Sake Production Process

Sake is made from simple ingredients: rice, water, and koji (rice malt), yet the production process is highly complex, with many factors that influence its quality and flavor. Each step requires extensive experience, skill, and meticulous control. Here, we examine the stages of sake production in detail.

1.Rice Polishing

The production of sake begins with rice polishing. Sake is made with special “sake-brewing rice,” characterized by a large starch core (shinpaku) and low protein and fat content. During the rice polishing process, the outer layers of the rice, which contain proteins and fats that contribute to off-flavors, are removed to create a clean, refined taste.

The rice polishing ratio indicates how much of the rice grain remains. For instance, a ratio of 50% means that half of the rice has been milled away, leaving only the center. The lower the ratio, the higher the quality, as it removes more unwanted components. However, this also increases production costs and time.

2.Washing and Soaking

Once polished, the rice undergoes washing and soaking. Washing removes rice bran residue, while soaking allows the rice to absorb the right amount of water for fermentation. The duration of soaking is finely controlled down to the second, depending on the rice variety, polishing ratio, and ambient temperature. This precision helps ensure consistent quality in the final product.

3.Steaming

After washing and soaking, the rice is steamed. Steamed rice becomes gelatinized, making it easier for koji mold and yeast to act. Ideally, the steamed rice should be firm on the outside and soft on the inside, a balance known as gaiko-nainan (hard exterior, soft interior). This texture allows optimal enzymatic activity, which influences the quality of the sake.

The steamed rice is then cooled to different temperatures depending on its purpose: around 30°C for koji, 15–20°C for yeast starter, and 10–15°C for the main mash. This cooling is critical for controlling flavor and texture.

4.Koji Making

Koji making, a key step in sake brewing, is said to be the foundation of quality in sake production. Steamed rice is inoculated with koji mold in a controlled koji room, where it ferments for about 48 hours. During this process, the mold produces enzymes that convert rice starch into glucose, essential for fermentation.

These enzymes also break down proteins into amino acids, which add umami and complexity to the sake’s flavor. Koji making thus plays a crucial role in shaping the final taste of sake.

5.Yeast Starter (Shubo) Preparation

After koji is made, the next step is preparing the yeast starter, or shubo. The yeast starter is a mixture of koji, steamed rice, water, and yeast, designed to ensure smooth fermentation. Lactic acid is added to prevent the growth of undesirable bacteria, allowing the yeast to thrive.

There are two main types of shubo: quick-fermentation, which uses added lactic acid, and natural (kimoto) fermentation, which relies on naturally occurring lactic acid bacteria. Quick-fermentation shubo has a fresh flavor, while the kimoto method produces a richer, more complex taste.

6.Main Fermentation (Moromi) - Three-Step Addition

With the yeast starter ready, the main fermentation process, known as moromi, begins. Koji, steamed rice, and water are added to the shubo in three stages, a process called sandanjikomi (three-step brewing). This staged addition helps stabilize fermentation, prevent bacterial contamination, and achieve a high alcohol content.

The stages include:

Hatsu-zoe: The first addition of koji, steamed rice, and water.

Odori (Rest Day): The second day allows the yeast to proliferate.

Naka-zoe: The second addition of koji, rice, and water.

Tome-zoe: The final addition, completing the moromi mash.

This three-step process enables controlled fermentation, enriching aroma and flavor.

7.Moromi Fermentation - Multiple Parallel Fermentation

Sake fermentation involves a unique technique called multiple parallel fermentation. In moromi, koji enzymes convert starches into glucose (saccharification), while yeast simultaneously ferments the glucose into alcohol. This simultaneous reaction over about three weeks results in an alcohol content of around 17–18%.

For ginjo sake, low-temperature fermentation at around 10°C is maintained for nearly a month, which enhances fruity aromas, resulting in a delicate and fragrant sake.

8.Pressing (Joso)

After fermentation, the mash is pressed to separate the liquid sake from the solid sake lees. This process, known as joso, is typically done with a pressing machine, but high-quality sake may use the traditional fukurozuri method. In fukurozuri, the mash is placed in cloth bags and allowed to drip naturally under gravity, yielding a refined sake with minimal off-flavors.

9.Settling, Filtration, and Pasteurization

Freshly pressed sake contains tiny solids, known as ori, which are allowed to settle naturally. The clear liquid is then drawn off, followed by filtration to remove any remaining particles. While some sakes undergo active charcoal filtration for clarity, others are left unfiltered (muroka) to retain a more robust flavor.

The sake is then pasteurized at 60–65°C to halt enzymatic activity, making it stable for long-term storage.

10.Storage and Aging

After pasteurization, the sake is stored in tanks to mature, usually for a few months to a year. Aging allows the flavors to mellow, creating a smoother and more refined profile. Generally stored at 15–20°C, some ginjo and namazake (unpasteurized sake) are kept at lower temperatures to retain freshness. Long-aged sake, known as koshu, develops rich and complex flavors, offering a unique tasting experience.

11.Bottling and Final Pasteurization

After aging, the sake is bottled. For high-alcohol sakes, water may be added to adjust the alcohol content to around 15%. During bottling, quality checks are conducted to prevent contamination, and a second pasteurization may be applied to ensure stability. Finally, labels are added, and the sake is ready for distribution.

12.Flavor Differences Created by Production Techniques

The flavors and aromas of sake vary significantly depending on the production process. Fermentation temperature influences aroma, while the timing of pasteurization and aging length affects flavor smoothness. Additionally, the choice of koji mold, yeast strains, and steaming techniques all contribute to the unique characteristics of the final product.

Understanding these production methods offers deeper appreciation for the craftsmanship behind sake and its diverse and profound flavors.