Whiskey Barrels
Oak barrels bring to mind images of tradition and quality. Made from American or French grown white oak and historically used for the storage and transportation of goods. Today barrels are made almost exclusively for the production of whiskey and fine wines. Barrels come in many sizes and qualities although the term barrel is conventionally used for a wooden container small enough to be moved. The barrel is made up of staves shaped into a bulging cylinder, with hoops around it, a flat circular head at both ends, and at least one hole, generally on the belly, for a bung. Staves: The trees selected for barrel staves must be straight and free of knots. Many of the chosen trees are more than 100 years old and cut during autumn or winter when the sap is low. They are seasoned by drying naturally in the open air from eighteen months to two years. The sun, wind, and rain will then help the wood mature. Staves are then trimmed into a double taper and set on their ends within an iron hoop where some cooperages may alternate narrow and wide staves around the hoop to build strength and structure. Next, a strong stave is chosen to be drilled for the bung hole. At this stage there are approximately 33 staves per barrel and looks like a skirt splayed out from the hoop at the top.
Whiskey Aging
Sherry barrel from Spain
Toasted Barrel
The quality of the Whisky barrels is carefully monitored because the new spirit is to gain character and colour from the wood in which it rests. Some casks will previously have been used to mature oloroso fino or amontillado sherries in a spanish cellars; some will have contained bourbon and some will be oak.
The type of Whiskey barrel used for maturation will have been determined by the Master Blender who is seeking a particular character and continuity of the whiskey.
Only after a minimum of three years maturation can the new make spirit be legally defined as Scotch Whisky.
In practice, most Scotch Whisky matures for much longer - from five to fifteen, twenty, or twenty-five years and sometimes longer.
It is this lingering period during which Scotland’s cool, clean air steals through the porous oak of the casks and charms their contents, contributing further to the smooth and golden character of each distillery’s unique creation.
A proportion of the whiskey in each cask evaporates annually and is lost to the heavens.
The type of Whiskey barrel used for maturation will have been determined by the Master Blender who is seeking a particular character and continuity of the whiskey.
Only after a minimum of three years maturation can the new make spirit be legally defined as Scotch Whisky.
In practice, most Scotch Whisky matures for much longer - from five to fifteen, twenty, or twenty-five years and sometimes longer.
It is this lingering period during which Scotland’s cool, clean air steals through the porous oak of the casks and charms their contents, contributing further to the smooth and golden character of each distillery’s unique creation.
A proportion of the whiskey in each cask evaporates annually and is lost to the heavens.
Oak Best Option
One of the most frequently asked questions is “Why do whiskey makers use Oak Whiskey barrels?”
The reason that Oak is utilized is its unique physical and chemical nature. Oak has strength - physically, its wide radial rays give strength when shaped for a cask;
Oak is also a "pure wood" as opposed to pine or rubber trees which contain resin canals that can pass strong flavors to maturing whisky.
But it’s not just the Oak itself, it’s the transformation that happens to the Oak as a result of the seasoning and heating treatments during the coopering process - these result in the production of pleasant-tasting Oak lactones.
Whiskey barrels made from Oak have three broad effects on the spirit:
As an additive - It adds to the taste and aroma of the spirit by providing desirable elements from the cask. For example: vanillin, Oak lactone (coconut, bourbon character), toastiness, wood sugars and color.
As an agent that removes undesirable elements from new make spirit. For example: sulphur compounds and immaturity.
Oak barrels also interacts with the spirit. It adds extractive wood elements from the cask and converts them to organoleptically desirable elements.
For example it will change tannins to acetals, and change acetic acid to fruity esthers.
It has been said that there are 5 specific constituents of Oak and identifies how they influence maturing spirit:
Cellulose - Which has virtually no effect other than to hold the wood together.
Hemicellulose - Which consists of simple sugars that break down when heated and provide:
Body: through the addition of wood sugars
"Toasty & carmelised aromas & flavors"
Colour (unaged or "new make" whisky is a clear liquid)
Lignin - The binding agent that hold the cellulose in wood together which, when heated yield:
Vanillin
Sweet, smoky and spice aromas
Oak Tannins* - Which play an essential role in maturation by enabling oxidation and the creation of delicate fragrance in spirits. Tannins combine with oxygen and other compounds in the spirit to form acetals over time.
