Microwave oven preparation of waffle

A package for cooking a waffle in a microwave oven is provided, comprising a microwave transparent tray about 28 to 38 mm deep, a lossy susceptor film lid having defined reflectance and absorbance, placed about 3 to about 10 mm over the waffle, providing means for moisture to escape. The waffle is coated with an edible food conditioner, to provide improved microwave susceptibility to the surfaces of the waffle. The waffle may be cooked alone or in the presence of a sausage side dish.

FIELD OF THE INVENTION 
This invention relates to the field of microwave cooking and particularly 
to the field of partially cooked, frozen foodstuffs such as waffles and to 
materials and packages useful in that field. 
Microwave ovens have experienced an enormous growth of acceptance among the 
public because of their speed, convenience, and energy efficiency. This 
has created a parallel interest among convenience food packagers to extend 
the number of products which may be successfully prepared in such ovens. 
To accomplish this goal, packagers must find ways to overcome the 
deficiencies characteristic of propagating and nonpropagating microwave 
energy modes which can produce adverse effects with some foodstuffs. One 
group of problems arises from standing waves set up by complete 
reflections from the oven walls, the packaging, and the foodstuff itself. 
Another group of problems results from the large differences in the 
microwave heating susceptibility among various foodstuffs. 
In applications involving the cooking or reheating of dense, wet, or liquid 
foods, these differences are not too troublesome. Serious problems are 
encountered, however, in achieving acceptable results on foods that 
require surface browning and crisping. Foodstuffs such as waffles which 
are packaged frozen and only partially cooked are particularly difficult 
to prepare in a microwave oven because of their low density and high 
transmissivity of the microwave energy. When the waffle is exposed to 
sufficient microwave energy to brown the surface, the depth of the crust 
is typically too thick for an esthetically pleasing texture and the 
interior is overly dried and toughened. The problem is compounded when the 
waffle is accompanied by a side dish such as a meat product typically 
requiring a different heating schedule with a greater energy demand. 
Much effort has gone into overcoming problems created by the special 
characteristics of common microwave ovens. One approach is found in U.S. 
Pat. No. 4,656,325, to Keefer. This patent discloses a package containing 
an article of foodstuff capable of being heated in a microwave oven, 
comprising a foodstuff holding pan and a nonreflecting energy cover having 
a dielectric constant greater than 10 and spaced from the top surface of 
the foodstuff about 0.8 to 2 cm. The dielectric constant and the spacing 
of the cover permit the passage of microwave energy through the cover into 
the package, while interfering with reflected microwave energy within the 
package. Thus the microwave energy is retained and concentrated within the 
package. Surface browning of the food occurs by field intensification at 
the food surface. 
U.S. Pat. No. 4,190,757, to Turpin et al., discloses a food heating package 
formed from a microwave transparent nonlossy dielectric material and a 
lossy microwave absorptive sheet connected to the package and associated 
in heat conductive relationship with the food. The sheet thickness and the 
temperature response during microwave heating are positively correlated, 
and the sheet is of the minimum thickness that will reach but not exceed a 
preselected equilibrium operating temperature. The sheet is usually bonded 
to a structural supporting sheet, such as aluminum foil. The package also 
has a shield, which may have holes, in order to provide a predetermined 
controlled amount of direct microwave energy to the food. The absorber 
heats the food to a sufficiently high temperature to provide searing or 
browning. 
U.S. Pat. No. 4,230,924, to Brastad, discloses a package containing an 
article of food to be heated in a microwave oven. The package comprises a 
flexible dielectric material conforming generally to the shape of the 
food, and individual electrically resistive islands, or pads, separated by 
crisscrossing nonmetallic gaps, carried by said dielectric material The 
islands convert some of the microwave oven energy to heat, modifying the 
color or crispness of the food adjacent thereto. 
