Experimental Grading Line for Washing, Sizing, and Sorting Sweet Potatoes Before Storage

An experimental grading line capable of washing, sizing, and sorting sweetpotatoes before storage was assembled in 1972 and tested in a continuing effort to develop a system that will harvest in bulk and therefore simplify and speed up harvesting, provide an opportunity to sort clean roots under good working conditions, and permit sizing of roots mechanically instead of visually by workers. Field-graded roots were run over the grading line seven times and field-run roots one time at approximately weekly intervals through the harvest season. Washing with water under high pressure adequately cleaned the roots in the absence of brushes, which usually cause injury. In all runs, removal of jumbos, canners, and No. 2's increased the percentage of No. 1's considerably. After grading, not less than 87 percent of the roots met No. 1 grade specifications, and gains in storage space were 17 to 36 percent for field-graded roots and 45 percent for field-run roots. Under good curing conditions and after washing, sizing, and sorting, roots lost about the same amount of weight and were about as free of decay as roots placed directly under curing conditions. When curing conditions were bad, roots washed, sized, and sorted did not keep as well as untreated roots and were in poor condition after storage. Treating roots with hot water (125° F for 2 1/2 minutes) was slightly detrimental to roots and was not necessary because black rot was not present. Chlorine in the dump washer (75 to 100 parts per million) or in the hot-water tank (30 to 50 parts per million) reduced losses from decay in two of three tests in which untreated roots did not keep well. In supplementary tests, the amount of root injury incurred on the experimental grading line was compared with that caused by a conventional grading line, and results showed that the experimental grading line caused less injury. Other test results showed that curing roots immediately after washing, sizing, and sorting for 4 days at 85° F kept weight losses reasonably low. A subjective evaluation of an entirely new grading line, built in 1973 for commercial operation, is also presented in this publication.