McDonald’s (NYSE:MCD) has announced that beginning next year, its Quarter Pounder will contain fresh beef patties, making the switch after several decades of using frozen meat. The switch applies only to the Quarter Pounder and the chain’s new Signature Crafted Recipe burgers right now. McDonald’s other burgers, including the Big Mac, will still use frozen beef patties.

The switch to fresh meat is being called the chain’s “most drastic menu change in decades.” The announcement comes after a year of pilot tests at 325 locations in the Dallas/Fort Worth area and in 77 restaurants in Tulsa, Okla. The move is expected to be rolled out nationwide by mid-2018.

Several McDonald’s franchisees that participated in the trials expressed concerns about the switch increasing the risk of foodborne illness. For safety reasons, fresh beef cannot contain even trace amounts of E. coli when it leaves the manufacturing facility and at no point can the worker leave it unrefrigerated. The bacteria multiply rapidly at room temperature. As a response to a survey from investment firm Nomura, one franchisee wrote, “If we do not handle the meat perfectly there is the opportunity for bacterial invasion of our product.”

Food safety has been a priority for the industry since 1993. That year, Jack in the Box had an E. coli outbreak in their burgers that killed six children and hospitalized more than 170. The tragedy sparked a national outcry and resulted in a number of lawsuits against the company.

Chain restaurants and the beef industry have made tremendous gains since then when it comes to food safety. Today, E. coli contamination in restaurant-served beef is relatively rare and the risk of people actually getting sick from the bacteria growth is very small.

This is just the latest move by McDonald’s to improve quality and increase customer satisfaction. McDonald’s CEO Steve Easterbrook said in a statement, “Over the past two years, we’ve made a series of bold, tangible changes for our customers. We are committed to transforming more aspects of our business, including offering a more modern and enjoyable dining experience, adding new levels of convenience and technology, and making more positive changes to the food we serve.”

In 2015, McDonald’s introduced All-Day Breakfast to the delight of many of its customers. This year, McDonald’s introduced new sizes of its iconic Big Mac sandwich and has tested Big Macs made with Sriracha sauce. The company also removed artificial preservatives from several of its menu items last year. The company is also rolling out a mobile order and pay app, with curbside service, in the U.S. this year and planning to bring its kiosk-centered “Experience of the Future” concept into most restaurants over the next few years.