Sake production is very complicated. (For a simple overview, click Production Process Flow Chart.) The process is somewhat similar to that of beer because of the inevitable use of enzymes for saccharification (converting from starch to glucose). However, there are several differences between beer, sake and wine production.
#1: Rice harvest
Several different rice varieties are used in sake production. Yamadanishiki is the most famous sake specific rice variety and harvest season commences mostly in October.
#2: Rice polishing
After harvesting, rice growers bring their rice to Japan Agricultural Co-operatives (JA). JA conducts inspection for the rice and assesses the rice quality and rates it. Rated rice is then brought to a polishing center and polished to the requirements of individual breweries. Sake breweries do not generally own or manage rice fields and rely on rice growers for the early parts of production.
Poloshing removes the outer part of rice, the proteins and oils of which would diminish the taste of sake. The polish ratio is determined by the how much of the inner part remains. If 30% of outer part of rice is removed, 70% remains, giving it a 70% polish ratio. This ratio is a deciding factor in the categories of sake.
#3: Rice washing and soaking
The process of washing and soaking sounds simple, but this very important processes is a major factor in the quality of the sake. Washing removes the rice bran which is produced when polishing, which would otherwise negatively affect the end flavor.
Soaking is one of the most nerve-wracking processes for brewers. The water absorption of rice decides the quality of the koji and even one second too long can be disastrous. That is why a lot of sake breweries use a stop watch to meticulously measure the process.
There are two purposes of steaming the rice.
Steamed rice is around 5000 time more easily saccharified than raw rice.In another words,saccharification of raw rice is just 0.02% of steamed rice.
Secondly, this process gives more moisture to rice, which is essential for the next step of sake production: koji
✔See Video: Rice Steaming
In the context of sake production, koji means the steamed rice propagated with koji fungus. These koji spores provide enzymes which convert starch into fermentable sugar(glucose).
Generally speaking, the quality of koji is the most important factor which decides the quality of sake.(For more details, click here.)
✔See Video:Koji production
At this stage, steamed rice and koji and water are mixed in a small container, then yeasts are added.
The koji enzymes break down the steamed rice starch to sugar, which is then converted to alcohol by yeasts.
As this occurs, the yeast multiplies.
Since sake can easily be spoiled by micro-organisms, this starter is maintained in a yeast-rich environment for 14 days to a month, to provide resistance against spoilage.
When the starter is ready, the liquid is removed to a bigger tank and added water and steamed rice and also koji as well.
Again, glucose is converted from starch by enzymes. Yeast converts glucose to alcohol at the same time. Normally this process continues for four days with three same works.
Yeast cannot survive in a high sugar environment and are not well resistant against the alcohol they produce.
Thanks to this three stage addition, yeasts can get used to the higher sugar and alcohol environment, they can propagate and produce alcohol.
This process is unique because fermentation and saccharification is carried out parallel.
That is why the production method of sake is called “Multiple parallel fermentation”compared to wine’s single fermentation.After three-stage addition, fermentation is carried out for about 24-31days.
If sake is in the non-jyunmai(rice with spirits)category,distilled alcohol is added before pressing.
There are several ways to press sake. One of the most common methods, ‘Yabuta’, is named after a company which produces pressing machines. Pressing takes about two days for filling the Yabuta and squeezing the contents.
The liquid is kept for 7-10 days in a tank to separate out the sediments, then filtered through active charcoal. Active charcoal removes not only any remaining sediment, but also undesirable aroma and color. However it removes desirable aromas as well.
For this reason, non-filtered sake has been gaining popularity.
Although sake is commonly pasteurized twice (after filtering, then just before bottling),there are specific sake categories which are either non-pasteurized or only pasteurized once. Normally pasteurization is done at the 150℉／65℃.
Sake is kept in a tank at 28.4 to 59℉(-2to 15℃）for between six month to one year ideally. Then blended to level the quality of sake in each tank.
Water is added to sake to reduce the alcohol content and make it more palatable. The sake before adding water has 17-20% alcohol by volume(abv) which is considered to be too high.
The final product has around 15%-17% abv (24 – 36 proof)