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Spontaneous Sake: A Walk On The Wild Side Of Brewing


In the clinical world of sake brewing, reducing risk is one of the most crucial challenges facing a master brewer. Each batch is made up of several meticulously prepared stages that gradually increase in size and scale. As the stakes get higher and higher with every addition to the mash, getting off to a good start is of paramount importance. This begins with a moto: a small mixture of rice, water and koji, the purpose of which is to propagate as much healthy yeast cells as possible to later kick-start the fermentation of a much larger tank known as the moromi. However, in the dog-eat-dog world of microorganisms, the fickle nature of yeast means that in the past this was not just simply a matter of good preparation, rather mother nature also had a hand in the final outcome.

For example, before every batch of moto was completed, a fiercely competitive game of thrones had to take place between the various living microorganisms that would all be vying for supremacy of the tank. If everything went well, after a tense month or so of waiting, the winner of this contest would be a nice robust yeast that ruled supreme in its chosen environment, eager to get to work converting sugar into alcohol. Of course, the opposite outcome was also possible, with the worst case scenario being an undesirable strain floating into the tank and going on to wreak havoc and outlive all the other challengers. This left the brewer saddled with a weak or unsuitable strain of yeast for the all-important main event of making the larger and more expensive moromi.

Fortunately for brewers these days, the majority of sake is made using solid and dependable cultured yeasts that are simply added to an already pre-prepared and ideally suited environment for them to thrive in. Tried and tested by the Brewing Society of Japan, these stalwarts of the sake industry, coupled with a better understanding of the chemistry in the moto, have not only alleviated virtually all of the risk of unwanted microorganisms high-jacking the precious starter tank, but will also consistently impart wonderful aromas and flavours into the final sake. With this kind of peace-of-mind on offer to the brewers, you would think it almost unquestionable that anyone would pass up on this altogether less stressful method. After all, it's one less thing for them to have to worry about, and it's a very important part of the brewing process to boot.

However, not all master brewers like to play it safe. Incredibly, some prefer to live on the wild side and seem to relish in taking the risks that caused so much worry and stress to their predecessors back in the day. Yes, this is the realm of modern brewing using completely wild yeasts, often referred to as "natural fermentation", or shizen-jikomi in Japanese. Although high risk, these super-rare varieties can reward an intrepid brewer by producing some of the most interesting and unique sake available on the market today. Moreover, amongst a sea of relatively similar, perhaps even a bit mundane, "clean" tasting sake, these wild brews offer a welcome change for us consumers who like their sake a little bit strange or unhinged. 

Kimoto School

The kimoto method at Daishichi in Fukushima.


In order to appreciate the true scale of how much risk is taken with this style of brewing we need to first compare previous methods with those of their more modern counterparts. Up until the early Meiji Period (late 19th century) sake was made using the kimoto school of brewing, a collective of several different methods of preparing the moto that also includes the tricky yamahai style. Brewers didn't know it at the time, but the critical stage common in all of these methods was the natural appearance of lactic acid, the presence of which ensures a safe environment for the propagation of yeast. However, it is prior to this that the aforementioned contest between the various microorganisms is at most competitive.

The battle commences when nitrate bacteria appear and begin to propagate their offspring of nitrous acid. This is then followed up by the appearance of lactic bacteria, which also has its own acidic byproduct. For a while these two microorganisms form a pact, working together to inhibit the growth of yeast. This allows for nutrients that would have otherwise been consumed by any outside yeasts to accumulate as the rice dissolves and saccharification takes place. However, the stronger of the two offspring is the lactic acid, which as it increases in volume begins to kill off the nitrate compounds. Lastly, in a changing of the guard of sorts, the sugar content of the mash increases and the once dominate lactic bacteria finally begins to die off. When everything is settled, the mash is hopefully high in both sugar and lactic acid, making it an ideal environment for yeast to finally drop in and flourish.

Fast Brewing with Sokujo

Association yeast still in their vials. 


The turning point for sake brewing came in 1904 when researchers discovered that the key all along had been the role that lactic acid plays in creating a suitable environment for yeast. This new knowledge quickly gave birth to the sokujo method of making moto, whereby all previous hostilities are avoided by simply adding lactic acid to a mixture of water and koji right at the beginning. As this immediately creates a safe environment for the yeast there is no need to wait on the lactic acid to appear naturally, which cuts down on the time it takes to prepare the moto from about one month to just two weeks. However, the sokujo method also depends on having high volumes of suitable yeast added for it to work. Therefore, two years after it was discovered, the Brewing Society of Japan made cultured yeasts available for distribution to the various breweries.

