How Shochu Is Made

Koji-Making (Seikiku)

The first step in shochu production -- and the one that sets the direction for the entire flavor profile. Steamed rice (or barley) is inoculated with koji mold spores, then carefully managed for temperature and humidity over roughly 40 to 48 hours as the koji develops.

The enzymes produced by the koji mold (particularly amylase) break down starches into sugars. The mold also generates large quantities of citric acid, which acts as a natural defense against spoilage bacteria.

Black Koji, White Koji, and Yellow Koji

Primary Fermentation (Yeast Starter)

Water and yeast are added to the finished koji and left to ferment in a tank or clay pot for about 5 to 8 days. During this stage, the yeast multiplies rapidly and begins converting sugars into alcohol. The resulting mixture is called the "primary mash" or shubo (yeast starter).

Temperature control is critical: slow, cool fermentation produces fruitier aromas, while slightly warmer conditions yield bolder, more assertive flavors. The choice of yeast strain also has a significant impact on the aromatic profile.

Secondary Fermentation

The primary mash is combined with the main ingredient -- steamed sweet potato, steamed barley, steamed rice, brown sugar, or another base material -- plus additional water, and fermented for another 8 to 14 days. The koji enzymes continue to convert starches into sugars, while the yeast drives alcoholic fermentation.

For sweet potato shochu, the potatoes must be used immediately after harvest because they spoil quickly. Distillers time their production to coincide with the potato harvest season from August through December -- a tradition known as "seasonal potato brewing."

By the end of secondary fermentation, the mash reaches an alcohol content of roughly 14 to 18%. This two-stage fermentation is a technique unique to Japanese shochu production.

Distillation

The fermented mash is loaded into a pot still, heated to vaporize the alcohol and aromatic compounds, then cooled back into liquid form. Honkaku shochu must always be distilled in a pot still (a column still would make it korui shochu instead).

Atmospheric vs. Vacuum Distillation

Atmospheric distillation is the traditional method. The higher temperatures extract higher-boiling-point compounds like fusel oils, giving the spirit a bold, ingredient-forward character. Vacuum distillation was introduced to the industry in the 1970s by barley shochu producers in Oita Prefecture. By reducing the boiling point, it minimizes the extraction of heavier compounds, producing a cleaner, more approachable spirit.

The raw spirit straight off the still typically runs between 36 and 44% ABV. Most producers then dilute with water to reach the standard 25% (or 20%) before bottling.

Aging & Storage

Freshly distilled shochu is rarely bottled immediately. It rests for a period -- from months to years -- to let the flavors settle and integrate. The choice of aging vessel has a major influence on the final character.

Kame (Clay Pot) Storage

The traditional aging method, particularly in Kagoshima and Okinawa. The porous ceramic walls of the kame allow trace amounts of air exchange, promoting gentle oxidation. Over time, the spirit becomes smoother and gains subtle mineral nuances from the clay. This method produces a distinctly mellow, rounded character.

Barrel Aging

Aging in oak casks -- sherry barrels, bourbon barrels, brandy barrels, and others -- imparts an amber color and layers of vanilla, caramel, and spice. However, Japanese liquor tax law limits how dark a shochu can be while still being labeled "shochu." If the color from barrel aging exceeds certain thresholds, the product may need to be labeled as "spirits" instead.

Tank Storage

The most common method. Stainless steel or enamel-lined tanks are highly sealed, minimizing outside influence. The spirit retains its original character while the harshness of fresh distillate gradually softens.