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No wood, no good” comes to mind for most of us in the winery as we approach the annual assessment to determine which of the new vintage wines are destined for oak maturation. The famous catch-cry of Wolf’s first winemaker, John Glaetzer, and the mantra that many like to associate with Wolf Blass wines, is still as an important part of the winemaking philosophy today as it was when Wolf first started making wine in the Barossa. The variables and choices we have to make regarding the number and type of barrels we use being as complex as our fruit sourcing and picking selection.

Of course, oak barrels for storage of wine have been widely used since the entrepreneurial and industrious Romans introduced them to the ancient world, rendering palm wood barrels, breakable clay amphora, and the presumably pungent goat skin bags effectively obsolete. Oak is not the only timber that offers the engineering and watertight properties required to fashion a serviceable container of liquids, but it is its unique compatibility with wine that has dictated its preferred use the world over. French and American oak are the main barrels of choice of the winemaker, with small amounts of other European oaks also used.

Types of Oak

Of the 400+ species of oak or Quercus genus, only a handful meet all the necessary requirements for wine barrel production. In Europe and most notably France, Q. robur (pedunculate oak) and Q. petraea (sessile oak) are used almost exclusively. In North America (the only other major region of oak forestation) it is Q. alba (white oak) that predominates in the central regions such as West Virginia, Minnesota and Missouri.

Oak Forests

The forests of France spread across 28% of its territory, however only 25% are oak trees and only 7% of all harvested trees are made into barrels. The state owned and managed forests are all part of the reforestation program started in 1669 by Louis XIV ensuring the long term renewable viability with average harvest age of the trees being 80 – 200 years. Similar programs are run across Europe and North American, being a mix of both state and privately run operations.

The various forest and regions of France (and greater Europe and the U.S.) offer very different oak characteristics due to the variation in climate and topography, with the oak being identified by regional names such as Allier, Vosges, Nevers, Chatillon and Tronçais, as well as grain sizes (growth rings) ranging from very open to extremely tight from the slowest growing trees.

How Barrels are Made

The forest lots are auctioned off as standing trees, harvested and cut to barrel lengths along the straight part of the trunk only. After splitting along the grain to ensure the timber is watertight, the staves are stacked out to ‘season’ for a minimum of 2 winters where rain and snow leech out the greener harsh tannins present in the timber.

After seasoning, the staves are shaved with the correct angles, cut to the right length and shaped wider in the middle with narrower ends to form the familiar barrel shape. The staves are held in place by metal hoops and bent to shape by the cooper (barrel maker) with fire, steam or water.  The barrels are always then toasted over open oak fires to winemaker specifications to further complex the various oak compounds producing synergistic flavours and aromas. Head boards are fitted at each end into the purpose cut groove and the barrels are now watertight without one nail, screw or glue.

Barrel Selection

Barrels arrive at the winery with all the variables of country of origin, oak species, growing conditions, grain size, seasoning location and regime, manufacturing processes such as stave bending, toasting profiles as well as barrel size and variations in shape. These inputs, some by nature, some by man, all contribute to the differing interactions each barrel will have with the wine that will spend up to 24 months maturing in this very unique vessel. The barrel will be watertight but not completely airtight and this extremely slow transfer of oxygen drives the maturation process where the wines structural components are strengthened, complexed, softened and flavour enhanced through this wonderful interaction of wine and wood.