Japan Sake and Shochu Makers Association | JSS

Professional Sake Brewing Processes and Flavor

The sake brewing process takes about two months. After brewing, sake matures for half a year to a year before brewers ship the final product. Each step of the brewing process is carefully managed and affects the resulting characteristics of the sake.

Rice Preparation

Selection of Rice Variety

There are approximately 900 rice varieties of which over 100 are sake rice in Japan. About 40% of the rice used in sake production is sake rice. When compared to table rice, sake rice is larger in grain size, low in protein, and has a porous core. The white, porous structure in the core, or shimpaku, is made of granules of starch and ideal for cultivating koji-fungi. There are some widely used strains and regional specialties for sake rice, each with subtle yet unique flavor attributes and harvesting seasons. For example, the yamada-nishiki strain tends to brew into a well-balanced, flavorful sake, while gohyakumangoku brews into a lighter flavored drink. Brewers may choose specific strains based on their flavor design and/or the harvesting season.

For more details, find more details on the FACT Ingredients page.

Rice Polishing

The first step to brewing sake is polishing away the outer layers of rice. Rice polishing in sake production is more than just simply taking off the grain’s bran and removing germs. The outer layers of rice grains contain fats, minerals, and proteins that tend to create bolder flavors. Therefore, the flavor design of the sake is influenced by the amount removed. Highly polished rice tends to result in a light, delicate-flavored sake. On the other hand, less polished rice turns into a fuller-bodied sake.

Polishing Rate

The rice polishing rate can be one of the indicators of the weight of sake taste. Usually, polishing mills around 30% of the grain’s outer portion away. This leaves 70% of the original grain behind for brewing. In this case, the polishing rate is 70%. Therefore, the more the rice is polished, the lower the numerical value of the polishing rate is.

Sake is divided into 2 sections - "special designated sake" and "futsu-shu", meaning normal sake. While there is no polishing rate requirement for futsu-shu, most of the special designation categories have to adhere to the following polishing rate brackets. The only exception is junmai-shu, which is a special designation without a polishing rate requirement.

For some specially designated sakes, there are minimum requirements for the rice polishing rate as follows;

Rice Polishing Rate Requirements for Specially Designated Sakes

Specially Designated Sakes Rice Polishing Rate
Daiginjo-shu / Junmai daiginjo-shu ≦50%
Ginjo-shu / Junmai ginjo-shu ≦60%
Tokubetsu junmai-shu ≦60% (or special process)
Tokubetsu honjozo-shu ≦60% (or special process)
Honjozo-shu ≦70%

Washing, Steeping, Steaming

After polishing, the rice is thoroughly rinsed with water, and then left steeping in water to absorb about 30% of its weight. After removing the water from it, brewers steam the rice for about one hour in a big steaming vessel called a koshiki. Unlike boiling, steaming allows the rice to cook evenly without getting too moist or sticky. During steaming, the rice absorbs approximately a further 10% of water. The control of the water content in rice is important for the subsequent brewing process. After the rice has cooled down, it is ready for making koji, shubo (mother culture), and the mash.

Is the Rice Polishing Rate
an Indicator for Quality?

The price of sake usually increases as the polishing rate decreases. Many people believe sake made with highly polished rice, such as daiginjo and ginjo, are "better" because of a higher price. However, this is not always true. The sake price increases because polishing rice reduces the amount of grain available for brewing. When polishing removes a percentage of the outer grain, the yield of sake goes down by just as much. Therefore, sake experts regard the polishing rate as an indicator of the sake profile and not necessarily for its quality.

Koji Making

Koji in Sake Making

The use of koji is one of the most unique processes of making sake. The enzymes in koji help break down rice starch into sugar, and protein into amino acid. Koji also provides vitamins for the yeast during fermentation. Koji used in sake brewing refers to steamed rice with koji-fungus (Aspergillus oryzae) cultivated on it. The rice used to make koji, called koji mai, makes up around 20% of the total weight of polished rice used for making sake.

Koji Making Processes

The first step of making koji involves sprinkling the spores of koji-fungus, or tane koji, over cooled steamed rice and mixing thoroughly. The spores germinate on the rice and spread filaments over the surface and inside the grain. Approximately two days later, the fungi will cover the grain, and the koji is ready. The completed koji is full of enzymes and nutrients for the yeast.

Temperature Control is Important
The koji making process occurs in a special room in a brewery called koji muro. The room temperature is maintained at around 30°C and a humidity of 50-80%. The koji-fungus grows best at around 36℃ but becomes inactive above 45℃. Therefore, careful control of the temperature is crucial.

