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What Happened To My Wine? Demystifying The Science Of Ageing Wine

Do old wines taste better than young wines? Why does a wine taste the way it does when you open it now but develops a whole new identity if it’s aged years later? And will a wine get better with age?

It has been widely understood that ageing certain wines could enhance the tastes and aromas – buy a wine, cellar it, and pray to Dionysus it doesn’t resemble something you’d toss in a salad as a vinaigrette. But does that mean all wines are worthy of cellaring or has there been a misconception and we’ve all been drinking wines too old to be fully appreciated?

As it turns out, 99% of wines out there are meant to be drunk now (in wine terms, that’s in the next 3-5 years); in fact, most wines are meant to be consumed within one year of production. So what makes a wine worthy of cellaring to be enjoyed later on, or uncorked and fully appreciated now? What exactly happens to a bottle of wine as it ages, and is there a way to direct this? To examine this, we’ll have to dive into the chemistry behind wine ageing (or at least a brief, brief summary of the chemistry involved).

Effects of Aging on Wine

Wine ageing results in a harmonious development of taste, aroma and colour – the flavour changes into softer, more delicate notes with less astringency (wine enthusiasts and experts will declare the wine has “opened up”); the aroma evolves into a multi-layered bouquet; and the colour gets lighter in red wine (from cherry red to deep red, then brick red) and darker in white wine (from light yellow to golden yellow, then finally barrel brown). However, science hasn’t yet been able to pinpoint when a wine is at its peak or has “gone over the hill”.

What we can surmise, however, are the chemical reactions that lead to these perception changes in the taste and aroma of a wine. The main components of wine responsible for changes are aroma, taste and colour are esters, tannins and anthocyanins.

Esters

That smell of fresh orange in the morning? Or that relaxing aroma of lavender during your evening baths? These are predominantly caused by a chemical compound called ester. Esters are created by the reactions between acids and alcohols, and they give rise to most, if not all, smells and aromas found in organic compounds. Research has found up to 83 different kinds of esters in wine, all of which can affect the wine’s flavour and taste to different extents.

The chemical formation of esters occurs as a reversible reaction, that is it has an equal chance of proceeding either way – forward to create esters, or backwards to form alcohols and acids.

Higher alcohols+Acetic acid⇌Ester+Water

The direction in which the reaction proceeds is dependent on the chemical equilibrium and external factors affecting the wine, which in this instance includes the type of yeast used, wine pH and fermentation temperatures. If you can imagine a huge ball pit, like the ones you find in kid’s playgrounds, and you start adding more and more balls to one side of the pit, eventually you’ll find that the balls fall towards the centre to reach a balanced level. That’s essentially what a chemical equilibrium is trying to achieve – a balance in chemical composition between all components.

As you age wine, one of the more common attributes noticed is the loss of the fresh, fruity aromas, which is associated with esters formed between acetic acid and higher alcohols.  This is because, over time, yeasts tend to produce more and more esters, which throws off the chemical equilibration of the reversible reaction. This imbalance tends to cause the reversible reaction to proceed in the reverse direction to form back its constituent alcohols and acids to restore the chemical equilibration, resulting in the destruction of these esters. This explains why the fruity aspect of younger wines fades with time.

Interestingly enough, this very reaction also explains why the addition of water to spirits like whisky (Scotch), and sometimes wine (all you wine zealots out there are probably grimacing at this point) has been touted to change and ‘open up’ its aroma, but this is perhaps a discussion for another time.

In a single bottle of wine, this reaction happens for all the different alcohols and acids present at the same time to produce a variety of esters, each with own unique aroma. On top of that, these reactions happen at different rates, all dependent on factors such as pH, temperature and oxidation. So you can only begin to understand the depth of complexity that goes into the development of a wine bouquet! For this reason, wine enthusiasts have come up with an “aroma wheel” – a useful way of picking out the different notes in a glass of wine.

Wine aromas wheel

Even more interesting things begin to happen for barrel-aged wine. Many fine wines, especially red, are almost always aged in oak barrels as it is believed to add tannin to improve the structure of the wine, enhance its ageability, finesse and complexity of flavours and aromas. Untreated oak barrels can impart a number of aromatic compounds into the wine, mostly resulting in earthy, woody or even sweet vanilla or coconut aromas. Even more unique aromas and tastes can be imparted when the oak has been treated or “toasted”.

