I like red wine, I admit it. But I’ll also admit that I have trouble identifying the individual tastes and aromas in wine. I can always tell if I like a wine or not, I just can’t say “It’s spicy with hints of almond and cedar”….or whatever. I guess my nose isn’t what it should be after too many years in the lab. But that certainly doesn’t stop me from enjoying a glass. Being a chemist, I can appreciate the analytical approach of identifying the source and chemical compounds responsible for at least some of the aromas from a nice, heavy red. I believe that red wine should be aged in oak barrels. The oak is responsible for a lot of the character of the wine. “Obie’s Out of Bounds” performs the primary fermentation, perhaps 95%, in a large plastic tub then the very, very young wine is pressed and pumped into French oak barrels to age.
The species and source of the oak itself can be a major factor in the variation in the aroma profile of a wine. Oak species differ greatly. The French Pedunculate Oak (Quercus pedunculata = Q. robur) is known for its relatively faint aromas compared to French Sessile Oak (Q. sessilis and Q. petraea). American White Oak (Q. alba) can have a strong, distinctive aroma, sometimes considered overpowering in certain wines. In contrast, Oregon White Oak (Q. garryana) seems to have more similarities to the French oaks than to American White Oak.
Other factors are geographic origin, hybridization, growing conditions, age and genetic variation. The stave’s position on a trunk can influence its aroma composition as well as stave seasoning and kiln versus air drying. The cooperage process adds additional variability with barrel to barrel and even stave to stave variations from toasting.
Toasting: Lighter toasting aromas are usually attributed to oak lactones. As toasting increases, vanilla and caramel aromas associated with vanillin, furfural and 5-methylfurfural increase. At even higher toast levels these compounds decrease and are replaced by spicy (eugenol, isoeugenol, 4-methylguaiacol) and smoky characters (guaiacol, 4-methylguaiacol).
Fermentation in barrel: When fermentation is done in the barrel aldehydes such as vanillin, furfural, and 5- ethylfurfural can be partially transformed by yeast into non-aromatic alcohols.
Synergistic effects: Compounds with chemical similarities are often released from oak together (such as eugenol, isoeugenol, or other volatile phenols). The combination of similar molecules can result in perceived synergistic sensory effects even when they are below their individual sensory thresholds. This can even occur between unrelated volatiles; for example oak lactone’s sensory threshold has been found to be 50-fold lower in the presence of vanillin.
Piney, resin, cedar and dill aromas: These aromas are often associated with American White Oak Quercus alba, and can be linked to high levels of cis oak lactone. Quercus alba can also contain relatively high amounts of terpenes; however, key compounds have not been identified.
Nutty, roasted almond and roasted hazelnut aromas: Nutty aromas may arise at least partially from the combined sensory effect of known volatiles coming from wine or oak. These include diacetyl (fatty, butter), free fatty acids (fatty, rancid), furfural and 5-methylfurfural (caramelized tones).
Cinnamon and nutmeg aromas: Cinnamon and nutmeg have both woody and spicy aromas and can be attributed to the combination of woody, coconut oak lactones and spicy compounds such as eugenol and isoeugenol.
Bread crust, toast and gingerbread aromas: Bread crust or toast character can be described as a yeasty flavor (from yeast byproducts in bread as well as in wine), or caramel aromas from carbohydrate byproducts such as furfural and 5-methyl-furfural, or smoky aromas from guaiacol, 4- ethyl-guaiacol. A gingerbread aroma, which may be less yeasty, can have additional contributions from spicy flavored compounds such as eugenol.
Disagreeable dusty or cardboard aromas: Chloroanisoles (TCA, TeCA and PCA) are powerful odorants with a musty, moldy odor generally referred to the “corked” smell. If wine seems “corked”, even prior to bottling, oak is one possible source of chloroanisole. Of course cork is the usual source.
Pharmaceutical, band-aid or horsy, sweaty aromas: Compounds responsible for these odors are 4-ethylphenol (4EP) and 4-ethylguaiacol and are byproducts of the yeast Brettanomyces. One should periodically screen for Brettanomyces activity during oak aging.
The information above was obtained largely from ETS laboratories, 899A Adams St., St. Helena CA 94574, 707 963-4806.
ETS analyzes oak aromas using solid phase microextraction headspace technology for sampling (HS/SPME) followed by analysis by gas chromatography/mass spectroscopy (GCMS).
SPEX CertiPrep sells a selection of single and multi-component wine standards (pdf) for GC, GC/MS, HPLC, and HPLC/MS analysis.
