vacuum distillation is a method of extracting volatile compounds by creating a vacuum in the system to lower the vapor pressure and boiling point of the volatile liquids while making the process more energy efficient. This is done by attaching a pump to the outflow pipe from the condenser, thus reducing the air pressure in the still. The key benefit of vacuum distillation is the lower temperatures needed to make aroma compounds volatile, which helps preserve heat-sensitive compounds.
When distilling the aroma compounds from delicate sources, like fruits and spices, the high temperatures found in normal atmospheric stills often degrade the compounds, resulting in a “cooked” flavor in the distillate. For example, instead of fresh strawberry aromas you may get cooked jam aromas.
Using a vacuum still allows the aroma compounds to be separated with a very low energy input, generally just warm water, which preserves the delicate flavors and gives a true representation of the fruit or spice.
Although this method of distillation is relatively rare in the production of spirits, it is not new—the British physician Richard Shannon detailed the technique in 1805, and it has long been used in Japan for making shochu. See shochu. It was also occasionally used in the United States for making brandy, and from 1950 until around 1973 the Mr. Boston company sold a “Vacuum Distilled Gin.” In 2009, that last idea was revived by the Bacardi company, with their Oxley gin, vacuum-distilled at the Thames distillery outside of London. See Bacardi and gin.
Vacuum distillation has found use in restaurants and bars where the extraction of unique flavor compounds is used as enhancements for cocktails. Benchtop rotary evaporators, commonly used in laboratories, are the preferred equipment, as they are compact and easy to operate. The key benefit of this method is the concentration of flavors that would normally be too subtle to detect or in the raw form would be inappropriate to add to a drink, like soil and flowers. These distillates capture and amplify the aromas, which can then be used to make a cocktail that is truly unique. See rotary evaporator.
Shannon, Richard. A Practical Treatise On Brewing, Distillation and Rectification. London: 1805.
By: Darcy O’Neil