U.S. Pat. No. 4,676,857, to Scharr, discloses a microwave heating material 
and method for its preparation. A preselected metallized pattern, such as 
dots, spirals, or circles, is disposed on at least a portion of a 
dielectric material using a transfer process, in any variety of patterns. 
Patterned cooking could be provided by the use of trays having metallized 
patterns which would heat and brown slower cooking foods at the same rate 
of speed as other faster cooking foods. 
U.S. Pat. No. 4,626,641, to Brown, discloses a carton for protection of a 
food product during shipment and for use in heating, crisping and browning 
the food. The carton includes a top panel having crisping means separated 
by a vertical distance of less than 2.7 cm from the top surface of the 
food product. The crisping means may be a metallized polyester, laminated 
onto the top panel. The food particularly disclosed is a pot pie. 
U.S. Pat. No. 3,983,256, to Norris et al., discloses that pancakes or other 
farinaceous griddle foods coated with sugar syrup containing an edible 
emulsified fat heat more readily and evenly in a microwave oven than do 
uncoated farinaceous griddle foods. 
SUMMARY OF THE INVENTION 
This invention provides a package for cooking a waffle in a microwave oven 
comprising: 
(a) a chamber in which the waffle lies, said chamber having sides and a 
bottom formed from a rigid or semirigid microwave transparent material, 
said chamber having a depth of from about 28 mm to about 38 mm; 
(b) a susceptor film lid having a microwave reflectance of from about 0.4 
to about 2.2% and a microwave absorbance sufficient to raise the 
temperature of the lid to about 100.degree. C. in about 20 seconds and to 
from about 160.degree. C.-200.degree. C. in about 120 seconds when the 
oven is operating, said lid being positioned as the top of at least the 
portion of the chamber where the waffle lies and placed from about 3 mm to 
about 10 mm above the top surface of said waffle; and 
(c) a waffle having its top and bottom surfaces coated with an edible food 
conditioner to provide microwave susceptibility, said waffle having a 
thickness of from about 20.6 mm to about 36.6 mm.

DETAILED DESCRIPTION OF THE INVENTION 
The invention comprises a disposable package and method for cooking in a 
microwave oven a frozen or unfrozen waffle, optionally along with a side 
dish, so that both are suitably cooked, browned, and crisped over the same 
time period. 
A waffle, which is approximately 100 mm square by 25 mm thick 
(4.times.4.times.1 inches) and has been partially cooked prior to 
packaging, sufficiently to establish its shape and interior texture, is 
placed within the package. Both the top and bottom surfaces of the waffle 
are coated with an edible conditioner to enhance its appearance, flavor, 
and crisping, or become coated during the process of microwave cooking. 
This conditioner typically contains sweet syrups such as corn syrup or 
equivalent materials known to the trade. It usually comprises a flavor 
enhancing oil in the form of salted butter or one of its substitutes. 
Lastly, the conditioner may contain other color or flavor enhancing 
materials such as caramel and spices. The exact consistency is primarily 
dependent upon taste. However, to obtain enhanced browning and crisping, 
it is important that the conditioner contain materials, preferably salted 
butter, with some susceptibility to microwave energy, and particularly to 
the magnetic component of the microwave energy. It has been found that a 
generous amount of butter spread over both sides of the 100 mm square 
waffle is adequate for this purpose. However, it is preferred to 
incorporate the edible, microwave susceptible food conditioner into the 
batter and hence into the waffle. The conditioner migrates to the surface 
of the waffle, both during precooking of the waffle in the waffle iron and 
during cooking in the microwave oven. About 10% by weight of salted butter 
may be incorporated in the batter. In addition, about 8% sugar, and a 
modest amount of salt may be used. The surfaces of the waffle iron used 
for precooking of the waffle may be conditioned with a spray of partially 
hydrogenated vegetable oil, such as "PAM".TM., available from Boyle Midway 
Inc., New York, N.Y. 10017. Some modest amounts of this oil may also 
transfer to the waffle surfaces. 
