Nearly every single person reading this blog is well aware of the fact that fermenting and aging wine in oak barrels adds wood-specific sensory characteristics to the wine, which come from certain volatile chemicals in the wood interacting with the volatiles in the wine itself. This extraction of volatile compounds from the wood to the wine also tends to decrease the astringency of the wine, as well as changes the color of the finished product. Microscopic pores in the wood also allow for minute oxygen transfer in and out of the wine, which significantly affects the flavor and quality of the beverage.
The most frequently used wood, which again a lot of you know, is oak heartwood, specific species including Quercus alba (American oak), Quercus petraea (Matt.) and Quercus roburL. (French oak) and which have all been extensively studied and dissected in the literature. Another species of oak that has frequently been used in barrel cooperage is Quercus pyrenaica, which comes from the Iberian Peninsula in Spain. More recently, other types of wood have been considered for barrel cooperage, including chestnut, cherry, acacia, ash, and mulberry, however, only oak and chestnut are approved by the International Enological Codex of the International Organisation of Vin and Wine for making barrels.
Historically, chestnut barrels have been used for storage and transport, due to lower costs and wide availability. Studies have found that chestnut oak is rich in gallic acid and tannins, and have therefore has been frequently used as a source for commercial tannin agents, protection against oxidation reactions, and stabilizing color. Studies have also found that chestnut oak has a higher concentration of low molecular weight polyphenols than oak, and those beverages that are aged in chestnut will thus exhibit higher antioxidantactivities than beverages aged in oak barrels.
One less desirable trait for chestnut barrels is that the wood has a higher porosity than oak. As a result of this higher porosity, more oxygen can diffuse into the wine, creating a situation where oxidation may occur much more rapidly than if the wood were aged in oak barrels. Therefore, longer aging regimes are not ideal for chestnut oak barrels, though wines aged for shorter periods of time may do well in these barrels.
To date, few studies have examined in great detail the composition of volatile compounds in chestnut barrels and how this may affect quality of the wine that is aged in them. The aim of the study present today was to study the composition of volatile compounds of chestnut wood, examine its chemical profile, and evaluation the aroma potential based on the presence of certain volatiles.
This study compared three oak species from the northwest area of the Iberian Peninsula in Spain; Q. robur L., Q. petraea Matts Liebl., and Q. pyrenaica; one oak species from the United States (Nashville, Tennessee); Q. alba; and chestnut wood from Lugo in northwest Spain; Castanea sativa Mill.
Disks were obtained from each tree from a distance of 1.3m from the base of the trunk. 20x20x40mm samples were taken from each disk for processing. These wood samples were dried and then ground using a mechanical mill and sieved, to create a homogenous sawdust sample for analysis.
Volatile compounds were isolated and analyzed using gas chromatography and mass spectrometry analysis.
- There was great variability in the levels of different volatile compounds in all of the wood species, which are explained by natural variations caused by geographical location and individual tree effects. Even though there was great variability, there were still significant differences with some compounds.
- The same furanic compounds were found in all wood samples.
- The most common furanic compounds were furfural, 5-hydroxymethylfurfural and 5-methyfurfural.
o Sensory characteristics of these compounds: caramel, toasted notes, honeyed notes.
- There were no significant differences between any of the wood species for the following compounds: furandicarboxyaldehyde and 2-furanmethanol.
- There were no significant differences between chestnut and the other oak species with any furanic compounds except Q. robur, which showed the highest levels of furfural, 1-(2-furanyl) ethanone, 5-methylfurfural and 5-hydroxymethlyfurfural.
- Chestnut samples contained intermediate levels of furanic compounds compared to the other oak species.
- Q. pyrenaica and Q. alba species showed the lowest levels of furanic compounds.
- There was an absence of β-methyl-γ-octalactone in chestnut samples.
o Sensory characteristic of this compound: intense coconut and wood.
- There were significant difference in lactone levels in Q. alba and Q. pyrenaica when compared with Q. petraea and Q. robur.
o Q. alba(American oak) had higher levels of β-methyl-γ-octalactone.
o Some samples of Q. pyrenaica had high levels of β-methyl-γ-octalactone.
- Sensory characteristics: floral, fruity, tea, tobacco
- 3-oxo-α-ionol and vomifoliol were not detected in chestnut samples.
- Only α-terpineol and methyl dihydrojasmonate were detected in chestnut samples, at intermediate concentrations compared to the oak species.
- Q. pyrenaica had the highest concentrations of terpenic and nonisoprenoid compounds, with very high levels of α-terpineol and methyl dihydrojasmonate.
