How to Make Sweet Doburoku | The Three-Stage Fermentation Technique and the Secret of Adding Steamed Rice Practiced by Sake Breweries

When you hear "doburoku," many people might picture a "sour, rustic drink."

However, sweet doburoku carefully brewed by a sake brewery transforms into an exquisite drink with a mellow, natural sweetness and the rich flavor of rice itself.

In this article, we will explain the traditional techniques that sake breweries employ to produce sweet doburoku, particularly the "three-stage brewing" method and how adding steamed rice during brewing enhances sweetness, from the perspective of a craft beverage brewer.

What is Doburoku? | The Difference from Nigori Sake

Doburoku is a traditional Japanese brewed alcoholic beverage, made from rice, rice koji, and water, which undergoes fermentation without a filtration process. While Japanese sake (seishu) always undergoes the "pressing of the moromi" (fermentation mash) stage, doburoku is bottled with the rice grains and koji's umami components intact, without pressing.

It is sometimes confused with "nigori sake," but nigori sake is coarsely filtered seishu and is classified as seishu under the Liquor Tax Act.

Doburoku, on the other hand, is classified as "other brewed alcoholic beverages," and its brewing license is also separate. Both are distinctly different beverages both legally and in terms of production methods.

Doburoku, which has gained attention as a craft brewed beverage in recent years, sees small-scale breweries producing unique products with their own recipes, significantly expanding the choices available to consumers.

 

Where Does Doburoku's Sweetness Come From?

To understand how sweet doburoku is made, one must first understand the mechanism of fermentation.

Within the moromi of doburoku, two reactions proceed simultaneously.

One is "saccharification," where enzymes produced by koji mold break down rice starch into glucose. The other is "alcoholic fermentation," where yeast breaks down that glucose to produce alcohol and carbon dioxide.

This parallel multiple fermentation, where these two processes proceed simultaneously, is the greatest characteristic of Japanese sake and doburoku.

In other words, the sweetness of doburoku is determined by a state where "the speed of saccharification exceeds that of alcoholic fermentation."

If saccharification proceeds quickly, sugars remain, resulting in sweet doburoku. Conversely, if fermentation becomes too active, sugars are rapidly converted into alcohol, leading to a dry finish.

To produce sweet doburoku, the technique of intentionally controlling this balance between saccharification and fermentation is required.

 

What is the "Three-Stage Brewing" Practiced by Sake Breweries?

A key factor in producing sweet doburoku is the traditional technique of "three-stage brewing," also used in sake production.

Three-stage brewing refers to the method of adding steamed rice, koji, and water, which are the raw ingredients, to the shubo (starter mash) in three separate stages over four days.

Specifically, it proceeds in the following steps:

• Hatsuzoe (First Addition) This is the process of adding the initial steamed rice, koji, and water to the shubo, which is the starting point of fermentation. At this stage, the goal is to prepare the fermentation environment and thoroughly multiply the yeast.
• Nakazoe (Middle Addition) This is the second addition, performed the day after the "odori" (rest day) that follows hatsuzoe. The amount of raw ingredients is increased to expand the scale of the moromi.
• Tomezoe (Final Addition) This is the third and final addition. A larger amount of steamed rice, koji, and water is added to complete the moromi.

The reason for adding ingredients incrementally in this way is that introducing a large amount of rice all at once carries the risk of diluting the yeast and making it susceptible to contamination by unwanted bacteria.

It can be said that the wisdom of sake breweries lies in gradually nurturing the scale of the moromi while maintaining a stable fermentation environment through three-stage brewing.

 

Will it get sweeter if we add "four" or "five" stages?

In theory, if you don't stop at three stages of brewing and continue to add steamed rice in four or five stages, the amount of glucose produced by saccharification will further increase, making the doburoku progressively sweeter.

One might be tempted to think, "Then why not add a lot of rice from the start to make a supremely sweet doburoku?"

However, in actual production, it's not that simple.

As more steamed rice is added, alcoholic fermentation proceeds in parallel with saccharification, and the alcohol content of the moromi increases.

Beyond a certain point, the yeast itself cannot withstand the alcohol it has produced and ceases activity.

