This image provided by McDonald’s Corporation shows a Quarter Pounder burger. McDonald's says it will swap frozen beef patties for fresh ones in its Quarter Pounder burgers by sometime in 2018 at most of its US locations. Employees will cook up the never-frozen beef on a grill when ordered. Courtesy of McDonald’s Corporation via AP
INTERNATIONAL - Following years of reformulating at McDonald's, most of the burgers it serves in the U.S. are now preservative-free.

As of Wednesday, the world's largest burger chain says classics like the Big Mac and Quarter Pounder with Cheese are preservative-free, with reformulated buns and sauces. 

Pickles on the sandwiches still contain artificial preservatives, but customers can request sandwiches without pickles.

McDonald's has been gradually removing preservatives from its menu for several years in an effort to appeal to more health-conscious buyers. 

In 2016, it removed high-fructose corn syrup from its buns and took artificial preservatives out of its Chicken McNuggets.

FILE - In this Saturday, Oct. 10, 2015, file photo, the sun sets behind a McDonald's in Ebensburg, Pa. A 94-year-old McDonald's worker in Evansville, Indiana, was honored for 44 years at the company on March 23, 2017. (AP Photo/Gene J. Puskar, File)
The Chicago-based company says around one-third of its sandwiches still have artificial colors , flavors or preservatives, including Egg McMuffins and Filet-O-Fish. 

It hasn't set a timeline for removing those ingredients.