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The term cask finish or secondary maturation refers to the use of another cask after the initial aging that ‘finishes’ the aging process before bottling. Often the purpose of cask finishing is to impart qualities of another spirit product which was also aged in barrels. 

Cask finishing works because as products, like spirits, wines, or even maple syrup, age in barrels the wood will absorb some of the contents. When used this allows the flavors of the previous product to impart onto the spirit. 

The secondary maturation will most often use freshly used barrels referred to as wet barrels to finish their products. Depending on how freshly used the barrels were, they may still have residual liquid from the previous contents. These wet casks are used primarily to expedite the process of flavor infusion. 

Some of the most common casks in the spirits industry are sherry and ex-bourbon. This method of aging can provide added complexity and character to the spirit. This secondary maturation can completely change the drinking experience depending on the cask used. 

The difference between finishing and aging is the amount of time. Typically a finishing barrel is only used for weeks or months at a time, usually not years. 

Common Barrels for Cask Finishing

Sherry Cask 

Sherry is a fortified wine from southern Spain. This wine comes from the Sherry Triangle which is a requirement for Sherry production. Scot whisky producers are often credited for highlighting the use of ex-sherry cases for finishing. Now the demand for these types of barrels has made them increasingly rare for distillers. Makers of sherry don’t rely on new barrels for aging and the sale of ex-sherry barrels provides revenue for these vintners. Ex-sherry casks can add notes of red fruit, figs, dates and raisin. These are complementary flavors for rum which can have similar tasting notes. 

Bourbon cask

Bourbon is an American spirit, and ex-Bourbon barrels are one of the most consistent types of barrels on the market. This availability is partially because the legal designation for Bourbon is the use of charred new oak barrels. Therefore, bourbon barrels fuel the barrel aging of many products including rum. Ex-bourbon barrels impart flavor notes such as caramel, maple, smoke and oak. These profiles usually do well with rum’s sweet fruity notes.

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