Two Styles of Koji

There are two types of koji: sohaze and tsukihaze. Each type is made carefully and in a controlled environment. Many call this the most crucial part of making sake as the amount of fungal spores, water content of the rice and temperature greatly influence the final product. The sohaze-style koji has fungi grown all over the grain, producing plenty of diastatic enzymes and vitamins. Also, it is highly effective at breaking down rice and results in a robust fermentation, producing sake with a strong body. On the other hand, for the tsukihaze-style koji, the fungus grows in spots on the grain. The enzymatic activity is moderate, but poor in vitamin and fatty acid content. The fermentation isn’t as active and produces light-flavored sake. Ginjo and daiginjo sake are produced with tsukihaze-style koji.

Fermentation

Selection of Yeast

The type of yeast used for brewing affects the resulting flavor and aroma of the sake. Historically, brewers had to rely on the wild yeast available in their own brewery. However, most yeasts used today come from the Brewing Society of Japan. This yeast, called kyokai-kobo, is originally isolated from different breweries across the country and cultured for distribution. There is a variety of yeasts available and are numbered to indicate the difference, with the most widely used being 6, 7, 9, and 10. More recently, brewers have begun utilizing high ester producing yeast developed by the Brewing Society or other brewing laboratories.

Mother Culture (shubo)

Before the main fermentation, brewers must prepare the mother culture, or shubo. By mixing steamed rice, koji, yeast, and water together, a relatively small portion of mash becomes home to an active yeast cultivation. This then becomes the starter for the fermentation process in the main mash.

Shubo Needs to be Acidic

It is important to keep the shubo acidic to prevent the growth of unwanted microbes. The sake mash, however, is naturally low in acidity. Historically, the method used to raise the acidity level is to grow lactic acid bacilli in the shubo itself. Another newer method involves adding lactic acid directly. As the acidity and alcohol in the mother culture increases, many of the microbes die off, leaving the surviving yeast. How the lactic acid enters the mash also affects the sake's flavor.

Kimoto / Yamahai-moto

The traditional way to acquire acidity is to cultivate natural lactic acid bacilli. This type of shubo is called kimoto or yamahai-moto, which is also usually indicated on the sake label. These bacilli exist in koji or in the wooden tools and tubs. Therefore, brewers first mix steamed rice, koji, and water at around 8°C and gradually increase the temperature to cultivate them for about two weeks. When the mixture reaches a significant level of acidity, brewers add the yeast to start the alcoholic fermentation. Another two weeks later, the acidity and alcohol kill the majority of the microbes except for the yeast. This type of shubo makes sake with a strong body and complex flavor.

Sokujo-moto

The main method of boosting the acidity in shubo today is to add lactic acid. This produces a type of shubo called sokujo-moto. It is a relatively new technique, invented in the early 1900s. It facilitates the shubo making by eliminating the traditional process of growing lactic acid bacilli. This way, the time needed to complete the shubo shrinks down to 2 weeks from 4 weeks. The resulting sake tends to taste lighter than the sake made with traditional style shubo.

Characteristics of Kimoto/Yamahai-moto and Sokujo-moto

Kimoto / Yamahai Sokujo
Source of acidity (Wild) lactic acid bacilli Ready-made lactic acid
Duration to prepare 4 weeks 2 weeks
Label description Kimoto / Yamahai Others
Flavor profile Strong body and complex flavors Light and delicate

Main Mash (moromi)

3-Step Fermentation
The fermentation process in sake brewing usually consists of three successive steps, known as sandan jikomi in Japanese. In the first step, a mix of shubo (source of yeast), steamed rice, koji, and water sit in a tank and ferment over a day. Then, brewers add a batch of steamed rice, koji, and water two more times to gradually increase the fermenting mash volume. Through this process, the growth of yeast to mash is well balanced and the active fermentation produces enough alcohol in the mash to prevent any microbial contamination. During the fermentation processes, the mash temperature stays between 8℃ to 18℃. These three steps occur over a period of three to four weeks.

Saccharification and Alcoholic Fermentation
In sake mash, two processes take place at the same time; koji’s diastatic enzymes break down rice starch into sugar, and the yeast ferments the sugar into alcohol. Sake mash is very dense and the ratio of water compared to the polished rice is roughly 1.3. If all the rice starch changes to sugar at once, the extract shows about 35 g/L, which is too high for yeast to thrive. However, since the sugar is fermented into alcohol as it gets produced, the mash's sugar concentration stays at an ideal level. Therefore, these parallel processes, together with the 3-step fermentation, actively support an efficient fermentation activity, producing a 17 to 20% alcoholic content by the end.

