**3.1 Hydrodistillation**

Hydrodistillation represents one of the most used traditional and a commonly methods of extraction used method of extracting essential oils from plant samples (wood and flower). This method may be further classified into the subcategories of steam distillation, water distillation, or a combination of water and steam distillation. Hydrodistillation include saturation of the powdered wood in the water in the first step, while the next step is to use the steam that result from the heating of the water reservoir then finally gather the oil that result after the reservoir cold. The advantage of this technique is that the required material can be distilled at a temperature below 100°C. There are many studies provided that the different extraction processes on yield and properties of essential oil from rosemary (*Rosmarinus officinalis* L.) by HD and solvent-free microwave extraction (SFME) [21]. While Golmakani and Rezaei (2008) [22] researched the microwave-assisted HD (MAHD), which is an advanced HD technique utilize a microwave oven in the extraction procedure.

MAHD was preferable in extraction time (75 min, compared to 4 h in HD). Ohmic-assisted HD (OAHD) is another advanced HD technique [23]. OAHD method had the extraction time of 24.75 min, while HD took 1 h for extraction of essential oil. No changes in the compounds of the essential oils obtained by OAHD were found in comparison with HD.
