ODOR

An odor or odour (see spelling differences) is a volatilized chemical compound, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also called smells, which can refer to both pleasant and unpleasant odors. The terms fragrance, scent, and aroma are used primarily by the food and cosmetic industry to describe a pleasant odor, and are sometimes used to refer to perfumes. In contrast, malodorous, raunch, stench, reek, and stink are used specifically to describe unpleasant odors.

The widest range of odors consists of organic compounds, although some inorganic substances, such as hydrogen sulfide and ammonia, are also odorants. The perception of an odor effect is a two-step process. First, there is the physiological part; the sense of the stimulus by receptors in the nose. After that, the psychological part follows. The stimuli are processed by the region of the human brain which is responsible for smelling. Because of this, an objective and analytical measure of odor is impossible. While odor feelings are very personal perceptions, individual reactions are related to gender, age, state of health, and private affectations. Common odors that people are used to, such as their own body odor, are less noticeable to individuals than external or uncommon odors.

For most people, the process of smelling gives little information concerning the ingredients of a substance. It only offers information related to the emotional impact. Experienced people, however, such as flavorists and perfumers, can pick out individual chemicals in complex mixes through smell alone. The measurement of odor concentration is the most widespread method to quantify odors. It is standardized in CEN EN 13725:2003 . The method is based on dilution of an odor sample to the odor threshold, at which the odor can just barely be perceived by 50 % of the test panel. The numerical value of the odor concentration is equal to the dilution factor that is necessary to reach the odor threshold. Its unit is the European Odor Unit, OUE. Therefore, the odor concentration at the odor threshold is 1 OUE by definition.

To establish the odor concentration, an olfactometer is used which employs a panel of test persons. A diluted odorous mixture and an odor-free gas (as a reference) are presented from sniffing ports to a group of panelists. In comparing the gases emitted from each port, the panelists are asked to report the presence of odor. The gas-diluting ratio is then decreased by a factor of 1.4 or two (i.e. the concentration is increased accordingly). The panelists are asked to repeat their judgment. This continues for a number of dilution levels. The responses of the panelists over a range of dilution settings are used to calculate the concentration of the odor in terms of European Odor Units (OUE/m3). The test persons must fulfill certain requirements, for example regarding their sensitivity of odor perception. The main panel calibration gas to verify this requirement used is n-Butanol.