Between Mr. Athena and I, we received a couple bottles of booze that tout they were put on ships and sailed around the world. I assumed that was marketing woo, but in looking at the respective web sites, they both claim that putting the casks on a boat and sailing 'em around for a while makes a difference.
Maybe back in the Olden Days, the swaying of the ship would provide a gentle stirring effect, and maybe that’s good for the booze. But modern megacargo container ships don’t sway to any significant degree. And humidity and air pressure will vary almost not at all on an ocean voyage (since you’re always at sea level, and always near a lot of exposed water surface), and temperature very little.
I could see the argument that keeping it in a cask for 3 months does something to it that having it in the bottle those same 3 months would not - I mean, they age liquor in wooden casks to absorb flavor from the wood, allow for evaporation, and so on.
And maybe the movement (from being on a ship) would allow for some mixing so that all the contents of the cask got contact with the wood, so it’d be a bit more even (part of the same reason we stir food as it cooks).
Me, I personally doubt that the humidity is that big a deal. That, the temperature, and the movement could easily be replicated in a warehouse by putting some kind of vibration-inducing mechanism on the storage racks, and having a climate-controlled warehouse. Far more controlled, and a lot cheaper than shipping the stuff around in casks.
In summary: I could see where it makes a little difference, probably not enough to justify the woo (assuming that otherwise, the product HAS been properly barrel-aged). I certainly wouldn’t know the difference and I doubt most people would.
I’m going with marketing woo. Those are emotionally charged words and in my experience if they actually had something there’d be a link to the chemistry or some justification.
That’s where I’m at. The three months in casks during the voyage? Sure, that will make a different. That’s three extra months of aging. That said, you could just age it for three extra months before shipping it off in bottles, too.
As for the humidity, temps, rocking back and forth–I can see that making some sort of a difference but, once again, you can replicate it and standardize it even when you’re cask aging it in your warehouse, if you wanted to.
I don’t know how much temperature makes a difference on aging distilled spirits (though with fermented/brewed alcoholic drinks like beer and wine, that does make a difference), nor humidity, but I suspect most of that would affect the evaporation rate and what the final alcohol content is. But does that matter? AFAIK, the alcohol levels get standardized before being bottled, anyway.
The reason they age booze in casks is because it is filtered in and out of the wood over time which imparts wood flavors into the booze and add a mellowness. Anything that accelerates the process of soaking in and out of the barrel will accomplish the same thing faster. Rocking in a boat or shaking in a paint can shaker would both work.
If it is aged as if it were the 1800s - i.e. in barrels in a sailing ship (likely a clipper) rather than the hold of a steamship - then there will be additional traces from the salt water in the Linie.