Costco is the largest wine retailer in the United States. That fact surprises most people the first time they hear it — because most people think of Costco primarily as a place for bulk paper towels and rotisserie chicken, not as a serious beverage destination. But the numbers are real: Costco sells more wine by volume than any other single retailer in America, and its Kirkland Signature spirits have generated a cult following among consumers who have discovered that the ware