Brewing saké is a time-honored craft dating back thousands of years. and yet, the practice continues to develop as new styles and technologies emerge, further refining the product. Saké today is as great as it has ever been. Here we have a general overview of the process a variety of styles go through, from husking the rice grain all the way to sealing the bottle cap.
STEP 1: Polish Saké Rice
Brewers set the foundation for saké grade and category first by selecting a polish or mill rate. Using a polishing machine, the batch rice is gently agitated for many hours and sometimes days. The movement grinds each grain against surrounding grains to strip away the outer layers of fat and protein which often create unwanted bitter flavors. Polish/Mill rate is measured based on the percentage of each grain that remains. The lower the percentage, the higher the grade. By law, ultra-premium daiginjo grade saké must be milled to a minimum of 50%, meaning at least half of the grain is milled away.
As you will find reading on, a saké's position as a premium or high quality product does not rest upon any singular metric and many choices such as polish rate simply contribute to achieving a desired style. There are many premium saké that begin with rice milled above 60%. When considering different saké, it is important not to draw conclusions based on singular metrics.
Fun Fact: Saké brewers use batch weight to determine how much of the grain has been milled away. Thus, a 2,000lb batch of un-milled rice will weigh 1,200lbs (40% less) after milling if the brewer is set to achieve a 60% ginjo-style polish.
STEP 2: Wash, Steep, Steam and Cool Polished Rice
After milling, rice is transferred to a holding tank where the heat created by the friction can dissipate before the rice is rinsed. It is important to cool the rice as a sharp change in temperature can cause the grains to break. Rinsing removes any dust created by milling before the grains are transitioned to a steeping tank. Depending on the type of saké rice and the brewer's intentions, moisture level is increased for a period of time by steeping.
After the rice has absorbed an ideal amount of moisture it is then steamed. In most cases, an industrial grade steamer forces hot steam through vents and completes this step within just an hour. From there, steamed rice is then gently cooled and prepared to accept the koji mold.
STEP 3: Koji Mold Cultivation
Cultivating the koji mold occurs over the course of about 48 hours. Once the steamed rice is brought down to the target temperature, it is then spread evenly across a large shallow bed. Koji mold spores in either a powder or granulated form are shaken down atop the bed of rice as evenly as possible. The next step is to mound and bundle the inoculated rice beneath layers of blankets for 8-12 hours to retain warmth and moisture so the mold has an ideal growing environment. Brewers monitor and manage temperature closely during this time as mold growth naturally creates heat.
At hours 10-12, brewers will uncover and break apart the rice mound to rid of heat spots and re-distribute the koji rice evenly across the bed. The warm temperature and humidity of the koji room promotes additional mold growth for the next 8-12 hours. For the next 7-10 hours, it is the brewer's arduous task to execute an appropriate method of managing the thoroughness and distribution of the mold growth to achieve the perfect mold pattern for their target style.
Between hours 30-38 the koji rice temperature will fluctuate beginning with a cooling from roughly 95F to 92F. Naturally the temperature will rise again to peak around 100F and the grains are gradually spread thinner to cover more surface area to both manage the mold growth and gently dry the grains of rice. When performed properly, the moisture levels of the grains will draw the mold growth inward towards the center and not just the outside.
When the brewer is satisfied with the mold coverage and penetration, they stop the koji growth by cooling the batch to the ambient temperature of the brewery. Roughly two days later, steamed rice has become brew-ready koji rice and yeast can finally be introduced to the process.
Fun Fact: Cedar rooms are often used during koji cultivation for their aromatic, humidity controlling and antimicrobial properties.
STEP 4: Moto Yeast Starter
For the first time, all four of the main saké ingredients (rice, water, koji and yeast) come together to nurture a dense yeast culture.
The starter - also known as moto - plays an integral role in generating a concentrated population of fermentation yeast to drive the main fermentation. A multi-stage step, yeast cultivation begins in a small tank with a relatively high proportion of koji to kick start the starch to sugar conversion. Temperature regulation controls the pace of yeast growth so it does not feed on the sugars faster than the koji can create them.
Fun Fact: There are a vast array of yeasts that can be used singularly or mixed to deliver flavor characteristics such as varied ranges of acidity, earthiness, aroma, fruitiness and mouth feel.
STEP 5: Fermentation
Bringing the main fermentation to size occurs over four days. On day one, the moto is transitioned to the larger tank along with additional water, koji and steamed rice. The total volume should be around 1/6 of the final target amount and temperatures remain relatively warm at 54-59F so the yeast can comfortably grow.
