The base spirit of a gin refers to the distillate to which botanicals were added. It’s helpful to think about the base spirit as a vodka-like spirit that the distiller used as a starting point— a blank canvas upon which the gin was designed.
Often times a gin will have the words “distilled from grain” on the bottle. In many cases this means that the base is distilled from multiple grains. The blends often include some combination of barley, rye, or wheat.
Gin distillers are not required to go into detail on their gin bottles. Therefore, sometimes that a gin was made with a grain base is all that we might now about.
Historically, the use of grain for gin is often seen by spirits historians as a major moment in the evolution of gin. In the 16th and 17th centuries, spirits distilled from a grape base— sometimes called burnt wines— would have been designated as brandies. The evolution of genever truly began when distillers in the low countries began using grain surpluses and grain deemed unacceptable by bakers to make spirits.