Note: Descriptions are shown in the official language in which they were submitted.
'WO 98108750
CA 02444820 2003-10-20
The present invention relates to containers for food products and in
particular to a microwavable container and to a tray for the same.
Microwave ovens have become a principle forth of cooking food in a
rapid and effective manner and the number of food products available for
preparation in a microwave oven is constantly increasing. As the market for
microwavable food products has increased, so the sophistication required from
such
food products has also increased. There is, therefore, a continuing demand to
improve the quality of food prepared in a microwave oven and to ensure that
when
it is presented to the consumer, the food is attractive and meets the
standards
normally associated with such food.
Foods that are specially prepared for cooking within a microwave
oven are delivered to the consumer in containers that may be used directly
within
the microwave oven to facilitate preparation. These containers must therefore
not
only be capable of containing the food product during transport in an
effective
manner but must also be capable of contributing to the cooking of the food
within
the microwave oven and the subsequent presentation of the food.
As the demand for more sophisticated food products increases, so the
demand for effects, particularly appearance, normally associated with food
preparation also increases. For example, it is desirable for a food product
that
includes a pastry shell or lid to have a browned appearance, so that it
appears to
have been baked. While these effects can be produced in isolation, it becomes
more
difficult to produce such an effect in combination with a container that can
also
uniformly heat the food within a time that offers advantages over conventional
cooking techniques.
Typically, the areas in which browning or crisping are required are
those on the outer surfaces of the food product. Those areas typically receive
the
highest proportion of incident microwave radiation and therefore cook or heat
the
SUBST1'TUTE SHEET (RULE 26)
CA 02444820 2003-10-20
wo ssios~so pcr~cwm~oo6o0
_2.
quickest. On the other hand, there are areas of the food product that are
relatively
shielded from incident microwave radiation or which exist in a region of a
minimum RF field strength and which therefore require longer cooking periods.
If,
however, a longer cooking period is provided, the outer surfaces of the food
product tend to char and burn, leading to an unacceptable food product.
Various attempts have been made in the past to provide containers
that will produce effects normally associated with cooked foods. For example,
U.S. Patent No. 5,322,984 to Habeger, Jr. Et al. suggests a container having
heating devices on the bottom wall and possibly the top wall of the container.
The
heating devices are designed to provide a charring effect normally associated
with
barbecuing by directing energy normally not incident upon the food product
into
specific regions. This is purported to produce a localised charring of the
food
product. Overall, however, such containers have not been successful. The
charring
effect produced on the food product may be attributed to the high field
intensities
and associated induced currents that result from the concentration of energy
at
particular locations. In practice it is found that those induced currents may
also
cause charring and burning of the container itself.
1t has also been found that in order to produce the required results for
the preparation of the food product, the container must be capable of
controlling
distribution of energy about the food product, to utilize the energy in the
most
efficient manner, and at the same time ensure that the food product and the
container provide a pleasant and acceptable finished food product.
It is therefore an object of the present invention to provide a novel
microwavable container, a tray for a microwavable container and a microwave
energy heating insert.
According to one aspect of the present invention there is provided a
microwavable container comprising:
an outer sleeve;
an inner tray within said sleeve and having a bottom wall and at least
SUBSTITUTE SHEET (RULE 26)
CA 02444820 2003-10-20
WO 98!08750 PCT/CA97I00600
-3=
one upstanding side wall about the periphery of said bottom wall;
a first active microwave energy heating element within said sleeve
and disposed opposite said tray; and
a second active microwave energy heating element on said tray, said
second microwave energy heating element having patterns of microwave energy
interactive material on the bottom and side walls of said tray configured to
permit a
controlled degree of penetration of incident microwave energy through said
bottom
wall to channel microwave energy towards a central region of said tray and to
promote browning of a food product carried by said tray about the periphery
thereof.
In one embodiment, the microwave energy interactive material on the
side walls has a plurality of slots formed therein. The slots adjacent the
corners of
the tray are curved upwardly to enhance browning of the food product in the
corner
regions of the tray. Preferably, opposed ends of at least some of the slots
are
bulbous to further enhance the heating effect by evening out the field
strength along
the length of the slots. A susceptor may be used to overlie the microwave
energy
interactive material on the bottom and side walls.
