Millesima Tips #4: Maturation (1/2)

Millesima Tips #4: Maturation (1/2)

The journey of wine from vine to cellar to glass involves many processes, both organic and technological. A finished bottle is a synthesis of the vine cycle – with the harvested fruit expressing the year’s climatic conditions – and human intervention in several forms. In the last episode of our Millesima Tips series, we discussed harvest, the most significant form of human intervention. The grapes are removed from the vine, thus blocking them from their natural destiny: to wither and drop, decompose and deliver their seeds to the soil, where the latter can sprout into new plants. In the fourth instalment of Millesima Tips we explore what happens after harvest, after the grape juice has been left to ferment into wine. At this point wine may be matured to improve its quality before bottling.

Maturation or Ageing?

You may have heard of a wine being “barrel-aged” or “oak-aged” to enhance its natural characteristics. In fact, “ageing” in English is often used interchangeably with “maturation,” which sometimes leads to confusion. To clear things up, it helps to look at French (the undisputed “language of wine”) for the definition. In French, the stage of winemaking that occurs between fermentation and bottling is referred to as “elevage,” which literally translated to the “raising” of the wine. This is correctly referred to in English as maturation.


© Serge Chapuis – Château Calon Ségur

What happens to the wine once it is bottled, in French, is “viellissement,” which literally translates to “ageing.” This linguistic ambiguity arises as a result of different ways to consider what happens when a wine is stored in oak or steel. Is the wine finished once it has undergone fermentation? If so, ageing begins in the barrel or tank. If, as the French do, we consider the barrelling or tanking to be the last step to creating a finished wine to then be bottled, this process ought to be referred to as maturation. The choice is yours! For the sake of this article, however, we will refer to this stage as maturation in order to distinguish it from bottle-ageing, which is another topic altogether.

Human Intervention during the Maturation Process

During fermentation, yeasts convert sugar into alcohol (in other words, grape juice is converted into wine). The maturation process that follows fermentation allows the wine to be refined, its natural aromas and flavours to become enhanced before it is bottled. In one way or another, the lees (deposits of dead or residual yeast left in the wine after fermentation) are removed in order to clarify and stabilise the wine. One method of doing so is “racking,” whereby the liquid is siphoned off the lees and moved to another barrel using gravity, rather than a pump. Removing lees prevents the wine from developing “off-tastes.” But sometimes, winemakers decide to keep the lees to add character to their wine, as well as reducing risk of oxidation and adding body to the liquid. Some wines, most notably Champagne, are left to mature on their lees, undergoing a second fermentation sur lies in the bottle. Several white wines – among them French Muscadet – are aged on lees, which are occasionally stirred (a process called batonnage in French) to increase contact and the exchange of flavour between lees and wine.

Some of the liquid evaporates during the maturation of barrelled wines, leaving behind an empty space above the wine. As this can lead to the wine becoming oxidised and losing many of its special organoleptic qualities, the barrel must be filled up to the rim to prevent the latter.

How wines change during the Maturation Process

Wines invariably change as they mature, but how exactly they do so depends on several factors, including grape variety, the amount of time left to mature and the type of container in which they are matured.

Oak Barrels
© Domaine des Perdrix

© Domaine des Perdrix

Barrels made of oak (French, American or Hungarian) are often used for wines destined to be sold in small volumes and for higher prices. In fact, the top 50 of the world’s most expensive wines are aged in oak. The main benefit of maturing wine in oak containers is the flavours and structure that the wood imparts to the wine. Barrel-aged red wines change colour from a robust, deep ruby or violet to a paler red, even orange. Since the barrels are made out of an organic, naturally porous material, wine matured in oak benefits from limited exposure to oxygen. The wine loses water through evaporation and osmosis through the walls of the barrel, while also gaining additional tannins from the oak (oak-tannins, which round out the natural grape-tannins in the wine). Depending on the type of oak and the depth of toast, the barrel also contributes a wide array of aromatic compounds, which results in notes of vanilla, clove and caramel, along with nutty and smoky touches in the wine. Wines matured in oak tend to also be matured for a longer period of time, allowing their tannins to soften and their bouquet to become more complex. This results in a higher potential for ageing in bottle. The difference is clear especially in the case of white wines which, if not barrel-matured, should be consumed in their youth.

While oak lends wonderful smoothness, character and complexity to wine, this form of maturation can be quite expensive. Each barrel can cost between 700 and 2500 pounds, depending on the origin, wood quality and brand. The tannins and flavours that a barrel can contribute to a wine gradually diminishes with each vintage of wine stored in that barrel. This is why you will often hear mention of more expensive wines “aged in new oak” or some being “matured in barrels of one, two or three previous wines.” One oak barrel can be used for a maximum of 8 wines and, depending on the budget of the winery, each barrel is replaced every few years, a costly process. Since oak barrels also allow for evaporation of liquid inside, it is required to top off each barrel to prevent oxidation. Finally, as barrels come from a natural material, using them in excess can lead to straining the world’s oak forests.

Stainless Steel
© Mathieu Anglada

© Mathieu Anglada

A cheaper and less labour-intensive alternative to oak-maturation is keeping wines in stainless steel tanks (a.k.a. inox). Unlike oak barrels, these metal containers are completely airtight, limiting the wine’s exposure to oxygen. This allows the winemaker to maintain stricter control over the flavour profile of the wines, which tend to result in a fresher, fruitier quality than those of oak-matured wines. Storing wine in steel tanks preserves its crispness and acidity. Many wineries have also started to add oak chips, chunks and planks to their steel tanks in order to endow the wine with aromas and flavours similar to those provided by oak barrels.

While wines do not “breathe” as naturally as they do in the barrel, the process of occasionally racking them allows the liquid to have some contact with oxygen. This is necessary for a wine not to become reduced, which can result in a “suffocated” wine with unwanted sulphurous smells.

It is a common misconception that wines matured in barrel are necessarily better than those matured in steel. This is not the case. Some wines are simply not meant to be “barrel-aged” and doing so can mean a waste of a precious resource. One clear example of the difference is Chardonnay, whose flavour and – even more so – mouthfeel depends greatly on the material of container it is fermented and matured in. While unoaked (stainless steel) Chardonnay is fruity, fresh and crisp, the oaked variation tends to be creamy and more buttery. The latter style fell out of favour with American wine drinkers in the late 1990’s when Chardonnay was over-oaked by some Californian producers. Just as some wines benefit greatly from the flavours and structure imparted by oak, others develop beautifully in stainless steel.

Learn more about additional maturation techniques here 




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