Water distillation may be one of the oldest extraction methods. Plant material is basically boiled in water, releasing essential oils in the steam. When the steam is condensed, plant oils and water separate. Water distillation is simple, but it is often an incomplete method, and for some plants, long exposure to high heat can affect the quality of the product.

Steam distillation is a commonly used method, especially for more heat-sensitive herbs and botanicals such as lavender or other flowers. Steam quickly vaporizes volatile compounds, and the vapor is condensed, allowing the two fractions (water and extracted compounds) to separate.

Fractional distillation takes this concept a step further, heating steam to specific, different temperatures at which each desired component vaporizes. This process fractionates the different chemical compounds in a plant, collecting them in separate batches. Camphor and ylang-ylang are commonly known products of fractional distillation.

This method is also used to redistill oils to remove unwanted or toxic components. Almond oil, for example, is fractionally redistilled — or rectified — to remove naturally occurring hydrocyanic acid. 

Finally, some hydrosols, or aromatic waters like oudwater and jasmine flower water, are valuable by-products of the distillation process.