Vacuum distillation stands out as a beacon of innovation in our industry. It’s representative of the type of evolution that has propelled the modern gin resurgence.
Be it via the rotary evaporator, or ‘rotavap’, or through other glass stills that are under vacuum – this advanced equipment is transforming traditional distillation methods. It’s allowing distillers to experiment with delicate flavours and intricate processes that were once thought impossible.
As we delve into the workings and impacts of one of the main items of vacuum distillation – the rotavap – we uncover how distilling under reduced pressure is reshaping the way producers think about gin distillation, offering new horizons for flavour and aroma.
How does vacuum distilling work as a process in the context of gin?
Distilling 101 recap – heat is used to separate the alcohol that has captured the aromatic compounds from the botanicals and water. This is because alcohol evaporates faster than water and boils at a lower temperature.
To do that, traditional distillation techniques apply high heat to reach boiling point 78C. When it comes to gin and using botanicals – it can lead to the loss of delicate flavours, or even the creation of unwanted ones. Boil a cucumber and see for yourself!
Some distillers use a vapour chamber to simply move the ingredients away from the extreme heat. For others, this is where the magic of the rotary evaporator comes in.
A rotary evaporator allows distillers to manipulate the pressure within the distillation flask. By using a pump, atmospheric pressure is removed from inside the vessels. With a lower pressure, the boiling point of the alcohol and other compounds decreases significantly.
This means that the gin can be distilled at much lower temperatures, as low as 25-35C helping to preserve those subtle, delicate flavours that might otherwise have been lost under conventional methods.
This ability to cold-distil ingredients – technically below raw food approved temperatures – allows the creation of gins with a truly remarkable clarity of flavours, and instances where the freshness is fully on display.
How do rotovaps work?
The basic principles are straightforward.
Placement. First, the mixture containing the desired substance (in this case, alcohol, water and botanicals) is placed in a round-bottomed flask. This flask is attached to a condenser, a long tube through which coolant is typically circulated.
Heat and rotation. The flask is then heated gently in a water bath. As the flask rotates (hence the name ‘rotary’ evaporator), it creates a thin film of the liquid mixture on its inner surface. This increased surface area accelerates the rate of evaporation.
Reduced pressure. Simultaneously, the pressure within the system is reduced using a vacuum pump. The decrease in pressure lowers the boiling point of the liquid, allowing it to evaporate at much lower temperatures than it normally would.
Condensation. The evaporated vapours (which contain alcohol and the aromatic compounds from the botanicals) then rise into the condenser. Here, they are cooled down and converted back into a liquid, which is known as the distillate.
Collection. The distillate drips down from the condenser into a collection vessel. This resulting liquid is a concentrated, purified form of the original mixture. In the context of gin, it’s a potent concoction full of carefully extracted flavours.
Other vacuum based equipment used in gin
The rotary evaporator is not the only device that employs vacuum distillation in the spirits industry.
There are other types of vacuum stills that do not rotate, as well as pot stills equipped with a vacuum system. They use the same fundamental principle of reducing pressure to lower the boiling point of the mixture.
Irrespective of if they are big or small, built in stainless steel or glass and how all the vacuum stills differ in their specific operations and applications, they all aim to achieve a similar outcome.
The first is to distil liquids at temperatures lower than their normal boiling points to preserve delicate flavours and increase efficiency. The second is to minimise the energy required for distillation.
The choice between a rotary evaporator and other vacuum stills often depends on the scale of operation, budget, and the specific goals a distiller has in mind.
At large scale, vacuum elements in big stills can be used to improve power efficiency. At small scale, it can simply be helpful as the likes of a rotavap isolates the distillation in airtight flasks. These small glass containers tend to be better suited to bar, semi-domestic or culinary environments (they are frequent sightings in food labs).
Why would a distiller choose to do harness vacuum technology?
There are three main reasons that make the likes of a rotovap an enticing proposition.
Flavour preservation
Distilling at lower temperatures offers the significant advantage of preserving delicate flavours. If you are making floral, citrussy or fresh flavours, it offers a straightforward point of difference to using other apparatus. It’s the difference between fresh citrus and marmalade.
Even with spiced botanicals and herbs, it will extract slightly different profiles that can be interesting to layer into a gin.
Precision and control.
The rotary evaporator gives distillers unprecedented control over the distillation process. They can adjust the pressure and temperature with pinpoint accuracy, allowing them to extract specific compounds and very specific flavours geared to a highly tailored outcome.
Scale & type of equipment
Glass flasks, standard electrical plugs, countertop placement can all be factors that sway people towards a rotovap. Many distillers don’t need large equipment, they don’t want to work with steam boilers or open flames.
Many glass vacuum set ups can offer a great solution that, once you get the hang of flavour concentration and multi-shot methods, can mean small apparatus but able to deliver reasonable scale.
What are the downsides to vacuum distillation?
Like all techniques and apparatus, the rotovap comes with its set of limitations. Here are some key downsides associated with its use.
Heat-dependent extraction
Certain aromatic compounds, which give a spirit its unique taste and aroma, are extracted most effectively at higher temperatures. By operating at lower temperatures due to the vacuum environment, distillers might miss out on capturing the full spectrum of flavours from such botanicals.
It’s main benefit, can also be it’s main flaw depending on the botanical.
Equipment size and scale
Rotary evaporators are typically designed for smaller-scale operations, making them more suitable for experimental batches or individual botanical distillates that are added into a larger batch made on a typical still.
Having to make everything on a rotavap can be limiting given there is a small maximum capacity. Typically, this is less than 10L at a time.
Single botanical approach
While the rotovap’s ability to distil individual botanicals offers precision, it can be a double-edged sword.
Distilling botanicals separately can indeed maximise flavour extraction and yield for each botanical. However, it can also be more time-consuming and labour-intensive than weighing botanicals in a recipe, distilling them together and making effective hearts cut.
Maintenance and fragility
The intricate parts and glassware used in rotovaps can be fragile. Breakages are not uncommon, leading to potential downtime and additional costs for replacement parts. Those replacement parts cost a lot too…
Vacuum distillation- cold process, red hot potential
Be it through the rotary evaporator or other vacuum equipment – cold distilling is a revolutionary process in the spirits industry. It offers a sophisticated approach to gin distillation.
It enables the preservation of delicate flavours and provides unparalleled control over the distillation process.
While it has limitations in terms of scale and the full spectrum of flavour extraction, its ability to distil at lower temperatures opens up new possibilities for flavour profiles and innovation in gin production.
The rotavap’s precision and efficiency in capturing the essence of botanicals marks it as a significant advancement in the art of distillation.
