Casks Manufacturing (Coopering)
Oak is by far the most commonly used wood to construct casks. It is even required by law that only oak is used for Scotch whiskies. Oak trees are extremely precious because they require many years to grow, usually anywhere from 80-100 years old, though some even reach 200-300 years old. Casks used in maturation are normally used for between 60-80 years.
Timber logs taken from the forest are allowed to dry naturally for several months. Later, cross-sections that are slightly longer than the length of the casks are cut from the logs. These are then split (quarter-sawn) perpendicular to the growth rings to produce quarter-sawn planks. Only quarter-sawn planks are suitable for whisky casks, as whisky inside the casks will not leak easily, transpiration is also kept to a minimum. The planks are gathered in racks and sun dried for approximately two years. After this, they are finally ready for the cask-making process.
The top and bottom surfaces of the planks are shaved with a planer, their length uniformly cut and, then shaved in a curve so that both ends taper. It is important that the joint, the surfaces of the planks that touch one another, join without a gap.
Next, several dozen staves are collected, bound together with a temporary hoops and steamed to make it easier for bending. After they have been formed into a cask, the inside of the cask is charred.
High heat is used to burn the wood, causing it to carbonize. Charring the inside of a cask produces the sweet, mature flavor compounds such as vanillin inside the wood. The inside of a cask is also sometimes toasted instead. Whether charred or toasted, the cask will burn differently depending on the extent to which it is treated, as well as the character of cask wood. This will result in significant differences in whisky maturation.
When the inside of the cask has been completely treated, the cask is left to stand for two to three weeks until its shape is stable. Once the groove (or croze) into which the head will be fitted is cut, the cask is ready for assembly.
The head is fitted to the staves, which held together with temporary bands. Next, the temporary bands are replaced with the actual metal hoops. Lastly, a hole called the bung hole is opened.
The cask is considered complete once it has been filled with water and checked for leaks. Any defects found are fixed by hand.
Casks are made from only wooden planks and metal hoops. No nails or adhesives are used at all.
Close to 90% of the casks used to mature whisky in Scotland are ex-bourbon casks from the USA, which means Scotland seldom builds new casks from scratch, however often the casks needs to be repaired or re-assembled to different cask sizes, and these are done at the cooperage.
In Scotland, most of the manufacturing and maintenance of the casks are outsourced to independent cooperages, only a few distilleries still maintain a working cooperage, and one of them is The Balvenie, located in the heart of Speyside.
Ian McDonald is the Head Cooper at The Balvenie, where he has 48 years of coopering experience under his belt. Ian was in HK early this year to demonstrate to a group of whisky connoisseurs on how a cask is being assembled, and selected people were given a chance to experience this craftsmanship, which is one the five rare crafts of The Balvenie.
以高溫燃燒木材使其碳化，燒灼木桶的內部會衍生出如雲呢拿的甜香、成熟的風味；有時酒桶內部只會經輕微烤烘。 燒灼或是烤烘，酒桶處理手法及木材性質，將造成威士忌熟成的差異。桶的內部經燒灼後，木桶需靜置2至3週直至其形狀穩定。安裝到凹槽的頭部（或小圓圈）切割完成後，就可以開始進行 組裝。