GB2206605A - Method of reconstituting casks - Google Patents

Abstract

The method comprises selecting from casks previously used for storing whisky, using liquid chromatography methods, a cask which is of European oak. The internal surface of the cask is then cleaned using a combination of steam cleaning charring and scraping to expose the bare wood of the cask. A process of controlled anaerobic thermal degradation may also be applied to the ask and finally the casks are filled with sherry and left to stand for a time to allow the sherry to penetrate the wood. The cask is then emptied ready for filling with spirit for maturation.

Description

Method of Reconstitutinq Casks This invention relates to a method of reconstituting casks for use in the production of whisky.

Sherry casks hold a pre-eminent position in the production of Scotch whisky in that they are reputed to produce the most mature, most full-bodied and most flavoursome type of whisky (usually malt whisky rather than grain whisky). By definition, a sherry cask (either a nominal 500 1. butt or a nominal 250 1. hogshead) was a cask which had been employed in part of the sherry production process in Spain and then subsequently used for transporting sherry from Spain to the United Kingdom. After disgorging the sherry from the cask, the empty cask was then sold to the Scotch whisky industry and was henceforth referred to as a "sherry" cask.

Following the introduction of tankered sherry from Spain to the United Kingdom, alternative procedures were investigated, both in Spain and the United Kingdom to simulate the authentic "sherry effect" from the genuine sherry cask.

It has been found that the so-called "sherry effect" was due not only to the presence of sherry in the wood, but also due to the type of oak heartwood (American or European) used in the manufacture of the cask and the interaction between the wood and the sherry. Analysis of the maturing whisky showed that the removal of undesirable flavour congeners, the addition of desirable flavour congeners and the interactive production of flavour congeners could be directly related to the type of treatment of the wood surface. In this respect European oak is the preferred botanical species.

According to the present invention there is provided a method of reconstituting a cask for use in the production of whisky comprising selecting from casks previously used for storing whisky a cask which is of European oak, cleaning the internal surface of the selected cask, adding sherry to the interior of the cask and allowing the sherry to penetrate the cask wall.

The European oak cask may be selected from a range of European and American oak casks by chemical means, for example by high-pressure liquid chromatography. Spanish oak is especially desirable.

The selected cask may be cleaned by steam treatment, charring and scraping in order to expose the bare wood of the cask.

In order to provide different flavour development profiles for whisky stored in the reconstituted casks, a process of controlled anaerobic thermal degradation is preferably applied to the cask. This process can be conducted, for example, by heating the cask after cleaning, for selected times ranging from zero to 180 seconds.

The selected cask preferably has lost most of its wood extract related value, which occurs after about 4 to 5 fillings with whisky, but has retained good physical integrity.

Embodiments of the present invention will now be described by way of illustration in the following Example.

EXAMPLE Sherry casks which have been used as containers during whisky maturation are studied to determine the extent of their remaining wood-extract related value, by considering the colour of the whisky which was most recently stored in them and noting also the number of times the casks had received fillings. Pale colouration of the whisky and 4 or 5 fillings indicated exhaustion of the wood-extract related value of the cask.

Exhausted casks were inspected for physical integrity and those in good condition were then tested chemically to determine whether they were of Spanish or American oak.

Scrapings were taken from the outside of each cask and reduced to sawdust, which was then extracted with 40% v/v ethanol by soaking overnight at a standard weight/volume ratio. The sawdust was filtered off and the residual liquid injected into a high-pressure liquid chromatograph, which produced a wood-extract profile after one hour.

From this analytical profile, one component, scopoletin, is selected and quantified. A wood extract with a high concentration of scopoletin is classified as American oak and a wood extract with a low concentration of scopoletin is classified as European oak.

The exhausted casks of Spanish oak were selected, the ends removed, and steam was passed through them to remove potassium hydrogen tartrate, which was in the form of a crystalline deposit on the casks' inner surface, and other residues. The inner surface of the casks was then heated using gas burners in order to subject the wood to anaerobic controlled pyrolysis which had the effect of loosening and charring the deposits on the surface. The charred surface was then scraped to remove the remaining residues and to expose the bare wood having lignin degradation products within it.

Alternatively the charring of the surface can be carried out first with the steam cleaning being carried out subsequently.

The cleaned casks were thereafter subjected to controlled anaerobic thermal degradation for times ranging from zero to 180 seconds. The temperature within the cask staves was varied as required but typically was 150-2000C, and uniform heat distribution was aimed for. By selecting the temperature and time appropriately different flavour characteristics could be obtained from the finallyregenerated casks.

After thermal degradation, if adopted, the casks were filled with a good quality fortified wine (usually sherry) and left to stand for 1 to 12 months (typically 3 months), after which the wine was disgorged and the casks filled with newmake malt spirit for maturation. Grain spirit could also be stored in the casks but best results are achieved with malt spirit.

By using this method oak casks, which were originally purchased as sherry casks but whose wood-extract related value has been exhausted by repeated use in whisky maturation, can be regenerated for further use in a manner which permits consistency and close control over the quality of the casks. This allows greater certainty in the flavour of whisky stored in the casks and allows longer production runs to be achieved, thus increasing the efficiency and effectiveness of the maturation process.

Modifications and improvements may be made without departing from the scope of the invention.

Claims (8)

1. A method of reconstituting a cask for use in the production of whisky comprising, selecting from casks previously used for storing whisky a cask which is of European oak, cleaning the internal surface of the selected cask, adding sherry to the interior of the casks and allowing the sherry to penetrate the cask wall.

2. A method as claimed in Claim 1, wherein the European oak cask is selected from a range of European and American oak casks by chemical means.

3. A method as claimed in Claim 2, wherein the chemical selection means is high pressure liquid chromatography.

4. A method as claimed in any one of the preceding Claims, wherein the cleaning of the interior surface of the cask comprises the steps of steam treatment followed by charring then scraping.

5. A method as claimed in any one of Claims 1 to 3, wherein the cleaning of the interior surface of the cask comprises the steps of charring the surface, followed by steam treatment then scraping.

6. A method as claimed in any one of the preceding Claims, wherein as a further step a process of controlled anaerobic degradation is applied to the cask.

7. A method as claimed in Claim 6, wherein the process of anaerobic degradation is carried out by heating the cask after cleaning for a selected time in a range up to 180 seconds.

8. A method of reconstituting casks for use in the production of whisky substantially as hereinbefore described.