LOUISVILLE, KENTUCKY – Japan is high on American whiskey, and Kentucky’s bourbon distillers are racing to the country, hoping to sell consumers on the merits of the iconic, corn-sweetened U.S. spirit. Greg Davis, master distiller at high-end bourbon producer Maker’s Mark Distillery Inc., a subsidiary of Beam Inc., embarked in May on his first trip to Japan, thirsty for a taste of its burgeoning whiskey market. U.S. whiskey exports to Japan have always been strong, but they recently entered a period of explosive growth, fueled by demand for the highball, a mix of whiskey and soda served over ice. In...