Vacuum Distillation of Gin and Food Items

In 2007, a team at Bacardi led by the food technologist Derek Greer filed a patent for a practical industrial method of cold distillation at subfreezing temperatures. Compared with traditional distillation, their method produces gin with an aroma much closer to that of the original infusion of juniper, coriander, citrus peels and other botanicals with which gins are flavored.

This fall, Bacardi started selling an English gin called Oxley that is distilled at around 25 degrees Fahrenheit, and includes fresh citrus peels instead of the usual dried peels. Tasted alongside a half-dozen standard English gins, Oxley stood out with an impressively intense, bright, almost sharp aroma.

In Lewisville, Tex., a suburb of Dallas, Carlos Guillem operates what he claims to be the only vacuum distillery in the United States. He started production and local distribution of DeLos vodka last summer.

Experimentally minded chefs and bartenders are also discovering the potential of vacuum distillation using laboratory devices called rotary evaporators, which fit on a kitchen cart and handle a few quarts of liquid at a time. They cost between $5,000 and $10,000.

The pioneers in kitchen distillation are the Spanish chefs Joan and Jordi Roca of El Celler de Can Roca in Girona. Joan Roca rocked the food world in 2005 when he served an oyster in a clear jelly flavored with an aroma that he had distilled from a handful of forest soil.

We have now looked at the physical properties which chemists use to define the solid, liquid, and gas phases. In a solid, atoms, ions or molecules, are locked into an organized, long range lattice structure, unable to move beyond an average position due to intermolecular forces. In a liquid, this structure breaks down, molecules can slip past each other, but they are still held together by attractive forces. In a gas, these attractive forces are overcome, and the substance expands to fill space, each particle having gained mobility to break free of the others.

Substances can transition from one phase into another. Solids melt into liquids, liquids boil into gases, and so chemists are also interested in these transitions between phases.

We are all familiar with the macroscopic properties of these transitions. The following video shows solid sulfur melting.

This is a highly familiar process. The solid changes to conform to the container shape, and is able to flow. Heat from a flame is needed to bring about this transition.

This macroscopic behavior demonstrates quite clearly that when energy is supplied (by raising the temperature), a solid can melt into a liquid. On a microscopic level melting involves breaking the intermolecular interactions between molecules. This requires an increase in the kinetic energy of the molecules, and the necessary energy is supplied by the Bunsen burner. This process can also be accomplished by lowering the pressure considerably.

Boiling is equally as familiar. Under the right temperature and pressure conditions, the liquid starts to bubble, and is converted to a gaseous form. The following video is a quick look at hexane boiling.

Heat energy is absorbed when a liquid boils because molecules which are held together by mutual attraction in the liquid are jostled free of each other as the gas is formed. Such a separation requires energy. In general the energy needed differs from one liquid to another depending on the magnitude of the intermolecular forces. We can thus expect liquids with strong intermolecular forces to boil at higher temperatures. It should be noted as well, that because there is a distribution in the kinetic energies of molecules, a equilibrium between gas and liquid phase forms even when not at the boiling point, and this behavior is another aspect of phase transitions that chemists study.

For phase transitions from solid to liquid, liquid to gas, or solid to gas, energy is required because they involve separation of particles which attract one another. Further, we can predict under which conditions of temperature and pressure such conditions will occur.

From ChemPRIME: 10.8: Phase Transitions

Contributors and Attributions

• Ed Vitz (Kutztown University), John W. Moore (UW-Madison), Justin Shorb (Hope College), Xavier Prat-Resina (University of Minnesota Rochester), Tim Wendorff, and Adam Hahn.