Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
MICROWAVE ST~AM-~Kh~UK COOKING 13 3 9 ~ 7 3
Field of Invention;
This invention relates generally to microwave
cGoking, and more particularly to subjecting foods stuffs
being cooked in a microwave oven to a vapour environment and
at a pressure greater than atmospheric pressure during
cooking. The invention is directed to both a method of
coGking and apparatus fGr use in cooking.
Back~round of Invention:
Domestic pressure food cookers are well known for
cooking with convection heating apparatuses but they are not
widely used. One drawback is that the pots for pressure
cooking are heavy, cumbersome utensils which are hard to
handle. Effectively, they are pressure vessels with a
removable cover having an over pressure release blow-out type
valve in the cover and a pressure control and release valve
removably mounted on the cover. The seals and~or Gver
pressure release valve require frequent replacement.
It is well known that foods cooked in a pressure
cooker are more wholesome, and pressure cooking substantially
reduces the cooking time. Pressure cooking, however, has not,
to applicant's knowledge, been used domestically when cooking
with microwave ovens, which, in recent years, have become very
popular. As a matter of fact, cooking instructions for
microwave users teach directly away from pressuri~ation by
directing them to ensure containers, plastic bags and other
1339273
- 2 -
cGoking vessels and containers be open. Microwave cooking is
extremely fast, and when the food stuff being cooked is
subjected to pressure greater than atmospheric pressure, it
may perhaps be even faster. This however is not applicant's
main concern because microwave cooking is of extremely short
duration, anyway. Cooking time in microwave cooking is quite
critical as a few seconds one way or the other can result in
undercook or overcooking. With the present invention, from
limited testing of the same it seems the cooking time is less
critical than it is with conventional microwave cooking
techniques.
Summary of Invention:
A principal object of the present invention is to
provide improvements in cooking foodstuffs in a microwave
oven.
A further principal object of the present invention
is to provide apparatus for use in improving cooking in a
microwave oven.
In keeping with the foregoing, there is provided in
accordance with one aspect of the present invention a steam-
pressure cooker for cooking foodstuffs in a microwave oven
comprising a bag of flexible elastically stretchable microwave
safe material and means for closing said bag.
In accordance with a further aspect of the present
invention there is provided a steam pressure fGod cooker
1339273
- 3 -
comprising a bag of flexible microwave safe material and a
closure for said bag including a pressure relief valve. The
valve and/or bag may be disposable or reusable and the bag
preferably is made of stretchable and particularly stretchable
elastic material.
In accordance with a further aspect of the present
invention there is provided a cooking utensil comprising a
flexible bag normally open at one end for receiving and
holding foodstuffs to be cooked and means permitting the
interior effective volume of the bag to increase and decrease
in volume in response to pressure changes therein.
In accordance with a further aspect of the present
invention there is provided a method of cooking comprising:
(a) providing a bag having an open end and made of
flexible material with at least a portion being of
predetermined elasticity;
(b) placing foodstuff to be cooked in said bag and
closing the otherwise normally open end of the bag,
and
(c) placing said bag with the foodstuff therein in a
microwave oven and su~jecting the same to microwave
energy of selected level for a selected period of
time.
A significant advantage of cooking under pressure in
a microwave oven is that the food value and flavour is
retained. The food is cooked effectively in a steam or vapour
1339273
- 4 -
environment (normally from the fGodstuffs own constituents)
and thus more wholesome. The foods so cooked are not dried
out and thus the present invention overcomes one of the most
common complaints of foods cooked in a microwave oven. It
seems from preliminary use and testing of the invention
the time of cooking is less critical when using the present
invention compared to conventional microwave cooking. ~erhaps
this is because the moisture is always present during cooking.
