Wood and wine: working together
Ever since the invention of the barrel, wine and wood have had a long-lasting love affair. Who can taste a fine Médoc or white Burgundy without noticing its hints of smoky vanilla mixed with the fruity aromas of the grapes? It is a perfect marriage, a symbiosis that results in undeniable enjoyment. Yet making this subtle union a successful one is far from simple. From the vine to the glass, wine goes through three successive stages: first, vinification, then maturing, and finally, ageing in the bottle. Wood usually comes into play during the second stage, and sometimes the first. During vinification, the sugar-rich juice from the pressed grapes begins to ferment due to the action of micro-organisms, namely yeasts. During this process, which takes about one to two weeks, the sugar is converted to alcohol, leading to a massive release of carbonic gas and an increase in temperature. When almost all of the sugar has been converted, fermentation ceases.Using wood in winemaking In earlier times, vinification was always carried out in wooden containers. Today, most winemakers prefer stainless steel tanks, which are easier to use and maintain. There are nonetheless many exceptions: the méthode bourguignonne, for example, involves producing white wines in wooden barrels with the aim of achieving a very unique end product. After vinification comes the maturing and refining process. At this stage, the still cloudy wine starts to develop its flavour characteristics and to become clearer and more stable. During this process, which can last from several months to several years, wood can play a fundamental role. We will return to this later.Finally, the wine is transferred to bottles, where it will age in an oxygen-free environment. According to its characteristics and its quality, over the years it will develop an increasingly complex bouquet. The fruity or floral aromas of young wines, acquired during the maturing process, blend together and give way to others more reminiscent of undergrowth, musk, toast or leather. It is as the wine matures that the magical symbiosis between wine and wood occurs, so this is the stage that we will examine more closely. Logic tells us that if a wine spends time in wood, it will extract certain woody flavours. However, it isnot quite so simple. Wood has an effect that is more complex (it does not only yield its aromas) and more mysterious. For simplicity's sake, it could be said that wood influences a wine’s colour, structure and bouquet. The wood itself is responsible for this, of course, as well as oxygen, which is constantly present during maturation, via the wood.Colour, structure and taste Grapes contain certain chemical constituents that occur naturally in wine. Of these, the most important are tannins, which are responsible, among other things, for the wine’s structure, and anthocyanins, which give it its colour. A young red wine contains a lot of anthocyanins in their free state. They are responsible for the deep red colour, bordering on purple, that is so characteristic of young wines. The problem is that these anthocyanins are unstable and have a tendency to disappear over time. Their decrease is responsible for the orangey-brown tints in old wines, and their only chance of survival is to combine with tannins to form complex molecules that are much more stable. This phenomenon occurs naturally in wine, whether or not it is in contact with wood. However, wood does seem to facilitate the process of condensation (also known as polymerisation). Like grapes, wood is of vegetal origin and itself contains tannins and anthocyaninsthat participate in the molecular combinations and enrich the process.Because wood liberates tannins in the wine, it also modifies its structure. One might think that it reinforces the structure, but in fact, it is more complex. While it does release new tannins in the wine, these then combine with other molecules which, if maturation is well managed, contribute to an overall polishing effect that smoothes out the tannins. As for the heaviest of these molecules, they precipitate to the bottom of the barrel. In this way, the wine loses its impurities and particulatesand becomes more refined. The objective is reached when the tannins of the wine and the wood have completely blended together. The result is a significant decrease in the astringency and bitterness of the wine.
A wine’s bouquet is possibly its most mysterious aspect. We know that every aroma corresponds to precise molecules. In grapes, these substances are essentially located in the skin and are incredibly diverse. Among the aromas contributed by maturing wine in wood, we can distinguish between those contained in the oak itself, and those developed when the barrel is ‘charred’ or ‘toasted’. To the former category belong lactones, which add hints of coconut, fresh oak and sap; and to the latter belong various substances such as vanillin (aroma of vanilla), eugenol (aroma of spicy carnation) or ethylphenol and guaiacol, which are responsible for a charred aroma.
As can be seen, maturing wine in wood plays a not insignificant role on the final outcome. But this should not be taken to mean that wood is the only thing involved in this process. Throughout maturation, oxygen has an important influence: an influence that wooden barrels seem to channel, to a wine's benefit. Oxygen can be wine’s best friend or its worst enemy. In excess, oxygen seriously damages wine, affecting its colour, structure and above all its bouquet; simply leave a bottle uncorked for a few days to notice the results. Yet a little oxygen does wine a lot of good. In fact, it is indispensable to effective winemaking, as explained above (oxygen is involved in the modification of the colour, the polymerisation of the tannins and the precipitation of complex molecules).
During its time in a wooden barrel, wine is in constant contact with a little oxygen. In order to limit this, the winemaker regularly carries out ‘topping up’, which involves adding wine to the barrel to replace loss via evaporation through the wood. Racking also brings the wine into contact with oxygen. This is the process of separating wine from the sediment, or lees, at the bottom of the barrel by transferring the wine to another barrel. Wine is racked four times a year. In total almost 30cubic centimetres of oxygen per litre of wine are accumulated during the course of the winemaking process. The length of maturation and refinement of the wine depends according to the region, the type of wine and the vintage. Generally it takes between one and two years, but this decision is left to the judgement of the winemaker. Not every wine benefits from spending time in wood. Only those destined to become wines to lay down and which have sound fundamental qualities really get the most out of wood. There is no point in putting a light, fruity, drinkable wine in a wooden barrel. It willlose its charm without gaining in quality. Equally, if wood is used in badly controlled winemaking conditions, for example, using barrels that are too old or in bad condition, the wine can end up with a taste of mould, mouth-parching tannins or an unpleasant bitterness. Essentially, a vintage wine cannot be created simply by putting it in wood!
Gilbert & Gaillard