Sagohachi is made by fermenting rice inoculated with koji with cooked rice and salt. Sagohachi is very similar to shio koji paste, but is much less well-known and more common among grandmothers in the countryside. However, sagohachi is a much finer ferment with a more rounded flavour than shio koji. Koji is a noble mould that plays a decisive role in the production of many foods in Japan. It is just as suitable for consumption as other mould cultures that are used to mature salami or cheese. Koji is traditionally cultivated on steamed rice, cereals or pulses and has been a tradition in China and Japan for thousands of years.

Koji has the remarkable property of changing organic substances and producing useful products for humans. This happens through the activity of the enzymes present in koji. These enzymes enable the breakdown of starch, proteins and fats, which contributes significantly to the development of the flavour and aroma of the fermented materials, especially the emergence of umami and sweetness. The metabolic products are also easier for humans to digest and much more digestible. Koji ferments are therefore not only flavourful, but also extremely healthy.