PepsiCo chairman and CEO Indra Nooyi has taken a 10-day "immersion" tour of China as part of her mission to improve the company's presence in emerging markets. What she saw, Gordon Fairclough and Valerie Bauerlein report, convinced her that Pepsi's current efforts, while good enough, have to expand to a "vastly different" model. China is PepsiCo's second-largest beverage market after the U.S. and one of its fastest-growing snack food markets. But figuring out how to effectively reach its diverging generations is a central challenge, Fairclough and Bauerlein write. Older people grew up without packaged goods and prefer local markets and …