The Best Oak For Aging Whiskey

Oaking or ‘aging’ whiskey is what gives it all of it’s color, and a lot of its taste an aroma.

In fact, Dan Szor, CEO and Founder of Costwalds Distillers estimates that wood contributes 60% to 70 % towards the taste of the final whiskey product.

“Wood is known to take out the bad through evaporation and bring in the good through the extraction of tannins and wood sugar.”

This highlights the importance of maturing the spirit to develop a distinct desirable taste. This article will aim to inform you about the best oaks for aging whiskey.

More About Aging Whiskey

Aging whiskey is an essential process that should not be underestimated. This is due to the visible effect identified in matured whiskey compared with unmatured whiskey- it generally possesses few of the desirable properties sought in taste and aroma.

Nishimura and Matsuyama (1989) highlight the following whiskey maturation points:

  • To accomplish satisfaction, the maturation age varies between 3years-10 years
  • There is an obviously significant flavor differentiated between matured and unmatured spirits.
  • During the maturation stage, large volumes and strength of the spirit are lost through the evaporation of water and alcohol through porous casks of wood.
  • Different factors such as cask size and wood type will determine the maturation time and quality of the matured spirit.

 The anatomical characteristics of wood may determine the quality influence of the maturation process, particularly the evaporation rate, oxidation, and extraction. Any factors with wood properties that distinguish variation will impact the influence on the maturation stage of the whiskey. 

What are the legal requirements for aging whiskey?

Maintaining tradition, the whiskey industry has always used oak casks for the maturation stage of the product.  Both in the United States and the United Kingdom, there are legal requirements for the use of casks in the production of whiskey. 

Legal requirements for aging bourbon in the USA

In the United States, legal restrictions allow the bourbon industry to store the raw distillate product for year-two years, in new charred oak casks.

The mash must be at least 51% corn. Nothing can be added to the mash, besides water. No additives, flavors, or coloring. The bourbon must be au naturel.  

The bourbon must be created in America. The bourbon cannot enter the barrel at higher than 125proof. It cannot enter the bottle at a proof less than 80. 

Legal requirements for aging scotch whiskey in the UK

However, in Britain, the law underlines that Scotch whiskey has to be stored for a minimum of three years in oak casks. The whiskey must be created in Scotland from cereals, water, and yeast.

The whiskey must be bottled at a minimum strength of 40% abv. 

The mash should be distilled below 94.8% abv so that the flavors and aroma are contained and do not derive from its raw materials.

No flavoring or sweetening is permitted.

How does wood affect the taste of whiskey? 

Wood Chemistry

To know the depth of the effects of wood on the taste of whiskey, one needs to have an idea of the chemical structure that makes up wood. 

Elizabeth Genthner (2006) underlines that “the major structural components of wood cells are cellulose, hemicellulose, and lignin. “

Cellulose is regarded as the main element that makes up to 50 % of the dryness of the wood. Cellulose, only slightly soluble in water, is a polysaccharide consisting of tens of thousands of β-linked D-glucose moieties in a linear chain.

Sjöström (1993) indicates that hemicellulose is soluble in water. Hence, it is a hetero-polysaccharide with branched chains typically much shorter than cellulose. The main hemicelluloses in wood are galactoglucomannan, arabinoglucuronoxylan, arabinogalactan, glucuronoxylan, and glucomannan. 

Therefore, hemicellulose is highly used as an active ingredient in the food and beverage industry due to its solubility in water. 

Vanholme (2010) notes that lignin is the most complex structural component of wood and accounts for about 15-30% of the wood plant tissue. It is a heterogeneous organic polymer responsible for the thickening of cell walls to make them rigid and impermeable. Its three main building blocks are monolignols, namely coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. 

These building blocks may vary according to the quality of the wood and cells characterizing the wood type.

Lignin is the predecessor responsible for the aroma components that are released during the maturation stage and enables unique flavors to collide together. 

Generally, flavorful whiskey is considered to contain high levels of wood-derived components in the final product. Experts have placed specific focus on the role of oak extracts as active agents of flavor congeners. Therefore, wood significantly adds a boost to a strong impression on the formation and production of whiskey. 

The best oak for aging whiskey 

So oak is oak, right? Well, not exactly. There are many different varieties of the oak species. Each with different properties that make them better or worse suited to what you’re trying to make.

1. Quercas Alba (White American Oak)

American oak properties are best suitable for the aging process of whiskey. This is due to the small and tight grains that release tannins slowly compared to other European counterparts. This enables flavors and aromas to flow easily with no constraints.  Therefore, investing longer in the aging process of whiskey and eliminating the overpowering woody character of the spirit.

