Plummy accent

We often hear about old barrels of sherry etc. etc. being used to influence the taste of our whiskies, but what happens to old whisky barrels when they retire? The clever fellows at Yamazaki distillery are using some of their cast-off casks to mature umeshu (Japanese traditional plum liqueur). I bought a bottle and it was delicious, as umeshu always is, but I will have to try another glass to see if I can detect what the whisky barrel is doing to it.