Japan Sake and Shochu Makers Association | JSS
Distillation in the production of shochu and other spirits is the process that extracts alcohol along with some flavor components.
Scientifically speaking, distillation is a process that extracts substances and components by leveraging the different boiling points of liquids and the target component. By heating a mixture to a certain temperature, some elements will evaporate. The vapor elements then travel through a cooling device where they condense back into a liquid. The target component is collected as a liquid in a vessel. In shochu production, fermented mash is distilled to extract alcohol and flavor components.
The boiling point of ethanol, or the target alcohol, is approximately 78℃ while it is 100℃ for water. As a result, distillers can extract alcohol by boiling the moromi mash at around 85-95℃. Before distillation, the alcohol content is around 14-19% in the second moromi. However, it goes up to 37-45% in the liquid (fresh shochu) collected after distillation. After a single distillation, the distillate still retains a lot of other components, and these remaining elements provide shochu with its rich flavor.
The basic device used in distillation is a still. There are two main types of stills: the pot still and the column still.
A pot still is the simplest type of distillation device used in all honkaku shochu and awamori production. This type of still is also used for authentic whiskey, tequila, and rum. The resulting distillate still contains several non-ethanol components that contribute to flavor and aroma.
A column still is a distillation device that allows for continuous distillation. Stacked perforated plates are placed inside the column, where each plate produces a higher concentration of ethanol in the vapor, ultimately producing a very pure alcohol. Vodka, gin, white rum, and koh-rui shochu use column stills.
Shochu production generally uses one of two distillation methods: atmospheric distillation or reduced pressure distillation. Recently, some producers have combined the elements from these two distillation methods and started to distill under slightly reduced pressure as well.
Atmospheric distillation is a traditional distillation method conducted under the same pressure as the atmospheric pressure. Under the atmospheric pressure, the boiling point of the mash and the components stays the same. Therefore, the previously mentioned temperature range of 85-95℃ is still ideal for extracting alcohol. The high temperature facilitates chemical reactions, creates new chemical compounds, and causes components other than alcohol to vaporize. These additional reactions and components tend to give the resulting shochu a characteristically rich flavor.
Reduced pressure distillation, or vacuum distillation, is a method of distillation done under a lower pressure than atmospheric pressure. A producer in Fukuoka Prefecture first developed a vacuum still for shochu making in 1973. As the pressure lowers inside the still, so does the boiling point for its contents. As a result, alcohol extraction only requires a temperature between 45-55℃ under reduced pressure distillation. The low temperature reduces both the processes that disrupt floral aromas and the evaporation of flavor components. This results in a shochu with lighter, more floral flavors.
Up until the 1970s, shochu had a distinctly rich flavor and a reputation as a regional, southern Japanese drink. However, after the development of vacuum distillation, light-flavored shochu entered the market. This expanded the popularity of shochu outside of the Kyushu region and triggered a nationwide shochu boom. Today, people know more about the diverse flavors of shochu. To meet market demands for all shochu flavors, many producers distill their products using both methods.
Most shochu production uses stainless steel stills. Stainless steel has an ideal heat conductivity and does not influence the flavor of the distillate. Traditionally, distillers in Kagoshima used wooden barrels and wooden vat stills with tin coils. The barrels and stills infuse the distillate with a hint of woody aroma and a unique flavor characteristic. Unlike in many parts of the world, copper stills historically have not been used in Japan.
