Patent Application
20090045185
This invention relates to food preparation equipment. More particularly this invention relates to an oven used to hold previously prepared foods at a relatively constant temperature until they are sold or served for consumption. Such ovens are often used in fast food restaurants to keep foods hot and ready for consumption.
The base cabinet 12 supports a food holding tray 24, preferably made from stainless steel. The food holding tray 24 has a bottom 26 and several inclined sides 28, the arrangement of which gives the food holding tray the shape of an inverted frusto-pyramid having an open or missing base, which faces upwardly toward an infrared energy source 20, which emits infrared energy 21 toward the food holding tray 24.
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An important feature of the oven 10 depicted in each of the figures is that the surface of the food holding tray 24 is roughened or “matte.” Experimentation revealed that when the food holding tray 24 with the matte finish was subjected to IR energy for long periods of time, the surface temperature of the matte-finish tray 24 was higher than the surface temperatures of prior art food holding trays having a shiny surface. It is believed that the surface roughness of the matte finish does not reflect IR energy as effectively as does a highly-polished surface used in prior art food holding ovens.
In a preferred embodiment, the matte finish on the stainless steel tray 24 was provided by peening the tray surface using a predetermined shot size. The shot size was selected to provide a resultant surface roughness of approximately 5-40 μm. (micrometers). As used herein, “surface roughness” is considered to be the arithmetic average deviation from the center line of the surface, or as RMS, which is the root mean square of the deviations from the center line.
Surface roughnesses much above about 40 μm tends to damage food product as it is removed the tray and can tend to retain food products, making the tray difficult to clean. Surface roughnesses below about 5 μm will tend to behave as do the prior art shiny surfaces and will not benefit from an increased IR absorption.
A matte finish can also be provided by chemical etching or sand blasting, brushing or otherwise abrasively treating the surface such that it has a surface roughness that diminishes the base material's reflectivity. The increased absorption of IR energy as a result of the matte finish produces a corresponding increase in surface temperature.
In a preferred embodiment, the oven has a maximum input power of about 5000 watts, most of which is output as infrared energy. A preferred embodiment of the oven provides sufficient infrared energy to maintain the tray's surface temperature above about 120 degrees Farenheit but below 180 degrees Farenheit, regardless of how long the IR source has been turned on.
In a food service or restaurant that cooks foods in advance of when they will be served to consumers, the oven 10 can be used to hold previously cooked food at a selected temperature. A method of holding previously cooked food in the oven requires the direction of some amount of infrared energy downwardly into the food holding tray 24 depicted and described herein. The heat energy applied to the food items in the tray 24 can be regulated by modulating the output power or by cycling the IR sources over time. Regardless of how long the IR heat source is left on and regardless of whether the tray 24 is full or empty, its surface temperature will not become so hot that it will burn either the foods kept in the tray 24 or the skin of users who might inadvertently touch the tray when it is in use.
While the preferred embodiment of the tray 24 is stainless steel, which is either mechanically, physically or chemically treated to have a matte finish, an alternate embodiment of the oven 10 uses an aluminum tray, the surfaces of which can be anodized or similarly treated to provide a roughened, matte finish.
Yet another alternate embodiment uses a carbon-fiber composite material the surfaces of which are also roughened to provide a matte finish.
