Essential oils are volatile and liquid aroma compounds from natural sources, usually plants. They are not oils in a strict sense, but often share with oils a poor solubility in water. Essential oils often have an odor and are therefore used in food flavoring and perfumery. They are usually prepared by fragrance extraction techniques (such as distillation, cold pressing, or Solvent extraction). Essential oils are distinguished from aroma oils (essential oils and aroma compounds in an oily solvent), infusions in a vegetable oil, absolutes, and concretes. Typically, essential oils are highly complex mixtures of often hundreds of individual aroma compounds.