The way a wine's bouquet changes as it ages is one of most fascinating aspects of enology. Over time, a wine may develop a surprising and pleasant bouquet of aromas, or it may lose its “personality” and take a turn for the worse.
There are many chemical reactions that occur in a wine during its evolution over the years, but the oxidation process is the only one that greatly affects the wine's aromas.
Oxidation of the wine's aromatic chemical compounds happens over time to all wines: red, white, sparkling, sweet, fortified, and others. Oxidation is due to the leak of air through the pores of the wood when the wine is aging in the barrel, and through the cap when the wine is aging in the bottle.
In white wine, oxidation occurs quickly. The main aromas due to an excessive white wine aging period are wax, honey, nut, hazelnut, pine resin, soap and fenugreek. In particular, the fenugreek aroma is given by a molecule called sotolone, which has been found to be the key aroma in most bouquets of oxidized dry white wines. In low concentrations, the sotolone molecule produces notes which recall caramel and maple syrup, while in higher concentrations, it recalls fenugreek and curry (most Indian curries contains fenugreek among many other ingredients).
The oxidation process is slower in red wines than in white wines and therefore, occurs over a longer period of time: years or even decades. This is because the poliphenols, which have a higher concentration in red wines, have strong antioxidant properties. In red wines the main aromas due to a long wine aging period are cooked apple, ripe prune, and all cooked red fruit in general.
Since the aromas due to oxidation are the same for all red wines or for all white wines, when the oxidation aromas become dominant, it is noticed and the wine loses its unique personality and becomes “old”.
There are specific aging processes to be chosen in accordance with the particular wine being produced in order to ensure that the “oxidation” aromas won’t suffocate the wine's aromas, but will enrich its overall bouquet. The ideal situation is that the particular wine becomes richer with these aromas, while maintaining its specific aromatic starting point: its uniqueness.
There are also some other aromas that develop through wine aging, which are not common to all the wines but are, in fact, characteristics of specific wines.
2 examples of wines which improve over time and develop specific aromas, because they have specific chemical “precursors” that evolve into aromatic compounds which are easily perceptible by our sense of smell, are Riesling, due to the kerosene aroma, and robust red Bordeaux wines, due to the truffle aroma.
- The keronsene aroma in Riesling is due to a molecule called TDN (1, 1, 6, -trimethyl-1,2-dihydronapthalene). The concentration of this molecule in wine grows over time and it is higher when the grapes are cultivated in warm areas and with high sun exposure. This aroma adds complexity to the wine's bouquet, but it must be subtle and not overcome the other aromas.
- The truffle aroma in Bordeaux reds is due to a molecule called DMS (Dimethyl Sulfide). When perceived in high concentration, DMS has an odor which can be very unpleasant and it is often considered as giving an "off" flavor to the wine, with notes of cooked corn, tomato and asparagus. However, in lower concentrations it can enhance the complexity of the wine's bouquet with delicate truffle notes. While a red wine ages in the bottle, the DMS concentration grows reaching a peak after 10-15 years. It can be found in many robust red wines, but it is considered to be a characteristic aroma of great red wines from the Bordeaux region that are aged 10-20 years.
Next time you taste an aged wine, try to decipher the aromas that have developed due to its aging process. You can also facilitate this process by training your sense of smell to recognize the aromas of the wines with TasterPlace.