Fresh koji vs dried koji: the white koji a tanekojiya makes

You open a recipe to make shio-koji and the ingredients say "rice koji" - rice grown with koji, the fermentation culture Aspergillus oryzae. Then you go looking in the shop and two kinds turn up: bagged and sitting on a room-temperature shelf, or inside the chilled case. The first is dried koji, the second is fresh koji.

Both are rice koji, but they handle a little differently, and they finish a little differently.

Whether the moisture has been taken out, or not

The difference is simple: whether or not the koji has been dried.

Fresh koji is koji mold grown on steamed rice and then bagged as it is, without drying. Because it holds moisture it does not keep, and the fridge or the freezer is the premise. In return the koji aroma is stronger, and the sweetness comes up more plainly.

Dried koji is that same fresh koji dried at low temperature to drive the moisture off. It sits at room temperature for a few months, which makes it easy to handle: you use as much as you need, when you need it. But because it is dry, it needs a step where it takes up water. Use a fresh koji recipe as written and you will come up short on liquid, so you adjust, typically by cutting the weight by around 10% and adding water to make up for it.

Neither is above the other. It is a question of how often you use it. If you use a little every week, dried koji is easier; if you make miso or amazake in a batch each season, fresh koji is.

The work that sits further upstream of koji

Go one step back up from here and you arrive at a trade called the tanekojiya (種麹屋).

To make koji, you need the koji mold that goes onto the rice. Raising that mold and supplying it to miso makers, shoyu makers and sake breweries is the tanekojiya's work. Almost all of Japan's fermented food hangs off this trade, of which only a dozen or so are said to remain. It is a position whose name rarely comes up, and which cannot be done without.

Ishikuro Tanekojiten's fresh koji: Fukumitsu, Nanto

Ishikuro Tanekojiten in Fukumitsu, Nanto (南砺市福光), Toyama Prefecture, is the only tanekojiya in the Hokuriku region. The family has made koji since the Bunsei era (文政年間) of the Edo period, and founded the business as a tanekojiya in 1895 (Meiji 28).

The shop's fresh koji is raised by the koji-buta method (こうじ蓋製法), which it has used since it was founded. Rather than a large machine box, the koji is divided among small wooden lids and finished by hand, with the temperature watched throughout. Koji made this way has been found, in testing by a public research body, to carry more enzymes and to be stronger than ordinary koji.

The rice is first-grade Koshihikari grown in Toyama Prefecture. The koji mold goes into every single grain, so it looks snow-white, with a natural sweetness. There are no additives. It is fresh koji, so keep it refrigerated once it arrives.

What to do with fresh koji

• Make shio-koji (combine koji, salt and water and leave at room temperature for about a week)
• Make amazake (hold rice koji and water at around 60°C)
• Marinate chicken or pork before grilling (the enzymes in koji soften the meat)
• Make your own miso
• Use it in a pickling bed such as Sagohachi (three parts salt, five parts koji, eight parts rice)

As with Sagohachi, handed down in Fukushima, cultures of using koji as a pickling bed survive in many parts of the country. Start with a single jar of shio-koji. It is the shortest way in to feeling what koji can do.

Frequently asked questions

Should I choose fresh koji or dried koji?

If you care most about aroma and the way sweetness comes up, fresh koji suits you; if you care about ease of keeping, dried koji does. Fresh koji still holds its moisture and has to live in the fridge or freezer, while dried koji keeps at room temperature for a long time but needs a step to take up water before you make anything with it. Another way to choose is dried koji if you use it day to day, fresh koji if you make a batch each season.

When I use dried koji in a recipe written for fresh koji, how do I change the amount?

Because the moisture has been taken out of dried koji, the same weight contains more koji itself than fresh koji does. The usual approach when swapping dried koji into a fresh koji recipe is to reduce the weight of dried koji by around 10% and add that much water. Moisture content differs by product, though, so follow the instructions on the package where they are given.

What does a tanekojiya do?

It is a specialist shop that raises the koji mold itself, the starter used to make koji, and supplies it to miso makers, shoyu makers and sake breweries. It is a rare trade, with only a dozen or so said to remain across the country, and it sits upstream of Japanese fermented food as a whole. Ishikuro Tanekojiten is known as the only tanekojiya in the Hokuriku region.