Aging spirits

So you have distilled moonshine, now let's make it drinkable.....

Freshly distilled alcohol usually does not taste very smooth. In order to improve the drinkability of your alcohol, you can use several techniques to 
artificially age the spirits, which I will describe in the next chapters.

The two main ways of aging your spirits are:

  1. Using wood (natural or toasted oak)
  2. Using smoothing agents (glucose or glycerin syrups).

Note: When aging your spirit, it is best done between 58-70% alcohol.

1. Using wood to age your spirit, some background information.

It is estimated that around 80% of the flavor of bourbon and whisky comes from the oak barrels used to store them in. We can replicate those flavors by soaking our spirits with oak chips or shavings.

The residual sugars in the charcoal give a slight sweetness to the finished spirit, and the limited absorbing ability of the charcoal only makes the spirit smoother, but doesn't strip the entire flavor out as you might think

Using oak: 

Typically two  (2) main types of oak are used in the whisky/bourbon industry:  American oak  and European oak. 

Quercus Alba

“White Oak” 

Commonly referred to as “American Oak” and is the most commonly used variety in whisky cooperage.

More vanillin than European varieties Fast growth High in lactones, which when toasted, provide woody, vanilla, and coconut flavors

Quercus Petraea

“Sessile Oak” 

Found across Europe, notably in France. Most commonly used for wine cooperage. Slow growth.

Fine tannins and more vanilla (compared to Pedunculate). Most common species in Tronçais forest.

Quercus Robur,

“Pedunculate Oak” 

Found across Europe. Spanish Oak most commonly used for cognac and sherry cooperage. Fast growth.

Generates more raisin, prune-like flavors. More tannins, thus more oxidative characteristics in the matured products (compared to Sessile). Most common species in Limousin forest

The reason that Oak is utilized is its unique physical and chemical nature. Oak has strength - physically, its wide radial rays give strength when shaped for a cask; Oak is also a "pure wood" as opposed to pine or rubber trees which contain resin canals that can pass strong flavors to maturing whisky. But it’s not just the Oak itself, it’s the transformation that happens to the Oak as a result of the seasoning and heating treatments during the coopering process - these result in the production of pleasant-tasting Oak lactones.

Whiskey barrels made from Oak have three broad effects on the spirit:

  • As an additive - It adds to the taste and aroma of the spirit by providing desirable elements from the cask. For example: vanillin, Oak lactone (coconut, bourbon character), toastiness, wood sugars and color. 
  • As an agent that removes undesirable elements from new make spirit. For example: sulphur compounds and immaturity. 
  • Oak barrels also interacts with the spirit. It adds extractive wood elements from the cask and converts them to organoleptically desirable elements.
    For example it will change tannins to acetals, and change acetic acid to fruity esthers.

There are 5 specific constituents of Oak that have been identified to some influence on maturing spirit:

  1. Cellulose - Which has virtually no effect other than to hold the wood together.
  2. Hemicellulose - Which consists of simple sugars that break down when heated and provide: 
    "Body" through the addition of wood sugar 
    "Colour"  as fresh distilled  moonhsine is a clear liquid as you have noticed.
  3. Lignin - The binding agent that hold the cellulose in wood together which, when heated yield:  Vanillin, Sweet, smoky and spice aromas
  4. Oak Tannins which is a naturally occurring preservative compound with a slightly puckery, astringent taste in the mouth, similar to the effect of strong black tea or fresh walnuts.  It plays an essential role in maturation by enabling oxidation and the creation of delicate fragrance in spirits. Tannins combine with oxygen and other compounds in the spirit to form acetals over time. 
  5. Oak Lactones - Resulting from lipids in the Oak, they increase dramatically during toasting and charring and can pass on a strong woody and perhaps coconut character; lactones give bourbon its distinctive character; and occur in higher concentrations in American Oak than in European varieties.


Manufacturing of casks:

The application of heat is integral to the process of making the barrel - wood fibers behave much like plastic polymers - they want to be straight. In order to bend the staves, they need to be heated. The straight staves are arranged inside a metal hoop and heated. I have heard that either an open flame or steam may be used. As they are heated they become more pliable and are shaped 

- hoops of various diameters are added to each end - six in total
- which are hammered down, towards the middle. Each hoop is held in place by the pressure exerted by the staves as they try to straighten themselves. The whiskey barells are then toasted which caramelizes the wood sugars.

This is where the construction of bourbon whiskey barrels casks and sherry casks diverge.


  1. Bourbon Casks

The Whiskey barrels, once formed, are charred - the inside of the cask is set on fire for a short period of time, which creates a black charred layer. There are various levels of charring which will have different affects on the spectrum of compounds and flavors the Oak will impart to the maturing spirit: more vanillins, lactones, "toastiness," spice characters, and tannins.  Charring casks causes further transformation. Char (carbon) removes sulphur compounds and immaturity from new spirit. Bourbon Whiskey barrels are typically charred for 40 seconds to 1 minute, but some distilleries have experimented with charring times of up to 3-4 minutes. The result of charring is dramatic changes on the surface - for example, wood sugars are caramelized, which will leech into the maturing spirit.
  1. Sherry Barrels

Sherry casks are only toasted and not charred. The casks used to mature Oloroso are the most popular with the Scotch industry. Sherry casks can be made of American Oak, but this is usually for Fino Sherries and are generally not used by the Scotch industry. It's accepted that European Oak adds more flavor thanAmerican Oak - sherry cask matured whiskies tend to be more full-bodied than bourbon Whiskey barrels matured ones, and this is likely the result of the type of wood, just as much as the type previous liquid occupant.

Barrel Sizes 
There are three Whiskey barrel sizes commonly used by the Scotch whisky industry: 

  • Barrels - 190 liters/50 gallons
  • Hogsheads - 250 liters/66 gallons
  • Butts - 500 liters/132 gallons

Butts come from the sherry industry while the majority of Whiskey barrels and hogsheads originate in the bourbon industry. All things being equal, the larger the cask the slower the maturation. Conversely, a smaller cask means that the maturing whisky is exposed to more wood and maturation is quicker - the Laphroaig quarter cask is an example of this.


From Bourbon to whiskey.....

Once a bourbon whiskey barrel has completed its "first life" that is, it has been used to age bourbon, it is ready for its second life as a whisky aging vessel. It is broken back down into separate staves and shipped to Scotland. In Scotland, coopers reassemble the staves into casks which will be used to age the whiskey that you will enjoy in a few years. Some bourbon whiskey barrels and all sherry casks are generally shipped whole - not broken down into separate staves. It's not common, but some companies re-char ex-bourbon whiskey barrels before use. 
Casks may be used for as many as four fills, i.e., filled with four separate batches of new make spirit. Generally, though, casks are retired after their second, or tthird re-fills. Sometimes when a whiskey barrel has reached the end of it's their useful life - after it has been filled and re-filled so many times that the spirit has taken out all the "good stuff" from the wood, some distillers will shave down the the inside of the cask to reach fresh wood and then the cask will be re-charred.

How ex-sherry casks are treated, once whiskey distillers get their hands on them, differs by distiller. Most will empty the cask of any residual sherry, nose the cask (to ensure the casks smells fresh, and then fill with new spirit.

 Are you ready to try it out???

...........then go to: Flavor & aging DIY