Inside a 19th century silk merchant's house in Katsunuma, Yamanashi Prefecture, the three Aruga brothers are pouring several white wines in their timbered tasting room. All are made at their Katsunuma Jyozo Winery Co. under the Aruga Branca label from Japan's unique grape variety, Koshu, and all are delicious: One is elegant and sparkling; another fresh, bright and lemony; a third succulent and tangy; still another savory and smoky; and a fifth barrel-fermented version is round, rich and smooth.