Steps in preparation of Potato products
Dehydrated chips
The potato chip is a fried snack food, which is most popular world over. However, frozen French fries have now superseded the chips in the developed countries. Before processing potatoes into chips, French fries, dehydrated products and canning, certain preliminary unit operations in preparing the potatoes are required. Some of these pre-processing operations, common to all the above processed forms, are as follows:
Grading: Grading
of potatoes is generally done according to the requirements of the product. For
instance, medium large round tubers are preferred for chipping since their shape
facilitates peeling. On the other hand, the French fry industry prefers large
and long or oblong potatoes longer than 90 mm. For canning, small size tubers
are selected so that they can be canned whole. The eyes should be shallow for
less loss in peeling, particularly during abrasive peeling. Grading is done with
the help of mechanical graders.
Sorting and washing:
During
sorting, defective potatoes such as damaged and green ones are removed. Stones,
any extraneous matter and other unwanted materials are removed manually or
mechanically before the potatoes enter the processing line. Potatoes are washed
to remove sand, dirt, mud and other extraneous matter. Barrel type washers are
commonly used in which the potatoes are simultaneously sprayed with water and
tumbled and rubbed against each other and against the sides of the horizontal
axis barrel.
Peeling: Potatoes
are peeled by the use of heat (steam), chemicals and abrasive action. Abrasive
peelers are available for batch or continuous peeling. Large plants are always
equipped with continuous peeling lines to provide smooth and continuous
processing. Freshly harvested potatoes can be peeled easily, while in stored
potatoes, the peel or periderm is thick and needs strong measures. In steam
peeling, there is partial cooking of the potato due to gelatinization of starch
above 71 oC, causing a heat ring or cook ring in some processed
products like in chips and French fries, which is unacceptable. All the potatoes
destined for French fries are peeled by conventional lye (alkali) peeling
or infrared dry caustic peeling, as tissue losses by abrasion
peeling are excessive. Lye
peeling uses a caustic soda solution of 5-15%. The dwell time may be between 10
sec to 1 min depending upon the age of the tubers, followed by thorough washing.
Washing, sorting and trimming: These operations are important to produce a clean potato free from defects before slicing. It is much easier and more efficient to remove a defective area ahead of slicer before frying. With small tubers, it may be cheaper to eliminate the whole tuber rather than trimming the defect.