Bourbon - Filling of the Barrels
In Kentucky and Missouri companies specialize in the production of barrels from American white oak. The barrels may only be used once for straight bourbon whiskey. They hold approximately 53 American gallons (about 200 litres). Americans often use the term 'barrel' rather than 'cask'. There are various definitions for a barrel. The most famous barrel is the petroleum barrel, which holds 158.97 litres. The normal American barrel, however, holds 31.5 gallons = 119.23 litres. 1 gallon corresponds to 3.785 litres.
The staves of the barrels are first joined but not yet completely closed. Then the staves are made flexible using hot steam and can thus be bent into their oval shape.
The next step is special and lends Kentucky straight bourbon its unique taste. The barrels, still open on one side, are held over a small fire. This process is called toasting and makes the wood sugar in the staves on the inside caramelise up to a certain layer. This red layer is later clearly visible when a barrel is disassembled. Toasting takes about 12 minutes.
After toasting the barrel is submitted to an even stronger fire treatment. It is burned on the inside with a large flame for 6 to 12 seconds, which produces a charcoal layer. The thickness of the charcoal layer can vary from grade 1 to grade 4.
After filling the barrel is closed with a bung and transported to the warehouse by truck.