Note: Descriptions are shown in the official language in which they were submitted.
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Description
VACUUM SKIN PACKAGE FOR CHEESE
Technical field
[0001] The present invention relates to a vacuum skin package for the
packaging
of cheese. In particular the present invention relates to a vacuum skin
package for the packaging of respiring cheeses and to a method for
vacuum skin packaging a cheese product.
Disd~ure of the invention
[0002] Vacuum skin packaging is a process well known in the art for using a
thermoplastic packaging material to enclose a food product. The vacuum
skin packaging process is in one sense a type of thermoforming process in
which an article to be packaged serves as the mold for a forming web. An
article may be placed on a support member, that can be flat or shaped, e.
g. tray-shaped, bowl- shaped or cup-shaped, and the supported article is
then passed to a chamber where a top flexible film is drawn upward
against a heated dome and the softened top flexible film is then draped
over the article. The movement of the film is controlled by vacuum and/or
air pressure, and in a vacuum skin packaging arrangement, the interior of
the container is vacuumized before final welding of the top flexible film to
the support member. In a vacuum skin package the upper heated film thus.
forms a tight skin around the product and is sealed to the support. Vacuum
skin packaging is described in many references, including FR 1,258; 357,
FR 1,286, 018, AU 3,491, 504, US RE 30,009, US 3,574, 642, US 3,681,
092, US 3,713, 849, US 4,055, 672, and US 5,346, 735.
[0003] The term "vacuum skin packaging" (hereinafter "VSP") as used herein
indicates that the product is packaged under vacuum and the space
containing the product is evacuated from gases at the moment of
packaging. The 'top flexible film is sometimes referred to as ° skin-
forming° film.
(0004] Several hundreds of different kinds of cheese are produced today with
different packaging requirements. Some cheese products, particularly
semi-hard cheeses, like Swiss cheese, emit a significant amount of carbon .
dioxide over time as a consequence of their curing process. The evolved
carbon dioxide must be allowed to escape the package in order to
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maintain the properties of the cheese and the integrity of the package. If
not allowed to escape the evolved carbon dioxide collects inside the
package creating a so-called " ballooning effect" , which is perceived by
the average consumer as a defect in the packaging and an indication of
possible spoilage. These cheese types are often referred to as
" gassing" cheeses.
[0005] On the other hand, moulded cheeses, such as blue cheese, require a type
of packaging that allows them to " breathe° , that is to exchange
oxygen
with the outer atmosphere, in order to maintain the moulds alive and
therefore the flavour of the product unchanged.
[0006] The gassing cheeses and the moulded ones are herein referred to as
" respiring" cheeses due to their gas exchange requirements.
[0007] Due to their different breathing requiremens gassing cheeses and
moulded ones are typically stored and sold in different types of packaging.
Gassing cheeses are generally available to the consumer in hermetic
packages, often under vacuum or under a modified atmosphere. On the
other hand moulded cheeses are mostly sold in non-hermetic packages,
such as waxed paper wrappings.
[0008] It would be desirable to provide a common packaging system for both
gassing and moulded cheeses having enough flexibility to adapt to the
different respiration requirements of these products and which would not
require burdensome inventory arrangements on the side of the cheese
producer.
[0009] It has now been found that vacuum skin packaging can offer a solution
to
this need. In particular it has been found that by carefully selecting the
oxygen barrier properties of the skin-forming film and of the support
member it is possible to obtain a vacuum skin package for respiring
cheese (both gassing and moulded) which guarantees the shelf life and
the optimal preservation of the organoleptic properties of the product.
Advantageously by properly selecting the oxygen barrier properties of the
support memebr of the package it possible to meet the different respiration
rerquirements of gassing and moulded cheeses by changing the skin-
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forming film. Thus only a limited number of inventoried packaging
materials is required to meet most respiring cheese requirements.
[0010] Of the prior art available in the field of VSP packaging only DE
4001272C
relates to a skin- forming film for the vacuum skin packaging of gas-
evolving products such as cheese, comprising an ionomer base material
and an outside coating comprising an anionic copolymer dispersion based
on vinylidene chloride and methyl acrylate and an aqueous dispersion of a
vinyl chloride based copolymer. Said skin-forming film is described as
having a carbon dioxide transmission rate of about 800 cm3 /m~-day-bar
and an oxygen transmission rate of less than about 200 cm3 /m2-day-bar.
No mention is made about the composition or the properties of the support
member.
