Onions that are promoted as “sweet enough to eat like an apple” are cultivated widely in the United States: primarily in Hawaii, Washington, California, Texas, Arizona, New Mexico, and Georgia. Add Chile, Peru, Nicaragua, Guatemala, and Mexico (and controlled atmosphere storage) to the domestic production and what was once a regional, seasonal specialty is now a year-round crop.
Whatever they are (an explanation follows), these are not onions that contain more sugar than common ones—and only a marketing maniac would eat them like apples. According to William Randle, an onion flavor researcher at the University of Georgia in Athens, “there are no standards that describe ‘sweet onions,’ but there are measurements—chemical tests correlated to sensory taste tests from an objective panel.” Sugar content is not the key. “A typical storage onion is in the 12 percent range of brix [the measure of sugars],” Randle explains, “while the Vidalia and others of the type are about 8 percent. It is mildness, the lack of heat and mouth burn [measured by an analysis of pyruvic acid], that best characterizes the onions.” He believes that they should be called mild, not sweet. “As the heat decreases, there is a chance to taste existing sugars. The heat of standard storage onions overrides the sugar.”