It is noted that American oak barrels are charred on the inside by firing the cask to open up pores for flexible movement of the distilled whiskey. “It also caramelizes the wood sugars, which is partially responsible for the vanilla, crème brûlée, and honey notes found in many bourbons,” Szor adds. 

2. Quercas Petraee (Sessile European casks)

If sweetness is not your forte, then this strong spicy character identified in the sessile European cask is the best option for you. Unlike the American oak cast, the sessile European cask releases a high volume of tannins and darker spicy notes. Therefore, this enriches the strong taste of the whiskey

3. Quercas Mongolica (Japanese Mizunara oak)

In Japan, the Mizunara oak is used for aging whiskey and imparting an extraordinary flavor to the whiskey. This is due to the high moisture content identified in the oak compared to other oaks. The Mizunara is quite porous and imparts flavors such as dried fruits, cloves, vanilla, and honey.   

How Does Toasting and Charring Affect The Whiskey

Charring and toasting both give the barrel a brown color, but they differ in how dark the barrel gets and what kind of effect it has on the flavor of the final product.

Elizabeth Gethner (2014) underlines that “the toasting or charring step dramatically affects the volatile composition of oak through hydrothermolysis and pyrolysis reactions. Some of the more familiar aroma compounds are derived from pyrolysis of the lignin during heating. These include guaiacol, 4-ethylguaiacol, 4-vinylguaiacol (smoky compounds), eugenol, isoeugenol (spice or clove-like), syringol and syringaldehyde (sweet smoke), p-cresol (bandage), and vanillin (vanilla).”

You can read our in-depth comparison of toasting and charring here.

Toasting:

Toasted barrels are made using a naked flame to gently toast the barrels. In this instance, the heat does not come into direct contact with the wood. Toasting is a slow process and it often takes 20 minutes for a barrel to undergo the toasting process. The determining factor for how long you toast your barrel depends on the flavor you want to be imparted into the spirit you’re making. 

Toasting mellows the tannins in the wood and gives off sweet, spicy vanilla notes. Winemakers and coopers usually use the toasting process to make wine or lightly colored whiskey. 

The toasting stage of the oak-preparation process enables chemical collaboration to take place. When oak is heated and toasted, hemicellulose (wood sugar) is broken down to release the pleasant taste of caramel. 

At this point, all oaky scents are exchanged to combine into sweet flavors. Next,  the lignin is broken down and decomposed to release a creamy vanilla scent. 

The art created in the heat of toasting and roasting oak contributes to the smoky-sweet almond aroma extracted to exchange with other complex flavors of the oak, in producing high-quality whiskey.

Charring:

Charring is when heat is directly applied to the wood. This process of heating up barrels is often used for distilled spirits. But full-bodied red wines can also be aged in charred barrels. Once the barrel is charred, the wood acts as an activated carbon filter. 

The carbon filter helps remove any sulfur compounds from whiskey to ensure a smooth final product. The reason why charred barrels are often used to make whiskey and bourbon is because of the dark, smooth and rich flavor you get from spirits aged in these barrels.

How to best use oak to age whiskey

In this section, we’re going to look at the major contributors that ultimately control the creation of the flavor in aging whiskey.

You can read our full guide on aging and oaking whiskies here.

Preparation:

The size of the cask is important. There are three different sizes; the largest cask measures 400L and is mostly used for American bourbon. 

The medium cask measures 200L-400L and can balance oxidation and maturation. However, the smallest cask measures below 200L and the extraction rate is high and occurs rapidly. This means these casks need to be monitored. 

Seasoning and Toasting:

As the wood is practically dead, the barrels are to undergo a sort of resurrection. Therefore, the preparation of wood to extract flavors is conducted.

This is accomplished by heating the wood on the inside of the cask at a temperature of 200 degrees Fahrenheit for three-five minutes. This is done to rejuvenate the wood’s ability to lend flavor compounds to liquids that come into contact with it. 

The toasting of the barrel is a mild alteration, which results in blackened smooth cask walls and notes of vanilla. 

Charring, on the other hand, burns the wood so much, as to leave it broken up an eighth of an inch deep. This results in a darker, smokier, and caramel-inclined whiskey.  Charring is more practical in bourbon production as it releases heavier notes.

This article takes a deep dive into the differences between toasting and charing oak.

Cask Reuse

It is noted that the more an oak cask is reused. The less flavor will be released during the maturation stage. Therefore, one can reuse the cask three-four times before all flavors and aroma are completely depleted.

Oak Cask size

The cask size is important to consider as different sizes lead to different maturation periods.

The largest cask measures 400L, the medium is between 200L-400L, and the smallest is below 200L. The largest cask is ideal for American bourbon. The medium cask balances the oxidation and maturation phases. While the smallest cask activates, the extraction rate is high and occurs rapidly. 

Oaking Duration:

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