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American Oak Character in Wine
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Devotees of rich full bodied Australian Shiraz wines from the Barossa, McLaren Vale and Rutherglen well appreciate it. Ah … , that rich sweet coconuty, vanillin character that melds wonderfully with the equally generous and supple sweet berry fruit flavours of Shiraz. Many Australian winemakers think that it is a match made in heaven. American oak and Shiraz…. Wines like Grange, Jim Barry Armagh, Rockford Basket Press, St Hallett Old Block, Wolf Blass Black Label, and E&E Black Pepper Shiraz, all owe part of their depth and complexity to the "sweet" oak characters imparted by the humble American oak barrel.
American and French oaks are sourced from distinctly different species of tree. This affects both the physical and chemical properties of the barrel staves and thus the sensory impact that the oak has on the wine. American white oak is the species Quercus alba (alba being Latin for white, pertaining to the lightness of its bark). The French oak typically used for winemaking is commonly called Sessile oak, and is of the species Quercus sessilis.
Unlike its French counterparts, American cooperage is rarely distinguished by the location of its forest. This is surprising as the major American white oak forests span 18 Eastern American states and Oregon. The major eastern forests range from Pennsylvania in the North East through North Carolina, Tennessee, Kentucky, Missouri and through into Arkansas and Mississippi in the south. In fact, the US Forest Service estimates there are 5.2 billion white oak trees (greater than waist high) covering a total of 235,000 square miles.
A few American winemakers have become keen students of the variations in oak character displayed by various important American forest regions. At an Oak Barrel Symposium held recently in Fresno California, Jeff Cohn winemaker from Rosenblum Cellars in California outlined the differences in American cooperage. He explained that oak from Missouri produces big flavours of vanilla, lemon custard and spice, and in less seasoned oak, a dried herbal character. Pennsylvanian oak is tightly grained, and is reminiscent of French oak except with some subtle coconut and vanilla notes. In contrast, Virginian oak imparts a burst of coconut and vanilla, but also gives the wines finesse and mouth-feel with time. Finally Oregon oak is very toasty, resinous, spicy and caramel like, but can impart a degree of harshness due to the pick-up of hard tannins. I sensed a general feeling of disdain for Oregon oak amongst American coopers and winemakers. "Tannic, sweet coconut, pencil shavings, cedar and without subtlety" seemed to be the chorus. Worth a try with our more jammy Shiraz I thought !
The flavours of coconut and vanilla are common descriptors of oak from many American forests. This is due to the occurrence of higher levels of the character impact compound cis-oak lactone in Quercus alba compared with European sessile oak. Cis-oak lactone imparts flavours of coconut, vanilla, and custard powder, and gives an impression of overall sweetness on the palate.
Given that approximately 70 million cubic feet of cooperage oak was felled last year from the state of Missouri alone, can we expect that American oak will continue to be available in the long term? At first glance one might guess the answer is no given that 1) oak trees are harvested at typically 60 to 80 years of age, and 2) twenty five times more oak is harvested each year for furniture and floor-board production than for cooperage. However, based on an extensive survey of tree demographics by the US Forest Service, it would appear that the US oak forest resource is in a pretty healthy state. The forested area has increased steadily since 1980, to near pre-1947 levels. Currently in the state of Missouri (the major source of oak for cooperage), a regrowth of 1.5 cubic metres occurs for every cubic metre of oak felled. West Virginia is doing better still, managing to replace 3 times the volume of oak it fells! These sustainability figures are remarkable given that 85% of the forest resource is in private hands. There is however a downward pressure on stocks in some upper states due to increased urbanisation and the progressive southward invasion of the oak pest, the Gypsy Moth. This destructive creature invades forests by hitching rides on the backs of unsuspecting hikers. It appears that the American oak forests are being harvested sustainably and will therefore continue to supply the magic ingredient that makes many of our Shiraz wines so delicious.
But the majority of oaked wines made in the new world never see an oak barrel, American or otherwise. The many different ways in which oak character can be imparted, other than through the expensive practice of barrel storage will be the subject of another article.