Water vs Steam – What’s the Difference?
Most essential oils on the market are still made using classic distillation. These methods are not glamorous, but they are robust, well-understood, and surprisingly elegant.
In this article, we’ll look at two of the most important techniques:
- Hydrodistillation (water distillation)
- Steam distillation
Both rely on the same basic idea: use hot water or steam to carry volatile aromatic compounds out of plant material, then condense and separate the oil. But there are meaningful differences in how gentle they are and what they pull from the plant.
Hydrodistillation: The Oldest Workhorse
Hydrodistillation is one of the oldest ways humans have captured scent.
How it works
- Plant material (fresh or dried) is placed in a still.
- Water is added directly to the still, submerging or partially submerging the plant material.
- The mixture is heated until it boils.
- Water vapor carries volatile plant compounds upward.
- The vapor is cooled in a condenser and turns back into liquid.
- The essential oil separates from the water due to density differences and is collected.
Pros
- Equipment is relatively simple and affordable.
- Well-suited for many robust herbs and spices.
- No organic solvent residues.
Cons
- Long exposure to boiling water can cause:
- Hydrolysis (water-driven breakdown of certain molecules)
- Thermal degradation of more delicate components
- Non-volatile or less desirable compounds (like waxes, coumarins, flavonoids) may co-distill or dissolve into the distillate, influencing appearance or aroma.
You can think of hydrodistillation as the “long, hot soak” version of extraction. It works — but it’s not always the gentlest option.
Steam Distillation: Similar but Subtly Kinder
Steam distillation was developed to solve some of hydrodistillation’s problems.
The basic principle is the same, but with one key difference: the steam is generated in a separate boiler and then passed through the plant material.
How it works
- A boiler heats water and generates steam.
- Steam is piped into a chamber filled with plant material.
- Volatile compounds evaporate with the steam.
- The mixture is condensed into liquid.
- Oil and water separate, and the essential oil layer is collected.
Why is this an improvement?
- The plant material is not sitting in boiling water, which can reduce hydrolysis.
- The temperature at the plant bed can often be kept closer to 100 °C (rather than prolonged contact with liquid water).
- The process can be more controllable and scalable for industrial production.
But there are still trade-offs
- Steam temperature, flow rate, and pressure must be carefully controlled.
- If the steam is too intense, sensitive molecules may still degrade.
- If it’s too gentle, yields may be low, and the process becomes inefficient.
Despite these challenges, steam distillation remains the standard method for many essential oils you see labeled as “steam-distilled”.
What These Methods Mean for Your Oil
For many sturdy botanicals (like certain mints, eucalyptus, or spices), classic distillation can produce beautiful, high-quality oils.
But it’s helpful to remember a few things:
- Not all compounds are equally heat-stable.
Some delicate notes are more easily lost or transformed during long, hot distillations. - Distillation pulls a specific “slice” of the plant’s chemistry.
It emphasizes volatile molecules and often leaves heavier or non-volatile components behind. - Process control matters.
Two producers using “steam distillation” can still end up with oils that smell and perform differently, depending on how they manage time, temperature, and post-processing.
In the next article, we’ll explore techniques that go beyond water and steam altogether: solvent extraction and CO₂ extraction. These methods can capture a different side of a plant’s aromatic personality — but they also come with their own caveats.