What's the next big food trend? If you ask Jeff Miller, Dunkin' Brands' (DNKN) executive chef since June, it's fermentation. "They're starting to teach it in culinary schools—classes on fermentation and how it affects food," he says of the genre that includes pickles, beer, cider, and even yogurt. "We watch trends and see how they move from fine dining to casual dining and then to fast food."

Miller isn't alone in picking up on pickling. Fermentation was called a "hot culinary trend" by NPR. And it offers some health benefits. But if Dunkin's top chef talks it up, might that signal the coming of a pickled doughnut?

The chain has in fact already tried a kimchi doughnut in Korea and a yogurt-filled variety in Greece. "We get pretty adventurous with doughnuts," Miller says. "I don't know that you'll see a kimchi doughnut [in the U.S.], but you never know. We try a lot of things in the lab."

The more likely and far less daring application for pickling at the doughnut chain: sandwiches. That food category has become a heavy Dunkin' focus these days, and Miller admits "it might be the most apt way to bring it into our menu."

Dunkin's sandwich sales have grown by double-digit percentages in the past few years, the company reported at a recent investor event. Food is now roughly 16 percent of sales, with bakery products making up 23 percent and beverage 57 percent. Dunkin' Donuts is working on redesigning restaurant kitchens to have quicker sandwich stations as it plans to further develop this part of the menu. With or without the pickles.