*Naturally occurring preservative compounds with a slightly puckery, astringent taste in the mouth, similar to the effect of strong black tea or fresh walnuts.
Oak Lactones - Resulting from lipids in the Oak, they increase dramatically during toasting and charring and can pass on a strong woody and perhaps coconut character; lactones give bourbon its distinctive character; and occur in higher concentrations in American Oak than in European varieties.
The reason that Oak is utilized is its unique physical and chemical nature. Oak has strength - physically, its wide radial rays give strength when shaped for a cask;
Oak is also a "pure wood" as opposed to pine or rubber trees which contain resin canals that can pass strong flavors to maturing whisky.
But it’s not just the Oak itself, it’s the transformation that happens to the Oak as a result of the seasoning and heating treatments during the coopering process - these result in the production of pleasant-tasting Oak lactones.
Whiskey barrels made from Oak have three broad effects on the spirit:
As an additive - It adds to the taste and aroma of the spirit by providing desirable elements from the cask. For example: vanillin, Oak lactone (coconut, bourbon character), toastiness, wood sugars and color.
As an agent that removes undesirable elements from new make spirit. For example: sulphur compounds and immaturity.
Oak barrels also interacts with the spirit. It adds extractive wood elements from the cask and converts them to organoleptically desirable elements.
For example it will change tannins to acetals, and change acetic acid to fruity esthers.
It has been said that there are 5 specific constituents of Oak and identifies how they influence maturing spirit:
Cellulose - Which has virtually no effect other than to hold the wood together.
Hemicellulose - Which consists of simple sugars that break down when heated and provide:
Body: through the addition of wood sugars
"Toasty & carmelised aromas & flavors"
Colour (unaged or "new make" whisky is a clear liquid)
Lignin - The binding agent that hold the cellulose in wood together which, when heated yield:
Vanillin
Sweet, smoky and spice aromas
Oak Tannins* - Which play an essential role in maturation by enabling oxidation and the creation of delicate fragrance in spirits. Tannins combine with oxygen and other compounds in the spirit to form acetals over time.
*Naturally occurring preservative compounds with a slightly puckery, astringent taste in the mouth, similar to the effect of strong black tea or fresh walnuts.
Oak Lactones - Resulting from lipids in the Oak, they increase dramatically during toasting and charring and can pass on a strong woody and perhaps coconut character; lactones give bourbon its distinctive character; and occur in higher concentrations in American Oak than in European varieties.
Bourbon Cask or Bourbon Barrel
The Bourbon barrels, once formed, are charred - the inside of the cask is set on fire for a short period of time, which creates a black charred layer.
There are various levels of charring which will have different affects on the spectrum of compounds and flavors the Oak will impart to the maturing spirit: more vanillins, lactones, "toastiness," spice characters, and tannins.
Charring casks causes further transformation. Char (carbon) removes sulphur compounds and immaturity from new spirit. Bourbon Whiskey barrels are typically charred for 40 seconds to 1 minute, but some distilleries have experimented with charring times of up to 3-4 minutes.
The result of charring is dramatic changes on the surface - for example, wood sugars are caramelized, which will leech into the maturing spirit.
There are various levels of charring which will have different affects on the spectrum of compounds and flavors the Oak will impart to the maturing spirit: more vanillins, lactones, "toastiness," spice characters, and tannins.
Charring casks causes further transformation. Char (carbon) removes sulphur compounds and immaturity from new spirit. Bourbon Whiskey barrels are typically charred for 40 seconds to 1 minute, but some distilleries have experimented with charring times of up to 3-4 minutes.
The result of charring is dramatic changes on the surface - for example, wood sugars are caramelized, which will leech into the maturing spirit.
Sherry Barrels
Scottish Single Malt Whisky receives its unique taste from a multitude of production and maturation factors. The following list shows the four most important factors of influence on the taste of the whisky.
