Why do we toast American White Oak barrels?

Distillers have many choices when it comes to the maturation of their spirit, what role does American White Oak play and how does charring or drying affect the end spirit?

By law, Bourbon must be aged in new, charred oak barrels. The law doesn't actually mention American White Oak, but it is the Oak that is available in the Kentucky region. Distillers have choices in terms of char and toast level, which will have major ramifications on the colour, aroma, flavour and mouthfeel of the whisky that lands in the bottle.

In this article we will look at the choices distillers have during the whisky production process:

WHERE IS THE WOOD FROM?

Like most things, regionality will greatly affect the flavour and make up of the white oak used to craft the barrels. When its colder, the trees tend to grow slower and will have a tighter grain. These flavours are much harder for the bourbon to absorb, and therefore end up creating a much lighter style.

DRYING THE WOOD

During the crafting of the barrel, the wood is harvested and it must be dried - or seasoned.

Kilning—which is drying the wood in a heated chamber—is often the easiest way.  After kilning, the wood will be dry enough to make barrels, but that’s about it. Other distillers choose natural drying, rough-cutting staves and headpieces and they are stacked up outdoors and left alone for 6 to 24 months. They feel the affect of all the natural weather elements Mother Nature can throw at them. This reduces tannin levels in the wood and helps to break down compounds which are incorporated into the whiskey as it matures. 

BURNING THE WOOD

By law, the barrel must be charred. This is usually done before the wood is turned into a barrel. Char depth, is the level of burn into the timber. Charring the wood acts as a filter, like charcoal filtering, to produce congeners in the distillate.  Congeners are substances produced during fermentation, other than ethanol, that give whiskey much of its taste and aroma. There are both good congeners and bad congeners. Some of the bad congeners are eliminated during distillation; the charred barrel takes care of the rest.

TOASTING

Toasting is another way of treating wood, though it is less common. Incidental toasting occurs during the charring process, as heat converts hemicellulose into sugar and creates a toasted layer below the char level. That incidental toast is limited, however, because a barrel can only be burned for so long before it starts to lose structural integrity. It is possible to toast barrels more deeply before charring, but because it is an extra step that adds cost, most distillers don’t do it. Some, however, do, as pre-char toasting releases more sugars that can be extracted during the maturation process. Variations in toast time and temperature, as well as in char level, create different flavor profiles.

TASTE THE DIFFERENCE

Many distilleries will tell you their barrel specifications, so you can taste-test to see if you can detect a difference. Most use the heaviest char but a few, such as Maker’s Mark, use something a little lighter.