In one embodiment, the pattern of microwave energy interactive
material on the bottom wall includes at least one and preferably a pair of
large
meandering loops. It is preferred that the length of the loops is
approximately equal
to an integer multiple of the effective wavelength of the incident microwave
energy.
It is also preferred that the pattern of microwave energy interactive material
on the
bottom wall further includes a ring about the peripheral edge of the bottom
wall and
wherein the meandering loops are open and are coupled to the ring by bridges.
Preferably, the first active microwave energy heating element
includes a pattern of microwave energy interactive material having a ring
about the
periphery of the microwave energy heating element and defining a centrally
located
aperture. In one embodiment, an array of microwave energy interactive elements
are located within the aperture. The microwave energy interactive elements can
be
in the form of circular or hexagonal islands. Alternatively, the microwave
energy
interactive elements can be in the form of loops with each of the loops
surrounding
SUBSTITUTE SHEET (RULE 26)
CA 02444820 2003-10-20
WO 98!08750 PCTlCA9'7100600
-4-
an island.
According to another aspect of the present invention there is provided
a tray for a microwavable container comprising:
a bottom wall;
at least one upstanding side wall about the periphery of said bottom
wall; and
an active microwave energy heating element within said tray, said
active microwave energy heating element having patterns of microwave energy
interactive material on the bottom and side walls of said tray configured to
permit a
controlled degree of penetration of incident microwave energy through said
bottom
wall to channel microwave energy towards a central region of said tray and to
promote browning of a food product carried by said tray about the periphery
thereof_
According to still yet another aspect of the present invention there is
provided an active microwave energy heating insert to be placed under a
microwavable container comprising:
a substrate: and
an active microwave energy heating element on said substrate, said
active microwave energy heating element including a pattern of microwave
energy
interactive material thereon configured to permit a controlled degree of
penetration
of incident microwave energy therethrough to channel microwave energy towards
a
central region of a microwavable container thereon.
The present invention provides advantages in that the microwavable
container design is such to heat generally uniformly a food product while
browning
and drying the outer periphery of the food product in one package. This design
is
particularly suited to cooking pies and other similar products having a crust.
Embodiments of the present invention will now be described more
fully with reference to the accompanying drawings in which:
Figure I is a side elevational view of a microwavable container in
SUBSTITUTE SHEET (RULE 26~
CA 02444820 2003-10-20
wo 9sros~so rc-r~c~~~oo600
_j_
accordance with the present invention;
Figure 2 is a plan view of an active microwave energy heating
element forming part of the microwavable container of Figure 1;
Figure 3 is a cross-sectional view of a portion of the microwavable
container of Figure 1;
Figure 4 is a perspective view of a tray forming part of the
microwavable container of Figure 1;
Figure 5 is a top plan view of a blank which can be constructed to
form the tray of Figure 4;
Figure 6 is a plan view of an alternative embodiment of an active
microwave energy heating element for the microwavable container of Figure 1;
Figure 7 is a plan view of yet another embodiment of an active
microwave energy heating element for the microwavable container of Figure 1;
Figure 8 is a plan view of still yet another embodiment of an active
microwave energy heating element for the microwavable container of Figure 1;
Figure 9 is a perspective view of another embodiment of a tray for
the microwavable container of Figure 1;
Figure l0 is a perspective view of yet another embodiment of a tray
for the microwavable container of Figure 1;
Figures l la to l lc are graphs showing three-dimensional surface
temperature profiles of food products cooked in a conventional oven and in a
microwave oven and supported by a number of microwavable containers including
the microwavable container of Figure I ; and
Figure 12 is a top plan view of an active microwave energy heating
insert in accordance with the present invention.