The food item or items to be cooked are contained in a microwave 
transparent tray, or chamber. The tray may be prepared from any convenient 
material, such as paperboard stock coated with a copolyester layer. The 
material should preferably be thin and lightweight, yet should have 
sufficient rigidity to maintain its shape. 
The tray and food items are covered with a film lid, located above the 
waffle and across the top of the tray or chamber, at a spacing which will 
be described below. The film lid has two major requirements. First, it 
must be a lossy material, and reach a temperature of about 100.degree. C. 
within 20 seconds and from about 160.degree. C. to about 200.degree. C. 
within two minutes when subjected to microwave energy having an electric 
field intensity of 242 V/cm rms, which is a typical field strength 
encountered in an oven cavity operated at full power (700 watts). A 
procedure for determining such heating properties is disclosed in U.S. 
patent application Ser. No. 002,980, filed on Jan. 23, 1987, the 
disclosure of which is incorporated herein by reference. Suitable films 
may reach 150.degree. C. in as little as 30 seconds, but should reach 
150.degree. C. within about a minute if they are to perform properly. This 
degree of heating is generally achieved by providing a microwave 
absorptivity of the lid at 2450 MHz in the range of 0.5 to 10, and 
preferably in the range of 0.5 to 6%, as measured in a coaxial transverse 
electromagnetic (TEM) test cell which emulates free space conditions. The 
above described temperature rise aids in browning and crisping the top 
surface of the waffle. The hot film lid also helps prevent condensation of 
moisture which evolves from the food during heating. Such moisture would 
otherwise result in a soggy or unappealing surface on the waffle. 
Secondly, the lid must further attenuate the incident microwave energy by 
reflection, in order to moderate interior cooking as the top and bottom 
waffle surfaces are being crispened. We have found that for the desired 
cooking action, the reflectance of the film as measured in a coaxial TEM 
cell approximating free space conditions should be in the range of 
0.4-2.2%. The specific amount of reflected energy will be related to the 
specific cooking conditions--for films with higher reflectance, longer 
cooking times will generally be required, and vice versa. 
The free space reflectivity of the lossy film, measured as described above, 
is, of course, only one factor in the total reflectance of the actual 
package of tray, foodstuffs, and lid. In the real instance, each interface 
provides a reflection, and, additionally, there are complex reflections 
from the oven sides, bottom, etc. 
The lid thus provides a controlled balance between the amount of the 
impinging microwave energy which is reflected back from the surface of the 
sheet, the amount absorbed by the lid, and the amount which is transmitted 
into the foodstuff. 
Suitable materials for use in constructing the film lid include those 
described in commonly assigned, copending U.S patent application Ser. No. 
002,980, discussed above. That application discloses a composite material 
for controlled generation of heat by absorption of microwave energy, 
comprising (a) a dielectric substrate substantially transparent to 
microwave radiation, and (b) a coating on at least one surface of the 
substrate, comprising (i) about 5 to 80% by weight of metal or metal alloy 
susceptor in flake form, and (ii) about 95 to 20% by weight of a 
thermoplastic dielectric matrix, wherein the surface weight of the coating 
on the substrate is from about 2.5 to 100 g/m.sup.2. Preferably the 
thermoplastic dielectric matrix comprises a polyester copolymer selected 
from the group consisting of copolymers of ethylene glycol, terephthalic 
acid and azelaic acid; copolymers of ethylene glycol, terephthalic acid, 
and isophthalic acid; or mixtures of said copolymers. Suitable susceptor 
flake materials include aluminum, nickel, antimony, copper, molybdenum, 
iron, chromium, tin, zinc, silver, gold, and various alloys of these 
metals. Preferably the susceptor flake material is aluminum. The flakes of 
the susceptor should have an aspect ratio of at least about 10, and will 
preferably have a diameter of about 1 to about 48 micrometers, and a 
thickness of about 0.1 to about 0.5 micrometers. In order to obtain 
uniformity in heating, it is preferred that the flakes be approximately 
circular, having an elipticity in the range of about 1:1 to 1:2. 
