Is that watermelon ripe for the picking?

Picking a perfect watermelon is an inexact science.

“You don’t really know until you bring it home and cut it open,” says Eric DeMange, who has about 25 acres of watermelon growing on his family’s farms in Southern Illinois. He expects to start harvesting melons this week.

How does he decide when the time is ripe to pick them?

For his first test, he uses a criterion well-known among watermelon lovers. “When you pick them up, they have a nice yellow area on their bellies,” DeMange says.

Then he performs a less orthodox test.

“I run my hand across the melon perpendicular to the stripes,” he says. “It should have a little ridge that you can just barely feel.”

Once the melon gets to market, he adds, people have their own tests.

“They thump and do all kinds of things,” DeMange says.

For the “thump test,” one commonly cited standard is that the thump should result in a sound similar to hitting a jug of water.

Then there’s the belief that seedless watermelons are less sweet than seeded varieties.

Not so, says Stephanie Simek, a spokeswoman for the National Watermelon Promotion Board, which says that 86 percent of watermelons sold in the U.S. are seedless.

Seedless and seeded watermelons “have the exact same nutrient profile,” Simek says. “And they’re both subject to the same minimum Brix level (a measure of sweetness) if they’re sold to the consumer.”

That, however, is only a minimum level — 8 degrees, as measured on the Brix scale. Most consumers, Simek says, are used to watermelon sweetness corresponding to 11 to 12 degrees Brix.

Numerous academic studies confirm that sweetness is less about seeds and more about variety of melon. A taste test conducted by Purdue University found that the Brix level for five varieties of seeded watermelons ranged from 11.6 to 12.1 degrees, while 16 seedless varieties ranged from 11.3 to 12.8 degrees. A joint study by the University of Missouri and Lincoln University found Brix levels in 15 seedless watermelons ranging from 11.5 degrees to more than 18 degrees.

Unfortunately for consumers, watermelons are rarely marketed by variety, and heritage and heirloom varieties are, by their nature, not widely available. So if you’re confused about how to choose the best watermelon, you’re not alone. Your best bet might be to shop at farmers markets and farm stands, where the grower is often there and will cut open samples of the day’s crop.

Blackened Watermelon Salad

Yield: 4 servings

Recipes by executive chef Trent Thrun of Steven Becker Fine Dining, which owns Nadoz restaurants

1/2 cup balsamic vinegar

About 4 pounds watermelon, peel on

1 tablespoon plus 1 teaspoon blackened seasoning mix

About 1 tablespoon olive oil

6 cups mixed salad greens

1/4 cup spiced or sweetened pecans, roughly chopped

2 tablespoons crumbled feta cheese

2 cups (about 4 ounces) sugar snap peas, blanched if desired

1/4 cup Watermelon Vinaigrette or to taste

Bring balsamic vinegar to a boil in a small pan over medium-high heat. Reduce heat to medium-low and cook until liquid has reduced to about 2 tablespoons. Remove from heat.

Meanwhile, cut the watermelon into 12 2-inch squares 3/4 of an inch thick. Discard the rind and reserve any excess flesh for Watermelon Vinaigrette. Dust one face of each square with blackened seasoning mix. Set squares, dusted side up, on a sheet pan lined with parchment.

Coat the bottom of a large, flat-bottom saute pan with oil. Heat over high heat until pan is very hot. Working in batches, place watermelon squares, seasoned side down, in the pan and cook for about 20 seconds without moving them. The seasoned face should have an almost-black color when removed; if not, return to the heat for a few seconds. Remove carefully; avoid crushing the watermelon if using tongs. Return to tray, seasoned side up, and let cool.

Drizzle balsamic reduction evenly among four serving plates or bowls, Place watermelon, blackened side up, on balsamic reduction. In a mixing bowl, combine greens, pecans, feta and peas; toss lightly with about 1/4 cup Watermelon Vinaigrette. Arrange the mixed greens alongside the watermelon and serve.

Note: Store-bought seasoning can be used, but be sure to get a product labeled blackened or blackening seasoning as opposed to Cajun seasoning. To make the seasoning from scratch, chef Trent Thrun mixes 1 cup paprika with 2 tablespoons kosher salt, 1 tablespoon each of garlic powder, onion powder, dried mustard and dried oregano, and 1 teaspoon each of ground red (cayenne) pepper and freshly ground black pepper.

Per serving (without vinaigrette): 235 calories; 10g fat; 2g saturated fat; 5mg cholesterol; 5g protein; 32g carbohydrate; 23g sugar; 5g fiber; 290mg sodium; 70mg calcium.

Watermelon Vinaigrette

Yield: about 1 1/4 cups

1 cup peeled and seeded watermelon

1/4 cup apple cider vinegar

1 tablespoon honey

Kosher or sea salt

3/4 cup olive oil

Freshly ground black pepper

Place watermelon, vinegar, honey and salt and pepper to taste in a blender; blend until smooth.

Slowly pour in olive oil through the hole in the cap, blending until emulsified. Check seasonings and adjust if necessary. If not using immediately, stir or shake in a container to recombine.

Per tablespoon: 80 calories; 8g fat; 1g saturated fat; no cholesterol; no protein; 2g carbohydrate; 1g sugar; no fiber; no sodium; no calcium.