The odorous substances used in perfumery are extracted using several processes depending on their concentration in the plant, their fragility (in particular their sensitivity to heat), and the cost constraints. Steam distillation (hydrodistillation), which produces the essential oils, is the most frequently used. The longer, more complex, and, therefore, more expensive enfleurage and maceration methods provide the absolutes. As for the simple pressure extraction of the citrus zests, it gives the essences.