Patent Application
20170291753
The present invention relates generally to methods for packaging of foods for microwave heating.
Microwave cooking is one of the most widely used cooking methods. Microwave cooking is fast, convenient, safe, and energy efficient. However, microwave-cooked food is typically associated with lower quality fast foods and not necessarily “gourmet” food.
One of the main problems with microwave heating of food is the heating uniformity. Methods have been invented, primarily in the design of the microwave oven itself, including stirring and rotating waveguides and turntables, to help with the heating uniformity. The uniformity problem is especially severe when the food is initially frozen.
A microwave susceptor is sometimes used to help with crisping or browning of food. It is usually made of a layer of metallized polyethylene terephthalate (PET) film that absorbs microwave energy and converts it to infrared heating energy. Typically microwave susceptors are not edible.
The rate of microwave heating depends on dielectric properties, specific heat, mass and shape of the food. The absorption of microwave by materials is given by:
Pv∝f∈″E2
where P=energy absorbed per unit volume, f=frequency of the microwave, and E=electric field strength. ∈″ is the imagery part of the dielectric constant of the food which measures the dielectric loss. The inverse of this dielectric loss factor, 1/∈″, is a measure of the penetration depth, i.e. how deep can microwaves reach inside the materials before the field strength decreases substantially.
The heating of the food in a microwave oven is proportional to the absorbed microwave energy. The temperature change of food after a given time tin the microwave can then be expressed as
where Tf is the final temperature and Ti is the starting temperature, Cp is the heat capacity of the food in the microwave, and A is a constant.
The heating of foods is therefore proportional to the dielectric loss factor, ∈″, of foods being heated. The dielectric loss factor can be different for different materials, including foods. The higher the dielectric loss factor of a food, the faster the food is heated by the microwave. The dielectric loss factor also affects the depth of microwave penetration into the food, which can impact the uniformity of heating.
Typically, the dielectric loss factor goes up with moisture content and salt content of the food being heated in a microwave oven. For example, ionic liquids and solids, and their mixtures have very high dielectric loss factors. Ketchup and mustard have dielectric loss factors of 30 or more while dielectric loss factor of raw pork is about 10 at the most commonly used microwave frequency 2450 MHz. Dry foods such as crackers may not absorb microwave at all and have low dielectric loss factor, e″˜0.
By the measure of penetrating depth, microwaves typically used in microwave ovens can only penetrate about 5 millimeters of ketchup or mustard before being substantially absorbed, while the penetration depth in raw (unsalted) meat may be close to 15 mm.
The dielectric loss factor usually has a large temperature dependence. For example, ham has a dielectric loss factor of 3 at 2450 MHz and −10 degrees Centigrade. But at 5 degrees C., the dielectric loss factor jumps to 527. At microwave frequency, the temperature dependence of the dielectric loss factor of water is especially large—below freezing ice has very low dielectric loss factor while the dielectric loss factor increases dramatically upon melting. Some data on dielectric constants, including the dielectric loss factor, of food can be found in (S. Narayan, et al, “Measurement techniques and application of electrical properties for non-destructive quality evaluation of foods—a review, J. Food Sci. Technol. Vol 48, 387-411, 2011).
Heating uniformity and efficiency is an especially serious problem for frozen foods because water, once frozen, does not absorb microwave efficiently.
It is a primary objective of the present invention to provide a method for the uniform heating of foods, including frozen foods, cooked in a microwave oven which can be incorporated into disposable packages or receptacles for pre-packaged food.
It is one objective of the present invention to provide a method for heating of foods in microwave wherein materials with high dielectric loss factors are dispersed in matrix of foods having lower dielectric loss factors. The said materials having high dielectric loss factors are preferably edible.
It is yet another objective of the present invention to provide a method for heating of foods in microwave wherein foods having higher dielectric loss factors are arranged in thin layers sandwiched between layers of foods having lower dielectric loss factors.
It is another objective of the present invention to provide a method for heating of foods in microwave wherein liquid foods having low dielectric loss factors are contained in pockets, said pockets comprising thin layers of foods having high dielectric loss factors.
It is yet another objective of the present invention to provide a method for a microwave omelet wherein raw eggs are separated by thin layers of foods having high dielectric loss factors.
In one method for a microwave omelet raw eggs are contained in pockets, said pockets comprising thin layers of foods having high dielectric loss factors.
Other objectives, advantages, and features of the present invention will become apparent from the following specification when taken in conjunction with the accompanying drawings.
