Oak Compounds That Affect Wine


In our Harvest Series Blogs 7 & 8, I touched on oak barrels and alternatives for wine aging.  Oak is a very important component in a finished wine.  In this week’s blog, I will list the compounds that add the nuanced flavors and texture to wine.

Tannin: As far as texture goes, oak adds much of the tannin to wine (some comes from the grape skins, stems, and seeds themselves).  It is also found in berries, pomegranates, nuts, herbs, spices, and chocolate.  Tannin is the compound that is found in tea, especially black teas, that give your mouth a drying effect and makes it feel a little like sandpaper.  A balanced amount of tannin will give a boost to the mid-palate and finish of a wine, keeping it from falling flat before you even swallow your sip.  In addition, tannin is a natural antioxidant, which is not only good for you but helps to protect the wine from oxidation, and boosts the aging potential.  The molecular structure of tannin starts out as a short chain of polymers that link together and become longer over time and more oxygen exposure, which is more pleasant to your tongue, and is why a tannic wine will soften with age or aeration.

Vanillin: A phenolic aldehyde found in oak that produces the vanilla character.  It is present even in untoasted or lightly toasted oak

Eugenol & Isoeugenol: Volatile phenols that impart a clove aroma.  It is present in oak before toasting, and will increase with longer air drying.  Toasting increases its ability to absorb into wine

Oak lactones: A group of compounds that supply the sweet, coconut, leather, spice, floral, and woody aromas.  They are the most highly concentrated in American oak, as opposed to French or Eastern European oak

Guaiacol & 4-Methylguaiacol: Volatile phenols that create the smoky, bacon, spice, and char aromas.  These aromas increase with heavier toasting.

Cresol: Imparts a tar-like aroma and comes out with heavy toasting

Ketones: A group of compounds that impart baked bread and caramel aromas with heavier toasting

Furfural & 5-methylfurfural: Aldehydic compounds created by toasting and caramelizing cellulose (wood sugars) that impart toasted almond, bread, butterscotch, and caramel aromas

When choosing barrels for each varietal, a winemaker must try to match the body, structure, and flavors of the wine to the barrel they think will complement it the most.  Unless that was the style they preferred, they wouldn’t generally put a white wine in a deep or heavy toasted American barrel---at least not the whole lot---because it would overpower the fruit and the delicate body of the wine.  Barrels should be used as an enhancement to the natural expression of the wine, much the way a chef uses seasonings, herbs, and spices to elevate a dish.  The source, the toast level, the method of toasting, and the length of air aging all factor into the finished product, and to the effect a barrel will have on each wine that goes into it.