Brewing quality sake requires a balance of science and artistry. The choices made during each phase of the brewing process impart unique flavors onto the final product.
Pre-Fermentation
Compared to table rice (the rice we eat), specialized sake rice varieties grow taller stalks and produce larger, heavier grains. Breweries select which rice to use based on the particular qualities they value- flavor, sustainability, or locality, for example. Some breweries, such as Izumibashi, even grow their own rice. In a future blog post, we’ll dive into the different varieties of sakamai (sake rice).
After being harvested, dry grains go through a process called seimai or “polishing.” Outer layers of bran, proteins and lipids are removed, which exposes the shinpaku, the center of the grain, where the starch is concentrated. This enhances the sake’s flavor and facilitates the growth of the koji mold necessary for fermentation. Learn more about this process here:
The next step in making sake is called senmai. Rice is rinsed to remove leftover powder from the polishing stage, then soaked in water until its weight increases by 30%. At that point, the rice has absorbed enough water to be ready for steaming.
The steaming process is called mushimai. Rice is put into a large metal steamer called a koshiki. Steaming the rice allows it to retain the moisture needed to successfully propagate koji.
After steaming, the seigiku or koji-making process occurs. In a separate room of the brewery called a koji muro, a portion of the rice is sprinkled with koji spores, then kept warm and humid as the koji continues to grow. Once the koji rice is ready, it’s spread into thin layers on trays and allowed to cool down.
Next, it’s time for shubo-zukuri, or starter-making. Called moto or shubo, which translates to “sake mother,” the job of the yeast starter is to propogate and sterilize yeast so it can ferment sugar into alcohol. There are multiple methods of making a moto. Today, the most common method is sokujo, where pure lactic acid is added to a mixture of yeast and koji rice. You can read about the different methods here:
Fermentation
After shubo-zukuri comes moromi-zukuri. In this step, the yeast starter is made into a moromi (mash) through the gradual addition of steamed rice, koji rice, and water. In a process called multiple parallel fermentation, koji breaks down rice starch into sugar, which is simultaneously fermented into alcohol by the yeast. Multiple parallel fermentation is unique to sake brewing. For the next 3-5 weeks, the temperature of the moromi is carefully monitored as it continues to ferment.
Post-Fermentation
When fermentation is complete, the finishing processes begin.
First, in a process called shibori, sake is pressed through a fine cloth to separate out the lees (rice solids).
After pressing, clear sake- but not nigori- goes through an additional sediment removal process called oribiki. Sake is put in a tank until any remaining lees settle to the bottom. The sake at the bottom of the this tank can then be bottled and sold as orizake/origarami.
At this point, most sake is pasteurized (hiire) to stop fermentation. Unpasteurized sake (nama) skips this step. Read more about pasteurization here:
Next, sake undergoes further filtration and clarification through the roka process. Activated charcoal is used during this step. Sake that forgoes the roka process is called muroka. If you want to try a muroka sake, Born Gold is a delicious option we carry.
Once the sake is filtered to the brewer’s satisfaction, it’s diluted with water to reach a specific alcohol content, usually 14-16% ABV. This dilution process is called kasui. Undiluted sake is called genshu.
Most sake undergoes a second pasteurization at this time, either before or after bottling. Some sake is specially aged, such as Taru (cedar barrel aged), Koshu (matured for a year or longer), and Hiyaoroshi (pasteurized once and aged for 6 months).
After all these finishing processes are complete, the sake is finally ready to be bottled, sold, and shipped out to sake-drinkers around the world.