The Production Process – Maturation
The new make spirit is placed in casks where it is allowed to sit undisturbed over a long period of time. Over the course of three, five, ten years, the spirit develops further aromas and flavors, while the color would gradually turn into gold, amber or brown. This transformation is called cask aging, or maturation.
Whisky casks are made from wood of oak trees. Oak wood contains compounds that are essential to the maturation of malt whisky. Its interaction with the new make spirit produces a deep, complex flavor.
Why does maturation in oak casks make it mellower and better tasting? While scientific proof is still lacking, the basic mechanisms of maturation are now clearer. The following phenomena help to explain what happens in the cask as the whisky matures.
1. The oak releases compounds such as lignin and polyphenol (tannin). As the years pass, these compounds decompose and react with compounds in the new make, producing a more mature fragrance. The lignin produces a fragrant, sweet substance called vanillin. Whisky’s deep color comes from compounds such as polyphenol that are released by the cask.
2. As it matures, whisky gradually evaporates through the cask. In a year in Scotland, evaporation will reduce the whisky by 1-2 percent, or what is called “angel’s share.” At the same time, however, air enters the cask from outside. In other words, the cask breathes. Through this process of breathing, evaporated water and alcohol remove undesirable, immature aromas, leaving behind a higher concentration of maturely flavored, nonvolatile compounds.
3. Air inside the cask causes some compounds in the whisky to oxidize. This changes the flavor and stimulates maturation.
4. The small water molecules in the whisky envelop the large alcohol molecules. This phenomenon softens the intensity of the alcohol and smoothens the whisky.
Maturation does not produce these kinds of changes uniformly across all casks. No casks are identical as there are no two wood planks with the same grain. Even slight differences between casks will produce subtle changes in how the whisky matures. The quality of the oak, the size of the cask, the age of the cask, the climate of the warehouse, seasonal changes in weather, the cask’s location in the warehouse – these are various factors that come into play and interact in complex ways.
As the malt whisky matures in the cask, it evaporates at a rate of 1-2 percent a year. A simple calculation shows that in 12 years 12-13 percent of the whisky will have evaporated. Imagine that 10,000 casks are filled in a given year, in 12 years’ time at least 1,200 casks worth of whisky, will have been lost to the angels!
At the same time, it is not necessarily true that the longer a whisky is matured, the better it becomes. Various factors affect a whisky’s peak maturity, for instance, the quality and size of the cask, the environment at the warehouse and whether the cask is new or has been used several times. Every casks of whisky peaks differently. Some peak at 12, others peak at 15 etc.
Once a whisky peaks, its balance of flavors begins to disintegrate. Products that can be aged say 30 years are very precious, and whiskies used in them must be watched very carefully during the maturation process to protect their flavor or else they will not be marketable.
新製成的威士忌一般會置於木桶中，防止其受外面環境的干擾。 經過三年、五年、十年後，威士忌將衍生出更多的香氣和味道，顏色亦逐漸變成黃金、琥珀色或棕色。 這種轉變就是木桶陳年或熟成。
威士忌酒桶由橡樹的樹木製成。 橡木中含有對麥芽威士忌熟成至關重要的化合物。 它與新的威士忌之間的互動，能產生出深遠、複雜的味道。
為什麼橡木桶熟成讓威士忌變得更美味柔和？ 雖然科學上仍然缺乏證據，但熟成的基本機制現已漸見清晰。 以下的現象有助於解釋威士忌在熟成過程中的變化。
不是所有的木桶熟成都保證會發生以上所有現象。世上沒有任何木桶是相同的，因為沒有兩塊紋理完全一樣的木板。在威士忌熟成過程中，酒桶之間的微小差異也可能帶來微妙的變化。橡木的質量、木桶的尺寸、年齡、倉庫的環境、天氣的季節性變化，倉庫所處之地 - 這些因素都能影響威士忌的熟成。