[0011] US 5,846,582 discloses the vacuum skin packaging of shingled food
slices, among which cheese slices. However, cheese products sold in slice
form generally have reached a stage of their curing process wherein no or
negligible gases are evolved and thus have no demanding " breathing°
requirements.
[0012] Accordingly, a first object of the present invention is a vacuum skin
package of a cheese product wherein the support member has an oxygen
transmission rate of 80 to 500 cm3 Im2-day-bar at 23°C and 0% relative
humidity and the flexible film draped over the cheese product has an
oxygen transmission rate greater than 60 cm3 /m2-day-bar at 23°C and 0%
relative humidity.
[0013] A second object of the present invention is a method of making a vacuum
skin package of the first object comprising the steps of: providing a support
member, loading a cheese product over the support member, and draping
a flexible film over the cheese product and over the support member and
wherein the support member has an oxygen transmission rate of 80 to 500
cm3 /m2day-bar at 23°C and 0% relative humidity and the fiiexible film
draped over the cheese product has an oxygen transmission rate greater
than 60 cm3 /m2-day-bar at 23°C and 0% relative humidity.
[0014] In its first aspect the present invention relates to a vacuum skin
package
comprising:
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a) a support member;
b) a cheese product loaded onto said support member; and
c) a flexible film draped over the cheese product and enclosing said
cheese product on the support member, characterized in that the
support member a) has an oxygen transmission rate of 80 to 500 cm3
/m~-day-bar at 23°C and 0% relative humidity and the flexible film c)
has an oxygen transmission rate greater than 60 cm3 /m~-day-bar at
23°C and 0% relative humidity.
[0015] The oxygen transmission rate (hereinafter "OTR") is measured according
to ASTM D-3985 using an OX-TRAN instrument by Mocon. Unless
otherwise stated the OTR values throughout the text refer to measures
made at 23°C and 0% relative humidity (hereinafter " RH" ).
[0016] The OTR value of the support member is independent of the OTR value of
the flexible skin-forming film, i.e. the two OTR values do not have to be the
same.
[0017] It is known that the oxygen barrier properties of certain materials,
such as
(ethylene-co-vinyl alcohol) copolymers (EVOH) and polyamides, vary
greatly with humidity, their OTR values generally increasing with
increasing humidity. The OTR values of the support member and of the
flexible skin-forming film may also have a different dependence from
humidity the one with respect to the other.
[0018] The possibility of combining a support member and a skin-forming film
having different oxygen transmission properties represents one of the
advantages of the package of the present invention with respect to other
cheese packages such as shrink bags or pouches. In fact it allows a
greater flexibility in modulating the gas permeation properties of the overall
package. For instance, gassing cheeses, like Swiss cheese, are better
preserved in an environment that allows a moderate passage of oxygen
whereas moulded cheeses, like blue cheese, are better preserved in an
environment with significant oxygen transmission properties. With the
package of the present invention it will be possible to meet these different
requirements by changing for instance only the flexible skin-forming film.
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[0019] Some examples of suitable combinations of oxygen transmission
properties for the support member and the flexible skin-forming film are
reported below, the numbers being OTR values at 23°C and 0% RH
expressed in cm3/m2-day-bar.
[0020] Support 80-250 / Skin-forming film 60-300; Support 80-250 I Skin-
forming
film 100-200; Support 80-250 / Skin-forming film 150-500; Support 80-250
/ Skin-forming film 500-1000; Support 250-350 ! Skin-forming film 60-300;
Support 250-350 / Skin-forming film 100-200; Support 250-350 / Skin-
forming film 150-500; Support 250-350 / Skin-forming film 500-1000.
[0021] OTR values of the skin-forming film can in some cases be as high as
10,000 cm3/m2-day-bar and even higher:
[0022] More specifically, shelf lives in the order of 9 weeks, can be obtained
for a
moulded type cheese like Roquefort by combining a support member with
an OTR in the range of 80 to 500 cm3/m2-day-bar, preferably in the range
of 80 to 250 cm3/m2-day-bar, with a skin-forming flexible film with an OTR
in the range of 500-1000 cm~/m2-day-bar, preferably in the range of 600 to
1000 cm3/m2-day-bar.
[0023] Gassing cheeses, like Asiago, Leerdammer and Emmentaler, were best
preserved in a package comprising a support member with an OTR in the
range of 80 to 250 cm3/m2-day-bar and a skin-forming flexible film with an
OTR in the range of 60 to 300 cm3/m2day-bar, preferably 100 to 200
cm3/m2-day-bar.
