In late spring on the Greek island of Samos, the gnarly vines claw their way out of the sun-scorched, stony soil on Mount Ambelos. Their branches, twisted, low-lying, and braced against sea-salt winds, hold up precious clusters of small, gold-green muscat grapes that have made this tiny isle in the North Aegean—just 27 miles long and 8 miles wide—a world-famous wine producer. Floral, honeyed, and with a delicious perfume, they are used to make some of the finest dessert wines in the world, but the best of them become a key ingredient in one of Greece’s most celebrated products: Metaxa….