Refill

The majority of cooperage in the rum industry comprises reused bourbon or French oak casks. The initial use of these casks by distillers is generally referred to as a "first-fill" or "fresh" cask, whereas each subsequent use sees it referred to as "refill."

With refill casks having been used to age rum before, they tend to impart less flavour from the wood and as such are preferred by distillers wishing to showcase the character of their spirit. Being less active, refill casks will also mature rum more slowly and by breathing less, will result in a far lower angels' share than a first-fill alternative. This makes refill wood particularly suited to longer maturations in tropical climates.

This is not to say that the wood is without continued influence however, and the rum held in the cask previously can often impart new flavour on the new habitant liquid. As distillers have experimented with maturation over the years, refill casks that previously held big flavour rum from the likes of Trinidad's Caroni or high-ester examples from Jamaica have become increasingly popular.

On the other hand, some distillers actively do not seek this added flavour from refill casks and prefer only oak influences on their rum. Bacardi, for example, will treat its ex-bourbon casks with steam and water for twenty-four hours in order to remove traces of the former inhabitant's flavour from the wood before use.