Manufacture of potato chips (french fries)Potatoes are delivered to the plant and are commonly passed through sorting equipment to remove stones, pebbles and other extraneous matter. The raw material is washed, graded and peeled. A number of peeling methods are available, including steam and lye peeling (caustic solution). Lye peeling produces waste with a very high pH and organic loading, which then adds to the water treatment costs. Large tubers are generally sorted for use in chip production.
Potatoes are cut into the required size using independently driven multiple knives. Off-cuts, slivers and broken pieces are removed before blanching. The chips are blanched using steam or water (generally at around 60 - 85°C). Multiple blanching stages may be used.
Excess moisture must be removed from the chips both to preserve the life of the frying oil and to lower the moisture content of the chips, but this leads to a reduction in the required frying time.
Conveyor dryers are used in large processing plants. The chips are fried, typically at around 160 - 180°C, the time of frying varies for finished fried and par fried products. Excess fat is removed from the chips before freezing; some manufacturers recover the fat for re-use.
Fluidised-bed freezing may be used for freezing the finished product, although belt freezing provides a more energy efficient option.