Referring now tO F:b~':~S 1 to 5, an er!~h~~~'iment of a microwavable
container is shown and is generally indicated to by reference numeral 10. The
container 10 includes a generally rectangular outer canon 12 and an inner tray
14
arranged to carry a food product preferably in the form of a pie having a
crust. The
SUBSTITUTE SHEET (RULE 26)
CA 02444820 2003-10-20
_6r
carton 12 is folded from a paperboard blank and has top and bottom major
panels
20, 22 interconnected by side panels 2d. Side flaps 26 extend about the edges
of
the major panels 20, 22 and abort the side panels 24. The side flaps 2b can be
folded w seal the canon 12. The exact details of the carton arid paperboard
blank
will vary according to the food product dimensions and characteristics of the
carton
and are provided for illustrative purposes only.
The top majot panel 20 of the canon 12 supports an active
microwave energy heating element 28 best seen in Figures 2 and 3_ The active
microwave energy heating element 28 is banded or adhered to the inwardly
directed
IO face of the top panel 20 so that the active microwave energy heating
element 28
overlies the inner tray 14 when the tray is inserted into the carton 12.
The octave microwave energy heating element 28 includes a substrate
30 formed of suitable material such as for example, polymeric film, paper or
paperboard. A pattern 32 of microwave energy interactive material is disposed
on
the substrate 30. The microwave energy interactive material may be
electroconductive or semiconductive material such as for example metal foil,
vacuum deposited metal or metallic inic. In the case of electroconduetive
material,
aluminum is preferred although other metals such as copper may be employed. In
addition, the electrocvnductive material maybe replaced with a suitable
electr~oconductive, semiconductive or non-conductive artificial dielectric ar
ferroelectric. Artificial dielectrics comprise conductive subdivided material
in a
polymeric or other suitable matrix or binder and may include flakes of
electroconductive metal such as aluminum. Alternatively, the microwave energy
interactive material may be in the farm of a patterned susceptor including one
or
more layers of suscepting material. In the present embodiment, the microwave
energy interactive material is in the form of metal fail.
As best illusuated in Figure Z, the pattern of microwave energy
interactive material includes an outer thick ring 34 defining a central
aperture 36.
Within the aperture 36 is an array 38 of islands 40, For the most part, the
islands
40 in the array 38 are generally hexagonal in shape although near the corners
and
slang the sides of the array, the islands 40 take different shapes.
Specifically, in
SUBSTrtUTE SHEET (RULE 26)
CA 02444820 2003-10-20
_ 7
the present example, at each corner of the array 38, is a group 42 of
hexagonal
rings 44 surrounding circular islands 46. The hexagonal rings 44 are arranged
in
two small rows and are surrounded along one side by smaller islands 47 shaped
to
fill in the spaces between the hexagonal rings 44 and the hexagonal islands
40.
Partial hexagonal islands 48 are positioned along the sides of the array where
there
is insufficient room for complete hexagonal islands.
A susceptor 50 including at least one layer of suscepting material
overlies the microwave energy interactive material and substrate 30. The
susceptor
50 produces a heating effect upon excitation by incident microwave energy as
is
well known. The susceptor may be in the form of a printed ink or alternatively
a
coating sputtered or evaporated over the substrate 30 and microwave energy
interactive material. Susceptor 50 may not be utilized or additional layers of
suscepting material may be provided depending upon the heating effect
required. If
the susceptor 50 is not used, a plain polymeric film will typically be used in
its
place.
As a principal form of control, the rings and islands are reactive with
the incident microwave energy so that their nature and the extent of their
coverage
of the top panel 20 of the canon 12 determines the amount and distribution of
energy transmitted to the upper surface of the food product carried by the
inner tray
14. The islands principally prevent transmission of microwave energy but they
also
provide a local excitation at their outer edges. Therefore, the islands
enhance the
excitation of the susceptor to increase its effect. The spacing between the
islands
and rings and their sizes are selected to control the transmission and
distribution of
energy to the food product to avoid charring of the food product while
ensuring the
upper surface of the food product is browned as desired.
Referring now to Figure 4, the inner tray 14 is better illustrated. As
can be seen, similar techniques to those used with respect to the active
microwave
energy heatine element 28 on the outer carton 12 are used on the inner tray.
