Maturation Flashcards
What are the SWR legislation rules regarding maturation of Scotch whisky?
Spirit must be matured for a minimum of 3 years in an oak cask no larger than 700L.
Why is oak the perfect wood for maturation?
Its structural characteristics prevent leakage but allows the liquid to breathe.
Oak comprises many soluble compounds, imparted at different stages of maturation to maturing spirit.
How does oak age influence the flavour of whisky?
For certain malts, the most significant flavour uptake is during the initial dwell time following filling.
Others take longer to develop as part of the oxidisation process.
Oak has many compounds that are differentially soluble in alcohol and water thus providing aroma, flavour and colour in the final whisky.
What is the fruit of an oak tree called? What is its significance?
Acorn; each acorn contains 1 seed and takes between 6-18 months to mature.
Name the 2 main varieties of oak in use in the Scotch whisky industry.
- American white oak (quercus alba): grows in North America. Fast growing, tall straight trunks, high quality wood with high levels of vanillins. Typically offers flavour notes of coconut, vanilla, honey and nuts.
- European oak (quercus robur): Grown in northern Spain. Also known as English oak, Pedunculate oak, French oak or Russian oak. Very porous. It offers flavour notes of spice and dried fruit.
Which cask type is used to mature the majority of spirit in Scotland?
90-95% in American oak casks.
What are the origins of the 2 cask types used for maturation?
American oak is used for casks that have their origin in the bourbon industry.
European oak has its origins in the European wine industry. European oak typically refers to Spanish oak, however other varieties are grown and used. Some companies are now using French oak and some oak from Poland and Germany are becoming available too.
Why are ex-bourbon casks used so prominently for Scotch maturation?
In bourbon production, the cask (American Oak) can only be used once. Bourbon producers are always looking for a market for used casks. These are now shipped to Scotland as barrels whereas previously they were dismantled and sent over as ‘shooks’ of staves.
How is American Oak treated?
Air or kiln dried, usually charred on the inside and filled with a single filling of bourbon. These are known as ex-bourbon casks or American Standard Barrels (ASB).
What was previously contained in European oak used for Scotch maturation?
Sherry, usually Oloroso; known as sherry butts/casks.
What is a American Standard Barrel (ASB)?
A 200L cask typically used to originally mature bourbon. Usually made from American white oak.
By law, bourbon casks must be charred before they are filled. So, ex-bourbon casks will always have been charred prior to use in the Scotch whisky industry.
What does Virgin Oak mean?
A cask which has not had any previous contents in it before it is filled with new make spririt.
How does Virgin Oak contribute to the characteristics of a Scotch whisky?
They impart a great deal of colour and flavour in a relatively short space of time. Great care is taken with the spirit in these casks and they tend to be sampled and monitored more regularly.
What is Finishing?
A procedure whereby spirit is matured in a caks of a particular origin and then spends time in a cask of different origin. Usually for a period of 6-24 months. This method adds different flavours and colour to the whisky.
Casks used for finishing include: sherry, wine, port, rum and beer among others.
For example, casks previously used to store port provide an extra touch of sweetness and reddish colour.
What are the most common cask sizes used in the Scotch industry?
- American barrels at 200L
- Hogsheads (hoggies) at 250L
- Butts at 500L
There are others of varying sizes but they are less common.
What is a virgin cask?
A cask that has not been previously used for another liquid.
What is a refill cask?
A cask that has previously contained another liquid. The most common types are ex-bourbon and ex-wine (fortifid or natural strength).
What is ‘first fill’ or ‘second fill’?
If an ex-bourbon cask is used for new make spirit, this is classified as ‘first fill’.
If it is subsequently used again for another batch of new make spirit, it is classified as ‘second fill’.
What are the limitations of the number of times a cask can be used for maturation?
Once a cask has been used 3-4 times, the rate of maturation slows with reduced uptake of flavour compounds. The wood becomes progressively exhausted and will impart little by way of colour or flavour. This is dues to the extractive compounds having been removed from the active wood layer by previous successive fillings.
How are the majority of casks heat-treated?
Casks can be charred, toasted or both.
These heat treatments are essential to get the flavour congeners out of the wood.
What is charring?
It is a heat treatment whereby the wood of the cask is ignited. It helps to break down the structure of the oak, allowing for an easier and deeper penetration by the spirit and a more intense interaction with the flavours produced through lignin degradation.
The charcoal layer also acts as a filtration system, helping to remove unwanted flavours, such as sulphur, from the new make spirit.
What are the 4 grades of charring?
- No.1 = 15 seconds
- No.2 = 30 seconds
- No.3 = 35 seconds
- No.4 = 55 seconds
The heavy char of No.4 creates layers of charcoal on the inner surface of the staves, hence its nickname, the ‘alligator char’.
What is toasting?
It is a heat treatment whereby the inside of the cask is heated for about 15 minutes at 350°C. This browns the wood and allows heat to penetrate in, thus creating what is know as the red layer. This is a layer where lignin degradation has occurred and is about 3mm thick, between the char and the untouched wood.
How does the number of cask uses compare to the used of a tea bag?
Casks used multiple times will eventually get to a stage of exhaustion. The more times you use it the less flavour and colour it has to offer.
Name some of the more influential compounds that are directly extracted from wood casks.
- Lactones
- Vanillins
- Tannins
What percentage of spirit may be lost to the Angel’s Share over a 10 year period?
Anything from 10-20% of its liquid.
The quantity, rate of loss and maturation benefits are dependent on warehouse temperature, humidity, location and time.
What are the climatic conditions relevant to maturation and how do they influence the ageing process?
- Temperature: affects the rate at which both ethanol and water is lost during maturation. Higher temperatures = more losses.
- Humidity: affects the relative rate at which ethanol is lost compared to water. The higher the humidity the greater the losses of ethanol over water.
Example: In Scotland the climate is cool and wet, meaning ethanol evaporates relatively more quickly than water, leading to a reduction in ABV in the cask over time.
In India, climatic conditions are much hotter and drier, meaning more water is lost relative to ethanol. This results in the ABV levels increasing over time.