Alternatively, the flakes, if not circular, can be applied to the film in 
two or more separate passes, which also provides an improvement in the 
degree of uniformity in heating. Films prepared from such material will 
typically have a surface resistance of at least 1.times.10.sup.6 ohms per 
square. 
The geometrical spacing of the lid over the waffle is important. In the 
package of the instant invention, the lid is spaced about 1/4 free space 
wavelength (30.5 mm at 2450 MHz) above the bottom of the tray and, 
secondly, from about 3 to about 10 mm above the top of the waffle 
component. The lid must be close enough to the upper waffle surface so 
that the heat generated within the lid material as a result of its 
microwave absorption can be readily transferred by radiation or convection 
to the upper surface of the waffle. At the same time, the lid should not 
touch the waffle surface and should provide sufficient clearance so that 
moisture evolved from the waffle during cooking can escape and not be 
trapped, causing sogginess. The waffle thickness and the tray depth should 
be arranged to maintain this spacing in the range of about 3 to 10 mm, 
preferably about 3 to 9 mm, and most preferably about 6 mm. In order to 
facilitate the escape of the moisture evolved from the waffle, the package 
should contain vents. These vents may be in the form of open lid ends, 
holes, or cutout portions in the covering film, or holes or notches in the 
tray portion of the package, or equivalent means. 
Needless to say, there is a great deal of variability in the composition of 
waffles, and a corresponding variability in their susceptibility to 
microwave cooking and browning. Individual waffles of nominally identical 
composition, for example, may vary by as much as plus or minus 7% in their 
moisture content. Such variation makes fine tuning of the characteristics 
of the lid and the package geometry important for optimum cooking of a 
waffle of a particular composition. Such adjustments are well within the 
abilities of the person skilled in the art. 
The package of this invention can prepare a waffle with or without the 
inclusion of a side dish such as a sausage. In the package of the 
invention, the lid is positioned over at least the portion of the 
container where the waffle is placed. If the only food in the container is 
the waffle, the lid can extend over the entire top of the container, with 
proper venting. If the container also contains a sausage, the lid covers 
the waffle only. Some small corrections to exposure time may be required 
for heating a waffle in the presence of a side dish, compared with heating 
the waffle alone, as a result of the change in total loading. However, it 
is well within the capabilities of one skilled in the art to make such 
changes. 
Referring now to FIG. 1, one embodiment of the present invention consists 
of a tray 101 with floor 103, and sides 105, which are pressed from a low 
cost, microwave transparent dielectric material. In this tray are placed a 
waffle 107 and a sausage 109. A lid 111, formed from a susceptor film, is 
placed over the top of the tray and its contents. The lid 111 is equipped 
with a removable window 113 in the area above the sausage, to provide 
transparency above the sausage and venting for the entire package. Vents 
115 may be provided in order to permit water vapor to escape from the 
package during cooking. Such vents are desirable if there is no other 
means for the water vapor to escape from the package. 
FIG. 2 shows a detailed sectional view taken along line 2--2, through the 
waffle 107. In this figure the edible conditioner 117 is shown as applied 
to the upper and lower surfaces of the waffle. The package can rest 
directly on a metallic bottom 119 of the oven cavity, or on a glass tray 
121, which is common in many microwave ovens. Alternatively, it can be 
placed on a metallic or partly metallic carousel or other metallic surface 
(not shown). An optional cover 123 can be used for shipping and sealing 
purposes. Cover 123 is removable by the user before microwaving, and 
typically will be a peelable plastic or paper sheet imprinted with 
advertising or microwaving instructions. 
FIG. 3 shows another embodiment of a package of this invention. In this 
view, a strip of film 125 containing the susceptor material is positioned 
only over the waffle, and the sausage is uncovered. Water vapor can thus 
escape through the uncovered area over the sausage. 
