Oak Barrels have a convex shape and bulge at their center, called bilge. This facilitates rolling a well-built wooden barrel on its side and allows the roller to change directions with little friction, compared to a cylinder. It also helps to distribute stress evenly in the material by making the container more curved[. Barrels have reinforced edges to enable safe displacement by rolling them at an angle (in addition to rolling on their sides as described).

The wooden parts that make up a barrel are called staves, the top and bottom are both called heads or headers, and the rings that hold the staves together are called hoops. These are usually 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.

Wine barrels typically come in two hoop configurations. An American barrel features 6 hoops, from top to center: head- or chime hoop, quarter hoop and bilge hoop (times two), while a French barrel features 8, including a so-called French hoop, located between the quarter- and bilge hoops (see "wine barrel parts" illustration). The opening at the center of a barrel is called a bung hole and the stopper used to seal it is a bung. The latter is generally made of white silicone.

Video Credits: www.tonnelleriesaintmartin.com

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