In the foodservice industry, it is common to serve prepared food from steam or “Sterno” flame tables. These are devices which hold hot for serving standard sizes of “pans” of food that are typically found in canteens, banquet halls, delis, corner shops and cafeteria serving lines. Typically, the food is prepared hot in the back room and is then placed into the pans for holding hot for serving. Serious food safety problems and in particular drying out of the food, are frequently reported with those heating tables. Some industrial companies also provide similarly prepared food products as quality and convenience alternatives for foodservice operators. These products are usually sold frozen or refrigerated, and heating is required before serving to a hot temperature, i.e. at least 71° C., for safety reasons, and for consumption at temperatures where consumers can enjoy the food the most, i.e. about 55° C. These products are most commonly manufactured and sold in partial “pan” sizes (e.g., ½ and ⅓ “pan” sizes) and most commonly packaged in a lidded container such as in gauge aluminum foil.
Most often, these products are heated to serving temperature in a conventional oven similar to a residential oven. However, this method of heating has proved to be slow, as radiation heat transfer from oven wall to the package surface is relatively poor in the case of the aluminum packaging. The aluminum package has a tendency to reflect heat, resulting in the primary mode of heat transfer to be natural convection in this case. Increase of the heat transfer may be obtained by circulating hot air around the packaging as in forced air convection ovens, which are used by foodservice operators. Another enhancement is to add steam to the air to get more rapid heating but, this method may adversely affect the quality of the food product. Other methods consist of microwave heating the food product by removing the food product from the original aluminum packaging and by placing it into a special plastic tray adapted to microwave heating. Apart from the fact this requires operator's manipulations, microwave heating provides uneven heating with hot and cold spots that require rest time for the temperature to even out. The use of a combination of microwave and convection is known which provides improved results, but is relatively expensive and requires high amperage electrical connections and large amounts of electricity and also requires special packaging adapted for microwave use. In all cases of these various types of ovens, the equipment is relatively expensive, complicated and large. Once located the equipment must be used in its “place”, most typically what is referred to as “back of the house”.
Regardless whether a conventional or convection oven is used, often the food at the edges and corners are overheated and sometimes burnt, lowering the overall quality of the prepared food. This occurs because the food product at the edges and corners is getting heated from 2 or 3 sides and at the same time is close to the surfaces. Thus, it would be desirable to have a heating method whereby the amount of heat can be controlled to a lower amount in the areas of the tray which are prone to overheating and burning. Also, if different foods are placed in a tray (e.g., meat loaf and mashed potatoes), it would be advantageous to have different amounts of heat to be applied to different parts of the tray for various food components. In conventional or convection ovens, there is no way, for the most part, to lessen the amount of heat to these edges and corners or to control different amounts of heat to different regions of trays, except to change to more complicated and expensive packaging.
In the foodservice area, the food may usually come in large-size frozen portions of several kilograms. As a matter of example, a standard “half-pan” lasagna packaged in an aluminum tray of 2.7 kg requires about 1950 kJ of energy (including moisture losses) and may take more than 125 minutes in a conventional oven to be heated from frozen to an acceptable hot temperature for serving. Foodservice operators are less and less inclined to accept so long heating times. One possibility is to divide the food in several smaller portions which are put in smaller containers, trays or dishes. However, this is labor intensive and it requires more attention from skilled operators. Therefore, there is a need for conveniently, rapidly and cleanly heating food originally packed in medium to large size packages without the requirement to remove the food from their packages so that labor is kept to a minimum and the food can be easily transferred to the point of service in hot conditions.
Usually, once the food is heated in the “back room” to serving temperature, it is brought to the “front of the house” and placed in a steam table, or a chafing dish with a “Sterno” flame, to be held hot. Steam tables, however, are quite large, not inexpensive, typically take about 45 minutes to one hour to preheat, and are very labor intensive to clean. Steam tables work by heating water to create a hot, humid air environment under the food tray. Consequently, the packaging of the food product is limited to things such as aluminum or plastic unless a special liner is used. Therefore, it would be desirable to provide equipment that is quicker, simpler and reasonably low in cost, small and portable in some situations, and easy to use.
