Why a little wood goes a long way....
What Does Oak Actually Do to Whiskey? The reason that oak is utilized is because of the unique physical and chemical nature that the wood possesses. Oak has physical strength, making for a very sturdy cask. Oak is also a pure wood, as opposed to pine or rubber trees which contain resin canals that can pass strong flavors to maturing whisky. But it’s not just the oak itself, it’s the transformation that happens to the oak as a result of the seasoning and heating treatments during the coopering process these result in the production of pleasant tasting oak lactones that flavor some of your (and our) favorite whiskies.
Whiskey barrels made from oak have three broad effects on the spirit: As an additive, it enhances the taste and aroma of the spirit by providing desirable elements from the cask (e.g., vanillin, oak lactone (coconut, bourbon character), toastiness, wood sugars and color). As an agent, it removes undesirable elements, like sulfur compounds and immaturity, from new make spirit. Oak barrels also interact with the spirit by imparting wood characteristics from the cask and converting them to desirable elements. For example, it can change tannins to acetals or change acetic acid to fruity esters.
It has been said that there are five specific constituents of oak that can influence a maturing spirit:
1.) Cellulose has virtually no effect other than to hold the wood together.
2.) Hemicellulose consists of simple sugars that break down when heated. 3.) The Body is enhanced through the addition of wood sugars, and toasty and caramelized aromas and flavors.
4.) Color is changed through this process - (Did you know?: Unaged (aka “new make”) whisky is a clear liquid).
5.) Lignin are the binding agents that hold the cellulose in wood together, producing vanillin compounds and oak lactones.
The oak tannins play an essential role in maturation by enabling oxidation and the creation of delicate fragrance in spirits. Tannins combine with oxygen and other compounds in the spirit to form acetals over time. Naturally occurring preservative compounds with a slightly puckery, astringent taste in the mouth, similar to the effect of strong black tea or fresh walnuts. The oak lactones on the other hand result from lipids in the oak, which increase dramatically during toasting and charring and can pass on a strong woody coconut character. Lactones give bourbon its distinctive character and occur in higher concentrations in American Oak than in European varieties.
Some distillers think that the method for drying the wood is only important for the first-fill of a spirit aged in a new cask, (e.g., wine or bourbon) and has little or no impact when maturing spirits in previously used casks. Of course, Scotch is aged in previously used casks. Of particular interest are the vanillin compounds and oak lactones, which actually come from oak’s lignin, and are derived to a greater degree from heating, as well as seasoning. These provide much of the flavor associated with bourbon, while broken down sugars from the wood’s hemicellulose and the tannins also play a role.
These are only a few reason that a little wood can go a really long way.... Sláinte!