A wooden container used to store spirits, normally made of oak though other woods (Woods for aging) are also used. Technically, an American Standard barrel is a type of cask that holds 53 gallons/200 liters. The terms are used interchangeably. Barrels are made by coopers at cooperages.
During the barrel aging process, some of the following chemical changes occur in the spirit:
- Leaching of oak flavors into the spirit, including vanillins, lactones, smokiness from the char, spice characters, and tannins
- Oxidation of spirit
- Evaporation of spirit through dry section of barrel, known as the Angel's Share
- The aldehyde level changes
- The color changes
- The concentration of esters changes
- The acidity changes
- The concentration of furfural changes
- The concentration of fusel oils change
- The pH changes
- The amount of solids change
- The proof changes
- The concentration of tannins change
- The total acidity changes
- Esters form
The most common size is the American Standard Barrel (ASB). It approximately 53 gallons or 200 liters. Sizes are not legal definitions so they will vary.
- Tun Cask: 250 gallons/1000 liters - Commonly used to rest, marry, blend, etc. liquids.
- Pipe Cask: 165 gallons/650 liters - Common for Port
- Butt Cask: 125 gallons/500 liters - Common for Sherry
- Puncheon Cask: 115 gallons/450 liters - Common for Sherry
- Hogshead Cask: 75 gallons/300 liters - Common for Cognac (barrique) and wine (225 liters)
- Barrel Cask: 53 gallons/200 liters - Common for whiskies, but also Rum and Tequila
- Tierce Cask: 38 gallons/150 liters
- Rundlet Cask: 25 gallons/100 liters - Barillet in French
- Quarter Cask: 13 gallons/50 liters - Trendy for small batch-craft
- Blood Tub: 11 US gallons/40 litres - These small casks traditionally have an elongated oval shape, originally to enable them to be carried on horseback.
- Firkin Cask: 10 gallons/40 liters
The wooden parts that make up a barrel are called staves, while the rings that hold them together are called hoops. The latter are generally made of galvanized iron, though historically they were made of flexible bits of wood called withies. While wooden hoops could require barrels to be "fully hooped", with hoops stacked tightly together along the entire top and bottom third of a barrel, iron-hooped barrels only require a few hoops on each end.
Although some barrels are new oak, many have been customized somehow:
Barrel Surface Area
The size of the barrel affects the surface area the spirit touches. The higher the surface area that the spirit touches the faster oak flavors are transferred to the spirit. The smaller the barrel the larger the surface area is compared to the spirit.
- First Fill: The first time a barrel is used. This is required in most forms of American Whiskey production. It will impart the strongest flavors of the wood.
- Second/Third/Etc Fill: Normally "Second (or further) fill" is used to describe the reuse of a barrel with a similar product. The Second and further fill reduce the wood flavors absorbed by the distillate allowing longer ageing before it gets over oaked. It is common to see third and forth fill barrels.
- Ex-(spirit/wine): Ex-barrels is used to describe re-use (Second+ fill) of a barrel when used with a dissimilar spirit. Scotch is commonly aged in Ex-Bourbon and Ex-Sherry barrels. Ex-Wine barrels are now starting to become common.
- Finishing: Finishing is taking a spirit from one barrel and being put in another before being bottled. Spending too much time in one type of cask may impart too strong of a specific flavor. Finishing allows to mix casks to create a unique flavor profile. Common with Ex-Sherry casks in Scotch. New make Scotch will spend most of its time (several years) in ex-bourbon barrels and the last couple months to a couple years in a Ex-Sherry cask. It is also becoming common to see 3 or more types of casks used to age a spirit.
If you can not store your spirit for years in a 55 gallon oak barrel, there are some alternatives which provide a reasonable approximation of barrel aging:
- Put oak chips in your spirit bottle
- Put charred oak chips in your bottles to simulate bourbon
- Stopper your bottles with a dry cork to promote evaporation
- Add a small amount of sherry to your spirit
- HD Post: The Badmotivator Bain-Marie and Oak Barrel
- HD Post: Everything you need to know about oak alternatives
- Barrel Terminology
- Boozewerks Podcast: Barrel Aging
- What a barrel does
- Barrel on Wikipedia
- Scotch’s Deep Secret:Wood
- Diageo Barrel flavor chart
- Cask Sizes explained
- Whisky.com's All About Casks
- Influences of casks
- Chart of flavor changes over time
- Barrel making video
- How vanilla flavor gets in to Whisky
- Master Thesis: Aging of Whiskey in barrels of non-traditional volumes
- Distilling Craft Podcast: Barrels
- Box Whiskey Masterclass on Casks
- Temperature's effect on aging in a barrel
- Distilled Sunshine: List of barrel articles
- Liberation of recalcitrant cell wall sugars from oak barrels into bourbon whiskey during aging