You're absolutely correct, Marc, there is nothing about concentration. I
believe that's the point. Remember that these regulations aren't in place to
grant us rights, they're there to restrict them (hopefully only to the
extents necessary to ensure a safer society). The fact that there is nothing
about it in that citation is enough. Concentration is legal by the simple
fact that there are no regulations prohibiting it.
In fact, most people think this regulation makes it legal to home brew beer in
the US. That's not true. This regulation makes it illegal to brew more
than the specified 100 or 200 gallon limits without paying taxes.
When you concentrate something, you don't change its label. Apple juice
concentrate is still apple juice. When you concentrate beer or wine, it's
still beer or wine. When you distill beer or wine, you're winding up with a
purified quantity of spirits. Not beer or wine.
While I understand your desire for a definitive statement in legal regulations
that allows you to make ice beer, applejack, honeyjack, or whatever, I think
you'll never see that, beyond the name of someone at the TTB that did verify
its legality. Such a thing would actually be a very bad legal precedent,
implying that a citizen does not have any rights but those granted by the law.
As I understand it, this is no longer under the auspices of the ATF as of
9/11. This falls under the TTB as far as I know, so unless the person you
spoke to did give you an explicit citation (maybe a state law?) then I'd say
you got questionable information.
So, how about this:
http://www.ttb.gov/forms_tutorials/glossary/letter_c.html#C_18
This is from a TTB glossary page, and it does explicitly state that beer
concentration and reconstitution are "considered authorized practices", though
it isn't that explicit (either way) with respect to wine. It also doesn't
clarify whether this applies to home brewing or not. It's also possible this
is referring to malt extract, it's hard to be sure.
You can also see how the gov't defines "spirits or distilled spirits" by going
to
http://www.ttb.gov/forms_tutorials/glossary_nf.shtml.
It's pretty obvious that sticking your 14% mead in a deep freeze and removing
1/3 of its volume is not going to meet this criteria.
So, you're obviously not under any obligation to throw your mead into a deep
freeze, but I think it's also obvious that you're not explicitly forbidden
either.