Colder waters encourage these prized bivalves to conserve their energy, becoming sweeter, plumper, and wonderfully firm. Their clean, briny flavor is particularly welcome at the holiday table, offering a refreshing contrast to rich roasts, indulgent dressings, and the generous pours of champagne that accompany the festivities. Passed among guests or served freshly shucked on a bed of ice, oysters have long held a place among the pleasures of holiday entertaining.