Shio koji (塩麹, pronounced “shee-oh koh-jee”; shio means salt) is a Japanese seasoning made from rice koji, salt and water, left at room temperature for one to two weeks until it becomes a thick, sweet-salty, savory paste. Koji is cooked rice that has been grown over with the mold Aspergillus oryzae – the same starting point as miso, soy sauce, sake and amazake. Used in place of salt, shio koji seasons food and, as a marinade, tenderizes meat and fish. It has long been made in Japanese homes and became hugely popular there again from around 2011.
How Shio Koji Works
Shio koji isn’t fermented by live microbes the way kimchi or yogurt is. The mold has already done its work while growing on the rice, producing enzymes; in the salty water those enzymes do the rest (Allwood et al., 2021):
- Amylases break rice starch down into sugars – the mild sweetness.
- Proteases break proteins into peptides and amino acids, including glutamic acid – the savory, umami taste.
Those proteases are why shio koji tenderizes meat. In a 2026 study, protease fractions taken from commercial shio koji broke down beef muscle proteins (myofibrils) and released free peptides – much more slowly at 4°C than at 37°C (Miyaguchi et al., 2026). In the fridge, then, a marinade works gently over hours, which is why overnight marinating is common. Shio koji contains no live probiotic cultures, and cooking stops the enzymes.
How Salty Is It?
The recipe below uses 60 g salt in about 560 g of koji, salt and water – roughly 11% salt: about 2 g of salt in a tablespoon (about 17 g) of shio koji, or the salt in a third of a teaspoon of table salt. Use it instead of salt, not on top of it.
How to Use Shio Koji
- Marinade: about 1 tablespoon per 100–150 g chicken, pork, fish or tofu, in the fridge, from 30 minutes to overnight (fish: up to a day). Wipe off the excess before cooking – the sugars brown and burn quickly.
- Quick pickles: toss sliced cucumber, cabbage or radish with a little shio koji and chill for an hour or overnight.
- Seasoning: in dressings, soups, stir-fries and roasted vegetables, in place of salt.
Shoyu Koji, Amazake and Miso
- Shoyu koji: rice koji steeped in soy sauce instead of salt and water – darker, more savory, used the same way.
- Amazake: rice koji with water and no salt, kept warm (about 55–60°C) so the starch turns to sugar – a sweet drink rather than a seasoning.
- Miso: koji mixed with cooked soybeans and salt and fermented for months, with yeasts and bacteria joining in – see our homemade miso guide and how long miso lasts.
Other Japanese salt-based ferments: salted umeboshi and bran-pickled nukazuke.