Steam ovens, also known as steamers, have been long used to cook food. Steam ovens operate by heating water to generate steam and then circulating the steam within a cooking cavity containing food to cook the food.
Conventional steamers are not pressure cookers; instead, conventional steamer cooking cavities are vented to the atmosphere so that the steam pressure in the cooking cavity is not greater than atmosphere. This arrangement is not thermally efficient. In order to maintain steam in the cooking cavity, steam must be continuously generated to replace that which is vented into the atmosphere. However, the amount of steam required to cook the food varies during cooking. Food can only accept steam energy at a rate that depends on its surface area and temperature. In the initial phase of cooking room temperature or frozen food products the amount of steam required is high. However, when the food products are thereafter in a heated condition, less steam is required to complete the cooking. Thus, when the food cannot absorb all of the steam being generated, the excess steam is wasted. As such, conventional steam cookers typically produce too much steam during the later portions of cooking, when the food is already at an elevated temperature. Thus, conventional steam cookers are not thermally efficient and they consume an excess of water for continuously making steam and cooling exhaust steam.
More efficient cooking performance is achieved when steamers operate at pressures above atmospheric pressure. On the other hand, if high pressure steam is used, then significant structural requirements must be met for safety reasons which increases cost. In addition, high pressure steamers may require certification as pressure vessels. As such, it is desirable for steamers to operate at pressures above atmospheric, but below the level where certification is necessary.
The food cooking industry has long sought efficient low pressure steamers. One recent approach is reflected in U.S. Pat. No. 5,549,038 to Kolvites which discloses a steamer having separate steam generation chambers which uses low pressure to cook food more efficiently. In this device, the steam is not vented directly to the atmosphere for the entire cooking cycle. Instead, a water seal and pressure valve arrangement is used to cause the steam in the cooking cavity to be at a slightly elevated pressure. This pressure is described as being somewhat above atmospheric pressure or one or two inches of water. Also, the device regulates the generation of steam according to the steam pressure so that steam is not continuously produced. When the food is absorbing all the steam, then the pressure will be low and additional steam is produced. When the food is not absorbing all the steam, then the resulting rise in pressure is directly sensed by a normally closed pressure switch which interrupts the steam generation until the pressure drops.
The Kolvites steam cooker has at least two main drawbacks. First, the Kolvites device employs separate steam generation cavities, which requires more space. Second, the Kolvites device does not reuse water that condensed from steam; this condensate is removed to a tempering water tank and then drained therefrom. Other known steamers suffer from these or other drawbacks.
Thus, there remains a need within the industry for efficient, compact low pressure steamers which conserve water.