Addition of Neutral Spirits
At the last stage of the fermentation process, brewers are allowed to add a small amount of neutral spirits, or jozo-alcohol in Japanese, to the mash. By doing so, the spirits extract the aromatic components, especially esters, and dilutes the acidity and amino acids to make the flavor lighter. The resulting sake tends to be smooth and easy to drink. Neutral spirits are made from molasses and/or grains and diluted to about 30% alcohol before addition. For specially designated sakes (ginjo, daiginjo, honjozo, and tokubetsu honjozo), the amount of its use is limited to less than 10% of the polished rice weight used for brewing. Junmai is the only type of sake that has no addition of neutral spirits. Therefore, any sake in the junmai category is free of neutral spirits.

Low Temperature Fermentation

When the fermentation process occurs below 12℃, the resulting sake becomes fruity and light. Under low temperatures, the enzymatic activity of the koji and activity of the yeast slow down. As a result, a light sake with little acidity and sweetness is created. Due to the slowing of the fermentation, the process takes about one week longer to complete. In addition, compounds such as isoamyl acetate and ethyl caproate, get trapped in the mash under a low temperature. This gives the resulting sake a fruity aroma. Sake like ginjo and daiginjo go through this fermentation process.

Post-Fermentation Processes

Filtration

When fermentation is complete, the mash is filtered to separate the liquid from the solids. There are 3 ways this can be done. The first, and modern method consists of using a horizontal filtration machine (similar to beer mash filtration). The second method involves brewers placing the mash into cloth bags and then pressing vertically. The third method, fukurodori involves letting the residual liquid drip from hanging cloth bags instead of pressing the mash. Sake filtered with this method tends to taste more delicate.

Specific Portions of Sake During Filtration

How brewers categorize the filtered liquid depends on when it was extracted during the filtration process. This is generally done in 3 parts, the abarashiri refers to liquid extracted during the first portion, nakadori refers to the middle, and seme refers to the last portion. These portions are usually mixed, but in some cases bottled separately to enjoy the different characteristics that came from the same tank.

Filtration with Coarse Mesh

Coarse mesh allows some solids of the mash to come through in the filtration. The resulting sake is a cloudy nigori with different degrees of turbidity based on the tightness of the mesh. The texture of nigori is thicker and creamier than standard sake, usually with a sweeter taste.

Sake Lees

The filtration process produces solid remnants of undissolved rice and yeast known as sake lees (cake) or sake kasu in Japanese. Sake lees has roughly 8% alcohol content by weight. It is very nutritious and sold for eating, cooking, and pickling. It is also used as an ingredient for shochu. Some bigger breweries have also started to incorporate it into beauty products.

Post-Filtration Processes

Sedimentation

The first filtration process takes away most of the solids, but the resulting liquid is still slightly cloudy. To clear the turbidity, the filtered liquid undergoes a sedimentation process, called orisage in Japanese. After filtering, the liquid sits at a low temperature over time, allowing the precipitants to sink. Brewers then remove the clear liquid and transfer it to another tank, a process called oribiki in Japanese. Alternately, high-performance filters may be used to shorten the time to bottling.

Secondary Filtration

There are a couple of types of secondary filtration after sedimentation. First is the use of persimmon tannin or colloidal silica to remove excess proteins that could precipitate during storage and cause turbidity. Second is the use of active charcoal to remove color and adjust the flavoring, stabilizing the quality during storage. Sake that does not undergo these secondary filtration processes, called muroka, tends to have fuller flavors.

Adjustment

The alcoholic content of sake up to this stage is usually high, around 17% to 20%. However, this can be slightly too strong when it comes to enjoying it with meals. Therefore, in most cases, the brewers add water to adjust the alcohol content down to around 15%. Nevertheless, brewers still sell some undiluted sake, called genshu.

Pasteurization

After sedimentation and secondary filtration, most sake undergoes pasteurization. The sake is heated to approximately 60℃ to 65℃ to sterilize and deactivate enzymes. Without pasteurization, diastatic enzymes make the sake sweeter while oxidizing enzymes change the aroma. Brewers usually pasteurize sake again during bottling to ensure sterilization. However, improved distribution and storage facilities have allowed brewers to safely sell unpasteurized sake. This sake, called namazake, has a fresh, vibrant flavor that makes it increasingly popular in recent years.

Maturation

Pasteurization often alters the aroma of sake and causes an unrefined taste. Therefore, pasteurized sake usually ages for up to one year to settle the flavors. In most cases, sake brewing takes place during winter. Brewers then let it sit and age over summer before selling it the following autumn.

Professional Guide

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