Just one in five Millennials have ever tasted a Big Mac, according to a memo from a McDonald’s top franchisee, in a measure of changing eating habits among young people.

Sales of the burgers have been flat at McDonald’s for the past couple of years, after sluggish growth in the years prior, according to the Wall Street Journal, which obtained the memo. The problem? Big Macs don’t taste good enough to compete with gourmet rivals that serve up better burgers in a fast, casual setting.

“The world isn’t waiting for another burger from McDonald’s,” one former senior McDonald’s executive told the Journal. “It’s waiting for a better burger from McDonald’s.”

It’s part of an industry-wide shift toward better-tasting, more nutritious, and more environmentally-friendly food, driven largely by the preferences of Millennials, who eat out more often than previous generations – an average of 3.4 times per week, as opposed to 2.8 times per week among non-Millennials, according to a report by the Boston Consulting Group. And as many young customers switch to fast-casual chains like Chipotle and Panera, traditional fast-food outlets are struggling to adapt.

Those young people are also paying more attention to how their food is produced. In 2015, The Christian Science Monitor's Cristina Maza noted that a string of food producers and restaurant chains, including Tyson Foods and McDonald’s, announced that they would stop using human antibiotics on their chickens, while Kellogg’s and Kraft Foods took steps to remove artificial preservatives and colors from their products:

Increased awareness about where food comes from and the nutritional value of ingredients has led many young people, like Mike Polans of Boulder, Colo., to adopt a different approach to eating from the way they grew up. “The biggest shift in my consumption habits happened when I stopped eating meat and became a 'pescatarian' for about seven years," says Mr. Polans, who runs his own food blog. "I became conscious about avoiding processed food and excess sugar. The way our parents were raised, there are so many sugared drinks. That was the biggest shift I made, cutting out excess junk.” Meanwhile, the sale of so-called superfoods has skyrocketed. Increased demand for the nutrient-dense kale drove the numbers of farms harvesting the leafy green up from 1,000 to 2,500, according to data from the US agricultural census.

McDonald’s, reports the Wall Street Journal, is trying to refashion itself by putting together a “sensory” panel of chefs, suppliers, and staff to rate the company’s core burgers against those served up by other chains. It’s also trying out using fresh beef instead of frozen, along with different cooking techniques and customized burgers.

But as Slate noted on Friday, McDonald’s faces a peculiar challenge in its attempts to make its food more Millennial-friendly: 70 percent of its business comes through the drive-through, which means it has about a 90-second time window to deliver whatever new burger variation the company devises.

Get the Monitor Stories you care about delivered to your inbox. By signing up, you agree to our Privacy Policy

It’s likely to turn to Millennial employees for help. In July, the Monitor's Ben Rosen reported that McDonald’s would relocate its headquarters from the suburb of Oak Brook, Ill. to downtown Chicago, in a bid to attract young people as both employees and customers.

“As McDonald's has attempted to redefine itself by becoming appetizing to Millennials,” it wrote then, “Mr. Easterbrook's statement indicates the fast-food chain believes it must hire young, innovative employees to do just that.”