The sense of smell is the key to enjoying wine, because it enables us to perceive both aroma and subtleties of flavour. When we sniff a wine volatile scented molecules pass into the olfactory ~L1COUS membrane at the top of the nose where the olfactory cells convert the molecules into signals which are transmitted to the olfactory bulb locates at the base of the skull. This organ enables the brain to perceive not only odours inhaled through the nostrils but also conveyed to it from the palate by way of the nasal passage at the back of the mouth.
The objective of the olfactory examination is to judge the intensity, length and quality of a wine's aroma, and subsequently to identify and describe the character of the specific odours of which it is composed.
Intensity
Is of relatively limited importance since it is a measure of quantity and not necessarily quality. In a fine wine an intense bouquet is an attribute but in a poor-quality wine a strong odour can be negative factor.
Length
Refers to the duration and continuity of aroma and is an indication of quality.
Character
It is usual to distinguish between three different types of aroma:

	Primary (or varietal) aromas: are odours intrinsic to the grape which are transmitted directly to wine. Primary aromas are the source of so-called varietal character of certain wines.
	Secondary (or fermentation) aromas: are the odours of the alcohols and esters produced during fermentation by the action of yeasts. They give the fruity character which is found at its most intense in young wines.
	Tertiary (or post-fermentation) aromas: comprise what is usually known as bouquet. The formation of these particular aromas is an integral part of the evolution of fine wine and they are generally most intense in mature wines. They are the result of the chemical action of enzymes on the natural components of the wine, and in the case of barrel-aged wines, those acquired from the wood.

Recognition and description
Is at the same time the most fascinating, poetic aspect of analysis and the most difficult since it requires an "olfactory memory" capable of storing and cataloguing a considerable number of smells (above all familiar, everyday ones) and matching them with those in the aroma of a wine.
It is important to remember that the sensitivity of the olfactory organs decreases with prolonged exposure to the same odour, to the point that we are eventually no longer able to detect a given smell, a phenomenon, known as "assuefaction".