If a 12 year old single malt Scotch has the label of double cask or double matured (some say double wood), assuming oak and sherry, does it mean
a portion of the whisky is matured in oak cask for 12 years, and a portion of the whisky is matured in sherry cask for 12 years and the final product is a mixture of the two in some ratio (e.g. 50:50). OR
the whisky in matured in oak cast for some years (say 8) and then the whisky from the oak cask has been transferred to sherry cask for the rest of the years (4) for further maturation.
I hope my question makes sense. Please answer if you know the answer but don't make guesses.