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Inside the "Koji Muro"
Several sake from a single tank.

# 64

Feb. 2005

Sake World Sake e-Newsletter

Issue #64
February 1, 2005

-- Inside the "Koji Muro"
-- Several sake from a single tank
-- In the Archives
-- Good Sake to Look For
-- Sake Events/Announcements

Inside the "Koji Muro"

Proper koji making is the heart of the sake brewing process. Koji, as we all recall, is steamed rice with a mold (koji mold, or "koji-kin," or worse yet, aspergillus oryzae) that gently spews enzymes that will convert starches in the rice into our beloved fermentable sugars. The timing, pace, and vigor of this starch-to-sugar conversion decides much if not most of how well fermentation will proceed. This, and the myriad of other acids, amino acids, and multitude of other compounds exert massive leverage on both the quality and style of the final sake. Indeed, first comes the koji.

Koji, in the end, will have comprised about 20 to 30 percent of the total amount of rice used in a batch of sake. And while the regular steamed rice added to a tank during the fermentation comes right from the steamer (after being cooled), the koji is prepared in a special room in the kura (brewery), a room known as the "koji muro." The construction, form and function of these rooms are unique and interesting, so let's have a look-see at what is involved.

First of all, it is helpful to consider what is important in making koji. The type of enzymes that come out, and their strength in activity, is related very much to temperature. As such, very precise temperature control is needed, like to one tenth of one degree Centigrade, within the koji itself. Next, humidity is also very important, as this controls moisture in the rice, which in turn aids and abets the growth of the koji mold, and where on the rice grains it propagates fastest.

So what we need is a room where temperature and humidity can be controlled, yet altered to fit ever-changing needs and circumstances. What developed traditionally in response to these needs were small, low-ceilinged wooden rooms. The size of course varies with the scale of the kura, but typical for the scale of might be five meters wide by ten meters deep.  Sure, many are much larger, but for the size of brewery that makes up many of Japan's 1500 sake breweries, this might be average.

The walls and ceiling are made of wood; "sugi," or Japanese cedar (actually, cryptomeria) is the wood of choice, and almost always the wood used in koji muro is of this variety. It "breathes" well, and does not impart its own smell as readily as other wood. This "breathing" is important in that the porous wooden walls tend to absorb excess humidity, yet give it back when the room starts to dry out. Also, the wood used in constructing these koji muro is not freshly cut. Perish the thought. It has been cut into panels, then painstakingly aged for years - sometimes three, sometimes twenty - before being used. This eliminates the chance of warping, and also allows it to air out enough to where it does not smell like freshly cut wood can smell.

The walls are insulated with as much as a meter all around of tightly packed rice straw embedded in earth to keep the temperature where it needs to be. For all I know, some today use fiberglass, but traditional construction calls for materials from the natural world.

Lately, though, innovation has encroached on tradition, and there are those experts and kura promoting the use of stainless steel walls. As the concerns of temperature and humidity are identical, the size and function of metal-walled koji muro are the same, but instead of sugi walls we have shiny, spiffy stainless steel.

Those that promote steel-walled koji muro insist that wooden wall are a haven for bacteria that could spell disaster for the koji, whereas such bacteria cannot exist or propagate on slick steel. But those that favor wood say that since the metal walls do not breathe at all, it is much harder to create koji with the proper moisture, and that often it gets damp or mushy during the process because of these non-breathing walls.

Balderdash, insist the metal-heads. There are many other ways to control the moisture content of your koji.

Touche, retort the wood-chucks; if you maintain good sanitation practice, bacteria on your wooden walls is a non-issue.

Several years ago at a small tasting in the back room of a premium sake pub in Ginza (seriously), a brewer hesitated before pouring her daiginjo from the large bottle she had schlepped from the boonies for the ten or twelve of us in attendance. "Ok, I have to apologize. We just rebuilt the wooden walls in our koji-muro, but we didn't let the wood dry out enough, and you can smell the sugi wood in the sake. It will likely fade with a bit of maturation, but at this stage, it's fairly obvious."

"Yeah, right," I thought. There's no way that could be true. She's either paranoid, or she's been sipping at the bottle on the train up here. Or both; I dunno. But how could the smell of the wooden walls get into the koji, survive a month-long fermentation, and end up in the final sake? No way.

Well, as is so often the case, I was wrong. It was faint, to be sure, but a light cedar-esque essence laced the flavor of her otherwise excellent sake. It was not even necessarily a fault, excepting of course that she did not intend it.

