Potato flakes and potato granules are the most common types of dehydrated potato products. Potato flakes and potato granules comprise dehydrated single cells, or aggregates of cells, of the potato tuber dried to a moisture content of about 6%-8%. As the names imply, potato flakes have a crystal-like shape, while potato granules have a granular shape. Both potato flakes and potato granules can be rehydrated (i.e., reconstituted) to make mashed potato products and fabricated snack products.
Various processes for making potato flakes and potato granules, are well known in the art. An object of most prior art processes is to provide flakes or granules that can be rehydrated to make a potato product that has the flavor and texture of fresh cooked potatoes.
FIG. 1 illustrates process steps in a conventional prior art process for making potato flakes. Initially, fresh potatoes are washed, peeled, sliced and optionally rinsed. The raw potato slices are then precooked, typically by immersion in water held at about 160.degree. F.-165.degree. F. (71.1.degree. C.-73.9.degree. C.) for a period of about 15-20 minutes. The precooking step gelatinizes starches within the potato cells, preferably with minimal swelling and bursting of the potato cells, such that retrogradation can take place during a subsequent cooling step. The bonds formed between the potato cells will thus be preserved during subsequent cooking and drying steps, and the reconstituted finished flake will have a reduced stickiness.
The cooling step is performed by immersing the precooked potato slices in water held at, or below, 75.degree. F. (23.9.degree. C.) for about 20-60 minutes. Following cooling, the potato slices are cooked, typically with steam, at a temperature of about 190.degree. F.-212.degree. F. (87.8.degree. C.-100.degree. C.) for about 15-60 minutes. One type of steam cooker includes a screw conveyor which moves the potato slices through a steam chamber containing live steam.
Following cooking, the cooked potato slices are riced to form a potato mash. Next, additives are added to the potato mash. Representative additives include solutions of sodium bisulfite for retarding non-enzymatic browning, and emulsions of a monoglyceride emulsifier, antioxidants and various chelating agents. Following the additive step, a drying step is performed on the potato mash, typically with a drum dryer. The drum drier dries the mash into a potato sheet having a moisture content of about 6%-8%. Following drying, the potato sheet can be comminuted into potato flakes using a comminuting apparatus such as a hammermill.
FIG. 2 illustrates process steps in a conventional prior art process for making potato granules. Initially raw potatoes are washed, peeled, sliced, precooked, cooled, cooked, riced and additives added substantially as previously described. During a mash mixing step hot cooked potatoes are mixed with dry add back granules until a homogeneous moist mix is obtained. Following mash mixing, a conditioning step equalizes the moisture throughout the mix, which is then passed over a fine mesh vibrating screen to remove large agglomerates and bruised portions of potato tissues. The product is then further mixed, and dried using a drying apparatus such as an air lift drier, or a fluidized bed drier. Following drying to a moisture content of about 12%-13%, a portion of the material is removed for add back, and the remainder is then finish dried to a moisture content of about 6%-8%, again by using a drying apparatus.
Both of the above described processes for making potato flakes and potato granules have been used in the art since about the 1950s. Over the years various processes have been proposed in which the above fabrication processes are modified. Representative processes are described in U.S. Pat. Nos. 5,707,671 and 5,292,542 to Beck et al.; U.S. Pat. No. 3,574,643 to Lewis; and U.S. Pat. No. 3,764,716 to Rainwater et al.
Most new fabrication processes are directed to improving the flavor and texture of the rehydrated potato product. The present invention is also directed to a process for making potato flakes and potato granules in which a primary object is improved flavor and texture in the rehydrated potato product.
However, another factor not generally considered by prior art fabrication processes is the large quantities of water that are required during various steps of the processes. As water resources come under increasing pressure, potato processors must compete with urban, agricultural, industrial and recreational interests for the available water rights. In addition, the water rights are expensive, which adds expense to the dehydrated potato products.
Besides requiring large quantities of water, prior art fabrication processes produce large quantities of waste water. Waste water is typically produced in all steps of the fabrication processes but drying. The precooking and cooling steps in particular, produce large quantities of waste water (e.g., up to 60% of the total waste water). The waste water from these steps also contains high concentrations of organic material.
Recently, potato processors have been experiencing difficulties in disposing of the large quantities of waste water produced by conventional potato fabrication processes. In the past, waste water has been disposed of by application to farmland at a rate approved by the Department of Environmental Quality. However, regulations and restrictions on the amount of waste water that can be applied to farmland have changed. Thus, it has become difficult, if not impossible, to dispose of the large quantities of waste water produced by potato fabrication processes.
Another problem with conventional disposal methods is that the waste water can contaminate ground water used for municipal and rural water supplies. Also, decomposing organic material in the waste water produces by-products, such as methane gas, that can affect air quality. The odor from decomposing waste water is a particular concern for processors located in close proximity to municipalities. In addition, the waste water can adversely affect crops by saturating the ground with too much water, particularly in wet years.
In view of the foregoing, the present invention is directed to a process and system for making dehydrated potato products in which water usage and waste water production are substantially reduced.