An Overview of Potstilling
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| Grainfather pot still |
When
a potstill is used to distill alcoholic beverages, an alcoholic wash is put in
a boiler and brought to a boil. The vapor produced by that boiling is directed
to a condenser, which cools the vapor, causing it to condense to a liquid. That
liquid is the distillate, the end product of distillation.
Distillation
has two major effects on the original wash. First, everything in that wash that
cannot be vaporized is left in the boiler, and will not be present in the
distillate. Second, because the wash is really a mixture of many liquids that
can be vaporized (a property called "volatility"), such as water,
ethanol and many flavoring compounds, distillation changes the concentrations
of those volatile liquids in the distillate, continuously, and throughout the
entire distilling run.
It's
not really important, or even helpful, to the hobby potstiller, to understand
the physical laws that control this sequential distillate change in any great
depth. It's enough to know that the first, last, and every other drop out of
that still has in it every volatile compound found in the wash, and at the same
time each drop has different concentrations from the drop before and the drop
after.
Much
of the art of distilling with a potstill is about what parts or fractions of
the still run the distiller saves for drinking, and what is discarded. To this
end, the distiller wants to reduce the concentration of water in the
distillate, and increase the concentration of ethanol, while minimizing the
bad-tasting compounds and maximizing the good-tasting ones, all while watching
the whole spectrum of these compounds come out of the still during a still run.
This
process of saving some fractions while discarding others is called "making
the cuts", and much of the art of distilling is aimed at making good cuts,
and therefore good liquor.
While
we usually don't think about it (or do it!), a "complete" still run
would be a run where all of the wash is evaporated and the boiler is boiled
dry, such that all the volatile liquids in the boiler end up in the distillate.
In such a run, the distillate would end up with all the volatiles in exactly
the same concentrations we started with in the wash, and that really doesn't do
us any good. Fortunately for distillers, all the interesting compounds have
mostly come through the still by the time about 25% of the wash has been
vaporized. The remaining 75% of a "complete" still run would be
mostly water, becoming purer water the closer to the end we get.
What
makes distillation work for us is that we distillers simply stop distilling
after that first (very roughly) 25%, and don't waste our time with all that
water in the last 75%.
The Stripping Run
Since
most washes are mostly water, a high-speed, indiscriminate still run, taking
about 25% of the wash without even attempting to make any cuts, can get
virtually all the alcohol and flavors out of the wash into the distillate. This
first-run distillate is called "low wines", and can be further
refined and separated by a later, slower, run, with careful cuts. Such a crude
high-speed first distilling run is called a "stripping" run, or a
"beer stripping" run, because it's particularly helpful as the first
step in distilling a necessarily low-alcohol beer into a high-alcohol whiskey.
The Spirit Run
If
the stripping run's purpose is simply to "strip" all the important
compounds, good and bad, from most of the water in a wash, the spirit run's
purpose is to separate the distillate into "fractions", distillate
samples, each with a different mixture of ethanol, water, and all those
flavoring compounds. Having all these fractions, the distiller can decide which
fractions should become part of the finished spirit, and which fractions should
be set aside for other uses.
A
major part of the distiller's art is how these fractions are accepted or
rejected. Using his nose, palate, and experience, the distiller judges each of
the fractions from a slow, careful distillation, and his judgement determines
the final quality of the whiskey, rum, brandy or other liquor. This process of
judging and blending or discarding is called "making the cuts".
An
easy way for either a new distiller, or an experienced distiller distilling
something new, to approach making the cuts, is to collect the spirit run's
output sequentially in small labeled containers. Each container has its number
in the sequence, the head temperature range over which it was collected, and
the alcoholometer readings for that range. For most new distillers, making
judgements real-time at the still's output usually does not work as well as
comparing the fractions at a later time. In that light, I like to make the cuts
the day after distillation, although it's still highly instructive to taste the
still's output as it emerges; for that reason, good distillers will have
teaspoons handy when the still is turned on.
When
Do We Strip, and When Do We Do a Spirit Run?
At
its extremes, the choice is between quickly stripping large amounts of
low-alcohol wash, and doing slower spirit runs on smaller quantities of
higher-alcohol wash. Of course, this means that the output of a stripping run,
low wines, is the perfect input to a spirit run, and that's how distillation is
often done.
For
a hobbyist, however, reality changes things a bit. For instance, beers for a
stripping run are easily made in large quantities, while getting enough of a
particular fruit to make quantities suitable for a strip-then-spirit run can be
difficult and/or infrequent. Because of that, often the hobby distiller has
only enough fruit wine to make a single still run, and that run has to be a
spirit run to get real drinkable product.
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