The importance of spacing the lid about 1/4 freespace wavelength above the 
bottom of the tray is not clearly understood, due to the various numerous 
and complex interactions among the microwave energy modes, the package and 
the foodstuffs. Although the invention is not bound by any particular 
theory of operation, it is believed that several factors are important to 
obtain the benefits of the invention. 
The small amount of microwave energy reflected from the susceptor material 
of the lid combines constructively with reflections from the vicinity of 
the package bottom, thus increasing the impedance mismatch between the 
oven cavity and the interior of the package. Although the spacing between 
the cover and the tray bottom is about one quarter wavelength of the 
microwaves travelling in free space, the actual electrical path length is 
longer because of the dielectric properties of the waffle or other 
foodstuff. The result is that less power is transmitted into the waffle 
than would occur without the susceptor lid in place. The foregoing 
interaction slows the rate of cooking of the interior of the waffle, 
effectively providing a moist and soft waffle interior while the top and 
bottom surfaces of the waffle are being crispened, and while the side 
dish, if present, is being cooked. This effect has been partially 
confirmed by measurements of the reflected energy from the package. The 
packages which gave successful cooking of the waffle showed a higher 
amount of reflected energy than in cases where the lid was omitted. 
Positioning the lid at 1/2 free space wavelength above the bottom of the 
oven can also give good results, provided that the distance between the 
lid and the top of the waffle is kept within the above specified distance, 
and a ground plane is established at the bottom of the package. If the 
susceptor lid alone is placed at the 1/2 wavelength position and the 
remainder of the package remains at the ground plane, a relatively good 
waffle may be prepared, with somewhat less top browning than desired 
because of the extended gap. However, the 1/4 wavelength spacing is more 
convenient, providing a more compact and effective package. 
The invention also provides a process for cooking a waffle, optionally with 
a side dish, in a microwave oven, using the package described above The 
package is placed in the oven and the oven is operated for a sufficient 
time to heat the interior of the waffle to the desired consistency, while 
browning and crisping the upper and lower surfaces of the waffle. 
The invention also provides a process for preparing a waffle contained in a 
disposable microwave cooking package having a microwave transparent tray 
and an electrically lossy film susceptor lid. The process includes 
preparing a precooked waffle with an edible food conditioner applied to 
its top and bottom surfaces, in order to provide microwave susceptibility 
to the magnetic field component of microwave radiation, said waffle having 
a thickness of about 20.6 to about 36.6 mm. The waffle is placed in the 
tray, a lid, as described above, is placed on the tray at a distance of 
about 3 to about 10 mm above the surface of the waffle, and the waffle is 
frozen in the tray. 
The invention is further illustrated by the following examples, in which 
temperatures are in degrees Celsius, and percentages are by weight unless 
otherwise indicated. 
EXAMPLES 
Example 1 
The lid material was a laminate including a layer of 30# bleached kraft 
paper stock and a layer of 0.023 mm (92 gauge) Mylar.RTM. polyester film 
obtainable from E. I. du Pont de Nemours and Company, Inc., Wilmington, 
Del., 19898. 
The lid material further included a resinous coating layer containing 
dispersed susceptor material. The coating matrix was prepared by combining 
15.8 parts by weight of the copolymer condensation product of 1.0 moles 
ethylene glycol with 0.53 moles terephthalic acid and 0.47 moles azelaic 
acid, with 0.5 parts by weight of erucamide and 58 parts by weight of 
tetrahydrofuran. This mixture was placed in a heated glass reactor vessel 
equipped with a paddle stirrer. After dissolving the solids at 55.degree., 
0.5 parts by weight of magnesium silicate and 25 parts by weight of 
toluene were blended in. Three thousand grams of this solution were mixed 
with 640 g of aluminum paste (70% aluminum solids in mineral spirits), 
commercially available as "Sparkel Silver.TM.," type 3641, from Silberline 
Manufacturing Company. 
