I'm not sure exactly why Mantensei refers to its junmai ginjo sake as the "Star-Filled Sky," but I think it might have something to do with the Tottori Prefecture (where Matensei's Suwa brewery is located) being the least-populated in all of Japan. I'm thinking that with so few people around and so little light disturbance from the lack of a bustling cityscape, one must be able to see the star-filled sky with relative ease. One thing I do know for sure is that Tottori has some of the softest water in the country, which allows the Suwa brewery to ferment its sakes at extremely-low temperatures for extremely-long periods of time. If you've learned anything about whisky from this blog over the years, you'll probably recall that long fermentations lead to gentle, soft-fruited flavors; think of Oban as an example.
Along with all that clean fruit flavor in the Mantensei "Star-Filled Sky" sake is a whole lotta earthiness—an earthy, almost umami note that practically screams for mushroom risotto or black truffles. Much like enzymes are introduced into a barley single malt mash during the cooking process, converting the starches into fermentable sugars, sake production uses a mold called koji to complete the same conversion with rice. Because the rice kernels are stripped of their husks, however, there can be no malting process which is why the enzyme must come from an outside source. The spores are sprinkled over the steamed rice, and then worked into the mixture either by hand or by a machine (as you can see from the above photo, they do everything by hand at Suwa). As most koji is cultivated by the producer itself in Japan, the Suwa brewery makes a very special style, utilizing higher temperatures to impart a different effect onto the mold. In the case of the "Star-Filled Sky" sake, quite a liberal amount of this special koji is introduced into the mix, resulting in a unique flavor in the final liquid.
As Monica Samuels, the national sake manager for the importer Vine Connections told me during our meeting, "Generally for ginjo/daiginjo types the koji-making is very delicate, referred to as 'tsuki-haze.' In this style, you can still see the rice after the koji making with the white koji flecks all over it. At Suwa, however, the koji-making is done in a style called 'so-haze,' where the koji is heavily applied, resulting in a white frosting of sorts that completely coats the rice grain. It creates a lot more umami flavor, but koji mold also accelerates fermentation, making it difficult to achieve precision, so you have to be careful."
On the palate the resulting flavors range from soy sauce to caramel with almonds, with a dry yet rich finish that is simultaneously clean and refreshing. There's even a bit of smoke underneath all that savory goodness. As Monica went on to say, "Generally when you have that intense soy-caramel koji aroma, the finish can be cloying or flabby, but this sake is surprisingly clean on the finish. The fact that the rice is polished to junmai daiginjo grade and the fermentation is so carefully controlled creates the umami aromas, but with that clean finish; resulting in a sake that is much more drinkable. It is also a higher ratio of actual koji rice to non-koji (kakemai), but the application is what makes it so intense." The "Star-Filled Sky" from Mantansei is a bold and fragrant sake with intense aromas and savory richness. It's also a sake you might want to enjoy at room temperature. It was also a huge hit with the staff at our Tuesday tasting.