New Zealand company Fonterra, the world's largest dairy exporter, has been criticised for how it handled the China tainted milk scandal.

Fonterra owns a 43 per cent stake in Chinese firm San Lu, one of several companies that sold dairy products tainted with the industrial chemical melamine.

Al Jazeera's Tony Birtley discovers that farmers' anger over Fonterra's perceived slowness to reveal the extent of the problem is now threatening further business ventures in China.