Shochu is a Japanese distilled spirit made by fermenting a base ingredient (most commonly sweet potato, barley, or rice) with koji mold, then distilling the fermented mash in a pot still. The process follows a two-stage fermentation that takes roughly two weeks total, followed by distillation, aging, and dilution to a typical bottling strength of 25% ABV. While the steps share DNA with sake brewing and whisky production, shochu’s defining feature is its reliance on koji, a mold that converts starches into fermentable sugars and shapes the spirit’s final flavor.
Koji: The Engine of Shochu
Every batch of shochu begins with koji, a mold grown on steamed rice (or sometimes on the base grain itself). Koji serves two purposes: it breaks down starch into sugars that yeast can ferment, and it produces acids that protect the mash from spoilage. The type of koji mold a producer chooses has a direct effect on the spirit’s character.
Three species are used. White koji and black koji are the traditional shochu molds, and both secrete significant amounts of citric acid. That acid drops the pH of the mash low enough to prevent bacterial contamination during fermentation, which matters especially in the warm climates of southern Japan where most shochu is made. Black koji tends to produce earthier, more robust spirits, while white koji yields a softer, cleaner profile. Yellow koji, the same mold used for sake and miso, creates more delicate, aromatic results but generates less citric acid, making it trickier to work with in warmer conditions.
To make koji, steamed rice is spread on trays or tables in a warm, humid room and inoculated with spores. Over about 40 to 48 hours, the mold colonizes the rice, penetrating the grain and building up the enzymes needed for starch conversion. The finished koji looks like rice dusted with a fine, fragrant coating of mold.
First Fermentation: Building the Starter Mash
The first stage of fermentation, called ichiji moromi, is essentially a yeast starter. Koji rice, water, and yeast are combined in a tank and left to ferment for about a week. During this period, the koji enzymes steadily convert rice starch into sugar while the yeast consumes that sugar and produces alcohol. The citric acid from white or black koji keeps the environment acidic enough to ward off unwanted bacteria.
This starter mash is relatively small compared to the final batch. Its job is to build a strong, healthy yeast population that can handle the much larger volume of ingredients about to be added.
Second Fermentation: Adding the Main Ingredient
Once the starter is active and healthy, the main ingredient goes in. This is where shochu gets its identity. For sweet potato shochu (imo shochu), steamed and chopped sweet potatoes are added. For barley shochu (mugi shochu), steamed barley goes in. Rice shochu simply adds more steamed rice. Water is also added to adjust the consistency.
The traditional ratio for the secondary mash is roughly one part koji to two parts of the main grain or starch by weight. This second fermentation, called niji moromi, runs for about one to two more weeks. The combined mash is denser and more complex than the starter, and the flavor compounds that define each shochu style develop during this stage. Sweet potato mashes produce rich, earthy aromatics. Barley creates lighter, more neutral flavors. Rice yields a clean, slightly fruity character.
Distillation: Atmospheric vs. Vacuum
When fermentation is complete, the mash is distilled in a pot still, a single-pass distillation that distinguishes honkaku (authentic) shochu from cheaper, column-distilled alternatives. Producers choose between two methods, and the choice dramatically shapes the final spirit.
Atmospheric distillation runs the still at normal pressure and higher temperatures. The heat triggers chemical reactions between compounds in the mash, creating complex flavors. One example is furfural, a caramel-like compound produced when sugars in the mash react under acidic, high-heat conditions. The result is a fuller-bodied spirit with deeper, more layered aromas.
Vacuum distillation lowers the pressure inside the still so the mash boils at a lower temperature. Because less heat is applied, fewer of those chemical reactions occur, and more of the mash’s original fruity, delicate aromatics carry through into the distillate. Vacuum-distilled shochu tends to be lighter, cleaner, and easier to drink for people new to the spirit.
The spirit that comes off the still, called genshu, is undiluted and typically sits around 37 to 44% ABV.
Aging and Maturation
Fresh shochu straight from the still can taste rough and sharp. Aging mellows it. The maturation period generally ranges from one to three months, though some premium bottles rest for years.
The vessel matters. Stainless steel tanks are the most common choice and produce a neutral aging environment that lets the base ingredient’s character come through without adding new flavors. Clay pots, a traditional option, allow a tiny amount of air exchange that softens harsh edges and rounds out the spirit over time. Wooden barrels or casks add color and flavor compounds from the wood itself. Barley shochu aged in wooden casks can develop a character strongly reminiscent of single-malt whisky, with noticeable oak and caramel notes.
Blending and Bottling
After aging, the undiluted genshu is blended and diluted with water to reach the target alcohol level, typically around 25% ABV for the Japanese market. Some producers release undiluted genshu at higher proof for drinkers who want a more intense experience. The diluted spirit may be filtered to remove oils or haze before bottling.
Making Shochu at Home
If you’re interested in trying this yourself, the process is achievable on a small scale with some caveats. You can purchase koji spores online and grow koji on steamed rice in a warm, humid environment (a cooler or proofing box set to around 30°C works). Combine finished koji with water and brewing yeast to build your starter mash, ferment for a week, then add your steamed base ingredient at roughly a 1:2 koji-to-grain ratio and ferment for another one to two weeks.
Distillation is where legality comes in. In many countries, including the United States, distilling alcohol at home without a permit is illegal regardless of the quantity. In Japan, home distillation is also prohibited. If you’re in a jurisdiction that allows it, a simple pot still will get you a single-pass distillate. Let the spirit rest for at least a month before tasting, then dilute with clean water to your preferred strength.
The ingredient you choose for the second fermentation is the single biggest lever you have over flavor. Sweet potatoes create a rich, earthy spirit. Barley produces something lighter and more approachable. Rice sits in the middle, clean and slightly sweet. Experimenting with koji types (white for softness, black for depth) gives you a second layer of control.