In our last Wine 101 email, we talked about the science of how Oak affects a wines texture, through the introduction of oxygen, in rather simple terms. We began to look at the differing types of oak and their attributes, but did not explore how each effects the flavors of a wine. That is a question with a very nuanced answer.
There are two distinct aspects to oak that influence the flavors of wines aged in barrel. The first are the flavors inherent in the wood, while the second are the flavors created during the construction of the barrel. One of the features of oak that set one species apart from another is the density of the wood. The structure of each stave in the barrel can have a surprisingly large impact on the way the barrel reacts with the wine it holds.
Another important, and frequently overlooked, aspect to managing the impact and profile of oak aging is the seasoning of the wood before the barrel is constructed. These two elements, wood structure and aging, each play an important role in determining how a type of wood can be used to improve a wine. Last week we took a look at a pair of producers from California who rely on American Oak, and today we look around the globe at a pair of Australian producers who have followed this same path.
What to expect: French OakFrench oak has historically been the preferred oak for wine barrels. Its tight grain, and balanced flavor profile, has allowed winemakers great lattitude in using French oak to accent a wines natural character. French oak contributes more tannin to wine than most American oak does, and the recent surge in demand for barrels has lead many coopers to reduce the seasoning time for their wood staves, accentuating this atrribute. This shortcut has allowed coopers to keep up with demand but at the same time has reduced the quality of many of the barrels entering the marketplace today.
So-called American and French oaks have both chemical and physical differences that distinguish one from the other. I say so-called, because the term American Oak is generally used to refer to the species Quercus alba, which grows In the US, as well as other regions.
One of the main differences between the two families of oaks is the density of the wood, referred to as the tightness of the grain, as well as the porosity afforded by that grain. French oak tends to have a tighter grain, due primarily to the cooler temperatures the French forests enjoy. At the same time they have fewer growths, know as tyloses, that are able to restrict the flow of liquid through the capillaries used to supply a tree’s newest growth ring with nutrients.
The Formation of Tyloses and how they block the flow of fluid
The end result of this structure is that French oak needs to be cleaved against the grain to prevent excessive exposure of these capillaries, while the less porous American oak can be quarter sawn into staves. This affects not only the flavor of the wine, by splitting the wood with the grain fewer cell walls are broken thus producing a more subtle impact on the wine, but it also affects the price of the barrels. By quarter sawing the wood, one not only reduces the labor cost involved in barrel construction, but at the same time one increases the yield from a set quantity of wood.
An example of quartersawn wood versus split staves
So, one of the fundamental differences between types of oak is the structure, which dictates how the wood is prepared for use as a barrel stave. The splitting versus sawing technique is responsible for changing the rate at which elements within the wood leach out into wine in the barrel.
One of the first things to recognize is that each piece of oak has a finite amount of these flavoring elements. The first time a barrel is used, much of these compounds get absorbed into the wine, leaving less for the next year’s wine. This is not necessarily a bad thing though. Many producers use new barrels each year specifically to impart their wines with the strongest oak flavor possible. Some people have even gone a step further, ageing their wine in a succession of new oak barrels while others prefer the subtle or neutral effects of used wood. Some barrels have longer lives than others. There are many reasons for this; among the most convincing is the need for proper seasoning of the wood.
Beyond structure, what's the season?One very significant element in the evolution of barrel making has been the use of kiln-dried wood to replace naturally aged wood. The demand for barrels is such that very few coopers can maintain the inventory needed to age wood naturally. Naturally aged wood is exposed to the elements for several years. This passing of the seasons, with their alternating cold and warm periods and regular washings of rain helps to properly season the wood.
This seasoning of the wood allows the green tannins that naturally occur in the oak to be washed away, along with a significant portion of the wood’s flavoring elements. While this reduces the impact of the first year of use for that barrel, it also gives a winemaker a more even, neutral tool to use in crafting their wine. Some of the elements that are washed away during this process are called lactones. These lactones add a sweetness to the wine, as well as a vanilla note.
In oak that has been kiln dried these lactones remain in the wood, as do bitter, green tannins. For the first three years or so the level of lactone in the wood is sufficient to cover up any bitterness that the green tannins may contribute to the finished wine. With time however the lactones are exhausted, yet the kiln-dried wood continues to contribute bitter tannins to the wine. Because of this many winemakers will only use a kiln-dried barrel for 3 or 4 vintages while the air-dried barrel might be good for 10 or more vintages.
Much American oak was traditionally kiln dried. The domestic cooperage industry in the USA was built to supply the spirits industry, where a burnt, vanilla flavor-filled barrel was a good thing. The evolution of the industry, and its accompanying focus on building a better wine barrel has lead them to emulate the techniques of French coopers.
American oak is now routinely split into barrel staves, and air-drying is becoming more commonplace. The results of these adjustments are clear: American oak barrels are finding new fans around the world as these techniques moderate the impact of American Oak on wines in barrels and more closely parallel the most desirable traits of French oak barrels.
This is part three of a four part series.
Read Additional reports in this Series on Snooth.
Part One: Wine 101 - How to speak wine and "Really" taste wine
Part Two: Wine 101 - Why Oak Works
Part Four: Wine 101 - Toasty Oak and why it's not all good Coming Soon
A Pair of Australian Wines that use American Oak to Great Effect2005 Parson's Flat Shiraz Cabernet
Fermented and aged in predominently American oak, 80% of which is new, this wine has classic, smoky notes on the nose that recall mocha, toast, vanilla and baking spices. On the palate this powerhouse is packed with rich fruit, and accented with licorice and coffee tones.
2004 penfolds Bin 389 Cabernet Shiraz
Penfolds is one of the most famous users of American oak in the world. Their trademark Grange Hermitage is aged in 100% new American oak barrels each vintage. This fine Bin 389 is often referred to as a baby Grange since it is aged in those same barrels one vintage later.