A common number that gets bandied around is that roughly 60% of flavour in whisky can come from the barrel. The conditions the spirit is kept in, the surface area to volume ratio, the type of barrel and wood, how long the spirit stays in there, all apply a significant role in the taste and appearance of whiskies and bourbons.
In Scotch, barrels are often second use coming from wine, port, rum or bourbon and are often shipped to Scotland broken up with coopers putting them back together once they arrive. This makes for much more efficient shipping. However virgin unused barrels are an absolute must for bourbon to be bourbon and so it was with some excitement I had arranged a trip to the Kelvin Cooperage in Louisville to see how these are constructed and learn about some of the techniques they use.
The Kelvin Cooperage was established in 1963 by Ed McLaughlin in Scotland where it would refurbish used barrels. In 1991 the business relocated to Louisville to get itself closer to the original source of the product and also expand into wine barrel production. I met Paul McLaughlin, Ed’s son, on site along with William Hornaday, production manager. Paul still speaks with a bit of a Glasgow accent and was good enough to translate some of the volumes for me out of US gallons and into litres. He explained that the business has a particular affinity with craft producers as they themselves still use some of the more traditional methods to treat the wood and form the barrels.
I was then taken on a tour with William to look at how a barrel was made.
The first step is that the wood is atemperated in two large humidity controlled drying blocks. This helps to manage the moisture content and improve the structural strength of the white American oak that is used. The moisture can be as high as 50% straight off the tree and is reduced down to low double digits before it can be processed. Some of this seasoning would have been done at the saw mills but the final accurate control is done here at Kelvin. Typically bourbon wood is matured for around six months in open air to season it to the required level.
Wood is cut to two lengths- for the barrel butt ends and for staves that make up the barrel body. The wood for these is typically cut with the growth rings running top to bottom on the short side of the cut to ensure better stability and a more leak proof finish.
The heads for the barrel are constructed through a series of these shorter cuts being held together with pieces of dowling. The 1st picture below shows you these in construction with a blank head board being created. These are then machined, taking place in the second picture, to create the barrel end with an edge around the diameter,, which will fit into the croze in the body of the barrel.
The longer stave pieces, creating the heart of the barrel, are made from pieces of wood that are machined in a precise manner. The barrel is convex in structure and the inner diameter is shorter than the outer diameter which mean the staves have to be slightly curved. Similarly the middle of the stave is slightly wider than the ends as the barrel has a fatter middle.
The next stage sees around 31-33 staves assembled around a forming ring to start to create the barrel body. Narrower and wider staves are selected to try to ensure an equal pressure is created around the barrel- too many of a single type can create leakage points. The ability to get the pieces in the correct order and form are down to the skill and judgement of the coopers.
I asked William Hornaday at this point about how they dealt with the waste and offcuts from the various stages of the operation. He smiled and explained all would become clear in the next few phases – he wasn’t kidding. Once the barrels are formed and have their first hoops on them they are wetted and placed over the first heat source. These are small brazier type units which use the offcuts as a fire source. In this first stage the barrels are not really being toasted as much as allowing some moisture into the staves so when more hoops are applied the convex shape of the barrel is created.
After new hoops are applied the barrel can then be toasted in earnest for as much as 20 minutes or to whatever level the client has specified. Toasting typically occurs over a longer period of time than charring and has the effect of browning the barrel. The effect of toasting is to stimulate and access the sugars that are lower down in the wood and allow these in turn to be dissolved by the alcohol and take part in the finished product. Charring is more of an action of burning the surface of the wood. Leaving this carbonised product in the barrel allows it to act on potential undesirable favour compounds and remove them from solution. Often charring is associated with the phrase subtractive maturation- where the carbon is filtering out compounds.
The charring at Kelvin is undertaken by skilled craftsmen who are familiar with the required char level through smell and know when to douse the barrel with water to halt the process.
After this stage the barrel is cooled before being cut so the butt end can be introduced and the bung hole is also cut. The butt ends are also treated in a similar manner on char and toasting again using a wood fire but on the purpose built set up that looks a bit like a cooker. The barrel once cooled has final hoops placed on it before being tested for leaks and pressure.
Once passed those tests the barrels can be stencilled before shipping out to clients.
Aside from the virgin barrel production Kelvin trades in returned barrels which is still a major part of the business. These barrels are shipped worldwide with many making the journey to Scotland and Ireland as well as being involved in rum or tequila production. These barrels essentially fall into three categories of ready to ship, require some rework or are taken for the staves and reused elsewhere.
Kelvin is a wonderfully traditional business. It employs craftsmen and the fascination of watching skilled guys put these things together isn’t lost on you. While there are undoubtedly larger and more modern cooperages Kelvin keeps to the tradition of coopering and I am hugely grateful to the guys for allowing me a bit of insight into the care and attention they take in their operation.