China is going nuts for California. At least that's according to some of the weird and wonderful food facts that will be on display at this week's Hong Kong Food Expo 2013. Apparently, California's biggest food export to China is the pistachio nut - with 35 per cent of its harvest exported to the mainland. And China has become the pistachio industry's fastest-growing export market, boosting its purchase of American pistachios from US$5 million (HK$38.7 million) in 2004 to US$109 million a year. The pistachio is known as the "happy nut" in China because its cracked shell looks like a smile, and because it tastes so good. The demand for pistachios from California peaks during Lunar New Year. They are also a traditional feature at other Chinese festivals when extended families get together and pistachios are exchanged as gifts and served as a holiday snack. Interest in US-grown pistachios accelerated two years ago when China's traditional supplier Iran suffered a drought and a cold spell which damaged the crop. US suppliers filled the gap, and Chinese consumers were hooked. As the Chinese market also learns about food safety and quality, they are appreciating the California pistachio versus the bleached shell from other markets. California pistachio shells are not bleached and a clean shell means quality. Overall Californian agricultural exports to Hong Kong, which exceeded US$1 billion in value in 2012, have enjoyed double-digit rates of growth since 2008, and increased 32 per cent in the last year alone. "Food and agricultural products are California's third largest export to Hong Kong, totalling more than US$1.5 billion in value," said Jeff Williamson, director of the California State Trade and Export Promotion programme. The Food Expo opens at the Convention Centre on Thursday and ends the following Monday.