Sake is gaining popularity around the world. Exports of the traditional Japanese rice wine have almost tripled since 2010. But the boom in the past decade has a catch: There's a minimum production quota for breweries. So it's been difficult for smaller firms to get into the industry. But things changed in April, when the government lifted the rule on production for exports. That opened the window to the global market - for minor players, too. The secret to success lies not just in tradition but a healthy splash of innovation.