[0024] Typically the materials suitable for both the support member and the
flexible skin-forming film have carbon dioxide transmission rates
(measured using an analytical technique analogous to ASTM D-3985 at
23°C and 0% RH) greater than 250 cm3/m2-day-bar, preferably greater
than 300 cm3/m2-day-bar.
[0025] The materials suitable for the support member have OTR values at
23°C
and 100% RH (measured using an analytical technique analogous to
ASTM D-3985 at 23°C and 0% RH wherein both sides of the specimens
to
be tested are kept in contact with water for four days before being tested)
greater than 100 cm3/m2-day-bar, typically greater than 140 cm31m2-day-
bar.
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[0026] The OTR values at 23°C and 100% RH of the materials suitable for
the
flexible skin-forming film are greater than 300 cm3/m2-day-bar, generally
greater than 450 cm3/m~-day-bar.
[0027] The support member and the flexible skin-forming film are mostly
obtained
from multi-layer plastic materials. They may include any number of layers
from 2 to as many as 20. Preferably they will include from 4 to 15 and
more preferably 5 to 10.
[0028] The materials to be used for the support member typically require some
rigidity and good thermoforming properties whereas the materials to be
used for the skin-forming film require stretchability and flexibility.
[0029] A key requirement for the skin packaging material in the VSP process is
a
high degree of formability/stretchability to avoid a common and recurrent
problem in such operations, which is the occur-ence of wrinkles and other
irregularities in the final packaged product.
[0030] Typically, plastic materials suitable for the support member of the
present
invention have a thickness greater than 100, 120, 150, 170, 200 N m.
[0031] The thicknesses of materials suitable for the support member are
generally less than 1200, 1000, 850, 700 N m.
[0032] Plastic materials suitable for the skin-forming film of the present
invention
have a thickness greater than 35, 50, 60, 70 N m.
[0033] The thicknesses of materials suitable for the skin-forming film are
less than
200,180, 150, 120 N m.
[0034] When the support member and the skin-forming film of the package of the
present invention are made of multi-layer thermoplastic materials, they
comprise at least one outer layer, optionally one oxygen barrier layer and
at least one heat-sealable surface layer.
[0035] The oxygen barrier layer, if present, comprises any of the polymers
known
in the art for their oxygen barrier properties, such as EVOH, PVDC,
polyesters, polyamides and blends thereof. Particularly suitable are
polyesters, polyamides and blends of polyamides and EVOH in weight
ratios from 10:90 to 90:10.
[0036] PVDC is any vinylidene chloride copolymer wherein a major amount of the
copolymer comprises vinylidene chloride and a minor amount of the
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copolymer comprises one or more unsaturated monomers
copolymerisable therewith, typically vinyl chloride, and alkyl acrylates or
methacrylates (e.g. methyl acrylate or methacrylate) and the blends
thereof in different proportions. Generally a PVDC barrier layer will contain
plasticisers andlor stabilizers as known in the art.
[0037] EVOH is the saponified product of ethylene-vinyl ester copolymers,
generally of ethylene-vinyl acetate copolymers, wherein the ethylene
content is typically comprised between 20 and 60% by mole and the
degree of saponification is generally higher than 85% preferably higher
than 95%.
[0038] Polyamides used as gas barrier layer can be homo- or co-polyamides.
This term specifically includes those aliphatic polyamides or copolyamides
commonly referred to as e.g. polyamide 6 (homopolymer based on ~ -
caprolactam), polyamide 69 (homopolycondensate based on
hexamethylene diamine and azelaic acid), polyamide 610
(homopolycondensate based on hexamethylene diamine and sebacic
acid), polyamide 612 (homopolycondensate based on hexamethylene
diamine and dodecandioic acid), polyamide 11 (homopoiymer based on
11-aminoundecanoic acid), polyamide 12 (homopolymer based on w-
aminododecanoic acid or on laurolactam), polyamide 6/12 (polyamide
copolymer based on a -caprolactam and laurolactam), polyamide 6/66
(polyamide copolymer based on a -caprolactam and
hexamethylenediamine and adipic acid), polyamide 66/610 (polyamide
copolymers based on hexamethylenediamine, adipic acid and sebacic
acid), modifications thereof and blends thereof. Said term also includes
crystalline or partially crystalline, aromatic or partially aromatic,
polyamides, like MXD6/MXDI that is an aromatic copolyamide formed in
the reaction between metaxylylenediamine, adipic acid and isophtalic acid.
