Oak is the most common wood used for producing the whisky we all drink, experiments have taken place to see what effects other wood has on the maturation but oak still seems to win out but why ?
Well other types of wood like pine that contain lots of resin that can pass on strong flavours when maturing whisky just don’t seem to work, the slow growth of oak helps give it the strength and more natural tannings also come from the long drying process and these factors make it more practical for maturing whisky. There are 3 main types of oak used.
Quercus Alba or ” white oak”, this is also commonly known as American oak, this is the most common oak used for maturing whisky. This type of oak is faster growing and gives us more lactones, which after toasting gives us the vanilla, coconut and woody flavours.
Quercus Petraea “European oak “. This oak is more commonly found in France and mostly used in the production of wine, it is a slower growing wood and gives us a finer tanning and therefore more vanilla compared to the other European types.
Quercus Robur ” pedunculate oak ” also know as ” European oak ” . This oak is mostly found in Spain and commonly used in the production of cognac and sherry. This is a faster growing oak compared to the French oak and therefore gives off more tannings.
So once we have the wood, once it is cut it has to be dried, there are different methods in drying the oak but the best way seems to be let it be dried naturally, this takes longer but it releases more vanillin and helps to reduce tannic astringency. There is also the method of drying by kiln, most bourbon barrels are made of wood using this method, it is a lot quicker, wood dried naturally might be aired for as long as 24 months rather than a few weeks by kiln.
Once a barrel has been made it helps impart the flavours we know by..
1, As the wood heats up and cools down it ” breaths” as the wood heats up it draws the spirit in, when it cools the spirit is forced out and this is how we get the natural flavours into the spirit. The flavours that can be found from the natural tannings like vanillin, coconut, and natural sugars and of course the oaky, toasty notes.
2, The wood also helps to get rid of some of those nasty undesirable flavours such as sulphur.
3, By Charing or toasting, this allows more of the natural flavours to release into the spirit maturing inside the barrel. Generally bourbon barrels are charred for anywhere between 40 seconds and 1 minute but some have been heavily charred for up to 4 minutes, wine casks and sherry casks are generally toasted.
So we now know that the natural tannings released from the wood itself gives us so many of the flavours and scents we find in whisky, there is also the liquid that has gone into the ” first filling ” of the barrels, this might be bourbon, wine, cognac, sherry or port. These other spirits also interact with the whisky when the wood ” breaths” this then gives us more of those sweet, dried fruit and succulent flavours we all pick up.. So next time you are thinking about what flavours you are picking up, just give the wood some time and consider the impact it has had on your whisky..