If the yeast dies, fermentation itself stops, and the environment that supports saccharification by koji enzymes is also lost.

As a result, the added steamed rice remains undissolved in grain form, and the outcome is a failed product resembling "sweet, alcoholic porridge with chunky rice grains."

This would not be viable as a commercial product.

That's why sake breweries rarely perform more than three stages of brewing. Instead, they primarily use three-stage brewing and then, while carefully monitoring the condition of the moromi,add small amounts of steamed rice at exquisite timings to balance both sweetness and fermentation.

Sweet doburoku is born not from "addition" but from the skill of "assessment."

 

The Key to Sweet Doburoku: Adding Steamed Rice During Brewing

 

Here's the main point. The biggest secret to how sake breweries produce "sweet doburoku" isadding additional steamed rice to the moromi in the latter half of brewing, or after the tomezoe is complete.

Doburoku produced with standard three-stage brewing tends to be drier because the yeast is highly active. However, when steamed rice is added a few days after tomezoe, the following changes occur:

1. Saccharification is reactivated. The starch in the newly added steamed rice is broken down by the koji-derived enzymes in the moromi, causing a rapid increase in glucose.
2. Alcohol concentration inhibits yeast. The moromi in the latter half of brewing already has a relatively high alcohol concentration. Therefore, fermentation slows down before all the additional sugar is converted into alcohol, leaving residual sugar.
3. The umami of rice comes to the forefront. Amino acids and umami components dissolving from the added steamed rice combine with the sweetness to create a mellow flavor.

This technique results in a sweet doburoku that draws out the natural sweetness of the rice itself, without relying on artificial sweeteners or added sugars. This is truly a testament to the brewer's skill.

 

Timing and Quantity of Steamed Rice Addition

The timing of steamed rice addition varies by brewery and recipe, but the following are general guidelines:

• Early addition (2-3 days after tomezoe): For a gentle sweetness and overall balance.

• Late addition (when fermentation has settled): To decidedly lean towards a sweeter profile.

• Multiple additions: To create complex flavors and a lingering finish.

The typical amount of steamed rice to add is usually around 10-20% of the total rice used up to tomezoe.

Adding too much can lead to undigested starch if saccharification cannot keep up, resulting in off-flavors, so it's crucial to observe the moromi's condition and adjust accordingly.

Furthermore, temperature control of the added steamed rice is also important.

Overly hot steamed rice can rapidly raise the moromi temperature, damaging the yeast, while excessively cold steamed rice can delay the onset of saccharification.

Brewers assess the condition and temperature of the moromi to choose the perfect timing for adding the steamed rice.

 

The Potential of Sweet Doburoku as a Craft Brewed Beverage

For breweries holding a "miscellaneous brewed alcoholic beverage" license, sweet doburoku represents a significant asset.

In the world of craft brewed beverages, there is a growing emphasis on "drinkability," "compatibility with food," and "sweetness that even beginners to Japanese sake can enjoy."

Sweet doburoku, with its accessible style, can attract new fans, including those unfamiliar with sake and international customers.

Moreover, depending on the rice variety, koji type, yeast selection, and timing of steamed rice addition, an infinite array of variations can be created, ranging from fruity sweetness to rich, full-bodied sweetness.

This is precisely the allure of craft brewing and a way for small-scale sake breweries to express their unique character.

Sweet doburoku offers high versatility in how it can be enjoyed—as a dessert wine after meals, mixed with fruits for cocktails, or paired with various dishes—and holds the potential to open up new markets for craft brewed beverages.

 

Summary | Natural Sweetness Born from Traditional Techniques

Sweet doburoku is not made by adding sugars or sweeteners, but rather by the natural sweetness of rice itself, achieved through traditional techniques like three-stage brewing and the addition of steamed rice.

By utilizing the fermentation management wisdom cultivated by sake breweries over many years, a drink with a balanced aroma, sweetness, and umami is created.

As a craft brewed beverage, doburoku will continue to delight drinkers with its diverse flavors.

We encourage you to try the sweet doburoku carefully crafted by sake breweries and discover your own favorite.