Like all of us, wine gets old, and like all of us it will change as it does so. And the circumstances of its ageing will affect how it changes, which aspects of its underlying character will be emphasised and which will diminish, when its peak will be, and when it will decline. Because, unlike what is sometimes believed, wine does not always simply improve with age, and certainly not forever – all wine will have a shelf life, all wine will have a moment where it is at its best, and all wine will, after this moment, diminish.
But the ageing isn’t just done by the customer or collector, in dusty bottles crowded in mouldy cellars as the decades pass. Wine begins to age the moment it is made, indeed before it has even finished – if that is even the right word, as the key with wine is that it is never ‘finished’ but is in fact always changing, never stable, never finalised. From beginning of the growing season to whenever the bottle is opened the chemicals which make the wine are in a constant state of flux, and the alchemical process which results in the magic of wine is always a live one.
In this article I want to take a closer look at two ways in which wine is aged deliberately: in wooden barrels prior to bottling, and then what actually happens in those bottles themselves. Why do winemakers choose to age their wine in wood, and when do they choose not to? And why do we then set bottles of wine down, and how can we estimate when to open them? Let’s get into it.
Ageing in barrel
Wine has been stored in wooden barrels since forever, and in fact it was only in the 17th Century that the glass bottle was pioneered and subsequently became the norm for storage. This was for good reason, as the great advantage of glass in general (for scientific experiments, for instance) is that is a chemically neutral substance, whereas wood reacts with the liquids it contains and influences them (though after a few uses wood can become more neutral substance for storage). Winemakers then, given an increasingly stable final vessel for the wine to arrive in, started to use barrel-ageing to achieve the particular effects wood interacting with wine was observed being capable of. And so was born the modern art of ageing wine in wooden barrels.
The wood in question is, of course, almost always oak (acacia, cherry and others are sometimes used, but rarely). These days, the oak used in winemaking is generally either French oak (quercus robur) or American white oak (quercus alba). Prior to being made into barrels by coopers, this oak is generally toasted (which is to say, exposed to a very high heat for a short time), which has two effects: firstly, to render the wood more pliable and easier to bend into barrels, though there are also other ways of achieving this; secondly, and more importantly, to transform some of the more obvious, ‘woody’ chemicals into some of the more complex aromatic compounds associated with wine that has gone into barrel.
The general idea is that these chemical interactions will give the wine more ‘rounded’ flavours, which is to say softened acidity, mellower fruits, and certain complex tertiary aromas associated with barrel-ageing such as butter, vanilla, and spices. Most red wine will spend time in barrel, whereas most white wine will not in order to retain that freshness which appeals to so many drinkers, with some exceptions (some of which, such as Meursault or Montrachet, are among the world’s most prestigious white wines). The generally accepted alternative to wood is stainless steel tanks, essentially neutral containers and are thus generally used for fermentation to prevent impurities from inveigling in. These days, almost all wine is fermented in stainless steel and then transferred to barrel or bottle, though some wine is still barrel-fermented to really accentuate that roundness of flavour.
But what barrel to use? What is the difference between French and American oak? Well, the generally agreed difference in flavour in the final wine is ‘butteriness’ against ‘vanilla’, but it’s more complex than that. The key is that French oak tends to be more variable in its grain – the annual growth rings of the tree – with the most prestigious oak forests of France (for instance Alliers and Tronçais) renowned for their fine-grained wood. Fine-grain generally means a greater concentration of aromatic compounds get released into the wine, whereas open-grain tends to deliver more of a certain kind of oak tannins known as ellagitannins while aromatizing the wine more slowly. Looser-grained wood (such as that notably grown in the area of Limousin) is often considered particularly suited to ageing spirits such as brandy or whisky.
This is also the key with the so-called ‘Slavonian oak’, in reality quercus robur that has been grown in the historic Slavonia region of Croatia, which is the traditional source of oak for much of Italian winemaking, most notably Piedmont and Valpolicella. Because of climatic conditions, the oak here grows more loose-grained than in the classic French regions, contributing to the traditionally less-intrusive oaking style of Italian red wine.
Another crucial choice for winemakers is the size of the barrel they use. Generally speaking, the smaller the barrel the more concentrated the oak effects, as a greater percentage of wine is interacting directly with the surface of the barrel, absorbing influences directly from the wood. For the purposes of Valpolicella, there are three principle sizes to bear in mind: barriques, which hold 225 litres; tonneaux, really a generic French word for ‘barrel’, usually meaning a standard volume of about 500 litres but which can vary; and botti, again a generic (Italian) word for ‘barrel’, but which implies a much larger size, anything from 1,000 to 10,000 litres.
Traditionally winemakers in Valpolicella, like their counterparts in Piedmont, have used large format botti made from looser-grained Slavonian oak, the combination of which leads to very gentle, unobtrusive ageing, often taking several years before the wine is considered finished. This can be somewhat uneconomic, leading to some winemakers to experiment with barriques and tonneaux, a practice once considered very controversial but which has now gained general acceptance as one of the weapons in the winemaker’s arsenal. Nonetheless, whether one uses smaller or bigger barrels, of finer or looser grain, is still considered a choice between innovation and tradition.
