Wooden casks for spirit maturation

Wood plays a significant role in ageing and maturing of spirits including wine and sherry. No wonder 60% to 80% of the total flavour in a whisk(e)y whether scotch or bourbon, aged rum or tequila is uniquely credited to the oak in which it matures. Once the fermented wash is distilled, it is the decision of the master distiller to decide whether the new make spirit has to be matured and aged and which oak flavours to develop and try to attain.

Maturation and ageing of spirit is carried out in oak wood casks. There are different types of oak wood used to make casks. From more than 500 species of oak wood, the species ‘Quercus Alba’ (American White Oak), ‘Quercus Robur’ (European Strong Oak) and ‘Quercus Petraea’ (European Strong Rocky Oak) are most common and to some extent, Oregon Garryana, Mangolian Oak, Japanese Mizunara & ‘Quercus ilex’ also known as Holm Oak.

The species ‘Quercus Alba’ or the American Oak have straighter trunks and tighter grains. These are richer in vanillin and hence impart vanilla notes. These have also high lactones which impart coconut notes to their first fill spirits. The cask made out of this species of oak are generally of 200 litres and is essentially used to mature and age whisk(e)y. Further, ‘Quercus Lobota’ which is the botanical name to California white oak and ‘Quercus Garryana’ the Oregon white oak is also used to some extent in maturing American whiskies.

The species ‘Quercus Robur’ is a strong oak and widely grown in France, Poland, UK and other regions of Europe. The casks made from this species of oak is mostly used to mature brandy and fortified wines. ‘Quercus Petraea’ is another species of European oak and used in maturing cognac and wines. The spirits and wines evoke coconut notes coming out of lactones present in the oak. These species are used to make oak casks ranging anywhere between 30 to 300 litres.

‘Quercus Magnolia’ is another species of oak wood which is softer and comes with lots of knots which does not make it easy for the coopers to make casks in the cooperage. However, the wood is rich in lactones and vanillin.

Akin to ‘Quercus Magnolia’ comes the Mizunara Oak which carries the botanical name ‘Quercus Crispula’ which is used in Japan to mature some of their whiskies.

French Oak or the Limousin oak, on the other hand, is robust and normally covers species ‘Quercus Robur’ and ‘Quercus Petraea’. These oaks are not straighter but impart good lactones and aromatic congeners good for brandy. French Oak is mostly used to make casks of 300 litres known as Barrique.

‘Quercus ilex’ or the Holm oak is an evergreen oak tree native to the Mediterranean region and the barrels made from this species of oak are used to mature tequila and wine.

The wooden casks made from different species of oak are made at the cooperage by the coopers. The process involved in the making of wooden casks starts from sourcing of oak, seasoning of oak, shaping of the cask by using staves, toasting & charring etc. Different sizes of casks are made depending upon the demand for such casks. The process involves harvesting of tall oak trees and then seasoning them by drying for six to eight months or more. Subsequently, the seasoned wood is cut into staves and shaped into a bulging cylinder and bound together by metal hoops in the cooperage. The head and bottom of the cask are flat and each is secured into the staves by a grove. No glue, paraffin, or nails are used in making barrels.

Down below is the list of some of the important casks and their capacity used for the maturation of spirits covering whisky, rum, tequila, brandy and wines including fortified wines namely sherry and Port wine.

A British Barrel has a capacity of 160 litres whereas the American Barrel has the capacity of 200 litres.

A Firkin cask is a quarter size of the British barrel and has a capacity of 40 litres and used to store ale, whereas, a Quarter cask is a quarter size of the American Barrel and has a capacity of 50 litres and Scotch and American whiskey normally use this cask to get the intense oak finish.

A Hogshead has a capacity of 250 litres to 300 litres and is used to mature Irish and Scotch whiskey as well as wine and beer.

A Barrique is a type of a cask which has a capacity of 300 litres and is popularly used for maturing French wine and Cognac.

A Puncheon has a capacity of 450 litres to 500 litres and is used to mature Rum and Sherry.

A Butt has a capacity of 500 litres and used to store Sherry.

A Port Pipe is a tall cask and wide and rounder with a capacity of 650 litres and essentially used to mature or store Port.

A Drum has a regular capacity of 650 litres and used to store Madeira.

A Tun is roughly having a capacity of 980 litres and generally used for fermentation of beer.

Today’s post, I have decided to bring out the effect of the boiling points of different liquids, more specifically of water and alcohol and how it impacts the production of spirits in the alcohol industry.

We all know different liquids convert into gas and start evaporating at different boiling points. In the case of water, the boiling point is 100 degree Celsius and this means that water will start boiling at this temperature. What happens if the temperature of a liquid is at subzero – Simple – the water freezes.

Now let us take the boiling the point of alcohol (ethanol – ethyl alcohol). Does it too start boiling at 100 deg Celsius or at higher or lower levels? The answer is alcohol has a lower boiling point and it means when heated, it reaches boiling point at 78.24 degree Celsius.

Similarly, boiling points of some of the other liquids are  – Ethyl acetate : 77.2, Acetaldehyde : 20.8, Acetone :56.08,  Alcohol – methyl (methyl alcohol, wood alcohol, wood naphtha or wood spirits) : 64.7, Ammonia at: – 35.5, Mercury at 356.9, Milk 100.5 and so on.

Now how does boiling point of liquid help the alcohol industry. Absolutely yes – it does so at the distillation stage of production of spirit.

A quick peep through the stages: Production of any grain spirit namely Whisky, Vodka, Gin,  involves mainly Milling, Mashing, Fermentation and then distillation followed by maturation or ageing process.

Milling is the process where the grain is milled to a rough flour called grist. The grist is added to a mash tun in the presence of hot water in order to get a porridge like substance which is then filtered to obtain what is called the wort, the sugary liquid. The sugary wort is then transferred to washback vessel for fermentation and yeast is added to convert the sugars into Co2 and alcohol. This liquid is the distiller’s beer or the wash with a strength ranging between 8% to 10 % of alcohol (ethanol = ethyl alcohol).

The beer or wash, which is a mix of alcohol and water, is then distilled. Distillation is the process that sets spirits apart from beer. To obtain this spirit, the wash(beer) is transferred to the column/pot copper still and heated. Since the boiling point of water is 100 degree Celsius and of ethanol 78.40 degree Celsius, the alcohol in the wash starts to boil first and converts into vapour. Along with-it other substances in the wash having lower and higher boiling points namely esters and heavy fusel oils also evaporate. On condensation the vapour cools and converts  to a distillate known as the low wines having a strength ranging between 21% to 24% alcohol by volume.

The low wines are collected in receiver and filled into the spirit copper pot still and heated. The spirit still has a bigger influence on the taste of the new make spirit. On heating the low wines, the volatile foreshots compounds evaporate first and are redirected for re-distillation with low wines. The middle cut is collected and the feints are again redistilled in the distillation run. The middle cut is collected is the new make spirit and has an alcohol by volume not greater than 80% in the case of whisky and can also touch 90 to 100 in the case of grain whisky and vodkas.

An example as to how the heating and the boiling point effects the volume of the wash(beer) vis a vis alcohol. A wash (beer) of 3000 litres which has a 10% alcohol by volume (300 litres)  volume significantly drops to around 1000 litres with 25% alcohol by volume (250 litres) of low wines after first distillation. So the boiling point of a liquid plays a key role in finally collecting the higher strength of alcohol.