- Storage (maturation)
Terms referring to the placing of seishu in tanks or other vessels for a certain length of time. With the exception of nama-zake and shiboritate-style products, most sake is stored pasteurized, and is adjusted to product specifications after a maturation period before being shipped. Due to the progression of maturation during storage, the umami and depth of flavour of the sake increases. Both external factors (heat, oxygen and so on) and internal factors (reactions of constituent compounds in the sake and so on) have an effect on ageing, so the storage environment has a large effect on sake quality. As sake ages, colour and aroma change, but responses to the same substance can be positive as in the case of jukusei-ka (熟成香, “aged sake aroma”), or negative as for hine-ka (老ね香, “old-stink”). For this reason, it is necessary to supervise the level of maturation in accordance with the style of sake required.
In the case of unpasteurized sake, the activity of yeast and enzymes has not completely stopped. For this reason, depending on sake quality and method of storage, change is swift and deterioration is common. Consequently, some breweries store unpasteurized sake in refrigerated warehouses.
The tanks used for storing pasteurized sake are called kakoi oke (囲い桶). They are numbered for convenience in the order in which they were pasteurized, and these “storage numbers” are called kakoi bango (囲い番号, long final “o”). When sake is stored without being pasteurized, this is known as nama-gakoi (生囲い) .