. A method of purging gases from and collapsing the head space of a flexible container having an unsealed mouth and being partially filled with a bulky food product, the container being of the type that forms reinforcing wrinkles in its walls when the headspace is being reduced, comprising the steps of closing the mouth of the container to provide a one-way valve which allows gases to flow out of the container but prevents the flow of fluids into the container, moving the container downwardly through a heated liquid both for partially collapsing the container about the product and simultaneously forming reinforcing wrinkles in the container walls which resist expansion of the walls and compressing gases in the headspace, and moving the container upwardly through the liquid so that the gradually diminishing hydrostatic pressure acting on the external surfaces of the container and the wrinkles formed in the container walls will cooperate to resist expansion of the container headspace providing a pressure within the submerged container which is great enough to open the one-way valve thereby alowing gases to purge from the headspace.

13. A method according to claim 12 wherein the liquid is water maintained at a constant temperature of about 212 F. throughout its entire depth.

14. A method according to claim 13 wherein the container is repeatedly moved upwardly and downwardly through the water bath for progressively collapsing the container headspace and purging gases therefrom.

15. A method according to claim 12 wherein the product has a suflicient moisture content to form condensible vapors within the headspace when the container is in said hot liquid and wherein each upward and downward cycle of the container in the liquid expells a portion of the air from the container headspace thereby progressively reducing the proportion of air to steam for each pass through the heated liquid.

16. A method according to claim 14 wherein the product has a sufficient moisture content to form condensible vapors within the headspace when the container is in said hot liquid and wherein each upward and downward cycle of the container in the liquid expells a portion of the air from the container headspace thereby progressively reducing the proportion of air to steam for each pass through the heated liquid.

17. A method according to claim 12 wherein the upward and downward movement through the heated liquid partially cooks the product, and additionally including the steps of completing the cooking of the product by moving the container through a second heat treatment medium, hermetically sealing the mouth of the container, and cooling the container to cause condensible gases therein to condense and further collapse the container head space.

18. A method according to claim 15 wherein the upward and downward movement through the heated liquid partially cooks the product, and additionally including the steps of completing the cooking of the product by moving the containers through a second heat treatment medium, hermetically sealing the mouth of the container, and cooling the container to cause condensible gases therein to condense and further collapse the container.

19. A method of purging gases from and collapsing the headspace of a filled flexible container having an unsealed mouth and forming reinforcing wrinkles in its walls when the headspace is being reduced, comprising the steps of applying a tensioning force across the mouth of the container to provide a one-way valve which allows gases to flow out of the container but precludes the flow of fluids into the container, heating the container by repeatedly immersing the container in and removing the container from a hot liquid causing hydraulic forces acting on the external surfaces of the container during each immersion to expell a portion of the headspace gases through the oneway valve, and cooling the container between each immersion of the containers in hot liquid for condensing the vapors therein and for progressively collapsing the container headspace.

20. A method according to claim 19 wherein the cooling occurs upon the immersion of the containers in cool water after each immersion of the containers in hot water.

21. A method according to claim 20 wherein each immersion of the container in hot water and in cool water has a duration of between about 15 to 30 seconds.

22. An apparatus for reducing the headspace of and purging air from a flexible container having an unsealed mouth and being partially filled with a bulky product, the container being of the type that forms reinforcing wrinkles in its walls when the size of the headspace is being reduced comprising, driven conveying means, a carrier on said conveying means, means on said carrier means for attaching the container thereto and for applying a stretching force across said mouth to provide a one-way valve therein, means defining at least one trough having a liq uid bath therein, guide means for the conveying means for guiding the containers along a vertical zig-zag path down wardly and upwardly through at least one liquid bath, and means for heating the liquid in said one liquid bath to about 212 F. thereby forming a steam-air mixture within the headspace of the container, the hydrostatic force acting on the external surfaces of the container during each downward movement in said bath gradually reducing the headspace volume and forming wrinkles in the container walls, and the wrinkles in the container walls resisting expansion of the walls during upward movement of the container in said bath causing a portion of the steam-air mixture to escape from the headspace during each upward movement.

23. An apparatus according to claim 22 wherein the container moves downwardly within the heated liquid a distance sufiicient to provide a pressure change acting on the external container surfaces of at least about 1 /2 p.s.1.g.

24. An apparatus according to claim 22 wherein said trough defining means defines a plurality of troughs, means for heating the liquid in certain of said troughs to about 212 F., means for maintaining cooling liquid in others of said troughs, said guide means being arranged to move container along said zig-zag path so that the container is alternately immersed in the hot liquid and thereafter in the cool liquid whereby a steam-air mixture is first formed in the container and a portion thereof is expelled through one-way valve during each immersion in the heated liquid and wherein the steam remaining in the container is condensed to create a vacuum which partially collapses the container during each immersion of the container in the cool liquid.

25. A method of purging gases from and collapsing the headspace of a flexible container having an unsealed mouth and being partially filled with a bulky food product, the container being of the type that forms reinforcing wrinkles in its walls when the headspace is being reduced, comprising the steps of closing the mouth of the container to provide a one-way valve which allows gases to flow out of the container but prevents the flow of fluids into the container, forming a steam-air mixture within the container, and thereafter condensing a portion of the steam within the container to cause the headspace to partially collapse.

26. A method according to claim 25 wherein the container is heated to form the steam-air mixture therein, and wherein the container is cooled to condense said portion of steam therein.

27. A method according to claim 25 wherein said portion of steam is condensed by application of pressure to the external surfaces of the container walls.

28. A method according to claim 25 wherein the pressure within the container never exceeds the pressure acting on the external surfaces of the container by more than 20 about one-third of an ounce per square inch.

29. A method according to claim 27 wherein the pressure within the container never exceeds the pressure acting on the external surfaces of the container by more than about one-third of an ounce per square inch.

References Cited UNITED STATES PATENTS, 2,380,134 7/1945 Waters 99 214 X 3,037,869 6/1962 Esson et'al. 3,261,140 7/1966 Long et al. 3,108,881 10/1963 Shaw et a1. 99 171 3,377,173 4/1968 Van Der Winden 99 214 FOREIGN PATENTS 4,743 4/1882 Great Britain.

TIM R. MILES, Primary Examiner US. Cl. X.R.