Inner
tray 14 includes a bottom wall 60 and upstanding major and minor side walls 62
about the periphery of the bottom wall. The side walls 62 terminate in an
outwardly extending rim 64. Tabs 66 extend from the side walls 62 through
SU6STITUTE SHEET (RULE 26)
CA 02444820 2003-10-20
_ 8 .
apertures 68 in the rim 64 and are folded and bonded to the rim 64 to enhance
the
structural integrity of the inner tray 14. The inner tray 14 in this example
is
conswcted from a paperboard blank best seen in Figure 5 although it should be
realized that the tray may be press-formed.
An active microwave energy heating element 70 is bonded or adhered
to the interior surfaces of the bottom and side walls 60 and 62 respectively.
Similar
to the active microwave energy heating element 28, active microwave energy
heating element 70 is in the form of a laminate including a substrate on which
a
pattern of microwave energy interactive material is disposed. A susceptor
including
at least one layer of suscepting material overlies the pattern of microwave
energy
interactive material and the substrate so that the susceptor is positioned
between the
active microwave energy heating element 70 and a food product carried by the
inner
tray 14. The susceptor may not be utilized or additional layers of suscepting
material may be provided depending upon the heating effect required. If the
susceptor is not used, a plain polymeric film will typically be used in its
place.
In this particular example, the pattern of microwave energy
interactive material on the bottom wall includes a generally rectangular ring
72
about the peripheral margin of the bottom wall. Within the rectangular ring 72
are
two Large meandering open loops 74 which generally resemble maple leaves. The
meandering Loops 74 arc coupled to the rectangular ring 72 by a pair of
bridges 76.
The length of each meandering loop 74 is preferably close to an integer of the
wavelength of the incident microwave energy. 1n this specific example, each
meandering loop has a length which is equal to approximately 57: where ~l is
the
effective wavelength of the incident microwave energy projected unto the
surface of
the active microwave energy heating element 70. By using large multi-
wavelength
meandering loops and providing tight bends in the loops, which may be used to
increase Localized capacitance, better and more uniform heating of a central
region
of the food product is achieved.
Surrounding the meandering Loops 74 on both the inside and the
outside thereof are a plurality of loops 78 and islands 80. The loops 78 are
in the
form of annular rings surrounding smaller circular islands. The islands 80 are
SUBSTITUTE SHEET (RULE 26)
CA 02444820 2003-10-20
-9=
provided at various locations and are shaped to conform with surrounding
islands or
loops so that a generally even spacing between adjacent islands and loops
exists.
The sizes of the loops and islands are chosen to achieve the desired
cooking result. For example, the sizes of the loops and islands may be
selected to
be sufficiently small so that the loops 78 and islands 80 are decoupled from
the
large meandering loops 74 and therefore, contribute very little to the heating
effect
produced by the active microwave energy heating element 70. Alternatively, the
sizes of the loops and islands may be selected to be sufficiently large to
contribute
to the heating effect.
The inner surface of each side wall 62 is also coated with microwave
energy interactive material. A plurality of spaced elongate slots 82 aie
formed in
the microwave energy interactive material on each side wall. The elongate
slots are
sized and shaped to promote localized fields adjacent thereto and enhance
excitation
of the susceptor to promote browning of the food product held by the inner
tray
IS when exposed to incident microwave energy.
The arrangement of the slots 82 formed in the pattern of microwave
energy interactive material on each major side wall is the same. As can be
seen, at
the end of each major side wall 62 are two pair of laterally spaced curved
slots 84
arranged to form a generally U-shaped configuration. Between each U-shaped
configuration is a generally horizontal slot 86 having cambered major edges.
Centrally located on each major side wall is another configuration of slots.
This
configuration includes a stack of vertically spaced, generally U-shaped slots
88.
The bottom slot in the stack is inverted. On each side of the stack is a pair
of
laterally spaced, generally upright slots 90 and 92. Both slots have cambered
major
edges. The interior slots 92 have intutned ends. Each of the slots formed in
the
microwave interactive material has bulbous ends to even out the field strength
along
the lengths of the slots.
