Basic distillation techniques were known in the early CE. During the high Middle Ages techniques improved and experimenters distilled many liquids. They thought of themselves as distilling the essence or spirit out of their raw materials, hence the term 'spirits'. The experimenters drank the results, and soon a consensus emerged that spirits of wine were highly satisfactory, and good belt of them at breakfast brightened up the day. Some experimenters thought they had discovered the elixir of life, hence eau de vie. See E J Holmyard's Alchemy