In our editorial series The Macallan Rare Cask Society—sponsored by The Macallan Rare Cask—we will be looking at the the qualities and characteristics that define Scotch whisky. Click here for more of our Rare Cask Society.

When you think of what it takes to make your favorite spirit, ingredients like grapes, barley, or herbs probably come to mind. But any aged liquor owes just as much of its flavor to something that’s not quite an “ingredient” at all: wood.

From cognac to bourbon, rye to añejo tequila, many of our beloved spirits spend years aging in wooden casks. Over time these casks impart all kinds of flavors. As the spirit seeps slowly into the barrel, it starts to pick up some of those aged flavors: perhaps vanilla or caramel, toffee or spice. And for Scotch in particular—which can spend decades in the barrel—wood is critical to the finished spirit.

A single malt Scotch, after all, has few ingredients. Malted barley, yeast and water. That’s it! So wood accounts for a huge part of a Scotch’s identity. In fact, casks are responsible for 60 percent of the whisky’s ultimate flavor.

Given that crucial importance, The Macallan is famously hands-on when it comes to its wooden barrels. They even employ a Master of Wood—yes, that’s a real job title—to oversee the distillery’s entire cask production. “We make a vast investment in these casks,” says Stuart MacPherson, the aforementioned wood master. He explains that these casks play a huge role “in the distinctive character of the final whisky.”

The story of the Macallan’s own Scotch begins not in Scotland, but in Spain. Whereas other brands purchase their barrels from big producers more or less off the rack, The Macallan starts in the forest. Working with Spanish cooperage Tevasa, they turn 150 year old trees into casks. After Tevasa assembles each barrel, it’s filled with Oloroso sherry for 18 months. Then it is ready for the Scotch.

Why all the effort? “The influence of the oak maturation casks on the final character of The Macallan is vital,” says MacPherson. Spanish oak, which has an open grain and high levels of tannin, gives you dried fruit, spice, and even chocolate flavors. The Macallan also creates barrels from American oak (also seasoned with sherry), which gives that whisky a lighter color and brighter vanilla and fruit characteristics. And why sherry at all? Well, the sherry allows more flavor to come out of the wood than could otherwise be extracted. Unless a whisky is ‘finished’ or ‘rested’ in sherry casks, it won’t really hold those distinctive nutty, fruity flavors.

Sure, it’s easy to say that wood matters. But can the average person tell the difference? Yes, and here’s the proof: Just look at a few different whiskies from The Macallan. (Or better yet, taste them.) Every single bottle the distillery makes starts from the same spirit. The malted barley, yeast, and water are cooked, fermented, and distilled exactly the same. That clear spirit is what goes into every barrel of The Macallan. It’s only the wood—the type of wood used, the way it’s seasoned, the length of time it’s aged, and the blend of the different barrels—that distinguishes the company’s expressions from each other.

Believe us, you’ll know the difference between a 12 Year and their new Rare Cask when you taste them. And since there’s no artificial color used in The Macallan, the hue of every whisky comes 100% from the influence of the wood. Just a glance at the different colors in The Macallan’s line and you’ll see just how much wood can matter.