On the second day, the yeast does all of the work as all additions and tinkering from brewers are generally held off until day three. This allows the yeast population time to build.
Day three sees the previously added amounts of water, koji and steamed rice doubled. This brings the total volume up to half of the final target amount. After 24 hours, the final addition is made and the current amount is once again doubled to reach the targeted total amount. At this time, temperatures are generally lowered to between 43-50F. Adding a portion of the water as ice is one method brewers will use to drop the temperature relatively quickly.
Depending on the style, fermentation can take between 21 to 35 days. The colder the temperature, the longer the fermentation but the payoff can be a wonderfully delicate ginjo or daiginjo style sakée with clean aromas and fruity/floral flavors.
Fun Fact: Saké brewing is a parallel fermentation. Koji enzymes convert rice starch to fermentable sugar and at the same time, yeast is fermenting the sugar into alcohol. It is imperative to keep these in balance or risk ruining the batch.
STEP 6: Pressing/Filtration
After three to five weeks of fermentation, it is time to remove the unwanted solids and sediments using one of a variety of pressing or filtration methods. For creamy and cloudy nigori style saké, coarse filtering is used to retain a portion of the rich and sweet sediments and solids. For clear styles, much finer filters are used and the saké is passed through multiple times. SakéOne uses a modern Yabuta press to accomplish crystal clear junmai ginjo style saké.
Fun Fact: By law, saké cannot technically be called saké until it has been pressed. Thus, there is no such thing as unpressed saké.
STEP 7: Pasteurization (Optional)
At this point, the brewing process can take a number of different branching paths including going directly to bottle. After the saké has been pressed, it is a nama genshu meaning it is both unpasteurized and undiluted. These styles contain the most vibrant flavor and a higher alcohol by volume (abv) content of around 18-20%. For what is gained in added flavor and alcohol content, storage flexibility and shelf-life are negatively impacted as nama saké must be cold stored at all times and must be enjoyed within a few months of bottling before becoming flawed.
However, most saké from low-grade table saké to ultra-premium is pasteurized at least once if not twice. A great many breweries pasteurize after filtration as it completely stops fermentation and inhibits spoiling. Pasteurization happens when the saké is heated to 140-149F and it then it is stable enough to be stored at room temperature in a tank or on a shelf in a bottle for much longer.
Fun Fact: Nama saké - aka 'namazake' - is often times an ultra-flavorful unpasteurized version of a pre-existing style. The difference can be so striking it's hard to recognize its lineage.
Step 8: Maturation (Optional)
After an initial pasteurization, many saké are transferred into large tanks where they will mature anywhere between 3 months to a year depending on the style. This allows the beverage to rest and balance out the flavors. Brewers mature saké in a variety of vessels and ways such as sugidama style where the saké is matured outdoors in a large cedar ball and the indication of readiness is the coloration of the moss that grows upon it. Generally, stainless steel tanks are used and brewers use temperature to guide how the saké develops. Fruity/floral styles will be aged at a colder temperature for shorter durations whereas saké with an umami profile tends to be longer at a higher temperature.
We should note that unpasteurized saké such as nama-chozo may also be matured for long durations.
Fun Fact: Aged saké or 'koshu' is extremely rare and may actually be a happy mistake resulting from when a brewery unintentionally leaves a batch in maturation for a long time but its journey has resulted in a pleasant flavor. Although unregulated, most saké labeled koshu has matured for at least two years.
STEP 9: Blend/Dilute (Optional)
As described earlier, whether pasteurized and/or stored for maturation, the saké is a genshu style to this point. Many brewers consider the 17-20% alcohol by volume level to be too high for the profile they're striving to achieve so they use water to hone in on flavor and reduce the alcohol content to generally around 15-16%. Dilution is not considered a sign of quality reduction.
This is also the brewing stage where a master brewer might use brewer's alcohol or proprietary flavorings to create their own refined style such as a honjozo or a specialty beverage such as an Asian pear infused saké. Like water dilution, adding brewer's alcohol is not considered an indicator of lower quality.
STEP 10: Bottling
There is one more optional step before bottling as some breweries choose to filter and/or pasteurize saké one final time as it transfers to the bottle.
There are a variety of shapes, sizes and colors of bottles. UV coated black, blue, brown and dark green bottles are common as they limit the negative effects of light.