Although there wasn't a selection of yeasts to choose from at first, the system soon changed to include several numbered strains that were isolated from various locations across Japan. If a new strain was identified and deemed suitable then it would receive the next number available starting from #1. The first of these so-called Association Yeasts (kyoukai-kobo), was isolated at Sakuramasamune in Nada in Hyogo prefecture, then number #2 from Gekkeikan in Fushimi in Kyoto, and so on and so on. The system is still in place today, with virtually all sake being made from Association strains. Currently, brewers can choose from a reasonably wide selection that includes the very famous #6 yeast isolated from Aramasa Shuzo in Akita prefecture, up until the super-modern varieties like #1901, a non-foaming variety famous for producing pronounced fruity bouquets.

Back to the Future

As is evident then, the kimoto school is significantly more challenging than the much quicker and safer sokujo method. However, as the various different techniques produce (sometimes drastically) contrasting flavour profiles, brewing with them is still a worthwhile endeavoured for those with enough skill and patience. Indeed, in recent years, both kimoto and yamahai have been enjoying a renaissance of such, with more and more breweries trying their hand at them every year. However, it is important to point out that the vast majority use a method that is slightly modified from the way they were made before the era of cultured yeasts. After all, brewers now have the relative luxury of being able to choose from the aforementioned list of dependable strains. The new orthodox method involves waiting for the moto to complete its cycle and produce lactic acid naturally before adding a pre-selected yeast directly to the tank, a kind of hybrid of sorts. Only a small handful of brewers go that extra mile in trying to recreate the sake of old by leaving the yeast fully in the hands of mother nature.

Spontaneous Fermentation

Yeast prepped and ready for addition to the moto.

Sake that are made without cultured yeasts therefore rely on the wild strains that are often present floating around in a brewery, clinging to the walls and various bits of machinery. In Japanese these have several names ranging from ie, yane or kura tsuki kobo: literally yeast that stick to the house, ceiling or brewery, respectively. In order for a successful brew, or in other words to result in a fermentation strong enough to produce good sake, the wild yeast must be able to survive the rollercoaster of temperature changes that each tank of sake will go through in its life cycle. Furthermore, as sake brewing is done by a parallel method of fermentation it must also be strong enough to devour high volumes of sugar, consistently, lest it get crowed out and die prematurely.

As mentioned previously, each batch of sake builds up gradually like a crescendo, and once the wheels are in motion it cannot simply be postponed if something goes awry. When you consider the substantial risk involved in putting all of your trust in such a vital ingredient simply appearing on cue and doing its job properly, it isn't surprising that this style of sake is so rare today. Master brewers are constantly thriving to reduce the uncertainties of brewing, and using wild yeasts as opposed to cultured ones certainly removes some of the influence he or she can have on the process. In a way, brewers must do their best to try and harness nature and guide the various microorganisms as best they can to reach the goal of making good sake. Therefore, when you consider the added risk, it is easy to see how this style has gained its rightful reputation as an extremely challenging method of brewing, and one that requires extreme conviction from the few that attempt it each season.

From those that do, there are several very notable brands that merit attention. However, my own experience with these idiosyncratic brews began when I was first presented with a glass of Tamagawa in a small bar in Kyoto. At the time, I was still very much a sake novice and up until that point had been selecting sake, rather ashamedly I must say, based simply on their classification. However, after the barman had established that I was from the UK, he insisted that I try a sake made by Philip Harper, a name that surely needs no introduction. To say that I was surprised when I took my first sip is a colossal understatement. The complex aromas and intricate flavours, coupled with a spectacular impact from the whopping alcohol content had such a profound impact that I immediately began trying to find out everything I could about this peculiar style.

What followed included a trip to the Kinoshita Brewery in northern Kyoto where Tamagawa is made. Their particular house yeast is an extremely lively variety that consistently produces sake in the region of 20-22% alcohol, sometimes even as high as 23%. Nowadays, the Spontaneous Fermentation series accounts for around 60% of everything they brew, mostly consisting of yamahai with one or two made by the kimoto method. This percentage is certainly testament to how popular these character laden sake have been with consumers, and nicely brings me to my final thoughts on what I feel is ultimately so appealing about them.

Considering the added risk and difficulties of brewing this rare style of sake, they would only be worthwhile if they offered consumers something different and appealing. This they do in spades, and personally speaking, they represent the absolute pinnacle of sake brewing. A bold statement perhaps, but the fact that they remain to me today as beguiling as they did all those years ago during my first encounter is testament to how unique and intriguing they are. Tamagawa is of course just one example, and I highly recommend the exploration of the other truly wonderful naturally fermented sake out there just waiting to seduce you with their wild charms.


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This piece was originally featured on Origin Sake. 

Origin Sake aims to uncover the many fascinating and complex aspects of Japan's national beverage. Through a better understanding of  brewing techniques, we can begin to unravel sake's numerous mysteries.

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