Opening the door to the work floor and you get hit with this wall of noise and a great smell of oak.The Blue Grass cooperage is an exceptionally busy place churning out high quality American white oak barrels which end up filled with Woodford Reserve and Jack Daniels among other spirits.The 185 employees turn out an average of 1,650 barrels a day in two shifts, this means that some 400,000 barrels leave the site in Louisville, Kentucky each year.It is a pretty stunning sight so see the various cuts of oak fashioned into barrels, accompanied by the soundtrack of clanging hammers, pistons and electric circular saws.American oak has long been the staple material for bourbon barrels, Neil McElroy, operations manager, explains why: “It is a tight grained hardwood with unique characteristics that make it suitable for maturing bourbon in.“Logs are quarter sawn rather than flat sawn to produce staves with the proper orientation of the growth rings and grain to give maximum strength and leak resistance.“White oak also contains a substance called tyloses that naturally blocks the sap conducting pores of the wood, adding to its water tight qualities.” The tour takes you through the five main important areas of barrel making, from the iron loops to final inspection.Despite the vast amounts of machinery, at each stage of the process there is a human making the decisions, and these chaps are proud of their product.One little secret to look out for next time you are wandering a Scottish warehouse is to try and spot a letter B stamped into the rivets holding the iron hoops together. This identifies it as coming from the Blue Grass cooperage.The iron for the barrel hoops arrives in big coils that are run through a machine that slices them in to the correct length, punchs rivet holes in the end and makes the hoop slightly flared to fit the shape of the staves.The next stop on the tour takes you to the heading department where pieces of wood are transformed into the round end pieces for the barrels.The coopers place the pieces into a machine that drills holes and inserts dowel pins. The boards are then squeezed together to form a square head.The heads are then planed and cut in to round heads. They are then charred in a special firing machine.Further down the line you can watch the actual barrels taking shape in the stave department.This physically demanding work starts with the staves, having been dried, being sawed to length and planed on the sides to create a proper angle for building.Next the barrel builders, or raisers, places the joined staves in to an iron ring.It is here you see the speed and skill of these raisers, who normally produce 270 barrels in an eight hour shift.You would think that given the heavy physical toll of putting these barrels together it would be an exclusively male preserve.However there in the thick of it is one woman, possible the only female cooper in the country – maybe the world.According to my guide, she gives the men a good run for their money. On the day I visited she was the second fastest raiser out of six.After all the staves have been placed in a head ring, a temporary iron hoop is placed on the opposite end and the barrel is sent to be steamed. This softens the wood and reduces breakages when the next iron ring is added.Once out of the steamer, a machine compresses the staves as the cooper places the second hoop on the barrel, and it is then sent for toasting.The dry fires used in toasting help to dry the wood out and set the staves in position.The most important thing about this process is that the oak gets a light toasting bringing out the sugars, flavours, colouring and other compounds.Once filled, the bourbon will extract these materials as it moves in and out of the wood during the aging process.This is a very critical part of the barrel making process as it affects the final flavour and colour of the finished bourbon.After toasting, the barrels move on to the charring machine. The inner surface of the barrels are set on fire for about 35 seconds.This visually impressive process is thought to help develop the extractable compounds and helps to filter the bourbon when it is removed after maturation.Once charred and cooled, the heads are fitted in to place and the head loops placed and tightened.The barrel is then pumped with one litre of water and 10 to 15 pounds of air pressure to check for any leaks.Inspectors examine each barrel and repair any cracks or problems before the barrel is loaded up and shipped out.