From The cRc: Sake

In Important Alerts, Newsletter Items by kosherqu

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Unflavored sake is acceptable without Hashgacha.  Flavored sake (e.g., Coconut Sake) and sake which states on the label that it was aged in wine casks require Hashgacha.  Nevertheless, due to potential Kashrus concerns, it is preferable to only consume premium sake labeled as Honjozo, Ginjo or Daiginjo.