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Wine, Wood, and the Cooper’s Craft

Wine, Wood, and the Cooper’s Craft

 Wine, Wood, and the Cooper’s Craft

CHOCOLATE, nutmeg, vanilla, or wet dog​—these are some of the imaginative terms winemakers use to describe the taste of wine. What factors produce these complex flavors? The grape variety, the soil quality, and the weather all contribute. Since the first century, though, winemakers have added another ingredient to the more than 400 compounds influencing the flavor and aroma of wine. This potent product is wood​—not just any wood, but a specific type known as white oak.

 How did wine and wood first form a partnership? And why is oak the timber of choice for makers of quality wines?

Wood Replaces Skin and Clay

Early in recorded history, man discovered the process of making wine. (Genesis 9:20, 21) Winemakers poured grape juice into vessels made of clay or bottles made of animal skin, where it fermented. Skin and clay remained the standard mediums of storage and transport up to the time of Christ. (Matthew 9:17) About this time, though, another method of storing and transporting wine started to gain popularity.

The first-century historian Pliny the Elder records that craftsmen living in Gaul, now France, devised a method of shaping and joining timber to form barrels. Barrel makers, called coopers, handed down from generation to generation the skills necessary to make these useful vessels. In addition to making the “tight” barrels, which could carry such liquids as wine and oil, coopers manufactured “slack” barrels, which were not watertight. But they were ideal for carrying dry items, such as flour or nails. In an age when the movement of goods depended on human and animal muscle power, the invention of the barrel was a great step forward. Why?

A Technological Leap

The barrel’s bulged shape not only made it very strong but also allowed it to function as a wheel. A square crate packed with heavy goods had to be moved by several men or a beast, whereas a barrel containing the same goods could be rolled and maneuvered by just one man. Because barrels were more robust than clay vessels and easier to move than crates, they stimulated the trade in all manner of commodities throughout the centuries.

Today steel, plastic, and cardboard containers have largely replaced those old-fashioned vessels. Even so, the cooper’s craft not only survives but also thrives. In California, U.S.A., alone, the cooperage industry employs some 12,000 people and generates over $211 million annually. Just one cooperage in Napa Valley, a famous California wine region, produces over 100,000 barrels a year. How are such barrels made?

 From the Forest to the Cooper’s Fire

The most highly valued barrels start life in the oak forests of France. Because of the quality and abundance of the timber, about 45 percent of all wine barrels are made in that country. After lumberjacks fell trees that are between 100 and 200 years old, a mill saws them into logs and splits them carefully along the grain, producing rough boards called staves. If the staves are split incorrectly, they will break when bent or will ooze wine when the barrel is filled. The staves are stacked in open yards where sun, wind, and rain slowly leach bitter tannins from the wood, while enhancing the oak’s aromatic compounds. The staves must weather from one to four years before a cooper will use them.

Stepping into a cooperage can be like stepping back in time. The oak-scented air echoes with the sound of saws, planes, and hammers. Following a time-honored tradition, the cooper shapes the staves so that they are broadest in the middle and taper toward the ends. He bevels the edges to an exact angle so that if stood side by side, the staves would form a cylinder. Then he hammers strong iron hoops over one end of a circle of staves, making the unfinished barrel resemble a flared skirt.

Heaving the heavy barrel over a fire formed on the floor, he warms the wood. Afterward, he dampens the inside of the half-made vessel with water, steaming and softening the timber. Next, the cooper loops a rope or cable around the splayed staves at the other end of the barrel and draws it tight, bending the staves into the familiar barrel shape. Then he bangs the remaining temporary iron hoops into place; the final hoops are fitted later. At this stage, the barrel is open at both ends.

“Toasting” the Barrel

Once he forms the barrel, the cooper cuts a groove on the inside at each end of the vessel so that he can later insert flat circles of timber, called heads, to seal the barrel. The heads are made from slats of oak with thin strips of reed inserted between them. The reeds act as caulking to ensure that the timber remains watertight should it swell or shrink unevenly.

 Before the heads are inserted, the cooper may again place the barrel over the open fire, toasting, or lightly burning, the inside with the flame. The toast level, from lightly to heavily charred, is determined by the winemaker who ordered the barrel. Toasting the wood in this manner intensifies the flavors that the oak will impart to the wine. The heads may also be toasted separately. The cooper then fits the heads and bores a bunghole in the side of the barrel so it can be filled and emptied. Finally, he sands and cleans the outside of the barrel and ships it to the winery.

“A Winemaker’s Spice Rack”

“Oak is the ideal material for aging our wines,” says Bob, the manager of a California winery. Guiding a tour group through the winery, he explains: “Oak is the only timber that has both the strength to make sturdy barrels and the ability to improve the flavor of the wine.” Pointing to the rows of barrels, Bob says: “As wine ages in a barrel, the vessel acts like a lung. Oxygen slowly seeps through the timber into the barrel, causing the wine to oxidize. This process stabilizes the wine’s color and softens its flavor. Meanwhile, the barrel transpires alcohol and water, which evaporate into the atmosphere. The lees, or yeast sediment, settle to the bottom of the barrel, and sugars and tannins from the oak slowly leach into the wine, imparting their distinctive flavor characteristics. Depending on the style of wine, the batch may be aged in the barrel for 18 months or more before bottling.”

Bob continues: “Wine barrels have a limited life expectancy. We age some of our premium wines only in new oak barrels because after one use most of the flavors have been extracted from the wood. Barrels can be used more than once, but after several uses they may start to impart undesirable flavors to the wine.”

Explaining why the origin of the oak is important, Bob says: “White oak grown in the soil of Limousin, France, will convey flavor characteristics different from those of the same species grown in Missouri, in the United States.” Why the difference? “The soil composition, the weather, and the age of the forest are among the many factors. The way the timber is dried, whether kiln-dried or air-dried, also alters oak’s effect on wine. The best wine barrels are made only from air-dried timber. Most of our barrels are made of either American or French oak or a combination of the two, but oak suitable for barrel making is also grown in China and Eastern Europe.”

At the end of the tour, Bob says: “All these options​—the type of oak used, the toast level, and the amount of time the wine is kept in the barrel—​are like a winemaker’s spice rack, allowing him to alter the flavor of the final product. So the next time you enjoy a glass of quality red wine, contemplate not only the time and effort that went into producing the wine but also the skill involved in building the barrel that nurtured the vintage.”

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Oak Barrel or Oak Powder?

Some white wines, such as chardonnay, are aged in oak. However, not all of them are aged in oak barrels. Some winemakers achieve an oak flavor by inserting slats of oak into stainless steel vats of wine or by adding oak shavings or powder to the wine as it ages in steel or concrete vessels.

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Only top-quality oak is used for wine barrels

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Logs are split with a hydraulic jack

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The wood must be sawed with the grain, otherwise the staves will not be watertight

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Rough boards ready to be transformed into barrel staves

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After the barrels are heated over a brazier, the staves are held together with iron hoops

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Seguin-Moreau, France

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Wine is aged in oak barrels to enhance its flavor

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Coopers in Paris, early 20th century

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© Cliché Bibliothèque nationale de France, Paris

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Testing wine matured in barrels, c. 1900

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© Cliché Bibliothèque nationale de France, Paris

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© Sandro Vannini/CORBIS