Methods are described herein for packaging of various foods in a structured fashion to optimize for microwave heating. Increase heating uniformity and heating efficiency may be achieved with these methods.
Herein the term food includes all edible foodstuff, including ordinary food, condiments, spices. The dielectric loss factor is herein used interchangeably with the term microwave absorption rate.
Herein the dielectric loss factors are referred to the imagery part of the dielectric constant of a material measured in the, but not limited to, the region of microwave frequency around 2.4 GHz used in most commercial microwave ovens.
Herein a high dielectric loss factor is generally referred to a dielectric loss factor with a numerical value of more than approximately 5.
Herein a low dielectric loss factor is generally referred to a dielectric loss factor with a numerical value of less than approximately 5.
In the above example material 120 may be an edible food or foods such as a thin layer of cheese, ham, salsa, or a thin layer of mustard or ketchup, or a mixture of foods. Material 120 may contain holes in order for microwave to go through. For example, material 120 may be in the form of a regular mesh. Food 110 may be made of dough, raw or cooked egg, rice, and vegetables. Food 110 may also be a mixture of foods with low dielectric loss factor in the microwave region.
Preferably material 120 may be a thin layer with holes, for example, in the form a mesh.
Alternatively material 120 may be a microwave susceptor, for example made of metallized PET. After the microwave heating, it is preferable to be able to pull the susceptor from the food.
In another embodiment, some 120 layer may be food with high dielectric loss factor and other 120 layers may be microwave susceptors.
An example of food 230 may be oil that absorbs microwave and heat quickly. Food 230 may also be salsa, Ketchup, and mustard.
Material 320 may be an edible food or foods such as a thin layer of cheese, ham, salsa, or a thin layer of mustard or ketchup, or a mixture of foods. Material 320 may contain holes in order for microwave to go through. Alternatively material 320 may be a microwave susceptor.
Often the main ingredient of a desired food is liquid. An example is uncooked egg or egg white that is used to make omelet.
In
As an example, we provide a method for packaging ingredients that can be microwaved to make fresh omelet.
Omelet is a favorite food, especially at breakfast. It is usually prepared on a stove. Microwave omelet usually is prepared with a plastic container. Fresh eggs are beat and mixed with desirable ingredients such as cheese, placed in the plastic container and heated in the microwave. It is desirable to provide a ready to cook, packaged, mixture that can be made into fresh omelet. Another type of microwave omelet is also available, wherein already cooked egg with cheese, and other ingredients are packed in a microwavable package. The following illustrate methods for making a microwave egg omelet according to present invention using fresh, uncooked eggs.
Method 1:
1. Start with a microwave susceptor that is non-sticking, coat with butter or oil.
2. Filled with raw eggs, including option for egg white.
3. Cover with thin layer of cheese or ham. The susceptor may contain ridge where the cheese can be placed to seal the raw eggs in to prevent leaking.
The cheese sheet may contain be waffle patterned, comprising both thicker grid interwoven with thin region. It may contain holes or may be in the shape of a mesh. During microwave heating, the cheese may melt and disintegrate to allow egg to mix with other ingredients.
4. Add ingredients such as chopped ham, chopped green onion, salsa, ketchup and other ingredients.
5. Cover with another layer of cheese or other edible film such as ham.
6. Fill with another layer of egg and cover with another thin layer of edible materials such as cheese or hem.
7. Seal with plastic film.
Optionally, the package may have two compartments, whereas after cooking in microwave, one part can be flipped on top of the other.
More layers can be added by repeating with same or different ingredients.
The finished package may be stored in a freezer. Upon heating in microwave oven the approximately uniformly dispersed granulated ingredients with high dielectric loss factors will help uniformly melt the frozen egg.
Method 2:
1. Fresh eggs are mixed with desired ingredients, such as chopped ham, chopped mushroom, chopped green onions, chopped onions, other chopped vegetables;
2. Pockets are made of thin layers of food with high dielectric loss factors, including cheese, ham. The thickness of the pocket wall can be from 0.5 millimeter to 5 millimeters thick. Pocket may be waffle patterned.
3. The pocket is the filled with the ingredient from step 1.
4. One or more of the filled pockets are then placed in a container lined with microwave susceptor.
5. The finished package may be stored in a freezer. Upon heating in microwave oven the pockets will heat up first and in turn melt and heat the egg mix inside the pockets.
It is to be understood that the present invention is not limited to the particular construction and arrangement of parts disclosed and illustrated herein, but embraces all such modified forms thereof as come within the scope of the following claims.
