With all the different varieties of trees out there, what makes oak barrels the go-to container for aging everything? Most commonly used for fine wines and spirits, these days you can find craft beer, cocktails, pickles, maple syrup, hot sauce, vanilla and even vinegars that have benefitted from spending some time tucked away in oak.
Barrels became the preferred method of transport for wine, beer, olive oil and other liquids around the first century BCE in Europe, when their convenient rolling shape and sturdy construction proved superior to fragile clay vessels. Why continue to use wood in the modern age, when stainless steel and nonreactive synthetics have benefits that outweigh both of these advantages? Flavor, of course. Over time, people noticed the flavor profiles oak barrels added to their products, which created a happy coincidence that has kept the craft of cooperage—barrel making—alive and well today.
Think of oak as the seasoning to your dish. The goal is to enhance the flavor of your pickles, not make them oak flavored. The variety of results possible from oak barrels is dizzying. Here’s a fast and dirty overview:
Types of Oak
White oak varieties from America, France and Hungary/Eastern Europe are most commonly used in wine and whiskey barrels. The French barrels are the most expensive and heavily regulated, with the highest tannin levels. Their government manages a handful of forests where trees grow slowly over 100 years in a cool climate, producing dense wood with a tight grain—perfect for aging wine. Eastern European oak is similar, but with lower tannins and a median price level, as the wood comes from a mixture of private- and government-operated forests.
In the U.S., barrels aren’t so distinguished, and our oak is grown in 18 different states from Oregon to the Appalachians. The vanilla, wood sugar and toasty flavors tend to be more intense than in French oak. They’re also about half the price of French barrels!
Beyond location, the number of variables that affect the chemistry of oak barrels can be mind numbing. Should staves be sawed or hand-split? Then dried in a kiln, or in open air? How does the use of wood fire, boiling water, steam or natural gas to bend the staves affect the final product?
In an interesting twist, California’s Robert Mondavi vineyard experimented with dense American oak using French barrel construction techniques—staves are split by hand, air-dried and formed over a low fire. Blind taste tests showed little difference between wines aged in the French versus American oak barrels, as long as the wood was treated the same.
White oak is about 50% cellulose, the most abundant natural polymer on the planet. It doesn’t do much in the aging process, except hold the wood together.
But, it is 25% lignin, a complex organic polymer found in the cell walls of plants, that makes them rigid and woody. (Think bark.) Alcohol breaks down the lignin in oak, releasing tannins and vanillins into the flavor profile of the wine or spirit. The higher the alcohol percentage, the faster this breakdown occurs.
This polymer begins to break down into simple sugars as soon as the wood is dried or begins seasoning. Toasting kicks in the sweeter flavors and aromas around 300°F and beyond, effectively caramelizing the inside. Crank the heat up to 420°F and toasty flavors come into play. Modern coopers have a number of methods to precisely measure the right amount of toast to produce specific flavors for customers.
You can geek out on barrel science for days on the World Cooperage Research page.
First or Second (or Third or Tenth) Use Barrels
To make all of this even more interesting, barrels can be reused, but the impact of the wood will diminish over time. A good rule of thumb is:
• Wine—1 use
• Whiskey/bourbon—4 uses
• Rum—7 uses
• Tequila—10 uses
But, you don’t have to use the barrel for the same product every time. A bourbon barrel can be used to age a cocktail, or add extra layers of flavor to a craft beer. You could then fill it with maple syrup or hot sauce to create something really unique! Or awful—you never know until you try.
Barrel-aged hot sauces have become all the rage in the past couple years. TABASCO® brand uses repurposed Jack Daniel’s barrels (after shaving down the bourbon-soaked interiors) to age their pepper mash for up to three years. When the barrels are retired, they’re chipped, bagged and sold for use in the grill. They’re actually the first hot sauce company known to barrel-age their sauce, going back as far as 1868.