The whisky code of honor
The problem of residual sugar in sherry casks and new barrels
The discussion about residual sugar in barrels – whether sherry barrels or new oak barrels – is a fascinating, yet complex, topic.
Both the natural properties of the wood and the production and maturation process play a key role here.
But how does this affect the final sugar content of the whisky, and why is this even relevant?
Ursprung des Restzuckers
Residual sugar in barrels can come from various sources:
Natural sugar content in the wood:
Oak wood naturally contains carbohydrates such as cellulose and hemicellulose. During the toasting of the barrels – a central step in barrel production – these carbohydrates are partially converted into sugar compounds such as glucose by the heat. This so-called wood hydrolysis is a natural process that influences the flavour and sweetness of the later distillate.
Pre-coating with sherry or paxarette:
In the whisky industry, sherry casks are traditionally used to give the whisky a special flavour. Originally, these casks were used to ferment grape must and then topped with sherry (often for 6-9 months). This can leave sugar residue in the wood, which later passes into the whisky. More recently, an upstream industry has developed that professionally carries out this pre-seasoning for distilleries – often with so-called ‘seasoned’ casks.
Influence on the whisky
The amount of residual sugar in whisky depends heavily on the type of pre-seasoning and the technique used. Studies from the 1980s (including from the UK) show that 8-year-old Lowland grain spirits matured in casks pre-aged with sherry can have sugar contents of between 125 and 2540 mg/L. These values vary depending on the method and intensity of pre-aging. These values vary depending on the method and intensity of pre-seasoning.
A remarkable finding is that the sugar that enters the wood through sherry or paxarette is only completely dissolved in the whisky after around two years. This suggests that sampling during maturation should be interpreted with caution.
Legal requirements
Whisky production is subject to strict regulations, particularly in the EU and the USA:
EU legislation:
According to Regulation (EC) No. 110/2008, no sugar may be added to whisky.
Traces of sugar that are detectable must result from natural processes.
USA:
Similar regulations apply in the United States, where whisky must by law be made purely from grain, water and yeast and matured in wooden casks.
Natural sources of sugar in whisky
Small amounts of sugar can be present in whisky even without a sherry pre-treatment.
The main sources are:
Wood decomposition products:
During maturation, the cask releases carbohydrates resulting from the chemical decomposition of the wood.
Fermentation by-products:
In rare cases, minimal amounts of unfermented sugar from the mash remain in the distillate.
The influence of the wooden barrel
The production of barrels has a significant influence on their chemical properties. The process is divided into three main steps:
Assembling the staves:
Oak wood is shaped into a circle in a working tyre.
Bending to the barrel shape:
Heating at around 120°C makes the staves pliable and bends them into a barrel.
Toasting:
This step is crucial for the subsequent flavour formation. Toasting produces flavours such as vanillin and sugar compounds. The wood sugars released by the heat of toasting give the finished distillate flavours of toasted bread, vanilla or even chocolate and caramel. These flavours are classified as sugar from a chemical point of view and should therefore not be neglected in the overall assessment.
Unser Küfer Jens beim Beigen eines Fasses über Feuer.
Conclusion
The issue of residual sugar content in casks and its influence on whisky is a complex interplay of natural processes and craft techniques.
Ultimately, the relevance of the sugar depends on the concentration in the end product – and it should be noted that the quantities involved are generally extremely small and harmless from both a legal and sensory perspective.
Nevertheless, the topic shows how profoundly the chemistry of cask maturation shapes the character of a whisky.
Cheers!
