In a book written by Emile Peynaud called "The Taste of Wine", Emile writes about the science and practice of wine tasting, detailing the senses and how they function, tasting techniques, wine balance and quality, wine tasting vocabulary, and the art of drinking. One topic that I found interesting in Emile's book was the difference between aroma and bouquet of a wine. In our wine circles and tasting events we frequently hear these terms used, but what is meant by aroma and/or bouquet of a wine. Aroma and bouquet are significantly different with regards to wines. Many people confuse the two terms and really lack a true understanding of what each is describing in a wine. There are three major categories for aromas.
Primary aromas (varietal aromas) which are distinct to grape varietal. For example one would detect blueberries for Syrah or cherries for Pinot Noir. These fruit profiles that are detected in the smelling of a wine and are indicative of a specific varietal.
Secondary aromas (vinous aromas) are the by-products of yeast activities during both pre and post fermentation process. During fermentation as the yeast converts the sugar into alcohol, various substances or chemical groups are developed. These chemical groups or products vary depending on the type of yeast used as well as the temperature that the wine was fermented at. A chemical group known as "esters", for example, are responsible for providing the fresh tropical fruit aromas in a white wine. Reverting to my beer brewing knowledge and experience, the effects of temperature on a fermenting beer can be seen in the Hefewiezens. If this German wheat beer is fermented at a warm temperature a phenol chemical group (4-vinyl guaiacol) is created producing aromas of bananas and cloves. Another influence on wines is malo-lactic fermentations which induces aromas of butter, caramel, etc. For you old world wine drinkers, that barnyard aromatic that you find in certain wines are the result of a wild yeast know as Brettanomyces that create a phenol compound known as 4-ethyl phenol.
Tertiary aromas are developed during post fermentation while the wine is developing (maturing) in oak barrels or bottles. Tertiary aromas ARE the bouquet of a wine. The bouquet is developed as a wine ages in the barrel or bottle where chemicals belonging to the chemical family known as "aldehydes" are formed. This chemical process involves oxidation of the wine. "Oxidation"!!! Yes, wine is a living biosphere and requires a certain amount of oxygen to live and develop. This is one of the reasons that I am firm on my belief that wines need to be bottled using corks. This is different than wines that have too much oxygen and are oxidized to a point where color, fruit and flavors are lost. The oxidation of the fruit acids and alcohol creating the aldehydes and esters during the post fermentation process add complexity and beauty to a wine.
I found this subject quite interesting in that the primary and secondary aromas blended together along with continued development of the wine in the presence of oxygen creating what is termed as the bouquet of a wine. The better the wine, the more complex the bouquet. Following is Robert Parker's description of bouquet, "As a wine's aroma becomes more developed from bottle aging, the aroma is transformed into a bouquet that is hopefully more than just the smell of the grape."