Food warmers are known which are designed to receive for heating an open tray-shaped member for different food containers such as dishes or pans. However, the heating capacity of those warming devices is limited as the energetic loss to the environment is high due to the open configuration. Increasing the electric power of those devices to compensate for heat loss may lead to the violation of domestic electrical safety regulations which require precise electrical power limits not to be exceeded. Thus, the food warmers are generally used just for holding food warm or heating small size portions from ambient to warm but they are not capable of handling the heating of large portions of food, especially, when the food is originally in frozen or chilled state in the plate. For instance, U.S. Pat. No. 3,043,943 to J. R. Moot relates to a portable food warmer, and more particularly to a tray adapted to heat food and dishes containing food to serving temperature. The food warmer comprises a dish supporting member, an inner heat diffusing member and heating elements between the heat diffusing member and a heat insulator. Sloping top flanges are provided to delimit the contour of the open upper cavity so that dishes of different sizes and capacity can be heated in contact to the dish supporting member.
Numerous patents relate to foodservice systems wherein individual portions of precooked food are supported on trays installed within moveable carts. The carts are usually placed in a chilled environment to store the food in a chilled state. Selected foods on the trays are rethermalized in the cart, i.e., heated to a hot serving temperature. The rethermalization method is usually directed to conductively applying heat to the selected food portions through a heating plate which is heated by a thermostatically controlled electrical heater. Examples of those systems are described in U.S. Pat. Nos. 4,068,115; 4,235,282; 4,584,466 and 5,285,051. The trays are intended to be served to the consumer as such and therefore are not adapted to heat large size portions of food but only individually portioned food in dish.
U.S. Pat. No. 3,608,627 relates to a combination refrigeration and cooking device. A plurality of casseroles are provided into a freezing or chilling chamber. Each casserole has an electric heating element associated therewith which is connected to an electric circuit controlled by suitable switching and/or timing means. Each casserole has a cover and an associated heating element which form a complete thermally insulated unit. The thermally insulated unit reduces the heat loss of internally produced heat so that there is no significant loss of heat to thermally affect adjacent casseroles that may be retained in a frozen or chilled state. Such a device is not adapted to heat packaged food such as standardized “pans” size of food. Furthermore, the heating casseroles need to be regularly removed for cleaning and/or washing which may lead to potential safety issues since the casseroles also include electrical means.
U.S. Pat. No. 5,445,062 relates to a cooker/rethermalizer especially suited for cooking or reheating of prepared, packaged meat and sauce entree items or vegetables comprising a food vessel retaining an aqueous bath, a food locator rack for supporting packaged food items and fluid outlets provided in the rack to cause fluid to exit into the bath and agitate the bath over and past food items. Such a heating apparatus is suited to accommodate flexible film packages, so called “sous vide” packages. However, the system is relatively cumbersome and requires a relatively long preheating time for the bath to be operational.
U.S. Pat. No. 5,948,301 relates to a food thermalization device which permits the food to be rethermalized and held warm which includes an electrically-resistance heated plate which is controlled to equilibrate at a set temperature in the range of 160° F. to 185° F., with a fluctuation not exceeding plus or minus 5° F.
U.S. Pat. No. 5,069,920 relates to a method of electric conduction cooking of food in a package. The package includes two electrodes including a raised portion of the bottom wall and a planar top electrode and wherein the recessed area between the raised portion of the bottom wall and the sidewall of the package defines a peripheral reservoir. The food is cooked by passing electrical current through the food and allowing the drainage and accumulation of exuded products from the food product being cooked so as to prevent contamination of the bottom electrode. However, the heating greatly depends upon the electrical conductivity of the food individual pieces contained in the package. As the electrical conductivity of the food product may also differ from frozen state to thawed state, and as a function of temperature, the heating pattern is difficult to control accurately. Furthermore, shock hazards are greatly increased when current is passed through the food itself whatever efforts are made to diminish the risks.
U.S. Pat. No. 4,102,256 relates to a cooking apparatus for use in conjunction with food which is held in a container whereby, thin-walled flexible members defining the cooking surfaces are thermally coupled to heating means maintained in position against the thin-walled flexible members by maintaining means including resilient means.
Therefore, there is a need for heating, and possibly holding hot, packaged food in relatively smaller, simpler, safer and more convenient ways using relatively low power requirements as compared to existing foodservice or even household ranges. There is also a need for efficiently and evenly heating food packaged in the standard container, in particular, aluminum lidded tray, or other differing packaging without the requirement of removing the food from the container to facilitate heating of the food to deliver the intended temperature and quality. There is also a need for controlling the heating of the food so as to optimize the heating time and reduce the risk of over heating and burnt food surfaces.