- Nonanal and trans-2-nonenal, decanal, and 2,4-nonadienal were present in all wood samples.
o Sensory characteristics: sawdust, vegetal, cardboard.
- There were no statistical differences between chestnut and the oak species; however, there were high levels of these compounds found in Q. robur.
- The flavors associated with these compounds can be reduced or removed in the toasting process.
- Chestnut had the highest concentrations of guaiacol, methyl guaiacol, and propylguaicol.
- Vinylguaiacol levels were not significantly different between chestnut and any of the oak species.
- High levels of syringol and allyl syringol were found in chestnut samples, however, propenyl syringol was not found.
- Significant levels of eugenol, methoxyeugenol, and isoeugenol.
o Isoeugenol levels were significantly higher than any other of the oak species.
o Sensory characteristics: spicy, intensely woody.
- Eugenol levels were highest in American oak, though they were not statistically higher than any other sample, except Q. petraea which had eugenol levels significantly lower than Q. alba.
o There is no clear relationship between eugenol levels and wood species.
- Overall, when comparing chestnut wood with other oak species used in barrel cooperage, it was found that chestnut wood has high levels of volatile phenols that are similar to most other oak species.
- Many phenolic aldehydes were also found in all species, the most abundant being vanillin, which is indicative of a vanilla flavor/aroma in the finished wine.
- The phenolic aldehyde profile of chestnut was very similar to all other oak species.
- Significantly higher levels of vanillin, acetovanillone, butriovanillone, vanillyl ethyl ether and methyl homovanillate were found in chestnut samples.
o Vanillin levels in chestnut were most similar to vanillin levels in the oak species Q. alba (American oak).
- Vitamin E was the only triterpenic compound that was significantly different in any of the wood species, with Q. alba containing the highest levels of the compound.
Can you identify the type of wood based on its chemical profile?
- After linear discrimination analysis, it was found that one can distinguish between different wood species based on some volatile compounds, including α-terpienol, decanal, 5-hydroxymethylfurfural, cis-β-methyl-γ-octalaone, vanillin, isoeugenol, acetovanillone, and coniferyl alcohol.
o This mathematical model represented 100% of the total dispersion.
- Using this mathematical model, 93.5% of the samples were properly identified solely based on their compositions of the above compounds.
|Figure 1 from Alanon et al, 2012.|
Based on the chemical analysis of this study, it appears as though Chestnut is a perfectly acceptable source for wood in barrel cooperage for wine, as it displays similar flavor profiles to many other oak species already used in cooperage. The sensory attributes of wine aged in chestnut barrels won’t be exactly the same as wine aged in oak barrels, however, since levels of all volatile phenols and other compounds aren’t exactly the same. Slight differences in the concentrations of certain compounds are enough so that the sensory characteristics of wine aged in chestnut barrels will be different than wine aged in oak barrels.
Even though the volatile and chemical composition of chestnut wood is similar enough to oak to provide a good alternative for barrel cooperage, it should be reminded that because the micropore size in chestnut wood is larger than oak species, oxygen will diffuse into the aging wine faster than it would in an oak barrel, thus allowing for possibly higher rates of oxidation. This is one aspect that wasn’t examined in this study, but only referenced. It should be noted that even while chestnut is a good alternative to oak in regards to the sensory characteristics of the finished wine, it should be noted that aging for extended periods of time may not be recommended due to higher risk of damaging oxidation. For those seeking an alternative to oak barrels and who are only interested in short-term barrel storage, it appears that chestnut may be the right answer.
One final result that I thought was particularly fascinating was the result from the linear/canonical discriminatory analysis. Based on a selected number of compounds, the authors were able to correctly determine the wood species in nearly all of the samples (93.5% of them, anyway). This result only received a small mention in the paper, and I think it would be interesting to see a more detailed study. According to the authors, future studies examining the consequences of the differences in chemical compounds and their sensory qualities in wine are on the way.
What do you all think of this study? Love it? Hate it? What would you like to see done differently? I’d love to hear what you think! Please feel free to comment below.
Source: Alañón, M.E., Castro-Vázquez, L., Díaz-Maroto, M.C., Pérez-Coello, M.S. 2012. Aromatic potential of Castanea sativa Mill. compared to Quercus species to be used in cooperage. Food Chemistry 130: 875-881.
I am not a health professional, nor do I pretend to be. Please consult your doctor before altering your alcohol consumption habits. Do not consume alcohol if you are under the age of 21. Do not drink and drive. Enjoy responsibly!