Distillation is a physical separation process performed by the heating a liquid to make it a vapor, following by condensing the vapor back in a more concentrated liquid. Among things made by the process of distillation is the creation of charcoal, as well as the manufacturing of narcotics and alcohol.
Rojan referred to the compact shape that came as a result of transforming a Human's flesh, brain, and personality into "the essence of what they were," by a process he described as distillation. (TOS: "By Any Other Name")
The Brekkians manufactured felicium through the process of distillation. Their improvement in the distillation process allowed them to make a 0.01 milliliter dosage pill where the same dosage years before would have filled five Galaxy-class cargo bays. (TNG: "Symbiosis")
According to Doctor Katherine Pulaski, the treatment for a flu virus that was acquired at Nasreldine was a tryptophan-lysine distillate, with a generous dose of Pulaski's chicken soup. (TNG: "The Icarus Factor")
In 2366, the Ferengi Doctor Arridor distilled DaiMon Goss's blood pyrocytes in a ploy to acquire the Barzan Wormhole by means of eliminating some of their competition, namely Federation negotiator Seth Mendoza. Though harmless to Goss, and undetectable by the USS Enterprise-D's biofilters, the pyrocytes, when absorbed through the victim's skin, provoked an extreme allergic reaction. (TNG: "The Price")