I’m curious about the cleaning process of casks before a distillery transfers its whisky to mature/age. To use one of the popular names, just as an example, before Macallan transfers its whisky into a sherry [or bourbon or port or ale] cask, is the cask cleaned? If yes, by what method? Does it vary by distillery or country (à la, whiskey vs. whisky)? Is it all arbitrary or are there laws dictating cleaning process?
I’ve researched (online only) but wasn’t able to find any (sourced) information. Hoping there are experts here who can enlighten us.