The coating solution was dispersed, using two passes, on a 280 mm wide 
doctor roll coater to obtain, after drying, a coating thickness of 
approximately 0.03 mm (1 mil). The total dry coating weight was 
approximately 30 g/m.sup.2. Due to losses and retained mineral spirits, 
the final concentration of aluminum on the film was 11 g/m.sup.2. 
A sample of the lid material was measured in a coaxial TEM cell, model 
SET-19, from ELGAL Industries, Ltd., Israel, which was excited by 2.4 to 
2.5 GHz signals from a Hewlett Packard HP8620C Sweep Oscillator. A Hewlett 
Packard HP8755C scalar network analyzer was used to obtain the scattering 
matrix parameters of the sample under test. This cell provides a 
transverse electromagnetic wave closely simulating free space microwave 
propagation conditions. These conditions are referred to as "SET," meaning 
"simulated electromagnetic test." Under the SET conditions, the sheet 
exhibited a microwave transmission at 2450 MHz of 95.2%, absorption of 
4.3%, and reflection of 0.5%. 
A sample of the lid material was also exposed to microwave power in a 
laboratory waveguide field measurement with an electric field intensity of 
242 V/cm rms, which is a typical field strength encountered in an oven 
cavity operated at full power (700 watts). Under these conditions, the 
film reached an average temperature of 150.degree. within one minute. A 
detailed description of this test is disclosed in U.S. patent application 
Ser. No. 002,980, discussed earlier herein. 
A paper based tray was used as the container with dimensions 15.5 by 11.4 
cm (not including a lip extending out on all sides by a distance of 8 mm) 
at the top; 12.4 by 8.9 cm with radiused corners at the bottom; and 3.5 cm 
deep. The tray wall and bottom thicknesses were about 0.5 mm, with the 
tray bottom convoluted to raise the waffle about 1 mm above the tray's 
resting surface. 
A Belgian waffle measuring about 100 mm square by 25 mm thick was lightly 
precooked from batter sufficient to fully form its shape and internal 
structure. The batter contained flour, milk, egg, vanilla, starch, baking 
soda, and salt, with in excess of 7% by weight of sugar and in excess of 
10% by weight of salted butter. This batter had a moisture content of 
about 36% by weight. After precooking, the waffle was frozen. A single 
link of precooked and prebrowned sausage approximately 20 mm diameter by 
90 mm long was obtained frozen from a local food store. The waffle was 
placed in the tray near one end, and the sausage link was placed at the 
other end, to form a composite breakfast platter as might be commercially 
distributed for the microwave convenience food market. 
A 100 mm wide strip of the lidding material was placed across the top of 
the tray containing the waffle and sausage. It was positioned so the lid 
material was directly over the waffle while the remainder of the tray 
cavity was left open. The tray was then placed on the floor of a 600W 
Amana oven and exposed to microwave energy. The cooking was done for a 2.0 
minute period using a "high" (full power) setting. After completion of the 
cycle the foodstuffs were examined and tasted. The sausages were 
adequately heated and tasty. The surfaces of the waffle, both top and 
bottom, were well browned and crisp, and not soggy. It was observed that 
the interior of the waffle was warm, tender, nontoughened, and exhibited a 
good, slightly chewy texture. 
Comparative Example 1 
The experiment of example 1 was repeated with the lidding material left 
off. Under these circumstances, waffle preparation was not satisfactory. 
At a 2.5 minute exposure, the top surface was still not browned and 
crisped. When the exposure was increased to that sufficient to achieve 
browning, the interior of the waffle was hard and tough and the sausage 
was overcooked. 
Comparative Example 2 
The experiment of example 1 was repeated except that the entire package was 
raised above the floor of the oven by the thickness of one package (i.e., 
about 1/4 wavelength), where a magnetic null for the predominant mode 
would be expected. The waffle cooked poorly and was soggy. 
Example 2 
A package similar to that of Comparative Example 2 was heated in an oven, 
in the same location as in Comparative Example 2, except that an aluminum 
sheet was inserted immediately beneath the package, providing a ground 
plane. The desirable cooking results of Example 1 were reestablished. 
