Roger C. Bohmrich, Master of Wine

April 7, 2020

Wine has an affinity for wood. In a manner of speaking, they are fraternal twins, each originating with a plant molded by soil, sunshine and rain. At the outset, a barrel was simply a practical container for storage and transport, gradually supplanting the amphora, linchpin of the ancient world. Barrels have been used to hold water, nails, gunpowder, salted meats, flour, pickles and countless other substances (Work, 2014). Wood of many types including cherry and chestnut has been employed to make wine barrels. Oak has been fashioned into wine containers for roughly 2,000 years (Zhang, 2015). The French were fortunate to have their own extensive oak forests, which currently enjoy an unrivaled reputation. Hungarian and Eastern European oak has also found favor during many periods of history. Italians have relied on oak from nearby Slovenia. Distinctive American oak has been preferred by winemakers as far away as Spain and Australia.

            There are in fact many species of oak tree around the world belonging to the genus Quercus. Three main species are utilized for wine containers. Quercus robur, referred to as pedunculate oak, is found across much of Europe (IFVV). It is rich in phenols and ellagitannins. Quercus petraea, commonly called sessile oak, grows from the far northern Iberian Peninsula to southern Scandinavia. This species contains a somewhat lower level of ellagitannins but is well endowed with lactones and eugenol. Sessile and pedunculate oaks provide the material for most French wine barrels, which enjoy disproportionate prestige across the globe.

            Another significant oak for wine as well as bourbon and whiskey, Quercus alba, comes from Eastern North America and the Midwest, extending to lower Canada. American white oak is lower in tannins yet significantly richer in vanilla-like compounds than its French counterparts (Zhang, 2015). However, these generalizations, studies show, fail to reveal that properties vary to a large degree among trees of the same species. That said, it has been found that sessile oak is “richer in sweet triterpenes and poorer in the bitter one” than pedunculate oak (Marchal et al., 2017).

            The remarkable French forests which supply the world’s most admired wine barrels have been called the “treasure” of Jean-Baptiste Colbert, a 17th century statesman (Vaslin, 2011). Colbert viewed France’s forests as a source of immense richness; they had both economic and military significance. He saw them as indispensable, the source of wood to construct the country’s naval vessels. Strict rules governing forest management were introduced in 1669. Interrupted only by the French Revolution, this diligent husbandry by the state has extended over three centuries and continues in the present day under the Office National des Forêts (www.onf.fr/). If you enjoy the qualities of a Pomerol, Chambolle-Musigny, Super-Tuscan or Napa Meritage – all of which have undoubtedly been enhanced by aging in French oak casks – thanks are due in part to Colbert.

            A French cooper such as Seguin Moreau has inventory of wood to cover three years of sales. French oak is first dried in the open air for a period of 24 months as a rule while 36 months is less common and commands a price premium. This implies the raw wood must be acquired up to four years ahead of delivery of a barrel (Lasky, 2019). In view of strong demand for oak from wineries and distillers, prices have been increasing for both American and French barrels. Genevieve Janssens, Chief Winemaker at Robert Mondavi Winery, explains that a new barrel of 60 U.S. gallons currently costs $900. She says that “if that barrel matured one vintage, the cost per bottle would be $3. But if it’s used for at least three vintages…the cost comes down to $1 per bottle” (Gordon, Sep 2019).

            For some time, the focus has been on the significance of origin: the forest where the wood is grown. For both oak tree and vine, the role of place – or terroir – seems fundamental. Yet, the names of most forests are unknown to wine amateurs. A very few such as Tronçais seem to have achieved special status, but only specialists have heard of Bellebranche, Châteauroux or Hesse (Taransaud, 2005). While forest identity retains intuitive appeal, attention in the trade has been shifting to the question of grain.  Andrei Prida of Seguin Moreau points out that the tightness of the grain – the width of the annual growth rings of the tree – is related to species. In general, fine-grain wood is understood to have less than 3 mm between rings (De Pracomtal et al., 2014). Fine and extra-fine grain wood comes predominantly from sessile oak whereas coarse grain is associated mainly with the pedunculate species.  It is nonetheless important to underline that species, not grain width, serves as a more accurate indicator of the wood’s chemical composition (Gordon, March 2019). This being said, a study by Chêne & Cie showed that tight grain discharges more aromatic compounds than coarse or open grain (De Pracomtal et al., 2014).  


            Taking this a step further, the significance of any given forest may be overstated in terms of dictating the characteristics of the finished barrel. Prida notes that most French forests contain both sessile and pedunculate species. Some say that the hand of the cooper, specifically the curing of the staves and the toasting process, has the greatest impact (Gordon, March 2019). It may count more if the barrel is crafted by François Frères or Taransaud than if the wood comes from the Tronçais forest in Allier or Bertranges in Burgundy. This is, it seems, just another version of a familiar debate – nature vs. nurture – which cannot be neatly resolved. The question may be moot to the extent coopers create branded “blends” from different forests for a single barrel such as the Omega of Radoux or Seguin Moreau’s Icône (Fig. 1 & 2). Winemakers around the world often buy barrels from numerous suppliers, insuring a diversity of both wood and coopering techniques. Apart from forest or grain, barrel size and age also govern the interplay of wood and wine. A smaller new barrel will have a far more pronounced effect than a larger one which has matured multiple vintages.

