How are barrels reconditioned?

reoaked STR oakbarrels

Why recondition an oak barrel?

Depending on the appellation and the estate, winemakers store their barrels for periods ranging from 1 to 10 years, sometimes even longer. The older the barrel, the less aromatic it becomes. In the Bordeaux vineyard, for example, most winemakers believe that a barrel can enrich wine for three years. After the third aging, the barrel is considered neutral in terms of wood contribution.

Distillers, due to specific regulations are required to use their barrels for a set period of time. However, used barrels that have contained other spirits or wine my be of interest, as they add complexity to spirits in certain situations. They allow their spirits to be made more complex under certain conditions.

When a barrel has held red wine, the inner surface is too impregnated, this can cause unwanted tannins and sulfur residues to be in contact with the alcohol.

Reconditioning is a solution that removes these residues and gives the barrel a second life.

Like blotting paper soaked in water, the wood absorbs wine as it comes into contact with it. However, the wine penetrates the wood to a limited thickness, generally three to four millimeters.
The reconditioning solution consists in shaving a few millimeters of the inside of the barrel to restore an intact wood surface, capable once again of exchanging aromas with the wine or alcohol.

Even though the operation may seem simple, it requires a certain amount of expertise.
Developed by Scotch whisky expert James Sneddon Swan, the STR reconditioning method is widely used in the spirits industry.

The STR Method (Shaved, Toasted, Re-charred)

The acronym STR stands for Shaved, Toasted, Re-charred. In French, a planed, bousiné and carbonized barrel.
This last stage (Char) was initially reserved for bourbon barrels. (Swan, 1988).
Toasting levels vary depending on the cooperage but four main types can be identified :

  • Light toast : This transforms few of the wood’s aromatic precursors and is generally reserved for products where freshness and fruitiness are to be preserved.
  • Medium toast : This creates several compounds, primarily vanillin and whisky-lactone, which respectively correspond to vanilla and coconut aromas.
  • Heavy toast : This produces guaiacol, eugenol and furfurylthiol, which respectively contribute to smoky, spicy (or clove) and coffee aromas*.
  • Char toast : This involves heating the wood to the point of charring. The flames come in direct contact with the wood, forming a layer of charcoal inside the barrel. Cracks appear on the inner surface, resembling crocodile skin. This toast creates new aromas while also degrading others. It increases the contact surface with the wood dur to the cracks.

The STR method is therefore intended for distillers who want to acquire quality barrels at a more affordable price.
The Char toast is a legal requirement for aging bourbons. It can also be used to aging other spirits such as Cognac, Rum and various whiskies.
The same method is possible without the char toasting for a distiller or winemaker who prefers a lighter toast.

*The listed aromas are not exhaustive of wood’s aromatic compounds. This list aims to show the interest and impact of different toasting levels.

Reconditioning stages

First, to access the inner surface of the barrel, it must but disassembled.

The steel hoops, heads, and staves are removed one by one.
The staves are then shaved, provided they are thick enough.

Barrels with a thickness of at least 27 millimeters are eligible for reconditioning.
Shaving a barrel with a thinner thickness poses a risk of leaks and makes them mechanically fragile.

After shaving, the barrel is reassembled, with the exception of the heads.

It is possible, using a specific tool, to shave a barrel by only removing the heads, which reduces the disassembly and reassembly time.

The barrel is then placed on a brazier for toasting, which forms the previously mentioned aromas.
Char toasting is carried out when needed by intensively feeding the fire for a few seconds.

The heads, which will also have been shaved and possibly toasted, are then used to close the barrel. It is also possible to recondition the outside of the barrel by sanding the wood and replacing the steel hoops.