by Nicolette L. Cagle, July 12, 2015 — written in Iguazu, Argentina
Three major species of oak are used in wine production worldwide: Quercus petraea (France & Eastern Europe), Quercus robur (France), and Quercus alba (United States of America). Barrels made from these species impart different characteristics in wine due to the 1) growth rate and site conditions of the tree species, 2) vascular qualities of each species and 3) phenolic and aromatic compounds in each species.
First, each of the three main barrel producing species grows at different rates. Growth rate is influences largely by site fertility, but also interacts with the natural genetic predisposition of the tree. American oak tends to grow faster than Q. petraea and Q. robur, resulting in a coarser grain (i.e., a coarse arrangement of the wood fiber).
When comparing among species, however, the coarseness of the grain does not directly correlate with porosity (pores are vessels that conduct sap), another factor that influences wine’s influence by oak. One of the reasons for this is because the xylem or pores of Q. alba fill up with large amounts of tylose, when becoming heartwood, essentially plugging up the pores created by the vascular system. This results in denser wood.
The increased density of white oak has a number of effects. First, barrel staves of white oak can be serrated and the grain doesn’t need to be parallel to the long edge of the stave to remain air and water tight. Thus, American white oak barrels can be made more efficiently. At the same time, the coarse grain of American white oak may result in less wood contact with the wine when compared to finer grained species. While this could result in the wine picking up less wood derived qualities, the high levels of certain aromatic compounds in Q. alba may ameliorate the effects of being coarse-grained.
In contrast, Q. petraea and Q. robur tend to be less dense due to lower amount of tylose in the xylem pores and tend to be finer grained than Q. alba. The decreased density and relative lack of tylose in the xylem pores means that barrel staves of Q. petraea and Q. robur must be cut with the grain, i.e., the xylem tubes parallel to the long side of the stave. If this isn’t done, barrels will leak and allow extra oxygen to enter the barrel. The finer grain of Q. petraea and Q. robur, when compared to Q. alba, may allow more oak contact with the wine.
It should be noted that between Q. petraea and Q. rubur, Q. robur tends to have a coarser grain. This accounts for the relatively cheaper price of French oak from Limousin, because this region is known for the production of Q. robur, while Allier, Never, and Troncais produce Q. petraea barrels that can sell for up to $4000 USD/barrel.
The variation in the relative abundance of specific organic compounds in various oak species largely accounts for the different aromas detected in wines aged in barrels from different regions.
In general, Q. alba has higher concentrations of lactones and vanillans and lower concentrations of ellagitannins than the European species. This results in increased oaky flavors, including coconut and vanilla, as well as a decreased astringency (and structure) of reds.
In contrast, Q. robur has relatively low concentrations of lactones and vanillans, and high concentrations of ellagitannins, resulting in less aromatic wine with more astringency and structure. Q. robur often has influence from spicy caryophyllenes and copaenes.
Q. petraea has intermediate levels of lactones, vanillans, and ellagic tannins, but has higher eugenol concentration than Q. alba (2x) and Q. robur (4x), often resulting in increased clove and spice notes in wines aged in Q. petraea. It also has a type of hemicellulose that breaks down more easily than in Q. alba and Q. robur, resulting in a more toasted, spicy, or caramel aroma.
It should also be noted that toasting oak barrels tends to increase the release of some compounds into the wine, including vanillan (vanilla aroma), eugenol (clove), and guiacol (smokiness). Lactones (coconut) tend to increase a little with toasting.
| Characteristics | Quercus alba white oak | Quercus petraea sessile oak | Quercus robur pedunculate/English oak |
| Octalactone levels | 138* | 77 | 16 |
| Vanillan levels | 11* | 8 | 6 |
| Eugenol levels | 4 | 8* | 2 |
| Ellagictannin levels | 6000 | 8000 | 15000* |
| Growth rate | Highest | Intermediate | Lowest |
References
Ribereau-Gayon, P., Glories, Y., Maujean, A., and Dubourdieu, D. 2006. Handbook of Enology : The Chemistry of Wine : Stabilization and Treatment. Vol 2. John Wiley & Sons.
Victoria Moreno-Arribas, M., and C. Polo. 2009. Wine Chemistry and Biochemistry. Springer.
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