2007 - Potatoes at WSU - Washington State University

2007 Postharvest Procedures
Early Harvest
Testing of clones in the early harvest Tri-State and Regional Trials involved French frying samples at
harvest only, following the same procedure as used in the late harvest trials. In addition to French
frying and chipping, culinary and quality characteristics of clones from the Red/Specialty Trial were
evaluated after oven-baking, microwaving and boiling. Four- to six-ounce tubers were selected for
the cooking protocols described below. After cooking, each tuber was halved from stem to bud end.
One half was immediately tasted and evaluated on a scale from 1 to 5 (5 is best) for texture, flavor,
tuber center, and skin characteristics. The remaining half was incubated for 30 minutes at room
temperature and after-cooking-darkening was then graded on a 1 to 5 scale based on a color chart
for white- and yellow-fleshed clones (1 = excessive graying, 5 = no discoloration).
Oven Baking - Tubers were pierced twice with a fork on each side and baked at 400°F for 1 hour.
Boiling - Tubers were cooked in a sieved double-boiler for 1 hour after coming to a boil.
Microwaving - Tubers were pierced twice with a fork on each side and cooked for 10 minutes at the
outer edge of a microwave oven (high setting). The tubers were then turned over and moved to the
center of the microwave where they were cooked an additional 10 minutes. Four-tuber samples from
each of two clones (eight tubers total) were cooked simultaneously.
Chipping - Tubers were cut longitudinally from stem to bud end. One half was used to make French
fries as described below. The other half was sliced into 0.05-inch thick chips. The first slice was
discarded to insure uniform thickness of the subsequent chips. The samples (12-tubers/clone) were
rinsed with water and fried in 375°F vegetable oil for 2 minutes. The chips were drained on paper
towels and chip color was graded using the Potato Chip/Snack Food Association (PC/SFA) color
chart (1 = light, 5 = dark).
Late Harvest
Testing of clones in the late harvest trials involved the following postharvest quality evaluations.
As soon as possible after harvest, tuber specific gravity and fry color (Photovolt readings) were
measured on 12 tubers from each clone. Clones designated as fresh processing were French fried
and Photovolt readings compared at harvest only. Additional tubers of each clone were placed in
storage at 40°, 44° and 48°F. Tubers stored at 48°F were evaluated for bruise potential, soft rot
susceptibility, consumer acceptance of French fries, and cooking time in October and November.
Reducing sugar content and French fry color were assessed in early December. The extent of
sprouting was recorded in late December. Tubers stored at 44°F were also evaluated for sugar
accumulation in December. Storage of tubers at 40°F until mid December was done to determine
the “cold-frying” potential of clones. Fry color and reducing sugar content were assessed in these
tubers but the results are not reflected in the final numerical rating for each clone (see below).
Statistical Analysis
Least significant difference (LSD) values are included in the tables to facilitate evaluation of
differences in fry color (Photovolt readings) and specific gravity among clones. Any two means
whose difference is greater than or equal to the LSD value are significantly different. LSD values
allow comparisons of the relative performance of any two clones for a particular characteristic, such
as fry color.
2007 Potato Cultivar Evaluations 6 WSU Potato Research Group