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CHICAGO – Kale has had quite a run.

Less than a decade ago, the leafy green vegetable was used primarily for decoration on salad bars. Now kale, known for its health benefits, is so ubiquitous that even ­McDonald's uses it in salads.

Za'atar, a Middle Eastern spice blend, may not be as familiar to many Americans, but it plays a starring role in one of the salads that Starbucks recently rolled out in Chicago as part of its new lunch menu. As Americans increasingly demand exotic flavors, spices like za'atar are expected to become more common on menus.

Identifying up-and-coming food trends is equal parts art and science, and it's a process that some in the food industry pay a lot of attention to.

"The Cronut went from nothing to Time magazine in no time; others peak and fall off," said Stacie Sopinka, vice president of innovation and product development at US Foods, a Rosemont, Ill.-based food distributor.

Food trends are influenced by a wide range of factors, from fashion and pop culture to health fads. They are sometimes created by chefs, often in the world of fine dining, and then mimicked and re-purposed by other restaurateurs. Sometimes, it's a consultant or distributor working with a big brand to develop a product that fills menu holes for a food company.

Menu trends

Datassential, one of several companies that track trends, calls that pattern the "menu adoption cycle."

Trends in the inception phase often start in fine-dining establishments and independent ethnic restaurants or markets, where the food item is considered unique in the way it's prepared, presented and tastes. Piri piri sauce, a spicy and tangy topping from Portugal, and togarashi, a Japanese spice blend, are in that phase now.

Both meet consumers' growing demand for exotic spices, according to ­Datassential.

The adoption phase is when mainstream restaurants catch on to the trend. Early adopters tend to be gastropubs, fast-casual and independent sit-down restaurants, and specialty or gourmet food stores. A restaurant like Rick Bayless' Xoco would jump on the bandwagon at this point, Datassential's Mike Kostyo said, but so would Panera, Whole Foods, and even the Cheesecake ­Factory.

In the proliferation phase, trends hit the mainstream and often are adjusted to have broad appeal. This means the up-and-coming ingredient is incorporated into burgers, pasta dishes and other menu items mainstream that America is likely to consume. ­Sriracha aioli, a spread that lowers the spice intensity of the Thai pepper sauce, is in the proliferation phase now. It's often served on sandwiches and with French fries.

In the final phase, a food trend can be seen across the industry. Brands like Denny's and Wal-Mart catch on, but so do convenience stores, schools and office cafeterias.

Food trends

Not all trends follow this common cycle. In fact, only about 30 to 40 percent of foods or ingredients in the inception phase ever continue on, according to Datassential. Consider bone marrow, a popular sight at some high-end restaurants, but not something that would ever make its way to a fast-food chain.

US Foods, which supplies restaurants with everything from produce to prepared meat, helps restaurants get on board with the latest food trends, with a special emphasis on the desires of millennials, the fastest growing segment of the U.S. population.

In 2011, the company rebranded, conducted extensive research and began positioning itself to better provide trendy ingredients to independent restaurants. That same year, it launched its own branded line of products, Sopinka said.

The items US Foods developed have to fill a lot of holes. The products have to be able to be used in multiple ways, be healthy but still flavorful, and in some cases, be fully cooked so that restaurants can save labor hours — a critical expense.

The company's offerings have evolved to include products ranging from riced cauliflower, which can be used in gluten-free pizza crust and sides and salads, to chicken shawarma that is fully cooked and ready to heat and serve.

"We don't need to be first. For us, it's a matter of figuring out which ones are going to stick," Sopinka said.

Kerry Ingredients and Flavours is also a major player in menu consultation and the translation of trends.

When a major quick-service chain like McDonald's wants to develop a new burger, Kerry, which has its North American headquarters in Beloit, Wis., pulls all the burger concepts developed industrywide over the last several years and examines everything from buns to toppings, looping in current trends, said Elissa Rempfer, Kerry's food service marketing research and insights manager. The resulting tests usually show up in fast-food restaurants as limited-time offers.

Because chains have huge footprints and need to appeal to a wide range of people, they aren't often early adopters of trends. To help chains get in the game, companies like Kerry often take a trend, like smoke flavoring, and mix it with something familiar, like mocha or vanilla, Rempfer said.

While an independent restaurant might try something bold like smoked ice cream, chains tend to opt for a more subdued interpretation. For example, Starbucks got in on the smoke trend with a Smoked Butterscotch Latte.

When trying to hook younger diners, many brands believe visual appeal tops all. Food, more than ever, has to be camera — or smartphone — ready.