Wine Press: How does oak affect our passion for wine?


I have often wondered why winemakers put their wines, white or red, in oak barrels and age them for sometimes months at a time.

The University of California Davis recently conducted a seminar on oak management and wine sensory issues. It looked at the use of oak barrels and oak adjuvants such as oak staves and oak powder with regard to how the oak may affect the wine’s chemical composition, aroma and flavors.

To me, the aroma of a wine is the “smell” of the specific grape varietal. But this very sensitive element can be easily influenced by the winemaking techniques and the use of oak barrels.

One obvious question is: why were oak barrels chosen to store wine in the beginning? The barrel is a perfect container to age wine in and is easily moved around manually. The answer seems to be related to the fact that oak barrels do not leak if properly coopered.

One of the most intriguing questions that was discussed at this seminar was what would have been the impact on wine tastes and wine’s appeal if a different tree had been chosen for barrel production. Has the effects of the oak barrel basically defined our tastes for different styles of wine?

Most European oak barrels are made from the Quercus petrea or Quercus robur while Quercus alba or the white oak is the main species used in American oak barrels. Today a good French oak barrel sells for around $1,000 a barrel and many of these barrels can only be used for several years before they lose their ability to enhance the flavors of the wine.

Oak barrels are usually toasted using a fire placed inside the open barrel, and the time of exposure and intensity of the fire will determine the level of toast in the barrel. You can create a light toast, a medium toast and the heavy toast. The heavier the toast, the more impact the barrel will have of the flavor components of the wine.

These flavor impacts are more pronounced in white wines than in red wines mainly because red wines are more complex and heavier in body. White wines may be fermented in stainless steel or in the oak barrel but red wines are typically fermented and aged in oak barrels and thus may have a greater expression of the oak sensory components.

So, exactly what does the toasted oak barrel do to the wine? The alcohol content of the wine also has an important effect on the transfer of the flavor components from the barrel to the wine. The most important class of oak factors that influence the flavor profile of the wine are related to what is known as the volatile oak compounds in the toasted inner surface of the barrel.

One of these is eugenol, which provides a smokey, spicy and clove element to the wine. Then there is furfural, which introduces that toasty, toasted almond and butterscotch flavors to some wines. Of course there is vanillan, which adds a taste of vanilla and oak to the wine.Another class of volatile compounds includes the lactones that produce the woody and coconut flavors in some wines.

It has been shown that the impact or effects of the oak barrel diminishes after four uses of the barrel and some elements like vanillan seem to be lost after just 12 months of wine contact. When you go to a winery and walk through the wine cellar, look at the face of each barrel and you will see either an L for light toast, an M for medium toast or an H for heavy toast.

It would appear that after many years and considerable research and discussion, the oak barrel is now viewed by many winemakers as a flavor component in today’s winemaking. Much of the American wine culture has been somewhat addicted to the “oaky” style of many wines, and I have often met wine lovers who are turned off by wines that do not project some level of oak. Many wine lovers are looking for that toasty, oaky, buttery chardonnay and nothing will ever take its place.

Over the past several years, I think we have seen a change in attitude with regard to high levels of alcohol in wine and the increasing levels of oak of many wines, especially some of our California favorites. A number of wineries throughout the world are now producing un-oaked white wines that are created using stainless steel fermentation techniques and very little, if any, contact with oak barrels. The flavor profile of these wines is quite different — refreshing and easy on the palate. In my opinion these un-oaked white wines are more food-friendly since we know that the oak component in the wine is often very hard to manage in food and wine pairing.

Here is an experiment you can try. The next time you are in your wine shop, ask the owner for a bottle of un-oaked chardonnay and a bottle of a good oaky chardonnay from California. Chatham winery on the eastern shore makes a rather interesting un-oaked chardonnay and there is a chardonnay from California called Toasted Head. Try them side by side and let me know what you think.

I wonder, as did some of the attendees at this UC Davis seminar, if our taste preference would be different if oak had not been used in barrel production in the beginning. But I think our love affair with oak will be around for a long time.

Roy Williams is professor emeritus in Old Dominion University's chemistry department. Write to him at

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