- Active-carbon filtration
The name for filtering sake after it has had active carbon stirred into it. Carbon itself is used as a pre-coat, but it may be used with a filter aid such as diatomaceous earth if it is in fine powder form. Active carbon’s most notable characteristic is its ability to extract sources of colour, but it also absorbs taste and aromas, so it is used to remove colour, zatsu-mi off-flavours, off-aromas, and to treat sake which has undergone hi-ochi or other contamination.
Filtration with active carbon lightens both the colour and the flavour of sake. It also has a retarding or preventative effect on colouring (chaku-shoku), hi-ochi contamination and excessive ageing. Different kinds of carbon have different-sized holes on the surface. Some extract colour well, some absorb odours, and some are good for reducing zatsu-mi , so it is necessary to choose from amongst the many kinds in accordance with the characteristics of the sake being aimed for. Sometimes different kinds are used in blends.