Connectionless food steamer with automatic electric steam trap

Details Connectionless food steamer with automatic electric steam trap Connectionless food steamer with automatic electric steam trap

2002-03-25

2002-09-24

Simone, Timothy F. (Department: 1761)

Foods and beverages: apparatus

Cooking

Automatic control

C099S331000, C099S467000, C099S468000, C099S483000, C126S020000, C126S369000, C219S401000

Reexamination Certificate

active

06453802

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a steam cooking apparatus and in particular to a connectionless steam cooker with an automatic cold air and steam outlet and close pressure control to enhance the efficiency of the cooker.
A wide variety of steam cookers are known. Market Forge Industries, Inc., the present assignee, manufactures a wide variety of steam cookers and food warmers that have found wide acceptance in the food service industry as a way to rapidly cook food, including frozen food, and/or maintain it at a serving temperature. While pressure cookers have long been used in homes and restaurants, the risks and extra costs of containing steam under high pressure have led to the growth of slow steam cookers that use steam to deliver heat to the food, but at a pressure that is typically just above atmosphere (1 to 2 inches of water). Most conventional slow (or “pressureless”) steam cookers have steam generators, typically boilers external to the cooking compartment and using electrical resistance or gas heaters that produce steam from a water supply.
U.S. Pat. Nos. 5,549,038 and 5,631,033 to Kolvites and assigned to Market Forge Industries describe one implementation of a commercial slow steam cooker. The Kolvites cooker has permanent connections to a water supply and a drain. It can continuously replenish the supply of cold water. Periodically, on demand, it can draw water from the supply, heat the water to produce steam, circulate the steam in an oven chamber around the food to cook it and/or keep it warm until served, and then direct the steam and condensed water to the drain.
While such units offer many advantages, such as rapid, efficient cooking of large volumes of food, including frozen food, their disadvantages include the need for water and drain hookups, a relatively large water usage, attendant high power requirements to heat the water, and burdensome maintenance requirements such as daily, monthly and annual cleanings to remove scaling (“deliming”) on heating coils, tubes and other components produced by the boiling, as well as to remove residue from the cooking process itself. These units are typically large and comparatively complex in their construction. They also are constrained in that a flow of steam is condensed to hot water that must usually be cooled before it can be drained into public sewer systems.
Another type of steam cooker, commonly termed “connectionless”, avoids some of these constraints of connected cookers. Connectionless cookers, as the term suggests, do not have permanent connection to a water supply. Rather, water is added manually to the unit. It is evaporated, condensed, collected, and reused. This type of steamer can operate for comparatively long periods of time without adding additional water, and with significantly reduced water and power usage as compared to the connected steam cookers because cold water is not added on demand to form the steam, and then drained after use. An earlier steamer sold by Market Forge Industries, Inc. under the trade designation “STEAM IT” is connectionless and holds a supply of water within its heating compartment. In general, connectionless steamers cook smaller quantities of food than connected ones, but are easier to maintain, more portable, and cost less to operate.
Steam cookers of both types—connected and connectionless—use a door to gain access to the cooking compartment to add and remove the food, typically food held in one or more pans that slide onto racks mounted on the side walls of the cooking compartment. The opening and closing of this door produce a loss of steam, fluctuations in steam pressure, and introduce cold air into the compartment. The efficiency and the quality of operation of the steam cooker is dependent upon the degree to which the temperature and pressure of the steam within the cavity can be maintained at or near a preselected optimal value, or within an optimal range of values.
It is also important in all steamers to have reliable and effective controls to prevent burnout of the heater, typically caused by a low water condition. In connectionless steamers, a critical low water situation typically develops as steam is lost from the cooking compartment, and more water is boiled to replace it. (There is usually loss at least when the door is opened, and via a bleed orifice used to introduce some flow in the steam to keep it “active”.) Eventually the water supply is depleted, causing the electric resistance heating element to overheat. Known connectionless steamers have water level detection arrangements, but they can fail. One particular problem is that certain foods when steam cooked release materials to the steam which collect in the condensed water and create a layer of foam on the water. This foam can interfere with the operation of the water level detectors, causing the heating element to overheat to the degree that causes permanent damage. Another problem with known connectionless steamers is that scaling (mineral deposits) produced by evaporation of the water, as well as the accumulation of residue from the cooking process, can be carried by fluids and interfere with the operation movement of moving components used to control the cooking process.
Another problem with steamers—and particularly connectionless steamers that are inherently closed systems—is that on start-up, or after the door is opened during cooking, cold air is trapped in the cooking compartment. The cold air takes heat energy from the cooking and makes the heat gradient and cooking rate within the over uneven. While mechanical steam vents, bleed orifices, check valves, and the like have been used, the rapid and controlled elimination of trapped cold air from the cooking compartment, without also losing any significant volume of steam, remains a problem.
The amount of heat produced by a steam cooker also must accommodate variations in the quantity of food, its temperature, and its surface area. A small amount of room temperature food will be cooked quickly with the steam generator powered. Continued heating will generate a dangerous overpressure and overcook the food. Various arrangements have therefore been employed to apply electrical power to a heater of a steam generator intermittently, as needed. The aforementioned Kolvites '038 and '033 patents, for example, use a pressure-sensitive switch connected in series in the power supply line. The switch responds to the steam pressure in a long outlet conduit from the oven. To control a possible dangerous outrush of steam when the oven door is opened, Kolvites provides a switch responsive to an opening of the door that opens a valve in a fresh water supply line. The resulting cold water flow quenches steam in the steam generator and also cools a mechanical steam trap to open the steam outlet line to atmosphere.
In connectionless steamers, Creamer et al, U.S. Pat. No. 5,869,812 disclosed a float switch that controls the application of power to a heater mounted under the floor of a heating chamber, adjacent a pool of water. The float switch operates by balancing atmospheric pressure on a supply of water in a reservoir external to the steam housing against the steam pressure in the cooker carried by a conduit from an upper portion of the chamber to the float switch. Depending on how this balance is struck, power to the heater is on or off. Creamer et al. slope the floor of the heating chamber to one corner to facilitate drainage of the pool of water held there. Outlet steam is condensed and cooled in the reservoir, and then gravity recirculated by a conduit back to the water pool within the heating chamber.
In U.S. Pat. Nos. 6,175,100 and 6,107,605, Creamer et al. propose a solution to the problem of cold air trapped in the connectionless cooler of the '812 patent. They place a small hole (bleed orifice) in the steam outlet conduit leading to the float valve. The hole is continuously open to atmosphere. Cold air may escape, as may steam.
It is a principal object of the present invention to provide a connectionless stea

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