UGA experts delve into the science behind Vidalia onions.
By Rebecca McCarthy/Photos by Andrew Davis Tucker
It's a good thing Daniel Jackson likes onions, because during the harvest season for Vidalias he can't get away from them. Once a week for five or six weeks, he travels to South Georgia and brings a carload of onions back to the Crop & Environmental Quality Lab in Athens for testing. The aroma of 2,000 pounds of onions, even mild Vidalias, could be overwhelming, but Jackson doesn't notice.
He's focused on getting back to his facility, one of three labs within the UGA Agricultural and Environmental Services Laboratories. The lab tests the quality of numerous crops, but during May and June, onions dominate. The Georgia Department of Agriculture and about 100 Vidalia growers help fund the lab, in its third year of operation, and they're counting on Jackson and his technicians to provide them with guidance on how to grow a better onion. With Vidalias representing a multimillion-dollar market, Georgia farmers want to continue growing onions that consistently out-perform challengers including Texas Sweets and Walla Walla Sweets-gently dismissed by Vidalia enthusiasts as adequate but not great. And certainly not as sweet.
A one-story building on College Station Road houses the lab, where three technicians-UGA students Alex Debese, Caleb Stephenson and Adam Gresham-spend their days prepping and sampling onions. The onions come from test plots at the UGA Vidalia Onion and Vegetable Research Center, in Toombs County, as well as individual Vidalia growers and seed companies. Growers want to learn best practices for producing onions, while plant breeders and seed companies want to know which varieties are sweetest.
In a small room the size of a galley kitchen, the three young men process 300 pounds of onions a day, five days a week. They test about 10 onions from each bag. After cutting the ends off, they crush a core sample from each onion in a special hydraulic press, squeezing the juice into a test tube with chemicals. They work quickly because some volatile compounds in Vidalia juice can break down rapidly, Jackson says.
"The smell of the onions bothered me at first, but now I don't even notice it," Debese says. "You get used to it. I gave my mother a bag of Vidalias for Mother's Day."
On the other side of the building, high-tech equipment provides a detailed analysis. The spectrophotometer tells the level of pyruvic acid, which indicates pungency. The HPLC machine measures the glucose, fructose and sucrose molecules that give the onion its sweetness.
The gas chromatography machine assesses the lachrymatory factor-what causes some people to cry when an onion is cut. A second gas chromatography machine measures methyl thiosulfinates, the compound that coats the tongue and causes "onion breath." Onions with high levels of lachrymatory factor and methyl thiosulfinate are hot, while sweet onions like the Vidalia have low concentrations of these intense flavor compounds.
Those who work with Vidalias love to tell how the beloved allium came to be: by chance. In 1931, with cotton played out and soils depleted, Toombs County resident and UGA alumnus Moses Coleman, like other farmers, planted vegetables. He harvested onions that were-surprise!-sweet instead of pungent. Initially, consumers were skeptical, but Coleman persisted and soon his 50-pound bags of onions, priced at only $3.50 a bag, began to sell. Other farmers followed, and the onions were stocked at a Piggly Wiggly grocery store in Vidalia. Gradually they became a springtime staple, gracing the tables and grills of Georgians in May and June.
Despite technological advancements, growing the sweet onions remains labor intensive. The majority are both planted and harvested by hand, as well as graded and loaded, says Cliff Riner, coordinator of the UGA Vidalia Onion and Vegetable Research Center.
Over the past 20 years, controlled atmosphere storage facilities have allowed growers to continue selling into the fall, with as many as 125 million pounds of onions going into storage. The longer selling season means an industry worth about $120 million annually.
"Even with 12,000 acres [planted], some years we just run out of onions," Riner says. "We own the market for major summertime holidays — Mother's Day, Memorial Day, Fourth of July and Labor Day. And the nicer the weather, the more onions people eat because they're grilling out."
While a machine can do a good job of determining whether onions have a high sugar or sulfur content, Daniel Jackson believes there's no substitute for the human taste bud. The Crop & Environmental Quality Lab is involved in a two-year study correlating tasters' preferences with lab results.
In 2014, the test was conducted at the U.S. Department of Agriculture facilities in Athens, where a dozen people learned "how to eat an onion," Jackson says. "They had to be able to taste the subtle flavors and identify the compounds."
For 14 days the testers nibbled pieces of Vidalias, grown at the UGA Vidalia Onion and Vegetable Research Center, to help researchers determine what they could taste, Jackson says. What they found was that the test panel could determine only whether an onion was hot and whether it could make them cry. They didn't taste the sugar content.
This spring, the onion tasting took place on UGA's Griffin campus. Over four weeks, 146 participants ate pieces of three Vidalia onions and filled out a survey about which one they liked best and which one was the sweetest.
The objectives of the tests were different, according to Jackson. The first year, the research team wanted to learn if people really can taste the compounds being measured in the lab. For example, if an onion has a high glucose reading, can a consumer taste the high sugar content? Well, no. Jackson found that "people aren't able to taste sugars because other compounds are overpowering them," he says. "So, it's what you don't taste that makes the onions sweet, not what you do taste."
This year, the taste panel is trying to determine at what point a sweet onion is no longer sweet, a determination that "could have an enormous impact on this industry and on sweet onions everywhere," Jackson says.
There are only so many varieties of onions-currently 26-that growers are permitted to raise and label as Vidalias, Cliff Riner says.
Unlike other crops in Georgia, the raising and distributing of Vidalias is governed by a federal marketing order that subjects growers to various rules and regulations. Since 1989, the name Vidalia has been trademarked, and the area where onions can be labeled as such has been restricted to counties in southeast Georgia circling out from Toombs and Tattnall counties, where 90 percent of Vidalias are grown.
The 20 Vidalia-growing counties-sometimes just slivers of a county-have sandy, loamy soil with low sulfur content plus mild winter weather, making them ideal for growing sweet onions, says Bob Stafford of the Vidalia Business Council. Sometimes called the Vidalia Onion Sheriff, Stafford makes sure growers comply with all the rules involving packaging and accountability associated with the Vidalia trademark.
Susan Waters serves as executive director of the Vidalia Onion Committee, a government-sanctioned regulatory panel in charge of researching and marketing the onions.
"We want good, hard evidence when we say our Vidalias are sweet," she says. "We want data."
The committee has given more than $1 million in research grants and support to the UGA Vidalia Onion and Vegetable Research Center since it opened in 1999. Waters promotes and markets the squatty, disc-shaped onions around the country, and happily says that today more people can distinguish Vidalias from yellow, Spanish, white or red onions.
For years, private seed companies have been testing Vidalia varieties for their sugar content, hotness and lingering onion-y flavor, Stafford says. Vidalia onion growers and the Georgia Department of Agriculture turned to the university for help in analyzing their products because they wanted "an unbiased third party to do impartial testing."
"And it's really working for us," he says, "because we're putting out better varieties."
— This article originally appeared in the September 2015 issue of Georgia Magazine