Plant material is submerged in an alcohol, or alcohol/water mix (depending on if the plant material is fresh or dry), menstruum, and allowed to infuse (steep) for a minimum of six weeks. In that time, the alcohol or alcohol/water mix extracts both the water soluble and the alcohol soluble chemical constituents from the plant.
A tincture is typically an alcoholic extract of plant or animal material or solution of such, or of a low volatility substance (such as iodine and mercurochrome). To qualify as an alcoholic tincture, the extract should have an ethanol percentage of at least 25–60% (50–120 US proof). Sometimes an alcohol concentration as high as 90% (180 US proof) is used in such a tincture. In herbal medicine, alcoholic tinctures are made with various ethanol concentrations, 25% being the most common.
Herbal tinctures are not always made using ethanol as the solvent, though this is most commonly the case. Other solvents include vinegar, glycerol, diethyl ether and propylene glycol, not all of which can be used for internal consumption. Ethanol has the advantage of being an excellent solvent for both acidic and basic (alkaline) constituents.
Glycerine can also be used, but when used in tincturing fashion is generally a poorer solvent. Vinegar, being acidic, is a better solvent for obtaining alkaloids but a poorer solvent for acidic components. For individuals who choose not to ingest alcohol, non-alcoholic e,g., (glycerite) extracts offer an alternative for preparations meant to be taken internally.
Some solutions of volatile or nonvolatile substances are traditionally called spirits, regardless of whether obtained by distillation or not and whether they even contain alcohol. In chemistry, a tincture is a solution that has alcohol as its solvent.