As well as adding botanicals directly into the still with neutral spirit, distillers can also add flavour (and colour) to a gin through infusion. Depending on the infusion method used, this can add a delicate or punchier flavour to the spirit.
Vapour infusion, used by distilleries including Bombay Sapphire and Sacred Spirits, sees a basket of botanicals placed in the head of the still. As ethanol vapours evaporate and rise up the still during distillation, they pass through the basket and pick up congeners (flavours) from the botanicals inside it. This is a useful way to add more delicate flavours, including from botanicals that would be adversely affected if they were heated in the still.
Infusion can also happen after distillation. If you make your own flavoured gins at home by adding fruits, teas or herbs to a distilled gin and leaving it to rest, this is a method of infusion! It also happens at professional distilleries, for example Bullards in Norfolk: its Strawberry and Black Pepper Gin is produced by infusing distilled gin with fresh strawberries. It’s also a common method for sloe gin production. This kind of post-distillation infusion tends to lead to a stronger flavour in the final product, particularly if you’re infusing with fresh ingredients.
Infusing can also add colour – and is sometimes used primarily for this purpose. To achieve its blueish hue, Sharish Blue Magic Gin from Portugal is infused with butterfly pea flower before bottling.