An old enemy of Saké – Hiochi-kin (火落菌)

An old enemy of Saké – Hiochi-kin

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.

Hiochic Acid Chem
Hiochic Acid Chem

Hiochi-kin causes sake to become turbid and acidic. The main acid created is, of course lactic acid, but some of these bugs also produce diacetyl (smells like nasty rubber, butter or butterscotch and may also seem like a slickness on the tongue). When diacetyl rises above our detection threshold in sake the aroma is called Tsuwari-ka.

To defeat these hiochi-kin there have been three methods used. The first method was low temperature “pasteurization” used with an estimated temperature of about 120F to 130F. In fact, this process goes back to at least 1568. While the Chinese had been using a similar method for at least 400 years by this time, it is unclear if the Japanese began based on the Chinese method. However, these low temperatures were not quite hot enough to do the complete job. In addition, after the sake was treated it was place back into wooden containers which, as we now know harbored the bugs even after they were thoroughly cleaned. So, while this low temperature pasteurization helped tremendously, faults remained.

Starting in the late 1800s, Salicylic acid was added to sake as a preservative. Salicylic acid worked so well that its use continued into the early 1970s when it was proven that pasteurization temperatures in use, 140F for 10 minutes, where enough to kill all the hiochi-kin. Given this it was now safe to stop adding the salicylic acid. No sakes contain salicylic acid today.

One other method is now possible but it is expensive so it is not used by many brewers. This final method is fine filtering using a membrane ultra-filtration process. All the bugs and enzymes are removed from the sake. With this process even namazake can be stored for maturation over the summer without refrigeration and without deterioration.

All in all there have been great strides taken toward victory over hiochi-kin!

 

 

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8 thoughts on “An old enemy of Saké – Hiochi-kin (火落菌)”

  1. Hi there. I believe this issue has occured in our first 2 and only batches. We have been very careful to sanitise. I am clueless on what more can be done to prevent this? Do you think temperature control could help prevent? Cheers.

      1. Hi Will,

        Few years since the original comment but I was wondering how do we effectively prevent the Hiochi-kin from entering the brewing process.

        Is the first pasteurization sufficient to stop the hiochic acid or will it have already ruined the sake by that point?

        My partner and I have two batches currently going and both appear to be quite acidic with an unusual smell. We are at a bit of a loss as to what is going on and are about to do our final pasteurization on day 88 of your guide.

        The SMV is 0.996 but it is very acidic and bitter, it also has a slight rubbery taste and a weird texture on the tongue.

        Any advice would be great.

        Regards,
        Jason

        1. Hi Jason,

          I am sorry to hear that. Hiochi-kin tend to infect sake that is aging in tanks and this is why multiple pasteurizations were adopted. However, from your description, it sounds like there is some other type of bacterial infection that started very early on. Are you adding lactic acid to the moto? When did you first notice the rubbery taste?

          Thanks,
          Will

  2. I don’t understan if the temperature of sake has to bring 140F in 10 minutes or it has to be at 140F per 10 minutes.

    1. Mirko,

      Starting with the bottles of sake in a cold water bath and bringing the temperature up to 140F and letting it cool on its own is enough. If you could raise its temperature very quickly, like in a heat exchanger, then you would want to hold the temperature at 140F for 10 minutes before quickly cooling back down.

      Does this explanation help?

      Will

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