The arrangement of the slots 82 formed in the r.::cre~~ave energy
interactive material on each minor side wall 62 is the same but the patterns
are
different than those on the major side walls. At the end of each minor side
wall is a
pair of vertically spaced curved slots 94, each having bulbous ends. Above the
pair
SUBSTITUTE SHEET (RULE 26)
CA 02444820 2003-10-20
10-
is a generally horizontal slot 96 having one upright end and an opposite
gradually
curved end. Centrally located on each minor side wall is a stack of vertically
spaced, generally U-shaped slots 98. The bottom two slots in the stack are
shallow
and have bulbous ends. The stack of slots is positioned above a generally
horizontal
slot 100 having cambered major sides and bulbous ends. On each side of the
stack
is an angled slot 102 having downturned ends that are bulbous.
The slots formed in the microwave energy interactive material
adjacent the corners of the inner tray 14 curve upwardly to enhance browning
of the
food product adjacent the corner regions of the inner tray. The bulbous ends
of the
majority of the slots further assist in the heating effect. Although a
particular
arrangement of slots has been shown, those of skill in the art will appreciate
that
other various arrangements can be used depending on the heating effect
desired.
Referring now to Figure 5, the blank used to construct the inner tray
l4 is better illustrated. The blank includes a generally rectangular central
panel 103
constituting the bottom wall and four generally rectangular peripheral panels
104
joined to a respective edge of the central panel by score lines 105. The
peripheral
panels 104 constitute the side walls of the inner tray. Intermediate panels
105
bridge the peripheral panels at the corners of the blank and have bisecting
score
lines 107 thereon. A tab 66 is formed along the outer edge of each
intermediate
panel.
When the inner tray 14 is to be constructed from the blank, the
rectangular panels 104 are folded upwardly about the score lines 105. The
bisecting
score lines 107 and the intermediate panels 106 are folded in a direction away
from
the interior of the inner tray 14. The intermediate panels 105 are then folded
to
overlie a side wall so that the tabs 66 can pass through the apertures 68 in
the rim
64. The tabs are then be folded to overlie the rim.
Referring to Figure 6, another embodiment of an active
microwavable heating element to be suppo.~. ;ci ~n the inwardly dircc~.ed
surface of
the top major panel 20 of the inner carton 12 and to overlie the inner tray 14
is
shown. In this embodiment, like reference numerals will be used to indicate
like
components of the previous embodiment with a "100" added for clarity. Similar
to
SUBSTITUTE SHEET (RULE 26)
CA 02444820 2003-10-20
the active microwave energy heating element 28, active microwave energy
heating
element 128 includes a pattern of microwave energy interactive material 132
disposed on a substrate. A susceptor including at least one layer of
suscepting
material overlying the microwave energy interactive material and the substrate
may
be utilized. If the susceptor is not used, a plain polymeric film will
typically be
used in its place. The pattern of microwave energy interactive material
includes an
outer thick ring l34 defining a central aperture 136. Within the aperture 136
is an
array 138 of loops 144. Each loop 144 is in the form of a circular ring
surrounding
a circular island 146.
Referring now to Figure 7, yet another embodiment of an active
microwave heating element to be supported on the inwardly directed surface of
the
top major panel 20 of the inner carton 12 and to overlie the inner tray I4 is
shown.
In this embodiment, like reference numerals will be used to indicate like
components of the first embodiment with a "200" added for clarity. As can be
seen,
the pattern of microwave energy interactive material includes an outer thick
ring
234 defining a central aperture 236. Within the aperture 236 is an array 238
of
circular islands 240. A susceptor including at least one layer of suscepting
material
overlying the microwave energy interactive material and the substrate may be
utilized. If the susceptor is not used, a plain polymeric film will typically
be used
in its place.
Referring now to Figure 8, still yet another embodiment of an active
microwave energy heating element 328 to be supported on the inwardly directed
surface of the top major panel 20 of the inner carton 12 and to overlie the
inner tray
14 is shown. In this embodiment, like reference numerals will be used to
indicate
like components of the first embodiment with a "300" added for clarity. As can
be
seen, the pattern of microwave energy interactive material includes an outer
thick
rectangular ring 334 defining a central aperture 336. A susceptor including at
least
one layer of suscepting material overlying the microwave energy interactive
material
and the substrate may be utilized.
