Which of the following is not an essential oil extraction method?

The correct choice, fermentation, is not typically recognized as an essential oil extraction method. In the context of essential oils, extraction methods are designed to isolate volatile aromatic compounds from plant materials, and fermentation does not directly achieve this purpose.

Cold pressing, solvent extraction, and steam distillation are well-established methods used to extract essential oils. Cold pressing is a mechanical method primarily used for citrus fruits, allowing the oil to be released from the rind. Solvent extraction employs chemical solvents to dissolve the essential oils, which are then separated from the solvent, making it suitable for delicate flowers that cannot withstand heat. Steam distillation, the most common method, uses steam to vaporize the volatile compounds, which are then condensed back into liquid form, isolating the essential oils.

Therefore, while fermentation is a valuable process in producing other products like alcohol or vinegar, it does not serve as a main technique for extracting essential oils.