Tannins

Raise your hand if you’ve ever taken a sip (read: gulp) of red wine (or black tea), only to be rewarded with a dry, cheek-sucking sensation that makes your mouth pucker. More often so when drinking younger vintages. You can thank tannins for that.

Tannins are chemical compounds found mostly in wine grape skins, pips, stalks and sometimes in oak barrels, which are important to wine in a number of ways – they provide stability for long-term ageing and preserving; ‘structure’ to wine (without which, reds would seem too flat); and bitterness that adds depth for flavour complexity. However, too many tannins and you’re left with a mouthfeel of chalk dust (slight exaggeration here).

This astringent-inducing property of tannins is due to its chemical structure. Research has found that tannins have a high affinity for proteins. In human saliva, tannins tend to bind to the protein molecules in saliva to form precipitates, inhibiting saliva lubrication in the mouth. More tannins = more tannin-protein precipitation = less saliva lubrication.

During the wine ageing process, tannins slowly undergo polymerisation – a chemical reaction that binds tannins together with each other and with protein molecules. As these tannins bind together and polymerise, the bigger compounds tend to precipitate out as sediment and fall to the bottom of the bottle, which is a common occurrence in aged wine. This in part explains why this sediment usually tastes strong and bitter – these are highly concentrated forms of tannins. The aged wine hence loses its astringency as more and more tannins precipitate out as sediment, leading to that softer, more mellow mouthfeel that has said to have become more “integrated” with the other components of the wine.

Anthocyanins – Nature’s colour pigment

The bane of all red wine-lovers: wine-stained teeth and lips.

This is caused by a chemical compound called anthocyanins – nature’s own colour pigment. In wines, anthocyanins are found in high concentrations in the skins of grapes, which contribute to the colour of red wine. They have been touted to have antioxidant properties, giving vindication to the belief that wines are “healthy” (even more reasons to have a glass tonight, I’d say). White wines, on the other hand, have little to no anthocyanins present, and the grape skins are usually kept separated from the pulp during fermentation.

During ageing, one of the most immediate observations is the gradual changing of colour; for example, the “browning” of red wine. This is in part due to the interaction of anthocyanin compounds with oxygen and tannins. Anthocyanin readily combines with tannins and oxygen, leading to a gradual decrease in the amount of this purplish-causing compound, which results in a colour change from deep purple to brick red. These interactions, however, are heavily influenced by the wine’s acidity and the addition of sulphur dioxide, where reactions of anthocyanins with sulphur dioxide further bleaches the wine, effectively taking away their colour.

Red wine ageing over time

How the colour of red changes over time. Image from WineFolly.com

Oxidation – a love/hate relationship

Oxygen and wine have a long history of love and hate – a relationship best described as a tumultuous love affair. As a wine is left to age, oxygen slowly diffuses through the bottle closure, mainly cork, to slowly oxidise the wine. This is actually important in the development of wine bouquet, where various oxidation-reduction reactions cause the fruity flavours and aromas associated with younger wines to fade and develop into something with more depth and multi-layered as the wine ages. This is why wine decanting is so important – it encourages interaction of wine with oxygen in order to speed up the ageing process and to help release the more mature, complex flavour profiles that have developed over time. However, too much oxygen and you’ll run the risk of oxidising your wine, ultimately losing its freshness and turning it into vinegar.

So what’s the ideal ratio of wine to oxygen?

Unfortunately, these chemical interactions are just beginning to be understood and science hasn’t quite caught up with the complexities of these oxidation processes to infer the ideal ratio. What we can appreciate, however, is the interconnectedness of all these different interactions within a wine bottle and how they all sing together in harmony during the ageing process. If you can imagine all the instruments of an orchestra strumming and playing to the tune of one symphony –  it may seem like a cacophony to the untrained ear, but as a piece they all come together to weave the most unique and melodious of lullabies – this is the best explanation I can offer for the great chemical mystery behind wine aging.

With all that being said, what does this mean for all you wine-aficionados out there? It means that age-old adage of “the older the wine, the finer it is” is not always true. Different wines have different ageing potentials, depending on many factors including its chemical composition and storage conditions. Further to this, just because a wine has been aged it doesn’t necessarily mean you’re going to enjoy it more. The enjoyment of wine is completely subjective so if you prefer the primary flavours of fresh fruit and herbs, then you may not enjoy the more subtle tertiary flavours of an older wine, such as mushroom, forest floor, tobacco, spice or nuts. The best way to discover what you like is to try different wines and grape varieties of various ages.

The Author

Kaylyn Chandran

Kaylyn Chandran

Contributor