Organoleptic testing involves the use of the human senses—sight, smell, taste, and touch. To expert distillers who are experienced in working with essential oils, their senses are used as the first line of quality testing standards to provide immediate clues about the acceptability of a product. Oil that has an unusual smell, an uneven consistency, or a strange color instantly tells the distiller that something is wrong. Often times this type of testing is used as a preliminary quality control step before any other testing is conducted.
Even those without expertise in essential oil quality can rely on their senses to understand how a high quality essential oil differs from other essential oils. Although humans have a poor sense of smell in comparison with most animals, the human nose is sensitive enough to detect even a picogram (1/1, 000, 000, 000, 000 g) of a substance. The reason essential oils have such a potent fragrance is that they are composed of volatile aromatic compounds that are small and easily move through the air to interact with the olfactory receptors in the nose.
The nose is an organ located centrally on the face that is specifically designed for the sense of smell. Inside of the nose are two nasal cavities (one within each nostril) that are lined with a layer of mucus. Anytime something elicits the sense of smell, tiny particles of the substance must first be dissolved by this mucosal lining. In the upper portion of the nose is a tiny cavity that holds millions of specialized olfactory cells. These cells function by detecting particles dissolved in the mucosal lining of the nose. In order to be perceived as a smell, these particles must bind to special receptor cells that in turn release proteins initiating a series of chemical reactions. From these reactions, a signal is sent from the olfactory cells, along the olfactory nerve, to a portion of the brain specifically designed to interpret smells. This area is located in the front of the brain and is referred to as the olfactory center or rhinencephalon. The full physiology of this portion of the brain is still under investigation; however, this area has been determined to be multi-functional, meaning it integrates smell with other parts of the brain.
Once the olfactory center of the brain has been triggered, further signals are sent to an area of the brain called the neocortex. This portion of the brain is responsible for both making the person aware of the smell and allowing them to identify the odor. Signals are also sent to areas of the brain that control pleasure, emotions, and memory. In particular, memory is associated with the sense of smell. This is evident even when a person recalls a specific memory after smelling just a small amount of a particular aroma. Smell can be a very powerful reminder of specific people, places, or experiences.
When using your own sense of smell to test an essential oil, it is important to remember that slight natural variances in the fragrance and appearance of an essential oil are common and expected. These physical attributes can vary based on season of harvest, weather conditions, etc., which all can cause slight changes to the ratios of aromatic compounds produced by the plant. These natural variances are in no way a sign of low quality products, but instead show the miraculous ability of plants to adapt to their environment and also demonstrate the sensitivity of your nose.
The power of smell is still under wide scientific investigation as the mechanism behind this sense is not yet fully understood. Despite the lack of a full understanding in this field, the power of scent has many benefits as an analytical tool and can give important insight into the overall quality of essential oils.