Types of Casks
The cask maturation of Whisky is one of the most influential processes that define the taste of Whisky. While the length of time the Whisky matures is important, the type of the cask however is crutial. The wood of the cask adds the different complex flavours to the distillery character that is already in the new made spirit. Different casks offer different flavours.
You can find a detailed description of maturation process in this article. It describes what kind of flavours casks add to Scotch Whisky, Bourbon or Irish Whiskey.
There are five major factors that influence the Whisky in the cask:
The Wood
1. Type of the Predecessor Liquid
| Predecessor | Type of Liquid | Alternation of Taste | Alteration of Colour |
|---|---|---|---|
| Bourbon | Whiskey | vanilla, sweetness, caramel, creamy | golden |
| Burgundy | Wine | very fruity, lightly sweet, lightly dry | dark red |
| Madeira | fortified Wine | spiciness, light fruitiness, sweetness, dryness | dark, amber |
| Port (sweet) | fortified Wine | sweet, dried fruit, spiciness | red |
| Port (semi-dry) | fortified Wine | lightly sweet, dried fruit, spiciness | red |
| Port (dry) | fortified Wine | dry, dried fruit, spiciness | red |
| Oloroso | Sherry | deep, dark, nutty, dark ripe fruits | red, amber |
| Pedro Ximenez (PX) | Sherry | very sweet, dark fruits, raisins, syrup | amber |
| Fino | Sherry | light fruits, sweetness, dryness, light wood | bright |
| Manzanilla | Sherry | salty, dryness, sea flavours, fresh, some fruit | bright |
| Amontillado | Sherry | sweetness, nutty, dry, fresh, acid | amber |
| Palo Cortado | Sherry | rich, sweet, dry, sweet spices, fruits | brown |
| Sauternes | Wine | sweetness, zest, acidity, light fruits | bright to amber |
| Bordeaux (red) | Wine | strong red fruits, grapes (wine), berries | red |
| Tokaji | Wine | light fresh fruits (citrus, mango), very sweet, | bright to amber |
| Ruby Port | fortified Wine | very fruity, dark fruits, berries | red |
| Barolo | Wine | fruits, tannins (bitter), dried fruits, heavy aromas | red |
| Chardonnay | Wine | lean, crisp, acidic, tropical fruits | bright |
| Muscat | Wine | floral , sweet, citrus, peach | bright/red |
| Muscat | fortified Wine | very sweet, dark fruits, raisins, syrup | amber |
| Rum (white) | Spirit | sweet, molasses, vanilla, tropical fruit, almond | bright |
| Rum (dark) | Spirit | sweet, syrup, dark fruits, oak, caramel, vanilla | amber |
| Amarone | Wine | tannins (bitter), dry, raisins, ripe fruits | red |
| Marsala | fortified Wine | sweet, complex, spices | dark red |
| Virgin Oak | - | vanilla, cloves, caramell | dark brown |
2. Size of the Casks
The sizes of casks are very difficult to define, because there is no ISO standard to define the volume of a standard cask. There is another major problem with the volume of the casks. The cask sizes were also a unit of measurement. Take the Butt for example. The normal butts come in sizes of 500 liters (132 galons). But there is also a measurement unit called a butt, which is 1/2 a tun and is 122 US gallons (477 liters). The following table shows the actual sizes the most barrels come in, not the sizes of the measurement units.
| Name | Liter | US. Gallon | Imp. Gallon |
|---|---|---|---|
| American Standard Barrel (ASB) /Bourbon Barrel | 200 | 53 | 44 |
| Butt | 500 | 132 | 109 |
| Quarter Cask | 125 | 33 | 27 |
| Standard Hogshead | 238 | 63 | 52 |
| Puncheon | 320 | 85 | 70 |
| Madeira Drum | 650 | 172 | 143 |
| Port Pipe (tall) | 500 | 132 | 109 |
| Sherry Hogshead | 245 | 65 | 54 |
| Cognac type | 300 | 79 | 66 |
| Bordeaux type | 225 | 59 | 49 |
| Barrique cask | 225 | 59 | 49 |
| Bloodtub | 50 | 13 | 11 |
The sizes of the the casks vary as different coopers produce different sizes of casks. It is important to remember the big differences between the casks.
| Size of Casks | Type of Casks |
|---|---|
| Big > 400 Liters (>132 US. gallons) | Butt, Port Pipe, Puncheon, Madeira Drum |
| Medium 200 - 400 Liters (53 - 106 US. Gallons) | ASB, Bourbon barrel, any Hogshead, Barrique cask, Cognac cask, Bordeaux cask |
| Small <200 Liters (53 US. Gallons) | Quater cask, bloodtub |
Here is a video of Horst Luening explaining 6 casks at the Old Midelton distillery.
