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Bringing Oak to Life: The Birth of a Wine Barrel

For as long as wine has been traded and transported, there has been a need for suitable  containers. Look back several millennia and we see that the clay amphora was the first vessel of choice, made waterproof by a coating of resin. When the barrel came to predominate over this ancient vessel is uncertain, but by the time Caesar's army was marching over western Europe barrels were certainly an established method of transporting goods, perhaps first manufactured by the Celts. Today wine of quality is generally transported in bottle, and there are newer, less costly methods for transporting the bulk wines of the 21st Century. Nevertheles the wooden barrel, although no longer first choice for transporting wine, still plays an important role in the winemaking process, sometimes in the process of fermentation, but most commonly during the élevage, the period of wood maturation that precedes bottling and sale.

For this reason, in spite of the vast and sweeping modernisation the wine industry has seen over the last century, the oak barrel remains a vital piece of equipment. The manufacture of a barrel by hand is a hugely laborious, skilled and lengthy process. Although today the process is mechanised to a degree it is still a very labour-intensive one and the end result is close to a work of art. In order to see and understand the process of barrel manufacture for myself I recently visited Murua, Logroño's leading cooper and suppliers to many of the leading bodegas of Rioja and to numerous other foreign clients. Some of what I saw there, particularly on the matter of oak selection and treatment of the wood before it is assembled did little more than jog my memory, but many aspects of the manufacturing process per se were completely new to me. For this reason it turned out to be a surprising and absolutely fascinating trip; the process of transforming weathered oak, with its rough and somewhat dishevelled grey-black appearance, into a new and gleaming oak barrel was remarkable. In each case the finished barrel, with its warm wood tones and bright silver bands, was to my eyes an object of considerable beauty.

Preparing the Wood

Here I attempt to relay what I learnt of the process, which begins with wood sourced from trees generally between 100 and 150 years of age. Before the process of barrel manufacture proper, there are two decisions to be made, as the wood can be either split or sawn into staves, and then kiln or air-dried. The first decision, whether to saw or split, depends largely on the source of the oak. American oak is rich in tyloses which block the radial pores, reducing the porosity of the wood, and so it can be sawn. With European oak, however, the quantity of tyloses is much less and the wood is more porous as a result. Thus for it to be suitable for barrel-making the wood must be split along the grain rather than sawn. There are several implications of this decision; first, splitting means a lower yield of staves from any piece of wood, increasing wastage and expense. Secondly, a sawn stave exposes different elements of the wood to the wine than a split stave would, and so its effect on the final flavour of the wine may be quite different.

Air-drying is generally regarded as superior to kiln-drying, but the latter has gained some favour as it is a much more rapid process. Adjacent to the Murua cooperage is a gigantic holding yard filled with hundreds of huge stacks of wood, of which just one is pictured above. This represents a massive financial investment, as the wood rests here for at least three years, occasionally longer. Kiln-drying, meanwhile, can be completed in a fraction of the time. Nevertheless, air-drying is generally regarded as superior, particularly with regard to the effect of the oak on the tannins in the finished wine. Possible explanations for differences in the finished product according to whether it has been dried naturally or in a kiln include fluctuations in the temperature of wood stored outdoors, exposure to the rain or its colonisation with microbes and moulds which may infiltrate the wood, although there is no experimentally derived evidence for any of these theories.

At Murua the wood is dried in the open air, slowly fading from golden brown to a silvery grey as the months pass, the ground beneath the stacks of wood turning black with the leaching of the tannins. The wood spends its time stacked in a peculiar fashion, with rows of staves positioned at an angle as pictured above. The purpose of this method is to improve the circulation of air around the wood, and to facilitate drying of the stack after rainfall.

Although much of the wood has at this point an uncertain destination, this is not universally true. Already some stacks are earmarked for certain clients who will have been involved in the selection and purchase of the raw materials, and some staves may be left drying for longer than the usual three years according to the demands of the buyer. One well-known Murua client insists on four rather than three years of air-drying, and they are willing to pay for it.

Shaping the Staves

When sufficient time has passed the wood is brought into the cooperage for preparation and assembly, and after three years of patient weathering it takes much less than a day for the rough staves to be transformed into a shining new barrel. First the staves must be cleaned but also shaped, a laborious process once achieved by hand using a shaped axe but today completed by machine in a fraction of a minute. The staves are shaped in two fashions, hopefully explained by the image above. First, in order to facilitate their assemble into a round barrel, wood is removed to give concave (inner) and convex (outer) surfaces, top and bottom respectively in the image.

Second, the staves are planed so that the finished barrel has the desired shape, this being a fatter middle and a slightly leaner top and bottom, as seen to the right. To achieve this more wood is removed from the top and bottom than from the middle of the stave, so that its middle has a larger girth (black outline in the picture) than the top and bottom (red outline in the picture). The extensive removal of wood from all four surfaces (somewhat exaggerated in my picture, admittedly) means that the staves now have a dramatically changed appearance. Gone is the weathered, silvery-black wood that was ferried into the cooperage by forklift truck; these staves now have a healthy, warm, honey-gold appearance.

The staves must then be raised into a barrel, and as the end result must have a standard size the staves are not chosen at random. As I watched, a Murua employee laid out a collection of staves against a measure, the length of which equals the circumference of a finished barrel at its fattest, central portion. Then, by a rapid process of mixing and matching, he rejects staves and introduces new ones until he has a collection which matches the measure, thus giving a barrel of the required circumference once assembled. And there must be at least one fairly wide stave, one that has the strength to take the drilling for the bung hole. They then are quickly passed to another worker who begins the process of raising the barrel. They are assembled in a circle, held together at the top by an iron hoop, until all of the staves are in place. At this point, although nicely assembled at one end, because of their tapered shape they naturally splay out at the other. It is now that the ingenious work of bringing the staves together at the other end without snapping them begins. (6/1/09)

• In part two the barrel is completed.