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.
But choice of base alone doesn’t mean that you’ll be able to taste it. Depending on choices the distiller makes, such as how many times the base is distilled, or to what strength it is distilled to— there might be no character at all coming from the base spirit.
Gin is rather unique among spirit categories. While many spirits are defined by the type of distillate— for gin this is not true. Gin can have any base spirit, and as long juniper is predominant. It’s gin.
When you hear the word “barley” you’re likely to also here the word “malt.” That’s because barley and other grains aren’t ready for distillation right of the plant. Malted Barley is barley that has been soaked in water until the point of germination. The that germination is halted with heat. [Malting is fascinating and worthy of articles unto themselves]
Single Malt whiskeys in Europe are entirely distilled from malted barley. Malted Barley is also a critical component of many genevers.
Some grains require barley’s malting prowess to get started, such as rye and corn. Therefore, even some base spirits which are not a barley base may have had incidental encounters with barley.
Barley Base has an incredibly distinctive flavor on its own. Some people describe barley as having a “funky aroma” when residual character is present. But it’s far more complex. A good barley base has nutty cereal, porridge and bran notes to it but also has a dark earthy complexity to it— you might get notes of grilled mushroom or toasted cocoa nibs. Barley can be a very fascinating base, especially when used for its character and designed around it.