Head back to Bourbon school with The Bourbon Review all throughout the month of August! Today, we’ll talk some science about the American White Oak wood used and charred in all Bourbon barrels.
So why do whiskey makers use Oak barrels? Oak is utilized for its unique physical and chemical nature. Oak has strength – physically, its wide radial rays give strength when shaped for a 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 treatments result in the production of pleasant-tasting Oak lactones.
Whiskey barrels made from Oak have three broad effects on the spirit:
1. As an additive – It adds to the taste and aroma of the spirit by providing desirable elements from the cask. For example: vanillin, Oak lactone (coconut, bourbon character), toastiness, wood sugars and color.
2. As an agent that removes undesirable elements from new make spirit. For example, the charcoal will filter sulphur compounds and immaturity.
3. Oak barrels also interact with the spirit. It adds extractive wood elements from the cask and converts them to organoleptically desirable elements. For example, it will change tannins to acetals, and change acetic acid to fruity esters.
Furthermore, there are 5 specific constituents of Oak that each influence maturing spirits in different ways.
1. Cellulose – Which has virtually no effect other than to hold the wood together.
2. Hemicellulose – Which consists of simple sugars that break down when heated and provide body through the addition of wood sugars for toasty & caramelized aromas & flavors, and color (unaged or “new make” whisky is a clear liquid).
3. Lignin – The binding agent that hold the cellulose in wood together which, when heated yield vanillin, for sweet, smoky and spice aromas.
4. Oak Tannins* – Which 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.
5. Oak Lactones – Resulting from lipids in the Oak, they increase dramatically during toasting and charring and can pass on a strong woody and perhaps coconut character. Lactones give Bourbon its distinctive character; and occur in higher concentrations in American Oak than in European varieties.
These white oak barrels give Bourbon 60-70% of their delicious flavor and all of their beautiful amber color. If you’d like to age your own whiskey, click here to shop, order, and personalize!