[...] China's biggest restaurant operator with 4,600 outlets, KFC is pursuing Chinese consumers so avidly it opens two more every day. The chain, based in Louisville, Ky., is reeling after a Chinese supplier was accused of selling expired beef and chicken to it, McDonald's and possibly other restaurant chains. Global fast food chains are rushing to expand in China but even experienced operators face costly pitfalls in a fast-changing food supply industry plagued by repeated safety scandals. Breakneck growth has strained the ability of companies to monitor thousands of farmers and meat processors, many of them small and remote, with incentives to cut corners, according to people who follow the industry.