**3.1 Steam extraction**

Steam extraction (**Figure 1**) is a widely used and official method for extracting essential oils from plants. This method accounts for 93% of essential oil extractions and can take anywhere from 1 to 10 hours depending on factors such as extraction time, temperature, pressure, and type of material [12].

In this extraction system, plant material is exposed to a stream of steam without prior maceration. The heat applied breaks down the cells of the plant material, releasing the essential oil. The steam, saturated with volatile compounds, is then condensed, and the essential oil is recovered by decanting the water/oil mixture [13, 14].

One of the advantages of steam extraction is that the absence of direct contact between water and plant material, and then between water and aromatic molecules, prevents hydrolysis or degradation of essential oil [15]. The "head" fractions, which contain the most volatile molecules, can be collected in as little as half an hour, with 95% of the volatile molecules being collected [16].

*A schematic representation of steam extraction of essential oils.*

The technique works by ensuring that the combined vapor pressure equals the ambient pressure at about 100°C, allowing volatile components with boiling points ranging from 150 to 300°C to be evaporated at a temperature close to that of water. It is also interesting to note that this technique can be carried out under pressure depending on the extraction difficulty of the EOs [17].