[0039] The term " polyesters" refers to polymers obtained by the
polycondensation reaction of dicarboxylic acids with dihydroxy alcohols.
Suitable dicarboxylic acids are, for instance, terephthalic acid, isophthalic
acid, 2,6-naphthalene dicarboxylic acid and the like. Suitable dihydroxy
alcohols are for instance ethylene glycol, diethylene glycol, 1,4-butanedioi,
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1,4-cyclohexanedimethanol and the like. Examples of useful polyesters
include polyethylene 2,6-naphtalate), polyethylene terephthalate), and
copolyesters obtained by reacting one or more dicarboxylic acids with one
or more dihydroxy alcohols.
[0040] The thickness of the oxygen barrier layer, if present, will be set in
order to
provide the overall laminate with an OTR at 23°C and 0% RH that is in
line with the specific requirements of the type of cheese being packed.
[0041] The heat-sealable surface layer comprises materials chosen from the
group of ethylene homo-and co-polymers, propylene homo- and co-
polymers, ionomers and the like as well as blends of these polymers in
any proportions. Suitable blends for the heat-sealable layer also include
peelable blends. As used herein, the term " copolymer" refers to a
polymer derived from two or more types of monomers, and includes
terpolymers. Ethylene homopolymers include high density polyethylene
(HDPE) and low density polyethylene (LDPE). Ethylene copolymers
include ethylene/alpha-olefin copolymers and ethylene/unsaturated ester
copolymers. Ethylene/alpha-olefin copolymers generally include
copolymers of ethylene and one or more comonomers selected from C3 to
Cao alpha-olefins, such as 1-butene, 1-pentene, 1-hexene, 1-octene, 4-
methyl-1-pentene and'the like.
[0042] Ethylene/alpha-olefin copolymers generally have a density in the range
of
from about 0.86 to about 0.94 g/cm3. The term linear low density
polyethylene (LLDPE) is generally understood to include that group of
ethylene/alpha-olefin copolymers which fall into the density range of about
0.915 to about 0.94 g/cm3 and particularly about 0.915 to about 0.925
g/cm3. Sometimes linear polyethylene in the density range from about
0.926 to about 0.94 g/cm3 is referred to as linear medium density
polyethylene (LMDPE). Lower density ethylene/alpha-olefin copolymers
may be referred to as very low density polyethylene (VLDPE) and ultra-low
density polyethylene (ULDPE). Ethylene/alpha-olefin copolymers may be
obtained by either heterogeneous or homogeneous polymerization
processes.
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[0043] Another useful ethylene copolymer is ethylene/unsaturated ester
copolymer, which is the copolymer of ethylene and one or more
unsaturated ester monomers. Useful unsaturated esters include vinyl
esters of aliphatic carboxylic acids, where the esters have from 4 to 12
carbon atoms, such as vinyl acetate, and alkyl esters of acrylic or
methacrylic acid, where the esters have from 4 to 12 carbon atoms.
[0044] Useful propylene copolymers include propylene/ethylene copolymers
(EPC), which are copolymers of propylene and ethylene having a majority
weight percent content of propylene, and propylene/ethylene/butene
terpolymers (EPB), which are copolymers of propylene, ethylene and 1-
butene.
[0045] Preferred materials for the heat-sealable layer are LDPE,
ethylene/alpha-
olefin copolymers, ionomers, ethylene-vinyl acetate copolymers and
blends thereof.
[0046] The thickness of the heat-sealable surface layer is typically comprised
between 2 and 80 N m, more preferably from about 2 to about 50 N m.
[0047] The outer layer comprises materials chosen from the group of ethylene
homo-and co-polymers, propylene homo- and co-polymers, ionomers and
polyesters.
[0048] The thickness of the outer layer is typically comprised between 2 and
400
N m, more preferably from about 2 to about 50 N m.
[0049] Other layers can be present in both the support member and the skin-
forming film, such as tie or adhesive layers, abuse layers and the like. Said
additional layers should serve the purpose of providing the necessary
mechanical properties, such as modulus, puncture resistance, abuse
resistance, etc. or to improve the bond between the various layers.
[0050] A non-limiting example of a suitable multi-layer film for the support
member of the package of the present invention is for instance an eight-
layer material with an ionomer heat-sealable layer having the following
layer composition:
[0051 ] Support # 1:
[0052] to (2 N m) / EVA (9 N m) / Adh (28 N m) I LDPE (144 N m) I Adh (7 N m)
/LDPE (11 N m) / Adh (10 N m) / PP (370 N m).