Examples 3-9 and Comparative Example 3 
Table I shows the results when different lid materials were used in cooking 
a waffle similar to that described in Example 1. A sausage was also 
present in the packages of these examples. Cooking was done in a 700 watt 
Sharp Carousel II.TM. microwave oven at full power for two minutes. It can 
be seen that cookability is a function of both temperature of the film 
lid, and cooking time. Examples 3, 4, and 5 illustrate that the cooking 
time must be correctly selected in order to achieve best results, even 
when the film properties are optimum. 
Compositions and heating properties of the lid materials used in these 
examples are described in Table II. The abbreviations used in Table II are 
defined as follows: 
adhes: adhesive, "Adcote 333," from Morton Chemical Div. of Morton Thiokol, 
Inc., Chicago, Ill. 
copoly: copolymer condensation product described in Example 1, coated on a 
film of polyethylene terephthalate. 
flake1: coating, prepared as in example 1, containing aluminum flake from 
Reynolds (L5B-548), 
flake2: coating, prepared as in Example 1, containing the same aluminum 
flake as in Example 1. 
paper1: 30# bleached kraft paper. 
paper2: 48# bleached kraft paper. 
polyest: polyethylene terephthalate film ("Mylar.TM."). 
It is apparent by comparing the result from Table I with the film heating 
properties of Table II, that when a film is used which reaches a higher 
temperature, a shorter cooking time is appropriate, and vice versa. 
Examples 10-24 
Table III shows the results of experiments in which the geometry of the 
lid, tray, and waffle were varied, using in each case a flake susceptor 
film lid, tray system, and contents as in Example 1, except as noted. The 
cooking conditions were the same as for examples 3-9, except as noted. For 
certain of the packages described in the examples of Table III, 
independent measurements were made of the total reflectance, R.sup.2, form 
the total package, including the tray, film, and waffle (without sausage). 
(For examples 21 and 23-25, reflectance measurements were made, but 
waffles were not actually cooked in the corresponding configurations.) To 
approximate conditions in a real microwave oven for this measurement, an 
open topped aluminum box was constructed, the size and shape of a typical 
microwave oven, with 0.6 mm thick walls and dimensions of 305 mm.times.305 
mm.times.298 mm. A tray containing waffle and sausage with susceptor lid 
was placed into the box, and the assembly irradiated with 2450 MHz 
microwave energy of 5 to 30 milliwatts introduced at the top of the box 
via an omnidirectional conical antenna (Singer Company, Los Angeles, 
Calif., part no. 90794-2). The cone antenna was centered in the aluminum 
box with the elevation between the bottom of the cone antenna and the 
inner bottom surface of the box being 191 mm. The top of the box was 
sealed with aluminum duct tape to avoid perturbation of the measurement by 
external factors. Instrumentation to measure reflectance, both in 
amplitude and phase, was provided by an HP8510 network analyzer from 
Hewlett Packard. 
It can be seen that quality of cooking is a complex function of film, 
waffle size, and tray geometry, showing evidence of periodicity as the lid 
and waffle are moved about in the microwave field. The results also show 
that the total package reflectance varies as a function of the distance of 
the tray from the bottom of the oven, a maximum reflectance being obtained 
when the package rests directly on the oven floor. It is in this position 
that the cover film is located approximately 1/4 free space wavelength 
above the ground plane, and it is in this position, furthermore, that the 
optimum cooking occurs. 
