In Marcia Pelchat’s family, every festive meal begins with chicken soup. And her grandmother’s sweet-and-sour meatballs.

"We always have chicken soup, even on Thanksgiving, then we have sweet-and-sour meatballs," says the sensory scientist at Philadelphia’s Monell Chemical Senses Center. "Who knows why. We just learned that they go with Thanksgiving."

Big holiday meals can be a hodgepodge of unrelated flavors, textures and sensations. The challenge for the host — especially at Thanksgiving, when the sheer volume of food is compounded by deeply held family traditions — is to tie it all together.

So how do you create harmony among otherwise dissonant dishes? The pros suggest threading a single flavor, say sage or citrus, throughout the meal.

"This technique orchestrates the meal," says Lisa Yockelson, author of "Baking Style," whose recipes build flavor by using the same ingredient in many forms, for instance, almond paste, almond meal and almond extract together. "The dinner becomes a delicious composite, rather than having to adjust your palate to too many different elements."

A single, unifying flavor can end the confusion. But it also presents perils. Pelchat says that unlike the process of "sensory adaptation" — where you become accustomed to an aroma, say dinner cooking — humans actually perceive a flavor or aroma more acutely when attention is drawn to it.

"It’s like a melody repeating throughout a symphony," she says. Which means the melody can clobber the diner over the head if it’s repeated too often.

"Rather than being an easy thing to do, it’s quite demanding," says Niki Segnit, author of "The Flavor Thesaurus," which arranges 99 ingredients into 1,000 flavor pairings. "You have to be sure you have the knowledge to express the flavor in different ways so your eater doesn’t feel like they’re eating the same thing over and over again. … It comes down to taking the ingredients and refracting the flavors in different ways."

Professional chefs do this all the time; in fact, it’s a bit of a hat trick. For instance, ginger might be sauteed in a stir-fry, as well as presented pickled, as a condiment.

None of this means you have to ditch the meatballs. While some items go together as a matter of science — for instance, the salt in cheese revealing the sweet-tart components in wine, says Pelchat — others simply pair because of culture. Segnit mentions chocolate and eggplant, a common duo in southern Italy. In ethnically diverse places, such as Hawaii, turkey and sweet potatoes often are accompanied by sushi and Spam.

"I don’t think it’s unusual at all for Chinese families to have dumplings, or an Italian family to have pasta," Pelchat says. "Family traditions die hard. If you skip something they’ll be upset."