Referring now to Figure 9, another embodiment of an inner tray 414
very similar to that of the first embodiment is shown. In this embodiment,
like
SUBSTITUTE SHEET (RULE 26)
CA 02444820 2003-10-20
_ 12' _
reference numerals will be used to indicate like components of the first
embodiment
with a "400" addcd for clarity.
As can be seen, the active microwave energy heating element 470 is
very similar to that of the first embodiment. However, unlike the first
embodiment,
the pattern of microwave energy interactive material on the bottom wall 460
only
includes a rectangular ring 472 and two large meandering open loops 474
coupled to
the ring 472 by bridges 476. In this embodiment, the loops 78 and islands 80
are
removed from the substrate.
Referring now to Figure J0, still yet another embodiment of an inner
tray 514 is shown. Similar to the previous embodiments, an active microwave
energy heating element is bonded or adhered to the interior surfaces of the
bottom
and side walls 560 and 562 respectively. As can be seen, the pattern of
microwave
energy interactive material on the bottom wall 560 includes a rectangular ring
572
positioned about the peripheral margin of the bottom wall. Two concentric
octagonal rings 574 and 576 respectively are centrally positioned on the
bottom
wall. The outer octagonal ring 576 is joined to the rectangular ring 572 by a
pair of
bridges 578. The inner octagonal ring 574 is joined to the outer octagonal
ring 576
by two pair of diverging bridges 580.
Generally rectangular rings 582 are positioned adjacent opposed ends
of the bottom wall and are spaced slightly from the rectangular ring 572. Each
ring
582 has a major transverse leg 584 and a major generally concave leg 586. The
two
major legs are joined by a plurality of spaced bridges 5$8.
A plurality of spaced elongate slots 590 are formed in the microwave
energy interactive material on each side wall 562. The elongate slots are
arranged
in staggard rows with the slots in row nearest the bottom wall being more
elongate
than those in other rows. The elongate slots are sized to promote localized
fields to
enhance the susceptor and promote browning of the food product held by the
container when penetrated by microwave energy.
In the embodiments descriued above, the microwavable container is
described as having an active microwave energy heating element bonded or
adhered
to the outer container to overlie the tray. Those of skill in the art will
appreciate
SUBSTITUTE SHEET (RULE 26)
CA 02444820 2003-10-20
- I 3 ~-
that the active microwave energy heating on the top major panel may be free-
floating and inserted into the canon 12 and rest on the tray 14 above the food
product. It also should however be appreciated that the trays may be used
alone
with or without a lid. if a lid is to be included, the lid may also be in the
form of a
polymeric film, metal foil or a susceptor. It should also be appreciated that
although the described embodiments show the pattern of microwave energy
interactive material being covered with a susceptor, the susceptor is
optional.
Referring now to Figure 12, an active microwave energy heating
insert is shown and is generally indicated to by reference numeral 700. The
insert
700 includes a paperboard substrate 702 on which an active microwave energy
heating element is bonded or adhered. The active microwave energy heating
element includes a pattern of microwave energy interactive material which may
or
may not be covered with a susceptor. The pattern of microwave energy
interactive
material is similar to that on the bottom wall of the tray illustrated in
Figure 9.
Specifically, the pattern of microwave energy interactive material includes a
thick
generally rectangular ring 704 about the peripheral margin of the insert
defining a
central aperture 706. Within the aperture are two large meandering open loops
708.
The open loops 708 are coupled to the rectangular ring by bridges 710. The
insert
?00 is designed to be placed under a conventional microwavable container to
enhance the heating effect so that the food product in the conventional
microwavable container is more uniformly heated when cooked.
Although the embodiments of Figures 4, 9 and 12 show an active
microwave energy heating element including a pair of large meandering loops,
it
should be apparent to those of skill in the art that one large meandering loop
or
more than two meandering loops may be utili2e.d depending on the heating
effect
desired.
This Example illustrates the beneficial effect obtained using the
microwavable container IO of the present invention.
