Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
1999-04-13
2001-05-15
Paschall, Mark (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S481000, C219S492000, C099S328000
Reexamination Certificate
active
06232582
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of cooking ovens and methods, including those using radiant energy in the infrared, near-visible and visible ranges of the electromagnetic spectrum. More particularly, this invention relates to apparatuses and methods for modifying lightwave cooking recipes to compensate for variations in the line voltage being applied across the cooking lamps.
BACKGROUND OF THE INVENTION
Ovens for cooking and baking food have been known and used for thousands of years. Basically, oven types can be categorized in four cooking forms; conduction cooking, convection cooking, infrared radiation cooking and microwave radiation cooking.
There are subtle differences between cooking and baking. Cooking just requires the heating of the food. Baking of a product from a dough, such as bread, cake, crust, or pastry, requires not only heating of the product throughout but also chemical reactions coupled with driving the water from the dough in a predetermined fashion to achieve the correct consistency of the final product and finally browning the outside. Following a recipe when baking is very important. An attempt to decrease the baking time in a conventional oven by increasing the temperature results in a damaged or destroyed product.
In general, there are problems when one wants to cook or bake foodstuffs with high-quality results in the shortest times. Conduction and convection provide the necessary quality, but both are inherently slow energy transfer methods. Long-wave infrared radiation can provide faster heating rates, but it only heats the surface area of most foodstuffs, leaving the internal heat energy to be transferred by much slower conduction. Microwave radiation heats the foodstuff very quickly in depth, but during baking the loss of water near the surface stops the heating process before any satisfactory browning occurs. Consequently, microwave ovens cannot produce quality baked foodstuffs, such as bread.
Radiant cooking methods can be classified by the manner in which the radiation interacts with the foodstuff molecules. For example, starting with the longest wavelengths for cooking, the microwave region, most of the heating occurs because the radiant energy couples into the bipolar water molecules causing them to rotate. Viscous coupling between water molecules converts this rotational energy into thermal energy, thereby heating the food. Decreasing the wavelength to the long-wave infrared regime, the molecules and their component atoms resonantly absorb the energy in well-defined excitation bands. This is mainly a vibrational energy absorption process. In the shortwave infrared region of the spectrum, the main part of the absorption is due to higher frequency coupling to the vibrational modes. In the visible region, the principal absorption mechanism is excitation of the electrons that couple the atoms to form the molecules. These interactions are easily discerned in the visible band of the spectra, where they are identified as “color” absorptions. Finally, in the ultraviolet, the wavelength is short enough, and the energy of the radiation is sufficient to actually remove the electrons from their component atoms, thereby creating ionized states and breaking chemical bonds. This short wavelength, while it finds uses in sterilization techniques, probably has little use in foodstuff heating, because it promotes adverse chemical reactions and destroys food molecules.
Lightwave ovens are capable of cooking and baking food products in times much shorter than conventional ovens. This cooking speed is attributable to the range of wavelengths and power levels that are used.
There is no precise definition for the visible, near visible and infrared ranges of wavelengths because the perceptive ranges of each human eye is different. Scientific definitions of the “visible” light range, however, typically encompass the range of about 0.39 &mgr;m to 0.77 &mgr;m. The term “near-visible” has been coined for infrared radiation that has wavelengths longer than the visible range, but less than the water absorption cut-off at about 1.35 &mgr;m. The term “infrared” refers to wavelengths greater than about 1.35 &mgr;m. For the purposes of this disclosure, the visible region includes wavelengths between about 0.39 &mgr;m and 0.77 &mgr;m, the near-visible region includes wavelengths between about 0.77 &mgr;m and 1.35 &mgr;m, and the infrared region includes wavelengths greater than about 1.35 &mgr;m.
Typically, wavelengths in the visible range (0.39 to 0.77 &mgr;m) and the near-visible range (0.77 to 1.35 &mgr;m) have fairly deep penetration in most foodstuffs. This range of deep penetration is mainly governed by the absorption properties of water. The characteristic penetration distance for water varies from about 50 meters in the visible to less than about 1 mm at 1.35 microns. Several other factors modify this basic absorption penetration. In the visible region electronic absorption of the food molecules reduces the penetration distance substantially, while scattering in the food product can be a strong factor throughout the region of deep penetration. Measurements show that the typical average penetration distances for light in the visible and near-visible region of the spectrum varies from 2-4 mm for meats to as deep as 10 mm in some baked goods and liquids like non-fat milk.
The region of deep penetration allows the radiant power density that impinges on the food to be increased, because the energy is deposited in a fairly thick region near the surface of the food, and the energy is essentially deposited in a large volume, so that the temperature of the food at the surface does not increase rapidly. Consequently the radiation in the visible and near-visible regions does not contribute greatly to the exterior surface browning.
In the region above 1.35 &mgr;m (infrared region), the penetration distance decreases substantially to fractions of a millimeter, and for certain absorption peaks down to 0.001 mm. The power in this region is absorbed in such a small depth that the temperature rises rapidly, driving the water out and forming a crust. With no water to evaporate and cool the surface the temperature can climb quickly to 300° F. This is the approximate temperature where the set of browning reactions (Maillard reactions) are initiated. As the temperature is rapidly pushed even higher to above 400° F. the point is reached where the surface starts to burn.
It is the balance between the deep penetration wavelengths (0.39 to 1.35 &mgr;m) and the shallow penetration wavelengths (1.35 &mgr;m and greater) that allows the power density at the surface of the food to be increased in the lightwave oven, to cook the food rapidly with the shorter wavelengths and to brown the food with the longer infrared so that a high-quality product is produced. Conventional ovens do not have the shorter wavelength components of radiant energy. The resulting shallower penetration means that increasing the radiant power in such an oven only heats the food surface faster, prematurely browning the food before its interior gets hot.
It should be noted that the penetration depth is not uniform across the deeply penetrating region of the spectrum. Even though water shows a very deep penetration for visible radiation, i.e., many meters, the electronic absorptions of the food macromolecules generally increase in the visible region. The added effect of scattering near the blue end (0.39 &mgr;m) of the visible region reduces the penetration even further. However, there is little real loss in the overall average penetration because very little energy resides in the blue end of the blackbody spectrum.
Conventional ovens operate with radiant power densities as high as about 0.3 W/cm
2
(i.e. at 400° F.). The cooking speeds of conventional ovens cannot be appreciably increased simply by increasing the cooking temperature, because increased cooking temperatures drive water off the food surface and cause browning and searing of the food surface before the food's interior has been brough
Minnear William
O'Neill John
Pettibone Don
Tatarian Chris
Limbach George C.
Paschall Mark
Quadlux, Inc.
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