List of Drawinqs:
The invention is illustrated by way of example in the
accompanying drawings, wherein:
Figure 1 is a diagrammatic o~lique view of a
disposable plastic bag with foodstuff therein in a microwave
oven for cooking;
Figure 2 is a partial diagrammatic view of a plastic
bag cooker of Figure 1 incorporating a modification;
Figure 3 is a diagrammatic view of a still further
embodiment;
Figure 4 is a cross-sectional view of a pressure
release valve detachably mountable on a plastic bag for
relieving over pressure;
Figure 5 is a side elevational view of a modified
version of the valve of Figure 4;
Figure 6 is a cross-sectional view along line 6-6 of
Figure 5 illustrating a modification;
1339273
- 5 -
Figure 7 is a left hand end elevational view of
Figure 5;
Figure 8 is a cross-sectional view similar to Figure
4 but illustrating a still further modified valve arransement;
Figure 9 is a side elevational partial sectional view
of a further valve detachably mountable on a bag in accordance
with the present invention; and
Figure 10 is a sectional view taken alons line 10-10
of Figure 9.
Description of Preferred Embodiments:
Referring to the drawings, illustrated in Figure 1 is
a plastic disposable bag 10 having foodstuffs 11 therein and
located in a microwave oven 12 for cooking upon closing the
oven door, making the appropriate settings and actuating the
start cycle. The open end of the bag is closed using a tie or
slip-type noose 13 or alternatively closed by a sealing
machine or simply by tying a knot in the sleeve defining the
bag. The bag 10 and tie 13 are of a plastics material and
~0 thus may ke considered as being no different than a garbage
bag. Garbage bags are flexible wall containers but what the
present invention provides is a flexible wall pressure cooking
vessel. Cooking and garbage disposal are completely unrelated
arts (or at least so they should be).
- & - 1339273
In the preferred form of the invention at least a
portion of the bag wall is made of stretchable elastic
material of predetermined elasticity so that it will stretch
during cooking with the elasticity being such as to provide a
maximum cooking pressure. Also the elasticity may, for
example, be such that the maximum cooking pressure for one
type of bag is two pounds greater than atmospheric pressure
while that for another type of bag is three pounds, and
another four pounds, etc. greater than atmospheric pressure.
These actual pressures referred to are by way of example only
and have no bearing on actual cooking pressures.
Experimentation will be required to determine the most
effective cooking pressures. More important than the pressure
aspect is confining the cooking foodstuffs to a closed
environment so that they cook in a moist environment. If
desired the cooking pressure for the bag and its colour can be
co-related so that one knows that if they take a red bag for
example, the maximum cooking pressure will be so many pounds
and another colour will be of another maximum cooking
pressure. The pressure within the bag builds up during
cooking from vapors given off from the foodstuff being cooked
and thus the food is cooked in the presence of its own vapGur.
Figure 2 illustrates an alternative to the embodiment
of Figure 1 wherein an overpressure relief reed or flap valve
20 is incorporated in the wall of the bag and covering a hole
21 so that should there be any sudden increase in pressure
1339273
- 7 -
within the bag or should the pressure exceed that for which
the bag is designed it can be released through the valve and
thus prevent the bag wall from rupturing.
S In Figure 3 there is illustrated an embodiment where
the bas cGoking vessel lOA is made of relatively inelastic
material and communicates directly with a bag 10~ of
predetermined elasticity. The bags are connected, for
example, by way of a tubular coupling 14. If desired a
pressure release valve 15 can be incorporated in the coupling
14 so that two way communication from one bag to the other
takes place only after the pressure in bag lOA reaches a
predetermined level. ~ag 10~ is effectively a stretchable
balloon of predetermined strength so as to determine the
cooking pressure within bag lOA holding the food content being
cooked. Ideally the bag, like a balloon, requires
ccnsiderable pressure to initiate stretching of the side walls
but once stretched a selected amount there is little or no
increase in pressure but instead substantially only a change
in volume.
In the embodiments illustrated in Figures 4 to 10 a
separate pressure relief valve is provided and which fits
partially into the open end of the bag and the bag is clamped
on to the body of the valve. In one embodiment the valve is
of a simple nature intended for disposal and in other
embodiments the valve is a little more sophisticated and
intended for reuse. These embodiments do however have the
1339273
drawback of releasing some of the cooking vapors to atmosphere
the release of vapors being particularly so when using a non-
stretchable bag. It is thus preferred the release valves of
Figures 4 to 10 be used with bags of stretchable elastic
material and normally set to blow off or release just prior to
bag breakage.