Yet, on one trip up north, the owner of a well-to-do kura led me into his large-ish wooden koji muro. "We built this room anew a while ago. For the first three years, the walls were metal. But we ended up stripping that off and putting wood back up in its place."

Oh? And why was that?

He shook his head slowly from side to side. "I don't know what to tell ya. All I know is that for those three years, the sake didn't taste as good, especially in our higher manifestations of sake. Things returned to our own high standards after going back to wood."

So there are those that swear by wood, and those that prefer metal. But there is no conclusive data touting one clearly over the other. And in facing this walls-breathe/no bacteria dilemma, in the vein of a "taste-great / less filling" kind of solution (although their sake is anything but lite!), a brewery in Fukui Prefecture came up with an interesting approach. They built a new koji muro that is half wood and half stainless steel. The wooden half and the metal half are divided by a sliding glass door, and both halves were constructed so that a minimum of reform work would make them into the other. In other words, the metal can be removed easily from the metal half, and the wood covered with metal just as easily.

So, for the time being (it has been three years now), they are playing the wood and metal off of each other. When I visited them last spring, I was standing there in the koji muro with the two young apprentices. So, how's it working out, I wanted to know. Which half is emerging as your preference?

One shot a furtive glance at the other, then they both shrugged. "We're not really seeing too much of a difference. But the wooden one somehow 'feels' better to work in," he added sheepishly. Hey, whatever works. Just keep making good sake. (They make a sake called Hanagaki, by the way.)

Note, too, that when koji making machines are used, they are often plopped right down into the koji muro itself. Unless it is one of those uber-koji-machines, the fully automatic jobs that are far too huge to fit into such a room, smaller manifestations of temperature and humidity controlling contraptions will sit there in the same environment.

An interesting innovation that is deceivingly simple in almost all old or traditionally designed koji muro is the way they circulate fresh air. This is done for several reasons, including temperature and humidity control. There are two small trap-door like openings on the ceiling. Above one sits a tall smokestack, above the other a short one. Since hot air rises, when both are opened, there is a natural circulation as cold air falls in from the short smokestack opening, while it rises out of the tall smokestack opening. Clever, clever. Heat, by the way, usually comes from gently warming electric heaters, not blowers or central air. Traditionally, before electricity was around, smokeless charcoal was how this was accomplished.

In the end, it seems that most of the time, at most places, most of the traditional methods and materials are used in making most of the premium sake out there. As you can tell by my painstaking efforts to be vague, there are enough exceptions that modern machines and metal walls cannot be written off.

Several Sake from a Single Tank

I recently visited a rather "open" sake brewer in the mountains of Hyogo, near the Sea of Japan. "Open" in this instance means he could talk a starving dog off of a meat wagon. But that is what I like about him.

We asked him how many different grades or types of sake they made. The massively abridged version went something like this: "Well, about nine, but we end up with about 20 different products from those." This reminded me of one of the cool aspects of sake brewing. Depending on the way that sake is processed after the actual brewing is complete can yield a wide range of products and styles from the same batch.

And how might this be? Well, let us assume we have a simple tank of junmai ginjo-shu. We could press that, and end up with a product at, oh, say, 18 or 19 percent alcohol. We can ship it right then, with no charcoal filtering, no added water, and no pasteurization. It would be a powerful expression of that sake known as a muroka nama genshu (unfiltered, unpasteurized, undilited). It would also be known as a shiboritate, i.e. freshly pressed, with all the attendant liveliness that make brash, young sake like that what it is. We could then lay this down for a few months to let all that brashness mellow out. We could also have either filtered it, or pasteurized it, or added a smidgeon of mellowing water, or any permutation of these just before its early release just after pressing. Each will yield a markedly different sake that would easily stand on its own as a unique product.

We could also gently charcoal filter it, and pasteurize it, and then lay it down for six months or so and ship it in what would be probably its most premium and orthodox form. But even then, we could dilute it with water to a more subtle and enjoyable 16 percent, or ship it full strength. And either one of those versions could be pasteurized either only once or the more-commonly performed two times, or not all. Each of these manifestation will yield varying degrees of freshness and liveliness (albeit balanced with potential instability due to still-active enzymes and micro organisms), and the alcohol level will give the sake either impact or subtlety. And again, each of these will be a markedly different sake that could be sold as a unique and enjoyable product.

And, had we remembered to pull a bit off before separating the white lees from the amber sake, so that we could filter that off with a coarse mesh and leave some of the rice solids behind, we could have shipped it as nigori-zake, or cloudy sake. This, too, could be sent through all the other iterations of possibilities such as pasteurization, and minimal dilution to create even more potential products. Finally, we could lay it down for years (at some risk) on an experimental whim to see what happens when such a sake is aged, even though this is not the norm, nor how sake was meant to be treated, although it can be interesting.