A 1 kg chicken pot pie was placed in a foil container (sample ~1), in
SUBSTITUTE SHEET (RULE 26)
CA 02444820 2003-10-20
-14-
a conventional microwavable container, i.e., a microwave transparent tray
(sample #2), and in a rnicrowavable container constructed in accordance with
the
present invention as shown in FIGS. 1 to 5 (sample #3). Sample #1 was cooked
in a conventional oven for 75 minutes. Samples #2 and #3 were exposed to
microwave energy for 20 minutes. The pie top, side walls and bottom of each
sample were evaluated. The temperature profiles of the cooked samples were
also
determined.
The results obtained are set forth in FIGS. 11 a to 11 c. In each of
FIGS. 1 la, l 1b, and l lc, several different subjective and objective
readings were
taken. First, the moisture loss of each sample pot pie was recorded a shown in
the
iop left tables of each figure. The "net wt" figure is the stated weight of
the pot
pie on the package. The "initial w" is the pre-cooked weight of the pot pie
and
particular cooking tray used in the sample and the "final wt" is the post-
cooking
weight of the pot pie and the cooking fray. The post-cooking weight is
subtracted
from the pre-cooked weight and the difference is divided by the "net wt" of
the
pot pie to provide a percentage weight lost figure. In this manner, the
moisture
loss of the different samples can be compared equally even though each of the
cooking trays used is a different weight. As noted, the moisture loss of the
pot pie
cooked in a tray of the present invention is significantly greater that the
moisture
loss of the pot pies cooked in the conventional oven or in a standard
transparent
tray in a microwave oven. This is reflected in the crisping and browning of
the
crust as next described.
The crisping and browning of the crust of the sample pot pies was
subjectively measured after cooking using the following rating scale noted in
FIGS. 11 a-11 c: 1 = Soggy/Mushy; 2 = Soft; 3 = Barely Dry; 4 = Dry; and 5 =
Dry/Flaky. Each portion of the crust, the top, the side walls, and the bottom,
were
rated on this scale. Further, each portion of the crust was further divided
into
three regions of generally equal area and each region of each portion of the
crust
was rated, respectively. As seen in the charts labeled "Top Crust Evaluation"
in
each of FIGS. 1 la-1 lc, the top crusts were divided into thirds from the edge
inward as noted ("Edge," "Middle," and "Central") and rated on the scale. The
CA 02444820 2003-10-20
-14A-
percent area of each region was multiplied by the rating to provide a weighted
rating corresponding to the particular region's contribution to the total
rating for
the portion. For example, for sample #1 the weighted rating for the edge
region
of the top crust was 1.65. The total rating ("Total AxR") for the top crust is
then
the sum of the weighted values for the regions.
Similarly, the side wall portions of the pot pie crusts were divided
into three generally equal regions ("Top," "Middle," and "Bottom") that were
then rated, weighted, and summed. Finally, the bottom crust portions were
divided into three generally equal regions ("Edge," "Middle," and "Central'
that
were then rated, weighted, and summed. Comparison of the subjective crust
ratings of sample #3 to sample #1 and sample #2 clearly shows that microwave
cooking of a pot pie in a tray according to the present invention more closely
approximates the crust result when a pot pie is baked in a conventional oven.
The
crust ratings for the top and side walls of sample #3 were both greater than 4
while the bottom crust of sample 3 was rated 3.66. This compares favorably to
sample #1, wherein each portion of the crust was rated above 4. In contrast,
the
crust of the pot pie of sample #2 rated in the range of 2 to almost 3 for each
portion. Comparison of the results of sample #3 to sample #2 show the benefit
of
using a tray of the present invention to regular microwave cooking.
