How Japanese sake is made 

1. Polishing the rice
The desired element is the heart of the rice, which consists almost exclusively of starch, so the rice grains are first polished to remove their protective layer (the rice bran) and the surface layers where the vitamins, proteins and lipids reside. Although these surface layers are regularly praised in nutrition (whole grain rice), they produce “parasitic tastes” (zatsumi) during the making of sake, which is why we try to obtain a grain containing only the starch core. A minimum of polishing can be considered as trimming 10% of the basic rice grain.

2. Washing and cooking the rice
The rice is then washed and moistened – a very controlled process, as the more the rice has been polished, the faster it absorbs water –, before being steamed for 1 hour in large tubs.

3. Making koji
The koji is the ferment that will be used to start the fermentation of the rice. Essentially made up of starch, rice cannot ferment on its own and must first be broken down by the process of saccharification (literally “turning into sugar”), a process well known to Europeans, since this is what happens when our saliva breaks down the starch in bread and makes it so delicious! This role of saliva is even one of the oldest methods of making sake (called kuchikamizake, literally “chewed sake”): a virgin woman would chew the rice and spit it into a vat, thus starting the fermentation of the rice that would then be used to make the divine beverage (sake was originally used as an offering to the gods). Such a kuchikamizake ceremony is featured in the animated film “Your Name” by Makoto Shinkai.

In order to create the koji, part of the cooked rice is sprinkled with fungal spores called koji-kin (“koji microbe”) and left to stand for 24 hours at a controlled temperature of between 28°C and 36°C, after which this first rice is divided into boxes called tana, stacked and covered, but evenly spaced so that the temperature of the whole production can be better controlled

4. Addition of yeast and fermentation
Once the koji has transformed the rice starch into glucose, yeast is added to transform this glucose into alcohol, which is the principle of alcoholic fermentation. This fermentation takes place in large vats and can last from 10 days to 7 weeks, depending on the process used by the sake brewery, including the choice of fermentation temperature (low temperature fermentation obviously takes longer).

5. Pressing, optional steps, bottling
At the end of fermentation, the sake is pressed to separate the clear liquid from the solid sake lees (kasu), which will then be used in cooking or cosmetics.
After resting for a few days, this new clear sake is usually filtered through a layer of charcoal to make it even clearer. Sake that does not undergo this filtration is called “muroka”.
Next comes the pasteurisation stage: in the tank, after bottling, or not at all! Pasteurisation allows for better preservation and also prevents a second fermentation after bottling. Some brewers, however, decide not to pasteurise their sake (or part of their production). These unpasteurised sakes, called “namazake“, are therefore more fragile and must be kept cool and consumed quickly.

6. Maturation
After pasteurisation, the sakes are left to rest for a period ranging from 3 months to several years in order to allow them to mature: this is often referred to as the “mellowness” that comes from long maturation.

7. Lowering alcohol
Finally, a little spring water is added to lower the alcohol content of the sake. Sake without added water are labelled “genshu” and are therefore often higher in alcohol.

Video explanation of sake making courtesy of Rodolphe Miez :

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