The most important evaluation of a coffee is performed by ones olfaction. Olfaction is what allows one to sense aromas and occurs when air carrying the aromas passes over the receptors which are primarily located behind the bridge of one's nose. There are four major stages in the olfaction evaluation of a coffee, the dry aroma, the cup aroma, the nose, and the aftertaste. The dry aroma (aka. the fragrance) is the smell of the roasted and ground coffee beans. It is composed of compounds that are gaseous around room temperature, while the other 3 stages are from aromas turned gaseous only at the elevated temperatures associated with brewing. The cup aroma is the smell of the coffee brew. It is formed from the aromatic compounds leaving the surface of the brew. The nose is composed of the aromas that are released from the brew when it is taken into the mouth. Finally, after the coffee is swallowed, residue remains on the palate, the residue then emits vapors which are then sensed by olfaction, resulting in an aftertaste.