Referring to Figure 4 there is illustrated a valve 30
having an outwardly flared open end 31 inserted into the open
end 32 of a bag 10. The bag is clamped onto the body of the
valve by an elastic 0-ring 34 or noose type plastic tie. The
valve has a cylindrical recess 35 in which there is
reciprocally mounted a piston 36 movable toward and away from
the recess closed end 37. The cylindrical wall of the valve
lS 30 has an aperture 38 which is covered and uncovered
respectively by movement of the piston 36. The chamber cavity
39, between the piston and closed end wall 37, serves as an
air cushion
against which the piston must act in order to release pressure
from the bag through valve body aperture 38. The size of the
cavity 39 and longitudinal movement of the piston in the
cavity can be predetermined (or a spring in such cavity can be
used) to relieve pressure from the bag 33 through aperture 38
upon reaching a predetermined pressure. A compression spring
such as shown in Figure 8 can be used in cavity 39 or a
tension spring such as spring 40 shown in Figures 5 and 6 can
be used to tether the piston.
' 1339273
The embodiment illustrated in Figures 5, 6 and 7 is
essentially the same as that illustrated in Figure 4 except
that the air cushion chamber 39 is disposed of and in place
thereof is an elastic member 40 used to tether the piston.
The elasticity of member 40 is chosen such as to allow piston
36 to move releasing pressure from within the container 33
through aperture 38 when the pressure in the cooking vessel
reaches a predetermined level. The elastic member 40 can be
fastened to the valve body and piston in any convenient
manner. In the embodiment illustrated in Figures & and 7, the
elastic member 40 is an endless elastic band looped around
tabs 51 and 52 provided by notches in the sidewall of the
valve casing. The endless band 40 passes under a lug 53
attached to the piston 36. In this embodiment elastic bands
of different strength can be provided for cooking at different
pressures such bands, if desired, being colour co-ordinated to
the different strength characteristics.
Another form of valve is shown in Figure 8 which is a
variant of the valve shown in Figures 5, 6 and 7. Referring
to Figure 3 there is illustrated a sleeve 60 flared outwardly
as indicated at 61 at one end and threaded as indicated at 62
at the other end. A cap 63 threads onto the stem and holds
captive therebetween a disc valve 64 and compression spring
means 65. The spring means 65 may be a piece of resiliently
compressible foamed plastics material. The disc 64, may be a
separate element or integral with the foamed plastic spring 65
1~39273
- 10 -
and bears against an annular ring 66 projecting from the stem.
The ring 66 can be a separate element or integral part of
member 60 and is of smaller outside diameter than the latter.
Such arrangement provides an air chamber 67 that opens to
atmosphere through one or more apertures 68 through the cap
wall. In this embodiment the valve release pressure can be
varied by turning the threaded cap 63 and thus changing the
force of spring 65 on the disc valve 64.
A further embodiment of a valve is illustrated in
Figures 9 and 10. Referring to these there is illustrated a
sleeve 70 having a piston 70A reciprocal therein and abutting
a spring means 71. Spring means 71 (a plastics material coil
spring or plug of foamed plastics material) bears against a
lug 72 projecting from a threaded cap 73 that screws on the
end of the sleeve.
The piston moves in response to changes in pressure
in the cooking bag 10 and at a predetermined pressure uncovers
one or more apertures 74 through the stem. When there is more
than one aperture they can, if desired, be offset from one
another along the a~is of the stem.
In the embodiment of Figures 9 and 10 the stem 70
tapers slightly inwardly as indicated at 75. This tapered end
projects into a hole 81 in a plate 80 and clamps therebetween
an end portion of the bag 10. This closes the open end of the
bag and places the end of piston 70A in communication with the
interior of the bag via central passage 76 in the sleeve.
1339273
- 11 -
In the foregoing embodiments the mcvable piston can
be provided with any convenient well known 3ealins means, for
example an O-ring, not shown, fitting partially into a groove
circumscribing the piston alternatively one or the other, or
both ends of the piston can be provided with a thin outwardly
flared rib i.e. ribs 36A and 36~ in Fisure 4.
As a final and extremely simple embodiment pressure
relief from the bag can, with reference to Fisure 4 take place
between the sleeve 30 and the wall of the bas throush the bag
end 32. In this case the strength of the elastic O-ring 34
can be such as to provide the desired release pressure. In
such embodiment it would be preferred to have no folds in the
wall of the bag where it engages the sleeve.
