All the Types of Oak Used for Spirit Casks [Infographic]

Spirits and oak have been almost inseparable since the 3rd century, back when the Romans swapped in barrels for the clay pots and other breakable vessels they traditionally used for booze-making. But the complex flavors these casks imparted were only later realized through sheer circumstance, after barrels were left to sit for extended periods in transit overseas. Eventually, Cognac producers began charring barrels to break down and caramelize the wood’s sugars, and distillers have never looked back.

Of course, not all spirits are stored in wood. Clear, unaged spirits usually rest in stainless steel for a short period before bottling to let their flavors soften and meld. But generally, any aged spirit will rest inside wood at one point: The longer it sits in a cask, whether for a few months or a few decades, the more compounds it will extract from the wood.

Although there are many types of wood employed in cask production, almost all are constructed with some species of oak. That’s partially for legal reasons: In the U.S., bourbon must be aged in new oak barrels, and anything that isn’t must be classified as simply “whiskey.” Across the pond in Scotland, Scotch must also be aged in oak, but Scotch distillers have the freedom to use barrels that previously held other spirits and wines. Meanwhile, in other whiskey-producing nations like Ireland, Canada, and Japan, there are no restrictions on the type of wood used for aging, yet oak still remains king. Oak’s ability to easily form watertight seals and impart lovely flavors on a spirit have made it the darling among cask producers (a.k.a. coopers) for centuries.

Here, we break down the types of oak used in spirits casks.

American White Oak (Quercus Alba)

This variety of oak grows across eastern North America, and serves as the foundation of the American stave business. It’s also primarily used for bourbon aging. Per law, bourbon must be aged in fresh, never-used charred oak. Contrary to popular belief, bourbon can actually be aged in any type of oak, but given the abundance of domestic white oak, it’s long been the go-to wood for American barrel producers and bourbon distillers. Distillers are also drawn to American oak for its ability to amplify a spirit’s flavor with notes of vanilla, coconut, honey, almonds, and subtle spice. When the American wine boom took off in the ‘60s and ‘70s, winemakers worldwide began adopting white oak for aging as well. As it’s lower in tannins than its European and French relatives, American oak can be used to soften highly tannic wines. Even sherry producers have started to age fortified wine in American oak.

European Oak (Quercus Robur)

The second-most common wood for cask production is European oak. It’s also known as English oak, even though its trees grow all over Europe and is commonly sourced from Spain and Portugal. While its history as a cask-friendly wood began with Cognac production, it’s most commonly used for aging sherry, in which it’s known to impart sappy notes of dried fruit and cloves — partly due to the wood’s high level of phenols, which exude a perceived spiciness when charred. Scotch whisky producers are also big fans of second-hand sherry barrels for finishing whiskies, so much so that businesses in Spain have started crafting sherry-seasoned casks specifically suited for Scotch finishing. Flavor aside, European oak also tends to affect a spirit’s color more than American oak does, generally yielding a darker liquid.

Sessile Oak (Quercus Petraea)

Now we’re getting to the fancy stuff: Sessile oak, also known as French oak. Sessile oak is the national tree of Ireland and grows in several parts of Europe, but the most sought-after Sessile comes from the French forests of Tronçais and Limousin. The oak from Limousin is more porous and tannic than that of the Tronçais forest, but regardless, casks made of Sessile can fetch price tags of over $4,000 while American oak barrels hover in the $400 to $600 range. With the exception of whisky-finishing and Cognac production, it’s most commonly used in the wine industry where it’s lauded for its high tannins and ability to impart savory, spicy notes in wine. Since American oak’s influence leans sweeter, some coopers have constructed Frankenstein-eque casks made with staves of American oak and barrel heads of Sessile.

Mizunara Oak (Quercus Crispula)

Mizunara oak, or Japanese oak, is unsurprisingly most often used to age Japanese whisky. Like all varieties of oak, it tends to do well in colder climates that encourage slow growth, but mizunara oak takes that pace to another level. This species takes a whopping 200-plus years to reach maturity. It also often grows in mountainous areas, so finding a straight, uniform trunk to harvest is no easy feat. And to make matters more complicated, it’s so porous that mizunara casks tend to leak and are often rebuilt or bolstered with additional staves to ensure a watertight seal. But for Japanese whisky producers, the juice is well worth the squeeze. Whiskies aged in mizunara casks are highly acclaimed for their long, spicy finish and resounding notes of sandalwood, coconut, and fresh flowers. Although these casks are almost exclusively used by Japanese distillers, some Scotch producers have employed them for experimental cask-finishing.

Garry Oak (Quercus Garryana)

We return to the U.S. for the most obscure oak variety used for cask production: Garry oak, otherwise known as Oregon oak. It’s native to the Pacific Northwest, and is generally regarded as an unsung or forgotten species, as its popularity has long been overshadowed by American white oak. In short, almost no one still uses it. The wood is high in tannins, so Garry oak barrels must be seasoned for quite a while to hush their inherent astringency. Regardless, more distillers have recently begun experimenting with it, namely Seattle’s Westland Distillery. Allegedly, when aged right, Garry oak can impart dark, austere flavors like molasses and smoke on whiskeys.

*Image retrieved from saiko3p via stock.adobe.com