Closeup of Sake Production: Joso

Closeup of Sake Productions: Joso

Greetings Sake Lovers, welcome to another KURAND Magazine article that introduces you to the world of sake.

So far in this series taking you on a tour of the sake production process, KURAND Magazine has looked at how the brewer prepares the rice polishing, washing, soaking and steaming it before dividing it up into batches to create the koji and shubo, which are all ingredients for the moromi (main fermentation mash). Once the fermentation is complete, the brewer carries out several stages of processing each with a different purpose. In this article, we look at joso.

Sake Making Process in a Nutshell

The chart above is a basic diagram of the sake brewing flow intended only as a basic outline. The actual process varies depending on the variety of rice and the target style of sake.

What is Joso?


Newly fermented sake is like rice porridge, a far cry from the clear liquid commonly associated with modern sake. That is because not all the ingredients dissolve into the moromi leaving solids made up of rice, koji, and yeast behind. Joso is the process of separating these solids from the liquid. Beer and winemaking also commonly leave behind these solids called lees and remove them before bottling. The Japanese word for lees is kasu. The brewer separates the lees and liquid by forcing the moromi through a mesh filter. There are different techniques to do this which we cover in more detail below.

The literal translation for joso is pressing, but because the solids pass through a filter, it is technically filtration. Sometimes it is better to use the word pressing though to avoid confusion with a later stage in the process where the brewer strips out color and aroma using charcoal, also translating as filtration (an article on this to follow). Both are okay.

There are many ways to press/filter the sake, varying from brewery to brewery, which break down into two categories: traditional and modern.

Methods of Pressing/Filtering

Fukuroshibori

Fukuroshibori is the bag press method (fukuro is Japanese for bag and shibori is Japanese for press). The brewer puts the moromi into 50cm by 20cm sakebukuro (literally, sake bags), bags made with a special material that does not impart unwanted flavors of aromas into the end product. The brewer then hangs the sakebukuro from a pole or plank of wood placed over the tank opening. This method relies on gravity to force the liquid to drip slowly out of an opening at the bottom of the bag. Fukuroshibori is often also sometimes called shizuku-shibori (literally, the drip-press method). This method of pressing/filtering produces the most natural flavor with the least zatsumi (off flavors) and relatively low risk of tainting the aroma. However, the time to complete this method of pressing puts the sake in contact with air for longer, increasing the risk of oxidation, which is a problem because oxidized sake loses its punch and freshness. Fukuroshibori is very time-consuming and requires tank space to press, so it only produces limited volume, which is why it is often reserved for special products and competition sake. After pressing into the tank, the brewer usually then decant the sake into 18L bottles called tobin. You may often see the term tobin kakoi on the label for this type of sake. Fukuroshibori sake can be some of the most expensive sake.

Funeshibori

Funeshibori is like fukuroshibori in that the moromi is put into sakebukuro. However, instead of letting the liquid drip out naturally, external pressure is applied from above using a vice-like mechanism.

The sake-bukuro are laid on top of one another in a large tub called a fune, which resembles the bow of a boat (fune is Japanese for boat). A large vice-like mechanism is lowered down onto the sakebukuro. The technology mimics a wine-press, only instead of crushing; the moromi is pressed gently to force the liquid out of small openings in the bags. The brewer then extracts the liquid through a small tap at the bottom of the fune. Like fukuroshibori, this method demands time and physical labor. It is vital that pressure is applied slowly so as not to create coarse off-flavors. Sake pressed this way has little zatsumi and is delicate, but as the sake is still in contact with oxygen for a long period, some oxidation often occurs, although the most-skilled brewers can keep this to a minimum. The hardest part of using the fune is maintaining it. The brewer has to care for their fune or risk future pressings tainting the sake. To avoid this, the sake-bukuro has to be washed thoroughly after each pressing. Many breweries have fune gathering dust in a corner somewhere, but no longer use it in favor of the much faster, more efficient and more cost-effective modern machine-powered methods.

Modern Method

As explained for the traditional methods, the biggest problem is oxidation. The longer it takes to press, the longer the sake is in contact with air, and this is not desirable. The traditional methods also often leave many solids behind so less of the raw ingredients make it into the bottle. The assakuki machine solves all these problems.

The machine resembles a giant accordion or bellows; rows upon rows of slats divided by bags. The sake goes into space between inside a lining. In between the lining, slats and bags is a filter. The machine pumps air into these bags which inflate squeezing the moromi between and forcing it through the filter. Just imagine putting the moromi between the gaps in an accordion and pressing and that’s pretty much how this machine works, although sadly without the music — more like a loud whirring noise.

The only problem with this method is the strength of the pressure; too strong to extract the delicate flavors of daiginjo sake without harming them. However, this machine is perfect for processing large volumes of moromi quickly and requires only a small labor force to run. Perhaps the most significant merit of this machine is the short time the sake is in contact with air. The most time-consuming part of this method is assembling the machine at the beginning of each brewing season and scraping off the thick lees off the slats at the end. There are various brands of assakuki, but the most famous one, used by over 90% of brewers, is the Yabuta. Very few brewers used the word assakuki in favor of the Yabuta brand.

Why the Need to Press/Filter?

Simple, Sake That Isn’t Pressed / Filtered Isn’t Sake

Simple, Sake That Isn’t Pressed / Filtered Isn’t Sake
The legal definition for sake is according to the liquor tax law is, “that which has undergone pressing removing the lees.” Therefore, sake that skipped pressing is not sake; it is something else—probably a home-brew sake called doburoku (see this article). Cloudy sake or nigorizake is also pressed. So why is not clear? You may wonder. The brewers press the sake, but they use a filter with bigger holes to let some solids through into the final product (or sometimes filter and then return the solids afterward)—a legal loophole if you will. It is perfectly acceptable under the tax laws though.

How Does Joso Affect Sake Brewing?

Pressing in Fractions

With both the fune and assakuki methods, the brewer can press in stages, applying different amounts of pressure to extract different flavors. These separate pressings are called fractions. The first fraction is called arabashiri (literally, rough run) and is pressed with very minimal pressure. The sake that comes out has a very rough, coarse flavor. The next fraction is called nakagumi (literally, middle fraction) and comprises of the contents from the middle of the tank where the flavors and aromas are best balanced. The last fraction is seme and comprises of the rest of the moromi, the contents at the bottom of the tank and sometimes includes off-flavors, so very few brewers use seme alone, blending it with arabashiri or nakagumi instead. As well as off-flavors seme includes umami, so it is worth the effort to extract this fraction.

Sake Kasu

The shape and consistency of the lees vary depending on the method used. The lees of sake pressed using the assakuki are sold in sheets, like pastry, whereas the lees from the traditional pressing are sold as a paste in bags. The paste is easier to use in cooking, but the sheet form is useful for making sake flavored cakes or biscuits.

The lees, called sake-kasu, have an alcohol strength of 8%. They are sold in the brewery shop or distributed to suppliers. Sake-kasu can be used to make a special miso soup called kasujiru or a sweet low-alcohol sake called amazake. It has several other applications.


If you have enjoyed this article and feel ready to embark on a voyage of discovery, why not head on over to Japan, to Tokyo, and visit KURAND where you can taste over 100 different types of sake without time limits at your own leisure. Each sake comes with a story of how it was made and no two sake are made 100% the same way. We look forward to welcoming you very soon!

Rice Preparation Stages: Recap
Polishing
Karashi
Washing
Soaking
Straining
Steaming

Koji Making Recap
Koji Making Recap
Shubo
Shubo Recap
Moromi/Shikomi
Moromi/Shikomi Recap