The final measurement of the cooking results of the sample pot
pies recorded in FIGS. l la-I lc is the temperature profile for each pie at
the end
of the respective cooking cycle. The bottom right table (labeled "Temperature
Profile") in each of FIGS, l la-l lc provides a matrix of temperature readings
taken across each of the sample pot pies. Temperature readings were taken in
35
locations in each pot pie at the same depth-within a perimeter band, within a
middle band, and within a center area. The 20 temperatures recorded in the top
row, bottom row, and far left and far right columns in the "Temperature
Profile"
tables are the readings from the perimeter band. For example, in FIG. 11 a
these
readings clocf~~-ise from the top left are: 206°, 188°,
175°, 177°, 182°, 194°, 201°,
189°, 181°, 191°, 201°, 194°, 187°,
182°, 184°, 194°, 184°, 194°, 188°,
and 195°,
all in Fahrenheit. The 12 temperatures recorded in columns 2-6 of rows 2 and 4
CA 02444820 2003-10-20
-14B-
and columns 2 and 6 of row 3 are temperature readings from the middle band.
The temperatures recorded in columns 3-5 of row three in each table are
readings
from the center of the pot pie.
The bottom left tables on each of FIGS. 11 a-11 c depict the
maximum and minimum temperatures recorded in the temperature profile tables
for each of the periphery, the middle band, and the center of the pot pies.
For
example, for sample 1 in FIG. 11 a, the maximum and minimum temperatures
recorded in the middle band of the pot pie were 166° F and 147°
F, respectively,
which correspond to the readings in the "Temperature Profile" table of row 2,
column 6 and row 4, columns 3 or 4, respectively. This indicates a temperature
difference of 19° F between the hottest and coolest parts of the middle
band of the
pot pie of sample #1 as indicated in the column labeled "Range." The average
temperature of the temperatures recorded in the middle band of sample #1 was
153.5° F. The standard deviation of all the temperatures recorded in
the middle
band to the average temperature of the middle band of sample #1 was
6.4° F. In
addition to calculations for each of the peripheries, middles, and centers of
the pot
pies, the bottom left table also provides information on the maximum and
minimum temperatures of each pot pie overall, as well as the temperature
range,
the average temperature, and an overall standard deviation. A comparison of
the
results of sample #3 in FIG. l lc clearly shows the beneficial effects of
cooking in
a tray of the present invention. For example, the standard temperature
deviation
for sample #3 is only 3° F over the entire pot pie. This compares to
21° F for
conventional oven cooking and 43.5° for microwave cooking in a
transparent tray.
The temperature profile readings are graphically represented in the
three dimensional temperature profile in the bottom center of each of FIGS. 11
a-
l lc. The markings 1-7 on the x-axis correspond to the columns of the
"Temperature Profile" tables. The markings S1-SS on the y-axis correspond to
the rows of the "Temperature Profile" tables. The z-axis depicts the
temperature.
As shown in the graph of FIG. 11 a, the temperature of the sample #I pot pie
was; , ,
greater about the periphery than the center during conventional oven cooking.
A
similar profile with higher periphery temperatures was found for sample #2
CA 02444820 2003-10-20
-14C-
cooked in a microwave transparent tray in a microwave oven, however, the
average overall temperature of sample #2 was over 16 degrees lower than found
in sample #1. The graphical representation of sample #3 in FIG. l lcprovides a
strong contrast to sample #I and sample #2. The temperature profile is
essentially
flat throughout the pot pie indicating very even heating. Further, the actual
average temperature of the pot pie of sample #3 was 30° F higher than
the pot pie
of sample #I cooked in a conventional oven and 50° F higher than the
pot pie of
sample #2 cooked in a microwave oven in a microwave transparent tray.
It will be seen from these Figures that by employing the
microwavable container structure of the present invention and especially that
illustrated in FIGS. 1 to 5, the core temperature of the cooked sample is
significantly increased as compared to sample #2 cooked in a microwave oven
for
a similar duration. The pie crust was also dry and browned unlike sample #2.
The
only comparable sample was sample #1 but that sample required a total
1 S preparation time of 90 minutes, 15 minutes to prewarm the oven and 75
minutes
to cook the sample, a significantly longer duration.
Summary
As those of skill in the art will appreciate, the present invention
provides for a novel microwavable container for food products and specifically
pies which generally uniformly heats the pie while browning and drying the pie
crust. Those will also appreciate that variations and modifications may be
made to
the present invention without departing from the scope thereof as defined by
the
appended claims.
