Oak & Cask
The oak used to make casks is known scientifically by the name Quercus and is a member of the beech family. The Latin word Quercus signifies beautiful tree and quality wood. White oak (Quercus alba) and common oak (Quercus robur) are the most popular species of oak used for whisky maturation. In addition, whiskies matured in Japanese oak (Quercus mongolica) casks have been viewed favorably and are highly respected by other blender and connoisseurs.
White oak – Q. alba
The word alba means “white.” It is a typical North American tree, commonly known as the American white oak. It is found over a wide area, stretching from southeastern Canada to eastern and southeastern parts of the U.S. Casks made of white oak tend not to leak because the xylem (tissue that transports water and nutrients) in the wood is effectively blocked by a tightly packed filling (called tylosis). White oak casks are used for products such as bourbon, sherry and wine. Currently, about 90 percent of casks used for Scotch whisky are white oak; of these, 90 percent are said to be reused bourbon casks. Typical flavors include vanilla and coconut.
Common oak – Q. robur
The word robur means “strong material.” It is a classic example of European oak and has long been used in Europe for brandy, wine and sherry casks. Common oak from Spain is called Spanish oak. Unlike white oak, it is difficult to work with and leaks easily because the tyloses are loosely packed. Compared to white oak, common oak releases more polyphenols (e.g. tannins) and gives whisky a deep, reddish hue. It produces a rich flavor of ripe fruits, dried fruits and chocolate.
Japanese oak – Q. mongolica
It grows over an expansive area, including Hokkaido and the Northeast region of Japan, as well as Northeastern China. The name mizunara derives from the fact that it retains a lot of moisture (mizu), making it difficult to burn. In the Meiji Period, beer companies used Japanese oak for casks. It was also used for railroad ties and for making high-quality furniture both domestic and overseas. Suntory’s Yamazaki Distillery originally used sherry casks for its maturation, it also used a small number of Japanese oak casks even before the start of the Pacific War. After the war, as it was difficult to obtain sherry casks and white oak, Suntory therefore decided to utilize more Japanese oak. A distinctive Oriental flavor, with an underlying sweetness of citrus fruits.
Types of casks
Barrel: approximately 200-liter capacity. Barrels are widely used as bourbons casks in the U.S. Casks that have been used once to mature bourbon are reused as aging casks for whisky elsewhere including Scotland.
Hogshead: approximately 230-liter capacity. Hogsheads are widely used in Scotland and Japan. It is a cask made from the staves of a barrel that has been taken apart and then reassembled.
Butt: approximately 500-liter capacity. Butts are distinguished by their elongated, firm shape. Spanish sherry casks and Japanese oak casks are often this type.
The flavors and color of whisky vary depending on the size of the cask and the method used to treat the inside. Cask size impacts the speed and the character of maturation. When a cask is large, less of the cask’s wood surface area comes into contact with the whisky. This allows maturation to proceed slowly. Heavily charring the inside of the cask produces a whisky with a deeper color and stronger cask flavor.
用於製作酒桶的橡木，科學名稱為Quercus，其實是屬於櫸木的一種。Quercus是拉丁語，其意為「美麗的樹木」和「優質的木材」。 白橡木（Quercus alba）和普通橡木（Quercus robur）是最常用於威士忌熟成的橡木桶種類。 此外，日本橡木（Quercus mongolica）酒桶也廣受調酒師和鑑賞家的高度評價。
Alba這個字的意思是「白色」。它是北美典型的樹木，俗稱美國白橡樹。 其種植地區廣泛，從加拿大東南廿部到美國東部和東南部地區都有。由白橡木製成的木桶比較密實，因為木材中的木質部（運輸水和營養物質的組織）被稱為tylosis的物質緊密包圍著。 白橡木桶用於波本酒、雪利酒和葡萄酒等產品。 目前，約90％蘇格蘭威士忌都用白橡木桶; 其中90％是重複使用的波本酒桶。典型風味包括雲呢拿和椰子。
Robur這個詞意味著「堅固的材料」，它是歐洲典型橡木，長期以來一直用於白蘭地、葡萄酒和雪利酒桶。 來自西班牙的普通橡木稱為西班牙橡木。 跟白橡木不同，它並不好相處而容易洩漏，因為橡木中的tylosis排列鬆散，不過它比白橡木釋放更多的多酚類物質（如單寧），賦予威士忌深紅色調，以及豐富的成熟水果、乾果和巧克力的味道。
它生長的範圍廣闊，包括北海道、日本東北地區以及中國東北部地區。水猶桶(mizunara)這別稱得名於這種木含大量水分（Mizu），因此難以燃燒。 在明治時期，很多啤酒公司都使用日本橡木，而鐵路連接和高品質家具也會用到日本橡木。在太平洋戰爭之前， 三得利旗下的山崎蒸餾廠主要使用雪利酒桶，加上少量日本橡木；戰後由於雪利酒桶和白橡木短缺，三得利於是增加了日本橡木的比例。日本橡木具有獨特的東方風味，賦予威士忌柑橘類水果的潛在甜味。
臀桶：約500升容量。 臀桶的特徵是細長而堅固的形狀。 西班牙雪利酒桶和日本橡木桶通常屬這種類型。
威士忌的風味和顏色，跟酒桶的大小和處理方法有莫大關係。 木桶尺寸會影響熟成的速度和特性。較大的桶，其與威士忌接觸表面積較少，減緩其熟成速度。 內部燒焦的木桶會衍生出深色和風味更強烈的威士忌。