Potato Chipping

November 9, 2011 was potato chip quality testing day in the VPSL. U.S. #1 size tubers collected at grading (11/2/11) were held under cool conditions until being processed. The first step in the process is to measure the specific gravity of the tubers using the weight in air, weight in water method. Tubers are placed in a wire basket.

Exactly 8.0 lb of potatoes are needed to measure specific gravity using the hydrometer.

The wire basket containing the 8 lb of potatoes are attached to a calibrated cylinder and air-filled chamber (float). The entire unit is lowered slowly into a container of room-temperature water.

The wire basket will sink to depth determined by the dry matter of the potatoes. The depth is recorded by reading the gauge at the water line. Small changes in specific gravity are very meaningful in potato processing.

In Stage 2, three tubers are peeled. In this case, a rotating peeler is used.

In Stage 3, these tubers are sliced. A mandolin is being used here but commercial methods differ.

It is important to obtain slices of the desired thickness consistently. Many factors, including slice thickness, influence the quality of the chip.

Potato tissue is living and will display evidence of oxidation when disturbed by peeling and slicing. Holding slices in cool water until frying slows oxidation.

In Stage 4, slides are loaded into the fryer being careful to keep slices separate.

In this research, a two-compartment fryer is used. One compartment is actively frying while oil in the other compartment is allowed to return to the desired temperature of 335 deg F.

Fry time is held constant across all samples at 2.25 min. Slices are loaded and the time is set.

Slices of tubers from different genotypes will develop varying amounts of color by the completion of the fry time.

Frying is discontinued promptly after 2.25 min and chips are allowed to drain and cool for 2 min.

The duration of the fry is not chosen randomly. It is among the factors that influence chip quality most. Here, slices of tubers of the same variety have been fried for 2 min 5 sec and 2 min 15 sec. Note the difference in color which developed in 10 sec.

The Snack Food Association produces many reference materials. The 6-point color chart is among these resources. As the last step in the chip quality test, the sample is assigned a value of 1-6 based on which SFA standard image to which it is most similar. This reference chart allows research teams worldwide to use a common unit in comparing chip color. On 11/9/11, the VPSL recorded the chip color and specific gravity of tubers representing approx. 80 genotypes grown.

In the potato germplasm evaluation and development project, data generated in Ohio and elsewhere are placed in searchable, online database managed by the Potato and Sweet Potato Breeding and Genetics program at North Carolina State University. The database is a resource for scientists, consumers and industry professionals.