I truly enjoyed my barrel-aging experience with the American White Oak Barrel I purchased on Amazon from Brew Naturally. *There are many other barrels out there that I’m sure are quite as good. I’m just sharing the specific one that I purchased…
Oak Aging is a process that I am fascinated with and passionate about. Once I learned the complicated – yet magical – chemical processes involved in aging spirits in wood, my respect for aged spirits deepened.
Let’s talk a little bit about wood. Wood is the PERFECT vessel to age spirits in. It has various natural sugars; chemical compounds called “lactones” that impart flavor and aroma; and tannins – which add color, aroma, and flavor. It is also porous – which allows evaporation to occur, and a small amount oxygen in (necessary for oxidation of the spirit, which also imparts color – browning apples, anyone?!) – whilst allowing spirit to stay in, as well.
American White Oak (Quercus Alba) is often used to mature spirits. There are several reasons for this 1) It is abundant in the Northern Hemisphere, particularly the Ozarks; 2) porosity allows for a) evaporation of spirit, b) oxidation (small amount of oxygen enters), c) pliability for barrel making; 3) high tannin content, w/potential for imparting over 400 different flavor/aromatic combinations to aging spirit
There are 3 components to Oak (Quercus genus) heartwood:
- Cellulose – 40% mass of the wood, this organic compound has strength and chemical resistance. It helps the wood maintain structure and remain durable.
- Hemicellulose – 25% mass of the wood, also an organic compound, and is present in most plant cell walls, as is cellulose. It has various sugars with lower molecular weights than cellulose- assisting in solubility of alcohol. We have hemicellulose to thank for the “red layer” in charred oak barrels.
- Lignin – 5-10% mass of wood – tannins! As mentioned above, these polyphenolic compounds contain the potential for imparting 400 flavor/aromatic combinations to aging spirit!
The constant interaction between the spirit and the (charred) wood barrel allows the 6 major processes of wood aging to occur:
- Extraction – Water and alcohol soak into the oak, extracting flavor and sweetness from the charred inside of the wood
- Evaporation – Depending on climate – evaporation (“angel’s share” ) can account for 3-10% loss annually
- Oxidation – Evaporated spirit creates space in barrel, allowing air to enter into the barrel. O2 in the air forms aromatic compounds by dissolving into spirit — this is where “terroir” enters – which gives various spirits their unique “taste of place” (I’m thinking briny, seaweed infused Islay Scotch)
- Concentration – Depending on climate – water evaporates faster than alcohol, or conversely, alcohol evaporates faster. Either way, the volume of spirit is reduced, concentrating the aromas and flavors the magical (ok, so – yes – science – but it seems magical!) extraction/oxidation aging processes have imparted
- Filtration – Charred inner layer (red layer) allows filtration to occur, smoothing the spirit by absorbing sulfur and aldehyde compounds
- Coloration – Red layer, now caramelized by charring the inside of the barrel, adds reddish color to spirit, and oxidation colors further, adding brownish shade
Phew! Amazing stuff! Now that we’ve distilled the oak aging process – don’t you just want some tawny, liquid sunshine?! Thank you oak, thank you chemistry, thank you terroir – thank you, thank you!!!!!
In closing, I am stoked and humbled knowing that so much dynamic chemistry is occurring during oak aging. The ability to age cocktails at home is no gimmicky, dismissive project. There is science/magic going on in there – and that is not to be taken for granted.
___________. Certified Specialist of Spirits Study Guide, 2015. Washington, D.C.: The Society of Wine Educators, 2015.