Grading
Once the onions are harvested, they are hand-graded by humans into U.S. #1, U.S. #1 Export or U.S. #2 commercial grade quality.
The USDA says a U.S. #1-Grade consists of onions of similar varietal characteristics which are mature, fairly firm; free from soft rot of wet breakdown, sprouts, bottlenecks, scallions, and cull material. The onions shall also be free from damage caused by seedstems, sunscald, sunburn, roots, moisture, freezing, mold or other disease, insects, mechanical or other means.
For more information on the USDA’s Agricultural Marketing Service’s Grades of Onions and Marketing Standards, visit their Onion Grading and Standards Page.