- Pasteurization (low-temperature sterilization)
Literally signifying the “putting-in” of fire, this operation is carried out to heat and sterilize sake, thereby killing off micro-organisms and deactivating amylase, protease and other remaining enzymes, in order to improve storage stability. Furthermore, by storing sake after pasteurizing, the characteristic roughness and other features typical of new sake disappear, and, with control of temperature during storage, the degree of maturation can be regulated and flavour be balanced.
New sake which has been pressed and filtered is commonly heated to 62-68°C, then transported to storage tanks which are sealed for storage. Temperature is maintained for about an hour before cooling is carried out quickly using showers or cooling jackets. This is the same operation as the low-temperature sterilization that Pasteur discovered to increase the storage potential of wine, but this technique was already in use in Japan some three hundred years earlier, around 1560.
It is important to remember that wherever there is sake, there will also be hi-ochi kin lactic acid bacteria in residence. As well as the obvious necessary care with cleaning and sterilization of equipment, it is vital to take note of any point at which temperatures may drop and ensure that heating is carried out sufficiently.
During the pasteurization process, the total heat from all the steam used compared to the total heat absorbed by the sake is represented by a value known as thermal efficiency. Plate heaters are more efficient than traditional jakan coils, with values of 92% and 69.7% respectively having been reported.