Some producers rather ingeniously split the difference by partially ageing the wine. This can have many definitions: ageing parts of the wine in different size barrels, or in the same size barrels but for different lengths of time, or ageing some of the wine but not the rest, or indeed any other combination prior to blending it together. The deployment of partial ageing is becoming increasingly sophisticated, and many winemakers are now exploring its potential to make ever-more complex and precise wines.
But what does oak actually do? There are three main aspects to oak-ageing the wine: flavour compounds, oxygenation, and malolactic fermentation. The barrels are full of particular chemicals which can influence the flavour of wine, many of which have been identified, such as vanillin (responsible, naturally, for vanilla flavours), furfural (which causes much of that characteristic oaky sweetness) guaiacol (that interesting smoky, leathery aroma) and many more. As mentioned above oak can also add a bit of tannin, reinforcing the structure of the wine for ageing.
The second aspect, oxygenation, occurs due to the fact that barrels are of course impossible to make totally closed, and this slight porousness allows a limited amount of oxygen from the air to help stabilise the wine, considered a contributor to those ‘rounded’ flavours.
The third and final aspect, malolactic fermentation, is the most complicated. This process, not really a fermentation at all, generally occurs after true alcoholic fermentation, in a process whereby certain bacteria ingest malic acid (that sharp kick found in green apples) into lactic acid (think the creaminess of milk). Now, this process is not really caused by barrel-ageing, and often will occur naturally unless prevented, but it is considered desirable for it to occur in-barrel as the combined chemical reactions result in wine better balanced between buttery-creamy and its inherent fruit flavours.
All of this is, of course, part of the process of crafting a wine, building up to the moment when something finished is put into a bottle. Except it isn’t finished – as mentioned before, wine is an ever-changing substance, not a shelf-stable product but in fact a living thing, one designed to change over time – even in the neutral security of a sealed bottle.
Ageing in bottle
In order to understand bottle-ageing, we first have to understand what it is that makes wine such a changeable substance to begin with. Wine is a chemically imbalanced substance, which is to say it is bottled unbalanced between the various components produced as a result of winemaking (fermentation, barrel-ageing and so on). Chief among these substances are esters, the primary flavour compounds in wine, and the ones responsible for most of the aromas we associate with fruits and flowers. Over 80 individual esters have been identified in wine, and they are most prominent early on in the wine’s life as they are produced as a by-product of fermentation, as alcohol reacts with acid.
This is one reason wines with higher acidity also tend to be fruitier younger than those with lower acidity. However, it is also a crucial aspect in bottle-ageing, as the production of esters is a reversible reaction, and as their presence chemically imbalances the mixture, esters are doomed to eventually break down. This is why wine loses that immediate fresh-fruitiness over time, and why high acidity is considered a plus, as the longer the wine can retain some of these flavours, the more complexity it can develop and the longer its peak can be.
Esters aren’t the only important chemicals in town, however. Tannins – the chemicals that cause the bittering, drying-out sensation in red wine, tea and coffee – are also considered crucial to the viability of much wine ageing. Tannins famously combine chemically with proteins, indeed reacting with proteins in the saliva to inhibit saliva production and produce that drying sensation – which is why so many so-called ‘big’ red wines are recommended to accompany red meats, whose own rich proteins cancel out the bitterness in the wine and allow other flavours to rise to the fore.
However, what is less known is that tannins will in fact combine not only with proteins present in the wine, but also with each other, in a process known as polymerisation. In this way, the heavier tannin compounds effectively filter themselves out, falling to the bottom of the bottle as sediment. This is the reason that powerful tannic structures diminish over time in the bottle – and also one reason big, old wines need to be decanted!
There is a final aspect, as with barrel-ageing – our old friend, oxygen. Corks remain the choice stoppers for long-term ageing, as some (though contentious) evidence suggests that its slight porousness allows a very slight amount of oxygen to seep in, which reacts with the anthocyanins that make red wine red to cause that tendency towards browning that wine has as it ages (a similar effect occurs in white wine). Those chemicals will filter out over time without added oxygen, but it helps. Oxygenation also helps release some of the aromatic compounds which cause tertiary flavours, which is the same reason we decant and aerate wine as well (and why some whisky drinkers add a few drops of water to their dram). Too much oxygenation can be disastrous and is considered a wine fault – wine is constantly trying to become vinegar, its shelf-stable final form, and should only be given so much encouragement.
Wine is always changing from the moment it begins its journey from ground to glass. The key, for both the winemaker and the wine consumer, is to learn how to manage that change. Wine which would be improved by some oak-ageing should take some, but only the right amount and in the right way. Furthermore, only wine which is designed to gradually release its subtler layers over careful years of cellaring should be laid down with reverence, while wine which is designed to be fresh and fruity should be drunk young, as ageing it would only diminish its strengths and reveal its weaknesses.
The key thing is to treat that bottle, and the juice in it, in the same way a surfer treats a wave: you bide your time, wait for the right moment, and only at its peak is it time to ride it.