American oak versus European oak

Different trees, different wood

American white oak is Quercus alba, grown mostly in the eastern United States. European casks usually come from Quercus robur (pedunculate oak) or Quercus petraea (sessile oak), grown in France, Spain and other parts of Europe. All are true oaks, but they differ in how dense the wood is, how much tannin it holds and which aroma compounds it releases.

Under a microscope, American white oak has many tyloses. These are growths that block the vessels in the wood and make it very watertight. European oaks have fewer, which changes how the casks are made and how they behave in the warehouse.

Sawn versus split

Because American white oak is so watertight, its staves can be sawn from the log in any direction. That is quicker and wastes less wood. European oak must be split along the grain (riven) so the staves stay watertight. Splitting produces fewer usable staves per tree.

That is one reason European oak casks usually cost more than American oak ones. It also explains why the most common cask in world whisky is the ex-bourbon barrel of about 200 litres, made from American white oak. Our guide to cask sizes shows where each type turns up.

What American oak tastes like

American white oak is rich in oak lactones, which smell of coconut and fresh wood. It also gives plenty of vanillin. With the char used on bourbon barrels it adds caramel and toffee notes too. Whisky matured in American oak often tastes of vanilla, coconut, honey, banana and soft spice.

It tends to give less tannin than European oak, so the mouthfeel is often softer and sweeter. If you have tasted a typical ex-bourbon cask Scotch, Irish or Indian single malt, you already know the American oak profile.

What European oak tastes like

European oak usually carries more tannin, especially the ellagitannins that give grip and a drying finish. It tends to give less coconut than American oak and more spice: clove, nutmeg, cinnamon. Over time its tannins contribute to colour and to the dark, rich notes of long matured whisky.

Many traditional sherry casks are European oak, so European oak often travels with sherry flavours: raisin, fig, walnut, chocolate. Be careful not to credit everything to the wood, though. A lot of sherry casks today are American oak seasoned with sherry, which gives a different result. Our guide to ex-bourbon, sherry and wine casks separates the effect of wood from previous contents.

Other oaks you will meet

A few other oaks appear on labels. Japanese Mizunara oak gives sandalwood and incense notes and is hard to work. Our guide to Mizunara oak explains why. Some distilleries also experiment with oak from Hungary, Portugal or other regions. Scotch whisky must mature in oak casks, so other woods such as chestnut or cherry are not permitted for it, though some other spirits use them.

Tasting the difference

The best way to learn is side by side. Pour two whiskies, ideally from the same distillery: one matured mostly in ex-bourbon American oak and one matured in European oak sherry casks. Look at colour first: European oak and sherry often give deeper red-brown tones.

Then nose. Search the American oak glass for vanilla, coconut and honey. Search the European oak glass for spice, dried fruit and a drier wood note. On the palate, notice how much the tannin grips your gums. European oak usually grips harder. Keep water beside you, sip slowly and stop when your palate tires.

Climate changes the picture too. Heat speeds the extraction of tannin as well as flavour, so a European oak cask in a hot warehouse can turn a young whisky grippy and dry sooner than an American oak cask would. That is one reason many distillers in warm countries lean on ex-bourbon American oak for the bulk of their maturation and use European oak with more care.

Learning to separate wood from spirit from previous contents takes structured practice. Once you can, every whisky label becomes easier to read.

Try it this weekend

Pick one ex-bourbon matured whisky and one sherry cask matured whisky. Smell each for two minutes and write down every aroma you notice. Then mark each note as coming from the spirit, the oak or the previous contents. You will not get them all right, which is exactly the point of trying.

Common questions

Which oak species is used for bourbon barrels?

American white oak, Quercus alba.

Why is European oak more expensive?

European oak staves must be split along the grain to stay watertight, which yields fewer staves per tree than sawing.

Does European oak always mean sherry flavour?

No. Many sherry casks are European oak, but many are now American oak. The previous contents and the wood each add their own flavours.