Ordinarily, shochu produced by means of normal pressure distillation is full and intense, hence possessing a strong, natural flavor that can make it difficult to drink for some people. However, using distillation tanks made of alternative materials can lend to a smoother and easier-to-drink flavor. Materials like stainless steel, copper, and tin, are highly heat conductive, which leads to a more intense boiling of the moromi and strong characteristics. Alternatively, shochu producers can use stills made of materials such as clay or even wood that reduce the intensity at which the moromi is boiled and results in shochu that is milder, sweeter, and easier to drink.
Distillation Methods
Distillation is an important process behind the production of any fine spirit; vodka, rum, whisky, and shochu. Generally speaking, the objective of distillation is identical for each: to extract the alcoholic properties from a fermented compound of water and other raw materials through the boiling and condensing of the compound.
After the fermentation stage of the production process, the moromi [material created during fermentation that is comprised of water, yeast, koji, and a base material] has a very low alcohol content: somewhere between 5%-10%. As a result, it cannot be classified as a spirit.
Distillation is truly a turning point in the production of shochu in the following ways:
- The distillation method provides a means for classification: Honkaku or Kourui.
- Honkaku is the product of a single distillation method.
- Kourui shochu production employs a continuous distillation method.
- Distillation has a profound effect on the flavor and aroma of shochu. Each distillation method achieves a different result.
Single Distillation
The single distillation method, also known as pot or batch distillation, is exclusively used in the production of Honkaku shochu. There is no exception. Honkaku shochu makers can utilize one of two different single distillation methods: normal (atmospheric) pressure distillation and low pressure (vacuum) distillation.
The most traditional of these methods is normal pressure distillation. Normal pressure distillation has been used since the inception of shochu production. It is also the most extensively used distillation method throughout the history of distillation.In normal pressure distillation, the boiling point of the moromi generally between 195˚ F and 210˚ F (90˚ C and 100˚C).
The high boiling point causes various chemical reactions between the components found in the moromi (koji, yeast, water, alcohol, glucose, et cetera), most of which are directly correlated with the shochu's flavor and aromatic elements. Aside from the contributions the raw materials make, another major contributor to a shochu’s flavor and aroma is furfurol.
In contrast, vacuum distillation, as the name suggests, reduces the atmospheric pressure found inside the still. The reduction in pressure creates an environment that allows for a much lower boiling point. Though slightly unconventional, its use has grown in popularity in the shochu industry. Shochu produced by vacuum distillation is light, gentle and sometimes fruity and most commonly used to create barley, rice, and buckwheat shochu.
Generally speaking, a shochu produced by vacuum distillation closely corresponds to the flavor and aromatic properties of the moromi prior to distillation, light and somewhat sweet. Additionally, the absence of furfurol attributes to the light and mild characteristics. Because of the low boiling point caused by low atmospheric pressure, furfurol is unable to be derived from its main reactant, aldehyde: a product of yeast fermentation.
Continuous Distillation
Continuous distillation was brought to Japan in 1896 by British traders and first appeared in the shochu industry in 1911. This distillation method was developed by an Irishman named Aeneas Coffey who was in search of a more efficient way to produce whisky. Just as in Ireland, a number of shochu producers were looking for a more efficient way to produce shochu in bulk amounts; continuous distillation enabled them to achieve this goal.
Continuous distillation is commonly used in the production of a number of distilled spirits including vodka, gin, and white rum. In shochu production, only Kourui shochu utilizes continuous distillation. Kourui shochu is often called “Japanese vodka”, and much like vodka it is quite neutral and lacks definitive flavor and aromatic characteristics.
In continuous distillation, as the name may suggest, the moromi is distilled multiple times. Much like batch distillation, the moromi is boiled and the vapor emitted is condensed into a liquid that is higher in alcohol content. Continuous distillation takes this concept and enables producers to perform the same batch distillation process successively and repeatedly.
When continuous distillation is used, the characteristics of the raw materials are stripped away, leaving a product that is extremely light in flavor and aroma, but lacking the impurities and congeners that are found in batch distilled products. In addition, with each successive distillation cycle, the alcohol content increases causing the final product to have a fairly high alcohol percentage.