Figure 1. The Omega barrel from cooper Radoux is a blend of woods from French forests “matured” for three years. Using a proprietary technique, OakScan®, the staves are selected based on a polyphenolic index. Photo Tonnellerie Radoux.
Figure 2. The Icône Elégance barrel of Seguin Moreau produced from oak selected for its chemical properties and “oenological potential.” This model is intended for concentrated red wines such as those based on Cabernet Sauvignon or Syrah. Photo Groupe Oeneo/Seguin Moreau.

There is a certain standardization of barrel formats offered by cooperages. This is logical because barrels need some type of support. Racks are designed to fit standard barrel dimensions and remain in place even as barrels are replaced. Perhaps the most universal barrel in terms of usage worldwide is the Bordeaux barrique holding 225 liters, which is usually offered in slightly varied iterations. The 228-liter pièce is the standard in Burgundy. At first glance, these two models (Fig. 3) appear nearly identical yet have subtle differences. The Château Tradition barrel from Radoux has staves 95 cm in length and 20 to 22 mm in thickness; it weighs 46 kg. In contrast, staves of the company’s Burgundy Tradition are 88 cm long and 25 to 27 mm thick; this barrel weighs 48 kg. The bilge of the Burgundy barrel – diameter of the center – is larger than the Bordeaux barrique, 72.2 cm as opposed to 69.5 cm. It also has double the number of decorative chestnut hoops: 8 vs. 4 (www.tonnellerieradoux.com). Simply put, the Burgundy barrel is shorter the long way and wider around the middle. Casks of other capacities such as 300, 500 and 600 liters are in general if more limited use as well. 

Figure 3. The Bordeaux Château 225-liter barrel (left) and the Bourgogne Caveau 228-liter barrel (right) from Tonnellerie Ermitage.

What exactly are the consequences of fermenting and aging wine in barrel? In essence, a barrel enriches the wine (Tiquet-Lavandier & Mirabel, 2014). For many wine drinkers, the focus is on the more obvious aromas conveyed by compounds extracted from oak. Lactones may be perceived as coconut or simply fresh wood. Vanillin, a phenolic aldehyde, brings vanilla to mind. Eugenol is perceived as clove while guaiacol may suggest spices or smoke. Charring or toasting the interior of the barrel induces roasted or even bitter almond, a furfural. Other effects of heating by fire (Fig. 4) may be perceived as licorice, burnt sugar or caramel (ITV, 2003). Yet, the consequences of toasting, research has found, are far from uniform due to variations in fire management practices even within the same cooperage (Todorov, 2020).

Figure 4 . The toasting process called “bousinage” or “la chauffe.” Photo François Frères.

While these aromas are the makings of tasting notes, the gradual and controlled oxygenation of the wine, aided by the ellagitannins, may have more fundamental benefits, as illustrated by the model below (Fig. 5). Oxygen enters the barrel through the bung hole, the joints between staves, and the wood itself, which acts as a membrane. Dry wood, it is estimated, contains 0.3 mg of trapped oxygen per gram (Pons et al., 2020). Racking and topping up are also contributors. Tannins and anthocyanins (the pigment of red wine) combine, resulting in a more stable color and softening of the tannins. Moreover, polysaccharides coming from the wood give a sensation of richness or fat and further lessen astringency (ITV, 2003). There is as well a loss due to evaporation romantically termed the angel’s share. Consequently, the wine becomes more concentrated (Tiquet-Lavandier & Mirabel, 2014). The temperature and humidity of the cellar play a part in these changes (Roussey, 2019). Finally, a barrel encourages natural clarification as unstable compounds fall to the bottom. 

Figure 5. Reactions and exchanges which occur as wine is held in a wood barrel. Source: Tiquet-Lavandier & Mirabel, 2014. Original model created by François Feuillat for Puisais, J., La Tonnellerie. Un art au service du vin (2000).

The transformations brought about by oxygen are comparatively subtle yet appreciably enhance and complete the wine if the maturation process is skillfully managed. Barrels are far from static containers: they are interactive partners in the winemaking process. What is more, the barrel has taken on symbolic meaning for many wine lovers, who expect to see a cellar filled with casks at any winery. Yet, there are significant exceptions. All wines may be restyled by wood to varying degrees, but not all are better as a result. Many aromatic whites based on Riesling or Sauvignon Blanc, to name just two, do not benefit from contact with oak. Likewise, a few Châteauneuf-du-Pape reds see only concrete. That said, the consensus holds that the finest red wines only fulfill their greatest potential if they are refined in barrel.


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