Barrels

A barrel, or cask, is a cylindrical vessel of wood that is flat at the bottom and top, with a slightly bulging middle. The three primary parts of a barrel are heads (bottom and top), staves (sides), and hoops (rings that bind the heads and staves together) (see Figure 1). Specifications are contained in the Department of Transportation regulations (1).

In architecture and physics, the arch is probably the stongest possible structure. The more pressure or weight exerted on the top (keystone) of the arch, the stronger the arch becomes.

The wooden barrel is designed according to the doublearch principle of strength. Like an egg shell, it is doubly arched, both in length and girth. The bend in the stave’s length is the first arch, and the bilge circumference of the stave’s width is the second arch. These arches impart great strength.

There are three basic cooperage operations: logging the timber, milling the logs, and assembling the barrel staves and heading material. Saws reduce the logs to length, produce edge-grained pieces of cylindrically shaped and jointed wood for the staves, and produce flat pieces of wood for the heading. In recent times, staves have been quartersawn as opposed to earlier cylindrical-sawn staves. The quarter-sawn straight staves are planed interiorly and exteriorly throughout their thickness to achieve a stave of cylindrical width. After the wooden material has been airand/ or kiln-dried to approximately 12% moisture content, the staves and heads are assembled into steel-hoop-bound barrels. Assembly operations include: setting up staves; steaming and winching staves to achieve the belly, bilge, or circumference arch; heating to make wood pliable and give one last drying after being steam bent; tapping out for uniform thickness; trussing to tighten stave joints; crozing interior grooves in each end of the staves where the heads will be inserted; heading up by inserting heads in the croze at each end of the staves; hooping up by driving riveted-steel hoops onto exterior of staves; boring for testing, lining, and future filling; bunging up the bored hole; and rolling the barrel out to the marketplace.

Dozens of species of timber from all over the world have been used to make tight (for liquid) and slack (for nonliquid) cooperage. Hardwood barrels for spirits and wine include oak timber from Limousin and Nevers in France; Alastian and Italian oak; and fork-leafed American white oak, found principally in the slow-growing forest regions of the United States of Missouri, Indiana, Tennessee, Kentucky, and Arkansas. Virtually all of the wooden barrels made in the United States today [1–2 million (10⁶)/yr] are 50-gal (189-L)-capacity barrels used by the bourbon whisky trade. Barrels for bourbon are charred interiorly about 1/16 in. (1.6mm) of their 1 in. (25.4mm) thickness to bring out the tannin in the wood. Tannin aids in the coloring and flavoring of spirits and wine.

Wooden barrels have had numerous names, depending on their size and use. A small sampling of these names include: pickled-pig’s-feet kit; fish pail; one-quarter, onehalf, and full-beer ponies; hogshead; salmon tierce; tallow cask; rum puncheon; and port wine pipe. A list of common international cask sizes is presented in Table 1 (2).

Wooden Casks for International Shipments of Alcoholic Beverages Table 1.

Just as the wooden barrel replaced the crude basketry used centuries ago, many other types of container have replaced the wooden barrel: steel and fiber drums, plastic pails, aluminum and steel cans, fiberglass and cement tanks, and so on; aluminum and stainless steel replaced wood for beer barrels (3).

To date, no industrial engineer has come up with a blueprint to replace the strength of a wooden barrel. In tests involving high stacking, they can perform better than steel drums.