The drummer taps frantically on the rim. The trumpet pips and pops, raising and falling, bubbling like liquid. Miles Davis’s compilation album ‘Birth of the Cool’ was first released in 1957 and has become a soundtrack to writing this article so it would certainly serve as a suitable soundtrack for reading should you be of such an inclination.
Cold distillation, or vacuum distillation, was as exciting and experimental as jazz when first discovered as an additional technique to much loved pot distilling. And, although it has settled nicely into the role of pot distilling’s new-fangled younger brother, there is still so much to be explored by using this equipment. What do we know so far, and what are we discovering? And importantly, what are the benefits that this cool technique can bring to a distillery? It is worth noting that it is a very common technique in gin distilling so +there will be a gin theme to this article. However, it is beneficial to many spirits and the creative potential is enormous.
To understand vacuum distillation, it’s important to dispel a common myth, boiling does not mean heat. Heat is a factor, however it’s not the only one. Does the ocean boil to evaporate into the sky? It does not. Boiling is the rapid vaporisation of a liquid. This happens when it’s heated to its boiling point. However, the boiling point is the temperature at which the vapour pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere, and if you lower the air pressure, you lower the boiling point too.
Essentially a substance put into a vacuum of less than normal pressure, 101 pascals, ATM, or one atmosphere will boil at a lesser temperature than normal pressure. In fact, it reduces the approximate 82C/180F boiling point in a pot still, down to somewhere inbetween 25-40C/77-104F. This opens a wealth of possibility in flavour extraction and energy efficiency, and I would propose these are the two main factors to consider with vacuum distilling. Heating a botanical cooks that botanical and this alters its chemical makeup and what elements of flavour are released into the spirit. For example, the difference between a strawberry and strawberry jam/jelly. The fresh strawberry, with its natural tartness and trademark sweetness, the fresh green notes of the stem, that ‘brightness’ of the fruit. Then we have the cooked strawberry, or strawberry jam/jelly. We have those deep sweet stewed notes. Denser and lacking in complexity compared to its fresh counterpart. This is a good representation of the flavour difference to expect between pot distilled and vacuum distilled. The makeup of these chemical compounds are complex and interesting. One example of this are monoterpenes. Monoterpenes are a class of terpene that are found naturally in plants, providing a defence against threat with their pungent aroma. They exist in anything using botanicals. However, vacuum distillation removes a lot of monoterpenes from the botanicals, leaving a spirit with a much fresher aroma quality. This is a sweeping statement as such, but an interesting idea. It is worth noting that the heavy flavours of pot distilling are quite wonderful, and this by no means a better or worse comparison, more that they are two different methods with two different results. It’s easy to see why some people blend distillates to achieve a deep complexity to their spirit.
And much like most things in distilling, this is not a one process fits all, this is science and there are variables to consider. Exploration and experimentation is key, one botanical might distil as expected, another could produce something unpalatable. Additionally, as pot distilling cooks botanicals, those strong flavours add a nice weight to the character of a spirit. It is also worth noting that some botanicals, juniper is a classic example, benefit from heat to release the botanical oils through distillation, though vacuum distillation with juniper is possible too and achieves a different result. Vacuum distillation tends to bring out lighter, delicate, more complex notes. Therefore, some botanicals would disappear in a pot still but excel in a vacuum still. This means you can capture certain flavour notes impossible to capture in a pot still. Also, there are some botanicals that are so delicate, they would be destroyed in a pot still. So vacuum distilling opens up the opportunity to distil some botanicals that otherwise would not be possible at all.
Oxley Gin, based in the UK, owned by Barcardi, is one of the notably earliest gins to use cold distillation. Released in 2009 and after eight years of perfecting the recipe, the gin is distilled at a very cold temperature for a cold gin -5C/23F in fact, which has some amazing results, including that there are no hearts and no tails! Contrary to drinkers’ myths, if you’re distilling with GNS, there are no dangerous ‘nasties’ that come out in the heads and tails, as they’ve already been removed prior to the GNS being sold. The cutting of the heart and tails in regard to gin is purely from a flavour perspective. Due to the varying flavours in botanicals through a distillation, the hearts are deemed the most palatable section. Matthew Pauley, Distilling Consultant of Distillers Nose Ltd, was the operator of that early pilot still. I was keen to check in with him as to how the use of vacuum distillation has progressed and he noted that, “In recent years there has been an increase in interest in vacuum distilling, as the market for gin evolves and producers are increasingly looking to differentiate themselves within the crowded shelves. Extraction techniques are one of the logical tools at the gin distiller’s disposal. The exciting thing for me about vacuum distilling is that the science stacks up behind it, as opposed to being simply a gimmick used to generate copy for marketeers. Recently there have been a small but devoted proliferation of small independents getting into the vacuum distilling market, which is always exciting, as it is the smaller producers that have proven a disruptive influence in so many markets.”
