I’d like to address some of the misinformation here, even by those claiming misinformation here.
To those who claim sherry casks are just a marketing ploy: Please explain why a distillery would use sherry casks when they cost around 9 times (yes, 9 times) more than a bourbon cask. And why would a distillery like Glenlivet use sherry casks in the vatting for Glenlivet 12 when it doesn’t advertise it and for the most part only tells you if you ask? Not much of a marketing ploy for the money invested.
To those who claim sherry casks don’t give taste: You may not be able to taste actual sherry, but a connoisseur can usually tell if a scotch is sherried: among other things, there is a taste of mellow dried fruit. There’s a kid in shul who can tell if the scotch he’s given is sherried–he hasn’t missed yet.
To those who think there is a direct and reliable connection between not saying on the label and not using sherry casks, I am sorry, but it just ain’t so. I can even list some common scotches that are 100% or almost 100% sherry cask aged that say nothing on the label.
It’s not such a secret which distillery did a run of scotches finished in Carmel wine casks: Bruichladdich. There were two bottlings, 1989 and 1994.
Somebody mentioned he ran out and bought Caol Ila after hearing a shiur suggesting there’s no problem with scotch. Research suggests Caol Ila’s main bottlings, the 12 and the 18, both are 100% ex-bourbon cask, so if that’s what you bought, you could’ve walked, not run.
To those who claim sherry casks are cleaned multiple times, soaked, coaled, and smoked: When the casks are first made, they are toasted. Only after that do they soak in sherry for a while, then are shipped to Scotland and filled almost instantly without any of those things done to it. They generally only fill with water if testing for leaks. The better distilleries discard casks after the second fill, which means in general none of the above were done. Other distilleries refurbish casks by shaving off a very small inner layer. They don’t like to do a full re-toasting if they don’t have to because it won’t come out so good with the sherry already in the walls being heated up that way. Regardless, they often re-soak with sherry or cook sherry back into the walls. Bottom line: the claim in the first sentence does not hold in general.
How many here have actually read Rav Moshe’s tshuva? Did you know he didn’t write about sherry casks? Rather he wrote about the practice of adding wine directly into whiskey to sweeten it, and mattired (even if you could taste the wine) as long as the ratio of whiskey to wine was at least 6:1. Yes, it would be a kol shekain to scotch in sherry casks, but only if there would be 6:1 against the entire wood, and there isn’t. Without this some poskim (if they knew this) might be troubled to mattir. Did you know Rav Moshe in his own tshuva gave four reasons why a baal nefesh shouldn’t drink? Do you know why? I’m not saying not to rely on Rav Moshe, but many Kashrus organizations do not want to rely (at least solely) on Rav Moshe.
How many here have actually read the Minchas Yitzchok’s tshuva? Did you know he has an additional requirement over Rav Moshe that it also must be true that even an expert cannot be able to discern the taste of actual sherry? While this may be true in general, would you bet your life this is so for every scotch aged 100% in first fill sherry casks?