Savory melon combinations have gone mainstream – even Au Bon Pain has a watermelon and feta cheese salad this summer – and it’s easy to make your own melon-based meals at home. But selecting a ripe melon can be a daunting task: It’s hard to tell what’s going on under that thick skin. I asked some experts for advice on how to pick them.

Katy Sparks, the executive chef at Balducci’s, says that a melon should feel heavy and dense; that means that the sweetness has developed inside. “Check for aroma by smelling the blossom end [the indentation that indicates where the stem used to be]. It should smell sweet,” she said. If there’s a musty smell, it might be a little overripe. When choosing cantaloupe, the color under the ribbing between the sections should be tan instead of green.

“Melons don’t get sweeter after they are picked, so they won’t get better like a peach or nectarine will,” says the regional produce buyer for Whole Foods, Richard Thorpe. So you want to be careful when you select them.

For watermelon, Mr. Thorpe recommends the thunk test: “Select a melon that has a reverberating thunk when you knock on it. If it doesn’t thunk or sounds like a solid piece of wood when you knock on it, then it isn’t ripe.” Sometimes a darker color green on the outside is also preferable.

Does size matter? Not really. Though we are used to seeing huge, heavy watermelons, and cantaloupes that fit in the palm of your hand, at Vanhouten’s Farm at the Union Square Greenmarket, small, spherical watermelons are about the same size as the generously round cantaloupes, and sell for about the same price (fresh Pennsylvanian watermelons are $4.50; cantaloupes, $4).