Alcohol is an alchemical consumable in The Witcher 3: Wild Hunt.
In order to craft most Potions and Alchemy-related items, Geralt will need to acquire Alcohol. Alcohol comes in many forms and from various sources. It can be brewed directly from Plants found in the enviroment, looted from dead creatures or bought in the form of drinks.
As soon as the required Alcohol is at hand Geralt can use a Recipe and the rest of the related ingredients to craft the item in question. After a Potion's initial creation is does not need to be re-crafted. It can be refilled using Alcohol during Meditation.