Adding charcoal to control the reproduction of bacteria is the origin of the term akumochizake (which incorporates the character for charcoal) and in comparison the common sake brewed since the Edo Period was heated during manufacture in order to kill the bacteria and is therefore called 'Himochizake' (which incorporates the character for fire).
灰を入れて細菌の繁殖を抑えるのが「灰持酒」の名の由縁であり、対して一般的な清酒は江戸時代より加熱による殺菌を行ったことから「火持酒」と称される。