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[0053] An alternative example can be a ten-layer material with an EVA heat-
sealable layer having the following layer composition:
[0054] Support # 2:
[0055] EVA (2 p m) / EVA (8 N m) / Adh (7N m) / PS (95 N m) / Adh (8 N m) / 50
wt.% PA6/12 + 50 wt.% EVOH (3 N m) / Adh (8 N m) / PS (98 N m) / Adh
(12 N m) / PETG (12 N m).
[0056] Support # 3:
(0057] Same layer sequence as Support # 2 with the following barrier layer
composition: 70 wt.% PA6/12 + 30 wt.% EVOH.
[0058] Still alternatively a ten-layer material with an EVA heat-sealable
layer
having the following layer composition:
[0059] Support # 4:
[0060] EVA (3 Ir m) / EVA (13 N m) / Adh (11 N m) I PS (140 N m) I Adh (12 N
m)
LDPE (12 a m) / Adh (14 N m) / PS (140 N m) / Adh (17 N m) / PETG (18
N m).
v (0061] Where: to is an ionomer; EVA is an ethylene-vinyl acetate copolymer;
Adh
is a tie resin, such as a malefic anhydride-grafted ethylene copolymer; PS
is a blend of polystyrene and styrene-butadiene-styrene block copolymer;
PP is a propylene homopolymer; PA 6/12 is a polyamide 6/12 and PETG
is a copolyester formed in the reaction befinreen terephthalic acid, ethylene
glycol and 1,4-cyclohexanedimethanol.
[0062] In order to provide the package of the invention with an easy-to-open
feature the EVA layer adjacent to the heat-sealable food-contact layer in
the materials described above might be replaced with a layer consisting of
a blend of resins having a low cohesive strength. Blends with low cohesive
strength that can be used are for instance those described in
W099/54398.
[0063] The multi-layer materials suitable for both the support member and the
skin-forming film are produced using common techniques known in the art
such as extrusion, co-extrusion or by heat- or glue-lamination, extrusion
coating and the like.
[0064] The materials, in particular the materials suitable for the skin-
forming film,
may be cross-linked. The preferred method of cross-linking is by electron-
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beam irradiation and is well known in the art. One skilled in the art can
readiliy determine the radiation exposure level suitable for a particular
application. Generally, however, radiation dosages of up to about 250 kGy,
typically between 90 and 220 kGy, with a preferred dosage of between
110 and 200 kGy.
[0065] A non-limiting example of a suitable mufti-layer film for the skin-
forming
film of the package of the present invention is for instance a nine-layer
material with a LDPE heat-sealable layer having the following layer
composition:
[0066] Skin-forming film # 1:
[0067] LDPE (5 N m) / LDPE (12 N m) / EVA (18 N m) I Adh (3 N m) / PA 6166 (6
a m) I Adh (4 N m) /EVA (12 a m) I LDPE (28 N m) / HDPE (10 N m).
[0068] Or alternatively:
(0069] Skin-forming film # 2:
[0070] LDPE (6 N m) / LDPE (14 N m) / EVA (19 N m) I Adh (3 N m) / PA 6166
(10 N m) I Adh (4 N m) /EVA (11 N m) I LDPE (26 N m) I HDPE (10 N m).
[0071] Alternatively an eight-layer material with a LLDPE heat-sealable layer
having the following layer composition:
[0072] Skin-forming film # 3:
[0073] LLDPE (13 N m) / EVA (28 N m) / Adh (5 N m) / PA 6/66 (10 N m) / Adh (5
N m) / EVA (28 N m) / Adh (6 N m) / PETG (5 N m).
[0074] Where PA6/66 is a polyamide 6/66.
[0075] Alternatively an eight-layer material with a LDPE heat-sealable layer
having the following layer composition:
[0076] Skin-forming film # 4:
[0077] LDPE (9 N m) / EVA (5 N m) / EVA (25 N m) / Adh (3 N m) / LDPE (7 N m)
Adh (3 N m) /EVA (36 N m) / HDPE (12 N m).
[0078] The oxygen transmission properties of the materials described above are
reported in Table 1.
