Hitting your SMV (Sake Meter Value) – To ameliorate or not
One question that comes up over and over in sake brewing is how to hit the SMV value desired. Puzzling over this question I asked one of the brewers from Yoshi-no-gawa when the opportunity presented itself. This was well over a year ago now, but what he told me was that they monitored the moromi (main ferment) and when it reached their desired SMV value, it was time for Shibori or Joso, that is time to press the lees from the sake. Using an assaku-ki machine (an accordion like press), often referred to as a yabuta, they are able to remove virtually all of the lees and even the yeast. Because this leaves only trace amounts of the yeast, fermentation is stopped and the SMV value is stabilized.
Very nice! However, if you have seen my videos of the pressing process you may be wondering if something is amiss. Well, yes, something is amiss. My pressing method leaves a large amount of the lees in my sake so there is no way I am removing the yeast. This is true for most homebrewers. There are filters used for brewing that may be able to do what is needed. I have one but have not used it yet. In any case to use it I will have to first press and let settle or fine before filtering because the amount of lees would hopelessly clog the filter if the sake isn’t pretty close to clear. So, for now, I can’t use their method.
An old enemy of Sake and the sake brewer is Hiochi-kin or hiochi bacteria that spoils sake as it grows and reproduces. Unlike most bacteria (bugs for short) hiochi-kin does not mind alcohol and some even like alcohol. So as most Lactobacilli, which are heavy lifters in Kimoto and Yamahai moto styles of sake, will die off as the alcohol levels increase hiochi-kin does not. The other factor that usually keeps the bugs out is low pH levels like those found in sake which are a result of acids created in or added to the moto. However these hiochi-kin also like low pH, highly acidic environments.
As it turns out, hiochi-kin is a lactic acid bug or more specifically it is one of two bugs Lactobacillus (L.) homohiochi and L. fructivorans (a.k.a. L. heterohiochi). These are the “true” or “obligate” hiochi-kin and need hiochic Acid (more commonly known as mevalonic acid) for their growth. Other hiochi-kin or sake spoilage bugs are referred to as “facultative” and include: L. fermentum, L. hilgardii, L. casei, L. paracasei and L. rhamnosus.
Koji produces the needed hiochic acid. The fact that “true” hiochi-kin need hiochic acid implies that these bugs are highly adapted to sake production. Thus they have few other environments in which they can grow. Hiochic acid is an intermediate compound in the biosynthesis of many other compounds so it is not normally seen in a stable state (i.e., not part of a biosynthesis process). The chemical makeup of hiochic acid follows.