3. Type of Wood
| Type of Wood | Effect on Taste |
|---|---|
| American white oak (Quercus alba) | mellow, soft, vanilla, caramel |
| European oak (Quercus robur and petraea) | spicy, bitter, stong on the wood |
| Mizunara Oak (Quercus crispula) | sandal wood, coconut, oriental spices |
| Maple (Acer) | sweet, maple syrup |
There are big differences between the two major types of oak. The American white oak grows in the east of the United States of America and a few parts of Canada. The tree grows rather fast for an oak tree and is therefore a bit less expensive than the European counterpart. Its wood is very dense (770 kg/m³) and contains a lot of monogalloyl glocose. This is later transferred into the typical Bourbon vanilla taste.
The European oak grows all over the European continent far into Russia and Turkey. It grows slower than the American counterpart and is a bit less dense (720kg/m³). It contains Gallic acid that is considered a pseudo tannin. This acid in combination with water gives the Whisky a slightly bitter note. The European oak has also a lot of other components that also add to the spiciness of the whisky.
Mizunara oak is very common in the forests of northeast Asia, where it is used primarily for high-quality furniture. Due to its high density and thin fibers, the staves must be cut along the fibers, which never grow perfectly straight. The Oak also lacks waterproofing oil enzymes, so much more Whiskey evaporates during aging than when stored in American or European oak. Despite these characteristics, which make it much more difficult to use for Whiskey barrels, Mizunara oak gained popularity for Whiskey aging in the early 20th century. Not least because of the special aromas it gives off to Whiskey, reminiscent of sandalwood, coconut and oriental spices, for example.
Maple grows in many parts of the world, including Eurasia, North Africa, Central and North America. With its relatively low density of 653 kg/m3, it is used primarily in the production of Tennessee Whiskey: the distillate is filtered through a charcoal layer of sugar maple before being stored in casks, which gives the Whiskey a particularly smooth texture. In addition, some American Whiskey producers age their new make in casks made of maple to give the Whiskeys the sweet notes of maple and maple syrup.
4. Charring and Toasting
The toasting and charring converts the wood sugars into vanilla and caramel flavours. The Cooper distinguishes between charring and toasting. Toasting just darkens the top of the wood and acts in the depth of the staves. It leaves the wood with a black flat layer on top. If you char a barrel then you burn the wood to a point where the surface breaks and leaves the wood with a surface like uneven structure. It looks like an alligator skin.
The level of charring is determined by the time the barrel is burned. This time varies with the cooperage or the specification of the distillery ordering the cask.
Jack Daniel's Cooperage
About 42 seconds of charring
Speyside Cooperage
About 15 seconds of charing
5. Reuse of the cask (First Fill vs. Refill)
Oak casks are very durable and can contain Whisky for many decades. However, over the years the aroma that the Whisky can absorb from the wood decreases. The cask is leached out. Whisky that is stored in new casks therefore absorbs the most aromas.
Bourbon is stored in fresh casks and is aromatic enough to be bottled after only two to five years. Scotch Whisky matures in used casks, which have already been used for e.g. Bourbon or Sherry. The cask has already released a large part of the aromas. Therefore the Scottish Malts only become really good after longer maturation. However, this also gives the Whisky more time to reduce the alcoholic spiciness. Nowadays, this historically developed system is an essential distinguishing feature between the Whisky types. Read more about the varieties here.
Casks are expensive these days. Therefore it is common in the Whisky industry to mature Whisky in casks more than once. A cask still contains a lot of aromas after ten years of Malt Whisky maturation and is therefore reused for the next Malt. In the industry they are called 'refill casks'. Refill casks are reused for up to about 30 years.
It is clear, however, that the influence of the cask on the taste is getting weaker and weaker. It is not surprising if a Whisky from a refill cask has absorbed very little flavour - and also colour. On the labels of some bottlers you sometimes find indications like 'Refill' or 'First Fill', which stands for the degree of use of the casks. This gives you as a customer an indication of the approximate intensity of the cask aroma. However, it is also common to add colour to Whisky with tasteless caramel. In this case the influence of the cask is hidden.
In the meantime, it is more and more common to refurbish casks, as this is cheaper than buying new ones. This brings out the oak aroma again. New Sherry, Port or Wine aromas cannot be produced in this way. These 'rejuvenated' casks make Whisky very spicy within a short time.
Here is a video of the rejuvenation of casks at the Speyside Cooperage.
