How is Sake made – Ask Decanter

It's much more complicated and time-consuming to make Sake than wine, says Slyvia Wu, who offers a step-by-step guide to exactly how Japanese rice wine is produced...

Japanese rice wine is gaining popularity in the west as consumers discover its delicate charms and wonderful ability to pair with all manner of foods. We find out how is Sake made, how important is the quality of the rice and water to the process, and does it ferment in the same way as wine?

The rice

Different from our everyday cooking rice, the most important virtue of Sake rice lies in a bigger white heart (‘心白’). If you put a grain of Sake rice in front of a black background and look carefully, you can see the white starch at its heart, and the transparent protein and fat on the outside.

The outside of the rice, when cooked, gives us the rich aromas and mouthfeel. But if used in Sake production, this part of the rice tends to slow down fermentation and bring in additional flavours, which are not always desirable. Therefore, Sake producers have to mill the rice down first.

The rate of the milling is measured with a percentage called ‘Semai Buai (精米歩合)’, which indicates the ratio of the rice left after milling. The lower the percentage, the finer the material is and the more water-absorbent it becomes.

Labelling terms ‘Ginjyo (吟醸)’ and ‘Dai Ginjyo (大吟醸)’ indicate that after milling, the Sake rice is left with less than 60% and 50% respectively. Extreme examples of Dai Ginjyo include the ‘Komyo (光明, Light)’ Junmai Daiginjyo from Tate no Kawa (楯の川), which is milled down to just 1%.

However, the milling rate is not always an indicator of quality. Some producers believe that those extra flavours derived from the outer layers of the rice are part of the unique characters to a specific Shuzo (Sake winery). They may choose to keep as much as 80% of the rice after milling.

Yamada Nishiki (山田錦) and Miyama Nishiki (美山錦) are among the best Sake rice varieties; producers can select several varieties, even some cooking rice to make up a complex recipe.

The water

Water, of course, is another essential ingredient in Sake production. It can bring significant impact to the flavour profiles of Sake, as the minerals and chemicals contained in the water may affect the performance of the microbes during fermentation. Therefore each Shuzo needs to choose its water source carefully.

Fermentation

The alcoholic fermentation process of winemaking is rather straight-forward; all you need to do is wait for the yeast to convert sugar – which naturally exists in grape juice – into alcohol.

For beer, that process is more complex, as you need to firstly convert the starch in barley into sugar through malting and mashing, before you can kick start the fermentation via yeast. Generally speaking, the process is still linear.

When it comes to Sake, the processes of converting rice starch into sugar, and sugar into alcohol operate simultaneously.

Allowing various exceptions, the most common production process for still Sake is as follows.

  • Steam; Producers first soak the grounded rice in water, then steam it to make it soft.
  • Koji; Then they take part of the rice to spread ‘Koji’ fungus, which can release enzyme that converts starch into sugar. This part of rice is called ‘Koji Kome (麹米)’.
  • Mother of alcohol; Next, they take part of this Koji-infected rice, and add more steamed rice and water, plus some lactic acid bacteria, creating the perfect habitat for yeasts to breed. When this part of the rice is populated by an enormous amount of yeasts, now we have ‘Shubo (酒母, the mother of alcohol)’.
  • Fermentation; It’s time to properly launch the fermentation. Shubo is dumped into a bigger vessel, where more steamed rice, Koji-infected rice and water are added in, little by little, in three to four stages across three weeks to a month.

It’s worth noting that the fermentation of Sake is conducted under a much lower temperature than wine – only 6 to 15 degree C – so that as the Koji bacteria gradually releases sugar, the yeast slowly feeds on it.

That combined with limited added water means higher alcohol level (sometimes above 20% abv) in the freshly pressed Sake. As a comparison, in most cases wine yeasts can only naturally reach around 15% abv, before they die from the alcohol they have created.

Before pressing, producers can choose to add a small percentage of alcohol to further refine the flavours, especially to release the lifted floral, vinous aromas. ‘Junmai (純米 pure rice)’ is a labelling term used to describe Sakes without added alcohol. These Sakes tend to have richer aromas and more pronounced savoury, umami notes.


Read more about Sake classifications from Anthony Rose’s beginner’s guide…


‘Treat with fire’ and storage

After pressing (timing is crucial!), the ‘Genshu (原酒, original Sake)’ is usually filtered to remove any undesirable colour and tastes.

Different from wine, Sake is still ‘alive’ at this stage, and it turns sour rather quickly in room temperature. This is due to a type of lactic acid bacteria called ‘Hiochi (火落ち, falling into fire)’, which breeds fast in the alcoholic and slightly acidic environment of raw Sake.

To resolve this problem, producers need to pasteurise the Sake. This is known as ‘Hiire (火入れor treat with fire); it is pasteurised twice with hot water in order to kill the bacteria. The first treatment happens right after filtration.

Then the raw Sake is aged for six months to a year to round out the flavour before adjustment and bottling. Now it goes through a second pasteurisation. At this stage, Sake becomes much sturdier and can be stored in room temperature.

However, stability comes with a cost – the fresh and glorious aromas of raw Sake may well be lost in the sanitising heat. Thankfully, there are also ways to preserve the freshness. For instance, ‘Nama (生, raw)’ Sake are bottled without any heat treatment; consequentially, they need to be stored at 0 degrees Celsius to keep the bacteria at bay.

Producers may choose to perform Hiire only once; if you see ‘Nama Zume (生詰, bottled raw)’ on the label, that means the Sake has been pasteurised only once before aging. ‘Nama Chozo (生貯蔵, stored raw)’, on the other hand, indicates that the treatment happened only after bottling.

Although these two styles are more stable than Nama Sake, it is still advisable to store them in fridge to retain their youthful and generous aromas.

Sake styles to know:

Daiginjo – Super premium, fragrant sake with minimum 50% polishing ratio and a very small amount of distilled alcohol added to enhance flavour and aroma. Often best served chilled.

Ginjo – Premium fragrant sake with minimum 40% polishing ratio, similar to daiginjo.

Honjozo – Light, mildly fragrant premium sake polished to a minimum of 70% with a small amount of distilled alcohol added to extract aroma and flavour.

Junmai – Sake made with nothing other than rice, water, yeast and koji with no minimum polishing ratio. When appended to daiginjo and ginjo, no alcohol has been added.

Broadly speaking, Daiginjo and Ginjo, with their beguiling fruity and floral fragrances, tend to be popular as chilled drinks while Honjozo and Junmai can often offer a broader range of value and versatility, especially when drunk with food, and can be served at a wider range of temperatures.


Got a question for Decanter’s experts?

Email us: editor@decanter.com or on social media with #askDecanter

Find more Ask Decanters here