[0079]
Table 1
Material OTR 23C and 096 OTR 23C and 10096
RH RH
(cm3/mz-day-bar) (cm3lm2-day-bar)
Support # 1 135 140
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Support # 2 83 200
Support # 3 200 170
Support # 4
220 220
Skin-forming film 182 650
# 1
Skin-forming film 106 456
# 2
Skin-forming film 97 303
# 3
Skin-forming film 970 -
# 4
[0080] Non-limiting examples of packages according to the present invention
are
for instance: Support #1 / Emmentaler cheese / Skin-forming film #3;
Support #1 / Asiago cheese / Skin-forming film #3; Support #1 / Roquefort
cheese / Skin-forming film #4; Support #2 / Leerdammer cheese / Skin-
forming film #1.
[0081] Packaging tests were performed to evaluate the shelf life of different
gassing cheeses with different support/skin-forming film combinations.
Chunks of approximately 200 g of the different cheeses were vacuum skin
packaged using different support/skin-forming film combinations and
stored at 6-7°C in daylight. Checks were performed 7 or 9 weeks after
packaging for gas formation (° ballooning" ), visible mould presence
inside the packs and odor and taste after unpacking. The results are
reported in Table 2.
(0082]
Table 2
Cheese SupportSkin- Weeks Moulds BalloningOdorITaste
# forming change
film
#
Asiago 1 3 7 No No Slight
Asiago 3 1 9 No No Slight
Asiago 1 Comp.* 7 No Yes Severe
Leerdammer2 1 9 No No None
Leerdammer3 1 ~ 9 ~ No I No TNon
(0083] * Comparative skin-forming film having an OTR value at 23°C and
0% RH
and 100% RH of 44 cm3/m2-day-bar and 90 cm3/m~-day-bar, respectively.
[0084] In its second aspect the present invention relates to a method of
making a
vacuum skin package for cheese, said method comprising the steps of:
- providing a support member;
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- loading a cheese product over the support member;
- draping a flexible film over the cheese product enclosing said cheese
product on the support member, characterized in that the support
member has an oxygen transmission rate (measured according to
ASTM D-3985) in the range of from 80 to 500 cm3 /m2-day-bar at
23°C
and 0% RH and the flexible film has an oxygen transmission rate
(measured according to ASTM D-3985) greater than 60 cm3 /m2-day-
bar at 23°C and 0% RH.
[0085] More in detail, the skin-forming film is fed to the upper section of a
heated
vacuum chamber comprising an upper and a lower section, and a vacuum
is applied thereto from the outside, thereby drawing the skin-forming film
into a concave form against the inwardly sloping walls of the upper section
of the chamber and against the ports contained in the horizontal wall
portion thereof (the top of the dome). Any conventional vacuum pump can
be used to apply the vacuum and preferably the skin-forming film is
suitably pre-heated prior to the foregoing operation to render it more
formable and thus better able to assume a concave shape in the upper
section of the vacuum chamber. The product to be packaged is positioned
on a support member, that can be flat or shaped, typically tray-shaped,
and placed on a platform that is carried in the vacuum chamber, in the
lower section thereof, just below the dome. The support member can be
shaped off-line or, alternatively, in-line at an initial station on the vacuum
packaging machine. Then the vacuum chamber is closed by moving the
upper section down onto the lower one and during this whole sequence of
operations vacuum is constantly applied to retain the concave shape of the
laminate. Once the vacuum chamber is closed, vacuum is applied also in
the lower section of the vacuum chamber in order to evacuate the space
between the support member and the top skin-forming film. Vacuum in the
upper section of the vacuum chamber continues to be applied to retain the
concave shape of the skin-forming film until the area between the support
and the skin-forming film is evacuated, then it is released and atmospheric
pressure is admitted. This will collapse the softened top skin-forming film
over the product and the support, as the atmosphere pushing the skin-
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forming film from the top and the vacuum pulling it from the bottom will
cooperatively work to have the skin-forming film substantially conform to
the shape of the product to be packaged on the support member. For
some types of cheeses, for instance the ones having a sponge-like
structure like Asiago, it might be necessary to control the speed of
evacuation of the chamber to prevent the collapse of the cheese structure.
Optionally, after the evacuation step has been completed, a suitably
selected purging gas or gas mixture could be flushed over the product to
generate a very low residual gas pressure into the package. In some
instances heat-sealing bars or other sealing means can be present in the
vacuum chamber to carry out a perimeter heat-seal of the skin-forming film
to the support member.
[0086] The packaging method of the invention could be performed on currently
available VSP machines, like the Multivac0 CD6000 or the Multivac4
8270.