The whisky production takes place in a comparatively short period of time. From the first soaking of the barley until the end of distillation usually no more than 2 weeks pass. Out of this time the malting of the barley takes the largest portion.
TONECOR Cooperage - Entrance
After the whisky leaves the pot stills, still colorless and as a clear liquid with an unripe flavour, the final process of maturation begins. In contrast to the production, maturation takes the most time. A maturation time of three years is the legal minimum in Great Britain. From then on a whisky may actually call itself whisky. These three years are obviously only the beginning for a Single Malt Whisky. The top-grade products of Malt distilleries only reach their height after 15 to 25 years. During its slow maturation over many years, the complex flavours of the young whisky becomes softer.
TONECOR Cooperage - Cask Treatment
The wooden casks consist of oakwood. Casks from resinous wood (softwood) are not suitable for maturation, since the resin between the wood fibres prevents the breathing of the whisky. The used casks also have to have a capacity of less than 700 litres. Three different cask types are generally used:
TONECOR Cooperage - Wood Processing
During maturation of the whisky chemical reactions take place between the alcohol and the wood. These reactions increase the amount of esters and aldehytes in the whisky. Beside the Sherry or Bourbon remainders in the barrel wall, the alcohol also extracts tannine and vanillin from the wood. During maturation it thus depends on the close contact of the whisky with the wood of the inner cask wall. Due to the larger volume in a Hogshead (250 litres) there is only 75% of the cask wall per whisky as for smaller barrels (158 litres). For a Sherry Butt (500 litres) it is only 50% of the surface. Distilleries with a high output (e.g. Glenfiddich or Glenmorangie) therefore usually use barrels and Hoghsheads, since the whisky matures faster in these smaller cask types.
TONECOR Cooperage - Assembly Machine
If the cask was used several times, its ability to mature whisky is reduced, since the wood is sucked out. These casks however can in a limited way be rejuvenated by removing the old charred layer and burning out on the inside again. This procedure sets free the vanillin and toffee tastes in the wood. In the past a sweet, boiled, sherrytype liquid from grapes (Paxarette) was pressed with high pressure into the cask walls in order to give to the whisky a sherrytype character. These procedures however fell into discredit and havn’t been practiced again for quite some time now.
If you calculate the costs of a Bourbon barrel for the price of the whisky which matures in this cask, you have costs of approx. 5 cent per 0.7 litre of a bottle of 10 years old Single Malt Whisky - (three times use assumed).
TONECOR Cooperage - Overview
During maturation the cask expands in the warm summer months and pulls together again during the cold winter and ‘breathes’ the surrounding air. This becomes particularly clear on Islay, where the sea-air delivers its character to the whisky. Usually the Whisky loses between 0,5% and 2% alcohol content per year during this maturation time. The Scots call this portion the Angels Share since it evaporates irrecoverably and ascends into the sky.
There are also exceptions of this principle. A maturation in a dry and hot environments leads to an intensified evaporation of the water content of the whisky. Closely under the roof of a new and high warehouse it can become so hot that the finished whisky rises in alcohol strength up to 66 - 67% during maturation. This rise of the alcohol content leads to different reactions with the wood and the production of different flavours. Most Scottish distilleries fill their whisky with 63,5% alcohol content into casks, since this means a reasonable compromise between a short maturation time and loss of alcohol by evaporation.
TONECOR Cooperage - Cask Testing Area
Starting only few years ago oak barrels which were used before for maturation of other products such as Portwine, wine or Brandy are also used for maturation of whisky. This leads to unique whiskies, which contain additional flavours from the products stored in the casks before. Important representatives of these kinds of maturation types are:
- Peatyness of the malt
- Geometric form and the number of pot stills (2 o. 3)
- Cask types used for maturation
- Duration of the maturation as well as the maturation place (Microclimate)
The whisky production takes place in a comparatively short period of time. From the first soaking of the barley until the end of distillation usually no more than 2 weeks pass. Out of this time the malting of the barley takes the largest portion.
