Final answer:
The predominant flavor required for a spirit to be classified as Gin is that of juniper berries. This became commonplace after the development of distillation in Europe during the 15th century, which led to a variety of spirits including gin becoming popular.
Step-by-step explanation:
The spirit that must have a predominant flavor of juniper berries to be called Gin is well-known for its unique taste profile. The use of juniper gives gin its distinctive herbal and piney flavor.
Before the Middle Ages, Europeans primarily consumed beer and wine, but with the advent of distillation in the 15th century, the production and consumption of spirits like gin, vodka, and whisky became widespread.
Unlike the quoted longing for ginger beer, which is non-alcoholic, gin's flavor is derived from its alcoholic base and juniper berry flavoring.
The poem 'I taste a liquor never brewed' reflects a metaphorical intoxication by nature's beauty rather than a literal drink, whereas gin represents a physical application of distillation mastery from the times when such spirits became an integral part of European culture.