I just read through the relevant Igros Moshes, yd 1 62 (63 and 64 are refutations of the machmirim)
and yd 3 19. He is talking about OTS wine which is blended into
whiskeys to lower the tarrifs. he quotes YD 134:5 where the
mechaber says that 6 parts water to 1 part wine is enough to be
mevatel the wine. in yd 3:19 Rav Moshe zt”l explains this
that even though there’s still a taste, it loses its status
of wine. Wine is different from other liquids. Rav Moshe zt”l
quotes the Shach by yd 134 that by other liquids we need
bittul beshishim. He goes on to refute the Shach with a
Tashbeitz that by sharp liquids you need even less than 6
parts. he still says a baal nefesh should be machmir.
By sherry casks, we are machmir if we know they exist.
But midin, it’s extremely difficult to claim that in a
huge barrel the wood is more than one in six.