The 'Gazette'
When tasting old whiskies, we can often smell a floral reminiscence that takes us on a sensory journey: rose, lilac, lily of the valley, orange blossom or violet. But how is it possible to smell such a diversity of floral aromas, even after several years of ageing? Part of the answer lies in the aroma’s precursors.
Terpenes are hydrocarbons, meaning compounds containing only carbon and hydrogen atoms with a number of carbon that may vary between ten and thirty. In particular, there are monoterpenes with 10 carbon atoms. Terpenols are sometimes referred to when an oxygen atom replaces a carbon or hydrogen atom. Monoterpenes and terpenols are the most involved compounds in the floral aroma, and are initially present in plants or cereals.
Simplified illustration of an initially bound aromatic molecule being released
Terpenes can be present either in a bound, odourless form or in a free, odorous form. When these aromatic molecules are bound, they are ‘trapped’ and cannot release their odour. In this case, the terpenes are attached to other, larger molecules that prevent them from volatilising: they have no odour. But these aromatic molecules can also be found in free form and are then able to express their aroma.
To better visualise this phenomenon, we can use a balloon to represent an odorous molecule. Naturally, this balloon can fly as far as our nose (this is the free form), but when weighted down by a stone, it cannot fly away (this is the bound form).
It is possible to break the chemical bond between the terpenes and the large molecules holding them in place (in other words, cutting the string that binds the balloon so that it can fly away).
Cutting the string releases the aromas. This can happen more or less quickly, both during fermentation and during barrel maturation. In other words, there are several stages to the aromatic expression. Terpenes can be expressed either directly, as they are already free and fragrant, or later, as they gradually detach.
The bound form of the terpenes can also be seen as an advantage, as they are protected from degradation reactions or evaporation phenomena, and remain preserved in the whisky. This olfactory reservoir therefore encourages a slow, gradual release of terpenes, which ultimately leads to the preservation of freshness and a more complex floral aroma throughout the ageing of the whisky.
The presence of terpenes in bound non-odorous forms acts as an aroma reservoir in whisky. By a gradual and continuous release of these aromatic molecules throughout the production process, this valuable reservoir complexifies the whisky and offers a multitude of floral nuances to the consumer. The type of barley, the fermentation conditions, the distillation recipe or the choice of oak wood are all parameters that determine the balance between the bound and free molecules. Therefore, they are important elements to take into consideration to optimise the aromatic potential and control the diffusion of floral molecules over time.
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Mendes-Pinto, M. M. (2009). Carotenoid breakdown products the—norisoprenoids—in wine aroma. Archives of Biochemistry and Biophysics, 483(2), 236 245
Kanasawud, P., &Crouzet, J. C. (1990). Mechanism of formation of volatile compounds by thermal degradation of carotenoids in aqueous medium. 1.. beta.-Carotene degradation. Journal of Agricultural and Food Chemistry, 38(1), 237-243
Aromas | April 2025 | Dr. Magali Picard