Aqua Vitae was made by fermenting grain mash or grape wine with yeast to produce a dilute alcoholic liquid, then distilling that liquid in an alembic to concentrate the more volatile alcohol and separate it from water and other components, a technique that spread through medieval Europe from earlier distillation traditions and became closely associated with monastic and university medical schools by the thirteenth century. Early distillers recognized quickly that a single distillation gave a relatively weak spirit and that repeated distillation, called rectification, raised the alcohol's strength and purity further, up to the practical limit imposed by the fact that a water-ethanol mixture cannot be distilled to complete purity by ordinary heating alone, a limitation only explained by modern azeotrope chemistry centuries later. The resulting spirit burned with a visible flame when ignited, a property that gave it the alternate name aqua ardens, burning water, and that was taken as visible proof of its fiery, vital nature.
Physicians of the period, working within a medical tradition that valued warming, vitalizing remedies, prescribed aqua vitae as a tonic, a preservative for other medicines, and a treatment for a wide range of complaints understood as arising from cold or weak vital spirits, a therapeutic reputation that outlasted the specific medical theory behind it and that helped establish distilled spirits as a permanent part of European pharmacy and, soon after, of ordinary drinking culture.