Unless you’re a wine aficionado, you probably haven’t explored deep into the world of oak. Chances are you know that oak can impart tannins, or vanilla, or char (depending on what you’re drinking). And chances are you’ve been forced to swallow down some buttery, flabby, aggressively over-oaked cheap Chardonnay. (We’ve all been there, and boy does it suck.)
But there’s actually quite a bit to know about oak, from the basic scientific rationale behind oak aging (why not age in plastic? Or clay? Or some weird ancient lamb’s bladder thingy?) to the varieties of oak used for aging, and what they can impart in your favorite wine, beer, or whisky.
Basic Facts of Oak Aging
Wooden containers were fashioned as early as 2690 B.C.E.
But closed wooden containers came about between 800 and 900 B.C.E., not just for wine but things like olive oil and honey.
We didn’t always use oak to age wine or spirits.
Romans were transporting their wine in massive, hulking clay amphorae. Only when the Romans encountered the Gauls using oak to transport beer did they realized a few things: oak was lighter than their giant, impressive-looking clay amphorae; oak had a tight grain (so it could hold liquid) but was more flexible than previously used woods like palm; and you could actually roll oak barrels, meaning a lot easier transport and a lot less backache.
And that’s what oak was for at first
Not aging. It was only when the wine inside began displaying the beneficial effects of contact with oak that the concept of intentional aging came about.
So what is oak botanically speaking?
Oak is a kind of tree in the genus Quercus (which sounds like a Harry Potter spell). There are many species within that genus—something like 400, though some soures say 600—but among the most commonly used for wine and spirits aging are just a few particular species, mostly Quercus alba, Quercus petreae, Quercus robur.
What can oak do to a wine or spirit?
That depends on so very much! (Sorry.) The chemical compounds in different species of oak. Whether the oak has been charred. The amount of oxygen in the barrel. And, oh yes, the kind of spirit with which it comes into contact.
There are a variety of influential chemical compounds in oak.
“Volatile phenols” containing vanillin (in both oak-aged wines and spirits, the presence of vanilla or vanilla-family flavors are very common). Charred oak barrels might also contain “furfural, a compound yielding a sweet and toasty aroma.” Terpenes will give wine that tannic tea flavor. Guaiacol, a result of charring, will (no shock) impart charred aromas. And lactones, a kind of organic ester group, which impart that classic “woody aroma” as well as certain tropical fruit flavors.
Oak barrels won’t behave the same with every wine or spirit.
Again, this depends on with which spirit or wine the oak is interacting, as well as how much oxygen is in the barrel, whether (and how much) it’s been charred, and how many prior uses it’s gone through (like your favorite pair of jeans, the more an oak barrel is used, it starts to fade).
Basic Types of Oak
Like American oak, French oak—either Quercus petraea or Quercus robur—is a “white” oak historically found in abundance in the forests of eastern and central France. There are a few major regions that produce the French oak used for aging: Troncais, Nevers, Allier, and Vosges. There’s also the famous Limousin oak, from the heavily guarded forests of Limousin. (Quercus robur comes exclusively from Limousin oak, which is more tannic.) Though the oaks within France vary, French oak tends to have a slightly softer impact, with subtle spice. Generally tighter grained, except for Limousin, French oak will impart smooth but substantial tannin.
Also known as Quercus Alba, American oak has a lot of hemicellulose, which, when charred, “will break down into wood sugars, allowing for some caramelization.” Important when you think about the classic caramel/toffee/brown sugar notes of bourbon—which is, by law, made in charred new white American oak barrels. American oak is also fairly heavy in lactones, which can impart woody but also tropical (think: coconut, banana) flavors. Whatever is aged in American oak could tend to get a bit more of a pronounced creaminess and flavors associated with vanillin.
Russian/Eastern European/Caucasian Oak
The farther East you go, the more you’ll encounter Quercus robur. Eastern Europe has a vast supply of oak trees. Hungarian oak is richer in eugenols, which impart spice, and tends to create a slightly richer mouthfeel with substantial tannin. Not that you’ll find too many differentiations on the back of a wine bottle, but Caucasian oak (as in from the Caucuses) imparts less tannin and aromatics, which is useful if you want a more fruity, straight-up expression of the grape itself. Bear in mind, Russian oak isn’t exclusively used in Russia. It’s used widely, for various reasons. Same goes for Slavonian oak, which will give less tannin and impart more sweetness, and it is used in a variety of Italian wines.
Also known as Mizunara, it’s not often found in the States, but you’ll get a sense for what it can impart if you drink Japanese whisky (and why not?). Commonly associated with flavors of sandalwood, incense, even citrus, and the same coconut notes you’d get from American oak—because, wait for it, it has a higher proportion of lactones.
Yep, we’re all oak experts now. Let’s celebrate with a drink, right?
By: Emily Bell