TABLE I 
______________________________________ 
Effect on Waffle 
Ex. Lid Time Top Bottom Inside 
______________________________________ 
3 a 2 soggy soggy undercooked 
4 a 2.5 crispy crispy slightly tough 
5 a 3 tough tough overcooked 
6 b 2 crispy crispy chewy, good 
7 c 2 slightly 
OK slightly tough 
soft OK 
8 d 2 mushy not done, 
chewy, OK 
little tough 
9 e 2 mushy little mushy 
little tough 
C3 none 2 overcooked throughout, oil released 
______________________________________ 
1. Lid films are described in Table II. Time is cooking time, in minutes. 
TABLE II 
______________________________________ 
Structure of film layers 
Layer composition/width, mm 
______________________________________ 
Film 1 2 3 4 5 6 
______________________________________ 
a paper 1 adhes copoly 
adhes paper 2 
flake 1 
152 152 152 102 102 102 
b paper 1 adhes copoly 
adhes polyest 
flake 2 
152 152 152 102 102 102 
c paper 1 adhes copoly 
adhes polyest 
flake 2 
152 152 152 102 102 102 
d paper 1 adhes copoly 
adhes polyest 
flake 1 
152 152 152 102 102 102 
(film d contained perforations) 
e paper 1 flake 2 adhes copoly 
152 152 152 152 
f paper 1 adhes copoly 
adhes polyest 
flake 2 
152 152 152 102 102 102 
g copoly adhes flake 2 
copoly 
152 102 102 102 
______________________________________ 
Film 
Coating,g/m.sup.2 
Temp..sup.1 
Film Al flake total.sup.2 
MD TD % Refl 
% Trans 
% Abs 
______________________________________ 
a -- 10 182 175 2 92 6 
b 11.2 30 195 184 1 95 4 
c 7.6 21 167 173 1 97 2 
d -- 14 181 159 1 95 4 
e -- 22 -- -- 0 96 4 
f 7.6 23 154 146 1.6 97.7 0.7 
g 14.7 32 195 200 1.6.sup.3 
90.sup.3 
8.sup.3 
______________________________________ 
.sup.1 Equilibrium temperature (4 min.) measured in waveguide with film 
oriented machine or transverse direction, respectively, parallel to 
electric field. 
.sup.2 Total of Al flake plus matrix resin. 
.sup.3 Estimated. 
TABLE III 
______________________________________ 
Waffle size (mm) 
Gap distance (mm) 
Reflect. 
Ex. Edges Thickness film-waffle 
tray-floor 
Power R.sup.2 
______________________________________ 
10 97 .times. 92 
25 6.3 0 -- 
11 " " 6.3 32 -- 
12 " " 6.3 0 -- 
13 " " 38.1 0 -- 
14 " " 6.3 19 -- 
15 " " 6.3 6.3 -- 
16 " " 6.3 13 -- 
17 " " 9.5 0 0.165 
18 " " 9.5 3.2 0.045 
19 " " 9.5 6.3 0.055 
20 " " 9.5 9.5 0.051 
21 " " 9.5 13 0.129 
22 " " 44.4 0 0.158 
23 83 .times. 86 
25 9.5 0 0.018 
24 76 .times. 76 
25 9.5 0 0.006 
.sup. 25.sup.1 
" 25 9.5 0 0.007 
______________________________________ 
Cook Time, Comment on Waffle 
Ex. Film min. Top Bottom Interior 
______________________________________ 
10 f 2 1/4 golden soggy OK 
brown 
11 f 2 1/4 soggy soggy soggy 
12 f 2 1/4 crisp soggy OK 
13 f 2 1/4 somewhat 
soggy somewhat 
crisp soggy 
14 f 2 1/4 somewhat 
somewhat 
OK 
crisp soggy 
15 f 2 1/4 crisp somewhat 
OK 
soggy 
16 f 2 1/4 crisp somewhat 
OK 
soggy 
17 g 2 crisp crisp chewy, 
good 
18 g 2 -- -- tough 
19 g 2 -- -- tough 
20 g 2 -- -- tough 
21 g -- -- -- -- 
22 g 2 slightly 
crisp moist, 
crisp chewy 
23 g -- -- -- -- 
24 g -- -- -- -- 
.sup. 25.sup.1 
g -- -- -- -- 
______________________________________ 
.sup.1 Same as Ex. 24, but package moved away from center of oven.