TONECOR Cooperage - Entrance
After the whisky leaves the pot stills, still colorless and as a clear liquid with an unripe flavour, the final process of maturation begins. In contrast to the production, maturation takes the most time. A maturation time of three years is the legal minimum in Great Britain. From then on a whisky may actually call itself whisky. These three years are obviously only the beginning for a Single Malt Whisky. The top-grade products of Malt distilleries only reach their height after 15 to 25 years. During its slow maturation over many years, the complex flavours of the young whisky becomes softer.
TONECOR Cooperage - Cask Treatment
The wooden casks consist of oakwood. Casks from resinous wood (softwood) are not suitable for maturation, since the resin between the wood fibres prevents the breathing of the whisky. The used casks also have to have a capacity of less than 700 litres. Three different cask types are generally used:
- First is the Sherry Butt or Puncheon. Both have a capacity of 500 litres, but the Puncheon is shorter and thicker than the Butt. They are made from European oak as well as from American oak. In Spain the Puncheon is also manufactured with 600 litres content.
- The second type of casks is the Bourbon barrel. Bourbon matures in toasted American oak casks (barrels). These have a maximum capacity of 60 American gallons (1 Gal. = 3.78 litres); however the barrels usually only contain 200 litres.
- The third type of cask is the Hogshead. There are two types of it. The Sherry Hogshead made from old sherry casks and the to the Hogshead increased barrel. The latter is made by increasing an American Standard Barrel with additional staves to a volume of 250 litres.
TONECOR Cooperage - Wood Processing
During maturation of the whisky chemical reactions take place between the alcohol and the wood. These reactions increase the amount of esters and aldehytes in the whisky. Beside the Sherry or Bourbon remainders in the barrel wall, the alcohol also extracts tannine and vanillin from the wood. During maturation it thus depends on the close contact of the whisky with the wood of the inner cask wall. Due to the larger volume in a Hogshead (250 litres) there is only 75% of the cask wall per whisky as for smaller barrels (158 litres). For a Sherry Butt (500 litres) it is only 50% of the surface. Distilleries with a high output (e.g. Glenfiddich or Glenmorangie) therefore usually use barrels and Hoghsheads, since the whisky matures faster in these smaller cask types.
TONECOR Cooperage - Assembly Machine
If the cask was used several times, its ability to mature whisky is reduced, since the wood is sucked out. These casks however can in a limited way be rejuvenated by removing the old charred layer and burning out on the inside again. This procedure sets free the vanillin and toffee tastes in the wood. In the past a sweet, boiled, sherrytype liquid from grapes (Paxarette) was pressed with high pressure into the cask walls in order to give to the whisky a sherrytype character. These procedures however fell into discredit and havn’t been practiced again for quite some time now.
If you calculate the costs of a Bourbon barrel for the price of the whisky which matures in this cask, you have costs of approx. 5 cent per 0.7 litre of a bottle of 10 years old Single Malt Whisky - (three times use assumed).
TONECOR Cooperage - Overview
During maturation the cask expands in the warm summer months and pulls together again during the cold winter and ‘breathes’ the surrounding air. This becomes particularly clear on Islay, where the sea-air delivers its character to the whisky. Usually the Whisky loses between 0,5% and 2% alcohol content per year during this maturation time. The Scots call this portion the Angels Share since it evaporates irrecoverably and ascends into the sky.
There are also exceptions of this principle. A maturation in a dry and hot environments leads to an intensified evaporation of the water content of the whisky. Closely under the roof of a new and high warehouse it can become so hot that the finished whisky rises in alcohol strength up to 66 - 67% during maturation. This rise of the alcohol content leads to different reactions with the wood and the production of different flavours. Most Scottish distilleries fill their whisky with 63,5% alcohol content into casks, since this means a reasonable compromise between a short maturation time and loss of alcohol by evaporation.
TONECOR Cooperage - Cask Testing Area
Starting only few years ago oak barrels which were used before for maturation of other products such as Portwine, wine or Brandy are also used for maturation of whisky. This leads to unique whiskies, which contain additional flavours from the products stored in the casks before. Important representatives of these kinds of maturation types are: