What's fresh at McDonald's? The beef in some burgers

McDonald's is offering fresh beef rather than frozen patties in some burgers at thousands of restaurants, a switch it first announced about a year ago as it works to appeal to customers who want fresher foods.

The fast-food giant, which has relied on frozen beef patties since the 1970s, said it's launching Quarter Pounders made with fresh beef in about 3,500 restaurants starting Tuesday. It'll be available in eight cities, including Atlanta, Miami and Salt Lake City, then roll out to most U.S. McDonald's by May.

McDonald's says workers will cook up the fresh beef on a grill when the Quarter Pounder and "Signature Crafted" burgers are ordered. The change is the latest by the Oak Brook, Illinois-based company to improve its image as more people shun processed foods.

A spokesperson for the Canadian operations of McDonald's told CBC News there were no current plans to introduce fresh beef in Canada.