Spirit Stills and Reboilers?

[tof toffer]

>
>I recently visited a couple of microdistilleries that had two-step
>distilling processes.
...
>Up to now, every distillery I've seen added heat to the spirit still to
>accomplish a second distillation.  Can any of the MALTS-L experts point me
>to something that discusses how this second distillation is accomplished
>without additional heat (it doesn't need to be too technical)?  I don't
>believe either distillery was using vacuum distillation.

Hi.

I poked around through my whisky library, and I was a bit surprised that I
couldn't really find a good discussion of the doubler/thumper.

Since you're asking for references that you can read, I'll point you to the
two that I found.

1) There's a brief discussion at homedistiller.org, buried under
Equiptment > Making a Still > Designs and Plans > Thumpers, Doublers,
and Slobber Boxes.

2) Thumpers are discussed in what's probably one of the best descriptions
of traditional American moonshining practice: "Moonshining as a Fine Art"
in The Foxfire Book, a.k.a. Foxfire 1.

Since neither of those give you the answer you really want, I'll give it
a shot myself.  (Please excuse my tendency to be long-winded.  No time
today for editing...)

If you've ever been to a coffee shop, you've probably seen someone making
a cappuccino.  They take cold milk, and bubble steam through it.  Pretty
soon, the milk is so hot that it burns your tongue.  A thumper works the
same way.  Bubbling steam through a cold liquid = a hot liquid.

There are a few different ways to use thumpers.  The basic idea is to
re-use the heat from your first distillation to somehow save energy,
time, effort, etc.  Every large distillery you'll visit does this somehow,
generally taking the heat from the condenser and using it to heat up the
mashing water, or to pre-heat the beer before it goes into the still, or
something like that.  Another possibility is the thumper in one of its
many forms.

Some of them merely increase the capacity of the still.
Some use fancy schemes to put the low wines from one distillation
into the thumper, and basically use the primary still to drive the
second distillation.  So you use the same rig for the first and
then the second distillation, but when you do the second, you're
also using up a batch of beer, so you cut the number of primary
distillations in half.
A thumper can also be used as a mini-"second distillation", increasing
the strength of the distillate.  I'm told that you can engineer the
thumper such that the liquid inside changes composition during the
distillation, moving more and more toward the composition of the
vapor that's being bubbled through it.  So the thumper contains what
is essentially condensed vapor off the first still, and is being boiled by
that same vapor.  You thus get a second distillation "for free".

The key to understanding why it works is to realize that the boiling
point of an ethanol-water mixture goes down as the percent of ethanol goes
up.  So if the contents of the thumper are, say, 30% ethanol, then vapors
from a still that contains 5% ethanol are hot enough to boil the contents
of the thumper.  No tricks with vacuums, pv=nrt, or maxwell's deamon.

I'll save my speculations and opinions about the relatve merits of a
thumper vs. a separately heated second distillation for another time.
In the end, it's all about the drinkin': if it makes a tasty whisky,
then it's a good thing.

Tim Dellinger

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