After the moromi (main ferment) has come to the stage where the ferment has run its course or it is time to stop it from going any farther, it is time for shibori; that is the pressing or squeezing of the moromi to separate the lees from the sake. This is mainly done in three different ways in kura (breweries) today and probably more ways than Sunday by homebrewers.
The most common way to press is to use a machine called Assaku-ki often referred to as a Yabuta; the name of the main supplier of assaku-ki machines. The moromi is pumped into these machines where it is squeezed by an air bladder to force the sake through a fine mesh that holds back most of the lees. As the lees build up on the mesh more and more of the lees are held back because the lees themselves become a part of the filter. In the most common configuration, the filtering action is so good that it filters out the yeast as well as the lees and hence stops all further fermentation.
Another method used for shibori is to use a fune. A fune is essentially a box with a lid that can be pushed down with great force to squeeze the contents of the box. Bags filled with moromi are stacked in the fune to ensure the pressure placed down on the lid will squeeze all bags with roughly an equal amount of pressure. The fune has a tap at the bottom of the box where the sake is drained off. The first runnings are collected with little or no pressure applied to the lid; this is called Arabashiri. The middle portion of sake collected from the fune is called Nakadori and is followed by the last portion called Seme. Arabashiri is more wild and brash while Nakadori is more refined leaving Seme as the least desirable portion.
The third method used in kura for shibori is to let gravity do ALL the work. This is done by putting the moromi into bags just like preparing for use of a fune and then hanging the bags to drip the sake. Here only the weight of the sake in a bag is used to release the sake from the lees while in a fune even arabashiri has the weight of all the other bags stacked on top. Sake “pressed” in this mannor is called Shizuku.
Producing shizuku is the most wasteful method but produces the best sake. Using a fune produces sake is next to shizuku in quality but is much less wasteful. Sake produced with an assaku-ki is still quite good and the process is very efficient.
Having read about the differences in these methods I found it hard to believe that there would be a noticeable difference in the taste of the sake. However, at a tasting of Nanbu Bijin Daiginjo produced with all three pressing methods, I as many others, found a noticeable difference going from the Yabuta (machine) pressed to the fune (box) shibori to the shizuku (drip) shibori. The consensus at the tasting whole heartedly agreed with conventional wisdom. All versions were very good but the fune version was better than the Yabuta and the shizuku version was better still than the fune version. I was blown away.
Homebrewers regularly use fruit and cheese presses to press their moromi. This is somewhat equivalent to the use of a fune. The moromi is placed into a bag or a cloth and placed into the press. Pressure is applied to the moromi with the press and the sake is collected. This is certainly more efficient than a shizuku style shibori which is also reasonably common. However the time involved for this drip method limits its use. Homebrewers have a third option; hand pressing their sake. This consists of placing the moromi in a bag or cloth and hand squeezing the sake from the lees. While too labor intensive for large batches it works well for small batches.
The shibori bags kura use are made of cotton with a pretty tight weave. Of course the tighter the weave the more lees they will prevent from leaving the bag. Because I hand press my moromi I prefer a very loose weave bag. This gives me a course filtering of the lees that I can do in a 30 minute to 60 minute session. However, because so much of the lees make it through I have additional racking steps to reach the levels of clarity I want. Basically I want my sake to be as clear as or more clear than commercial Muroka (pressed clear but not charcoal filtered).
For many first time sake homebrewers, pressing (shibori) is the most intimidating step in making sake. However, as with all other steps in sake making, it can be very strait forward and simple. Even using a cloth, rather than a bag does not have to make it hard. One way to ease this process is to use a large bowl and lay a linen or muslin cloth over the bowl making sure that the cloth is large enough to wrap a good amount of moromi and leave room to hold the top. Scoop the moromi into the middle of the cloth and then wrap the sides up and hold the newly formed bag of moromi above the bowl. The sake will drip through the cloth on its own but will take too long for you just to hold it. At this point you can either hang the bag for dripping or help it along by squeezing it. Use your hands or a press if you have one. It doesn’t have to be any harder than that.
See my video of the pressing process on day 32 in the step by step sake making instructions.