What Matthew began with the pilot still, was taken on and progressed by Anne Brock, Master Distiller of Bombay Sapphire, Barcadi, as one of her first projects in the role. Scaling the equipment up from a 25L to a 100L had it’s difficulties. The unique set up, made from stainless steel takes up an entire room, although is still small in comparison to its 3000L that make Bombay Gin. Anne found it strange as “in a chemistry lab, vacuum distillation is used as a waste disposal unit, a way of removing solvents from reactions at the end of a reaction sequence. However, the same principle applies, instead of removing the solvent, you’re collecting it”. Despite the still producing all Oxley gin. Anne still experiments. “I distill fresh and frozen botanicals in the vacuum. Using fresh bright herbs in a tradition still, can give you a vegetal note. There is something beautiful in fresh bright notes keeping their purity”.
Ian Hart of Sacred Gin is another long-standing pioneer of vacuum distillation. Ian discovered vacuum distillation in his very early years when playing with a syringe and noticing that if he held his finger over the hole whilst pulling out the plunger, the water bubbled. This idea stayed with him and he progressed it over the years, with substantial findings when looking to re-engineer Bordeaux wine without boiling. Research showed a lot of the technology existed in oil refinement, so the systems were already “very well explored”. In applying this technology to the wine, Ian found he was able to “dismantle the wine without damaging it”. With this he could then “reassemble” the components how he wanted and do “fun things like cross blending different wines”. Ian recognised the enormous creative potential and set about creating his own bespoke multi-modular vacuum system, and one that fits together slightly differently every time he takes it apart to clean it. When he began to distil spirits, he immediately noticed the difference in orange peels “They smelt different, there was a different texture. The botanicals were dramatically different as when heated they stew”. Ian now proudly distils all of his spirits in this fashion and acknowledges that ‘people are becoming aware that “it is a different universe for distilling”.
Another fundamental benefit is that there is a sustainability aspect to the technology. The industry is becoming increasingly aware of the importance of sustainability in distillation processes. With most vacuum distillations running at between 20-25C/68-77F or around room temperature, this means it uses less energy for heating and for cooling than a pot still. Ian has made the provisional calculation that his vacuum distillation runs at around 8-9% energy usage of a pot still distillation, which is a phenomenal percentage of energy saved. This is hugely beneficial for the environment and for the distillery. This is important for the integrity of your process, and secondly, having clear sustainable processes makes a distillery very appealing to external capital investment. (Further research has suggested there are some distilleries using a partial vacuum being used on a continuous still to reduce the boiling temperature slightly and save on energy. A little digging here proved fruitless but speaking to the experts it does seem that it is feasible. It would be interesting to see how this idea develops over the coming years).
Abbie Neilson of Cooper King Distillery uses cold distillation in order to extract the most delicate notes from her botanicals. For a delicate flavour profile there can be some pitfalls worth considering. “Cold vacuum distillation is a gentle process. The extraction of flavour compounds is not as efficient in the absence of heat (think of it like brewing a cup of tea or coffee with cold water instead of hot) and can result in more subtle-tasting spirits. These make for wonderful sipping gins but are less able to tolerate dilution with a mixer. This can be overcome by increasing the amount of botanicals used, crushing them or macerating them for longer in neutral spirit prior to re-distillation, producing a more robust spirit that holds its own with a mixer.”
And in the US? To give an insight I spoke to Lee Katrincic, Founder and Distiller of Durham Distillery, based in North Carolina. Durham Distillery was the first distillery in the US to use a rotovap. They combine pot distilled and rotovap, with the tagline that their gin, Conniption is a marriage of art and science (respectively). The reason for the combination is that they needed to pot distill the Juniper to release the botanical oil and deliver the distillate they were looking for. However, they also wanted to include cucumber and honeysuckle which would have been compromised. So, these botanicals go in a vacuum still and are distilled at room temperature. Since setting up Lee has received calls and given advice for others to set up their own stills, so we can speculate that vacuum distilling is on the rise, though we cannot say for sure. For Lee, it’s helped them to create “different layers” to their gin. “Using the technology and treating botanicals the way they want to be treated, means you get the flavours that you’ve been hoping for”. It’s not always plain sailing and there has been experimentation. Previous efforts have seen vacuum distilling figs at room temperature, which Lee found interesting as “the sugars don’t distil, but the essence comes through and that was surprising”. The rotovap can be rinsed very easily with water, but distilled figs left a caramelised layer so despite the essence it isn’t a practical botanical for vacuum distillation.
Cool distillation was discussed on some panels during the Craft Distilling Expo this year, which was held virtually. A question regarding vacuum stills was asked to the ‘How to Grow Your Distillery Panel’. The general consensus was that those that had experienced vacuum stills found them to be really interesting pieces of equipment and the range of flavour profile is just so different compared to standard pot stilling. Considering the difference in the flavour profiles that are being captured, it’s understandable why combining these two methods can create a spirit with more depth and complexity. It seems that vapour distillation certainly has a lot of merits and still has new ground to be broken and explored. As Ian Hart so beautifully put it, it is a whole “different Universe” and much like jazz, it’s very, very ‘cool’.