All of this from the same tank. The point here is that how a sake treated *after* the fermentation stage is complete can be just as important in determining what the final product will look like, taste like and smell like.

In the Archives

At the risk of shameless self promotion, I want to encourage readers to scour the archives of this newsletter at either:

The archives include a wide range of topics that have been covered over the past five years in this newsletter.

The archives go back to August 1999. Within them are covered just about anything related to sake, from what it actually is (8/99, 6/03) to how it is made (9/99, 4/00, 7/04) to what makes for good ingredients (water: 2/01, 6/03, rice: 11/02, 3/03, and yeast: 10/99, 12/02). The topic of sake and region is covered, with articles on the sake of Niigata, Shimane, Fukui, Yamagata, Nara, Fukuoka, and Hyogo Prefectures. There are many more regions to be covered, but these are certainly worth knowing.

More focused, less general topics like un-pasteurized sake (11/99, 5/00, 7/03 and 12/04) and nigori-zake (10/03) are there, as are culturally supplanting topics like history (11/00, 7/02) and official government sponsored tasting contests (June or July of each year). Detailed (overly so?) discussions of processes like the yeast starter (8/00, 10/00) and its more interesting manifestations like yamahai (3/04) and kimoto (12/04) and pressing sake from the dregs after fermentation (4/01) along with discussions on aging sake (8/03) and warming sake (11/99, 10/03). And much more.

And while shameless self promotion is not usually my bag, being useful and informative is. I simply want readers to know the information is out there. Please check it all out at your leisure.

Good Sake to Look For

Kurodajo Otemon (Fukuoka Prefecture), Junmai Ginjo
Otemon is one of my favorite sake. There. I said it. While recognized as fine, it is certainly not hyper-popular, and not on the top of *everyone's* list, but I stand by it. Otemon sports an autumnal, mature fruity aroma, albeit slightly reigned in, and a full, fat, viscous, chewy, solidly structured weight and feel replete with grounded, earthy tones and rice-like sweet touches as well. This sake is very representative of sake from this part of the country, especially Kyushu island. While there is a junmai daiginjo version as well as this junmai ginjo version, the junmai ginjo version here gives much more zen for the yen, in my opinion. I am not sure if this sake is imported out of Japan yet, but if not, it is only a matter of time.

Komagura (Fukuoka Prefecture), Junmai Ginjo
From the same producer, Morinokura, that brews Otemon above, comes this more earthy and matured expression of an earthy, almost smoky, yet ever-so-mildly fruity sake, tinged with dried apricots and prunes. The region was once famous for tops, as in the spinning variety, and top craftsmen abounded, no pun intended. Komagura means "kura of the tops," with the intended reference being both regional, but also that they put as much craftsmanship and effort into their sake as the traditional top makers did into their regional specialty. Or so explained the owner. Komagura is indeed being exported into the US. Search it out, and enjoy it at a range of temperatures, with room temperature being perhaps the most wonderfully revealing.

Masuizumi (Toyama Prefecture), Junmai Daiginjo
Certainly the one overriding characteristic of this sake is its balance; balance between the flavors themselves, and moreover balance between the aromas and the flavors. It's apple and melon tinged aromas are sharpened and focused by an acidity that ties this into an otherwise full and comparatively thick flavor, textured and (again) balanced. This one is a real crowd pleaser; it would be very, very hard to find anyone that would not enjoy this sake. It has plenty of presence in flavor and aroma to stand on its own, and may in fact steal the show from much food. This sake has been in the US for a good, long time.

Sake Events and Announcements

Sake and Pottery Seminar at Takara, Saturday February 19, 2005

On the evening of Saturday, February 19, Rob Yellin and I will hold a sake and pottery seminar at Takara, in Yurakucho. Rob's topic will be the pottery of Kyushu. I will speak about the use of different yeast strains in sake brewing, and how the affect flavor and aromas, as well as which ones to remember, and which to forget.

The cost for the evening - half a dozen sake, ample food, a lecture and printed material - is 7,000 yen. Those interested can reserve a spot (no deposit is required) by emailing John at:


Takara is located on the B1 level of the Tokyo Forum, the convention center just outside Yurakucho Station. More detailed instructions for getting there will follow with the confirmation email. Stay tuned until next month, when I will hopefully announce the beginning of a set of new seminar-events at a different location, a very famous and very traditional sake pub in another part of Tokyo. Details are being hammered out as you read this.


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