Anatomy of a cask.

An American white oak study: hoops, staves, heads, bung and the charred interior. Enable JavaScript for the interactive 3D model.

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The hoops

Six steel bands encircle this cask. They hold the staves together under compression. The familiar barrel shape depends on the relationship between the tapered wooden shell and its driven hoops.

Head hoops sit near the ends; quarter hoops and bilge hoops sit farther inward. Small rivets join each hoop’s ends. Counts and positions vary by cooperage; six is the chosen reference format.

The staves

Curved lengths of oak meet edge to edge to form the barrel wall. One wider stave carries the bung hole. Their fitted edges, curved profile and hoop compression create the wooden vessel. Inside each end, a groove called the croze receives the head.

The model uses 28 staves, including a wider bung stave, to show the construction. This is a modelling choice; real stave counts and widths vary. The char remains attached to the inner face when the staves move.

The heads

Two circular assemblies of fitted wooden boards close the ends of the cask. Their edges seat in the croze grooves. The inward-facing wood is part of the spirit-contact surface too. This study shows charred inner heads and pale outer faces.

Head treatment is specified separately: heads may be toasted or charred. These charred heads are a chosen configuration, not a rule for every American oak barrel. The exploded view lifts them clear so both faces can be inspected.

The bung

A tapered stopper closes the drilled bung hole. Here it sits at the bilge, in the widest part of the cask’s side. The opening provides access for filling and emptying. Pull the cask apart to see the stopper separate from the actual hole in its stave.

This is a wooden bung, with its timber species unspecified. American oak describes the cask wood; it does not establish the bung’s species. Silicone is another available bung material. Shape and fit are illustrative.

Inside the char

Flame burns the inward-facing wood into a dark, fractured char surface. The black surface follows every stave and, in this configuration, the inside of both heads. Below that char lies heat-altered wood, often called the red layer. These zones help explain why cask treatment changes what the spirit encounters.

Char is transformed wood, not a coating poured or painted onto it. It can adsorb some compounds; extraction from wood is a separate process. This enlarged illustration shows the relationship, not a measured char depth, microscopic scan or flavour prediction.