Making rum and vodka

While touring Flag Hill Distillery in Lee, New Hampshire  I had the chance to interview their distiller Brian Ferguson.  I first sampled their apple cranberry fruit wine, and then got a chance to document how they distill and age bourbon. Next I was able to interview Brian, and learn how they make vodka, and a new product, heavy rum:

Flag Hill discussion

We make rum here at Flag Hill, but not typical clear rum, nor the big funky rum like from Jamaica. Rather, we’re making something new called heavy rum. We don’t have a dunder pit, but we do some funky bacteria, some gram positive bacteria, for a complex rum.

Rum Esters by CompoundChem Compound Interest
Rum Esters Andy Brunning/Compound Interest

We double pot distill the rum. We create what we call low wine. This goes back into the still for a 2nd distillation. On on that distillation we get a nice clear crystal clear rum.

On the 1st pass it will be 60 proof. On this next pass it will be around 140 proof, 70% alcohol by volume.

That means that 30% of solution is water plus flavor molecules, aroma compounds, esters, etc.

Next this goes to a barrel where it has been sitting for 4 years, and will be aged for at least 6 years when we release it. It’s aging in ex-bourbon barrels from our own bourbon production. We currently make white rum from fancy grade molasses, distilled to a higher proof than this heavy rum. Goes through a cleaner fermentation to produce less esters. We do want some of the oils and heavy organic compounds, but not as much as that in heavy rum. This goes through the center column, and isn’t double pot distilled.

Flag Hill Spirits
(c) Flag Hill Spirits

When we make vodka, this is a product that has no flavor – that’s the purpose of the product. That tall column on the end, with portholes, has many plates/trays. The rising vapor hits the copper, which is one hell of a heat conductor.


It sucks the heat energy out of the vapor – bringing the heat from the inside of the column, out to the room that it’s in. That condenses some of the liquid. As that happens we get a little bit of reflux. What we’re doing is raising the proof. So every time we go up a tray vertically we’re raising the proof. When we get to 95% alcohol by volume – that’s when we make vodka. You can make vodka from apples, which we do; or vodka from potatoes, which Russians do; vodka from grain; theoretically vodka from a tree if you could get it to ferment!

If someone says that they make 8X or 10X distilled vodka, what that means is that they used a ton of energy to accomplish the same thing as what we can accomplish in 2 or 3 passes – or, if a still is efficient enough, in 1 pass.

Our change in temperature from evaporation to condensation in each tray (for the sake of this argument) is less than 0.1 degree Fahrenheit. Which gets the proof higher much more efficiently than 10+ distillations. If we did all these distillations then every one of them would require us to heat the solution to over 174 degrees F and cool it back down to 60 degrees F vs the process outlined above.

Single column Tray Distillation Tower
Single column Tray Distillation Tower, by H Padleckas for Wikimedia

First it is heating the entire solution up to 174 degrees and then cooling it all down to 60 degrees F. That’s a major change in temperature; that’s a lot of thermal energy. So by using the column on the end, what we’re able to do is make vodka more efficiently. We do ours in just 3 passes.

Consider that the azeotrope of water/ethyl alcohol is 95.6 percent – the absolute maximum place that we can distill alcohol to (without adding other organic chemicals or having other distillation processes.)

So if you take the law of man – vodka, as defined by TTB regulations – which is 95%, and the law of nature – the max we can distill alcohol to (the azeotrope, 95.6%) then all vodkas in the world are really just 0.6% different from each other.

And the reality is that it’s often just 0.2 or 0.4% different. So the difference between a $30 bottle of vodka and a $60 dollar of vodka… is really just $30!

Now what some distillers do to make spirits taste soft – and some vodkas are definitely smoother than others – is add glycerine or glycerol or citric sugar solutions. Things that trick your brain into thinking that the spirit is softer, because they put a microfilm on the tastebuds on your tongue. We don’t do anything post-production here. Instead, we use apples: We fill this 2200 gallon stainless steel tank with apple cider from Apple Hill Farm. That cider gets fermented and then distilled 3 times.

The reason that we use apples is that they have a high amount of malic acid. Malolactic fermentation and the conditions we place the alcoholic fermentation under allow the creation of diacetyl to occur, which give the perception of a buttery flavor. This creates a silkiness to our vodka without having to add things like glycerine or glycerol.

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