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Casks Manufacturing (Coopering)

木桶製造

 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. 

Processing staves 

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. 

Charring 

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. 

 

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. 

 

 橡木是迄今最常用來製作木桶的木材。蘇格蘭更有法律規定,只可以使用橡木製作用於蘇格蘭威士忌的木桶。橡樹是非常寶貴的,因為它們需要許多年才能用作製桶,一般介乎80-100歲,部分更有200-300歲。木桶的壽命可達60至80年。

從森林採伐回來後的木材自然風乾數月後,木匠將其切成長度略長於木桶橫切面,然後以垂直於年輪的角度再分割成四分一木板,其大小適用於威士忌酒桶,讓酒桶裡的威士忌不易洩漏,蒸騰率亦保持在最低限度。收集後的木板要在陽光下日曬約兩年,準備製成木桶。

木板加工

木板的頂部及底部表面經刨床均勻地切割,然後刨削成曲線,使其兩端呈錐形。接駁位及木板表面之間要緊密連接起來,不能有間隙。

收集了幾十塊木板後,以環箍紮合起來置於蒸氣中,使其更易拗彎。形成桶子的形狀後,以火灼燒桶的內部。

燒灼

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。

組裝

以臨時箍紮合的木條與頭部接合,取出臨時箍換成金屬環箍,最後木匠會在上面開一個叫做BUNG HOLE的洞。

木桶經注滿清水通過滲漏測試後,已算大致完成。所有的缺漏都以手工檢查及修復的。

一個木桶的製作,是由木板和金屬箍組成,當中不會使用一根釘或粘合劑。

蘇格蘭近90%用於熟成威士忌酒的木桶都是來自美國、曾用於熟成波本的酒桶。這意味著蘇格蘭很少自己從新製作酒桶,不過卻經常修理或重新組裝木桶成不同尺寸, 這些工序都是在製桶廠中完成。

蘇格蘭大部分的木桶製造及維修都已外判給獨立製桶廠,只有少數蒸餾廠仍然會自己製桶,其中一個是位於Speyside中心的The Balvenie蒸餾廠。

Ian McDonald是Balvenie的首席木匠。他擁有48年的製桶經驗。今年初Ian曾來臨香港向一群威士忌愛好者示範如何組裝酒桶,有幸獲選的人有機會現場體驗這種工藝,這是Balvenie五種獨特手工技藝之一。