Which koji should I buy?

I’ve been asked, understandably, which koji to buy. A choice of 6 different strains may be a bit overwhelming when one is just starting out.

The most important thing to know is what you are most likely to make with the koji. Do you want to make barley miso, rice miso, soy sauce, amazake, etc.?

Generally speaking, rice koji will grow on soy beans too. It is a bit like buying vegetable seeds in southern Spain. They are meant to be grown there, but they will also grow in Austria – albeit just not as well.

In Japan koji has been bred to fit different applications, i.e. for soy sauce, for different misos, sake etc. So some strains have been bred to produce a lot of amylases, some to produce a lot of proteases, others to grow fast and on “difficult” substrates.

If you are planning to make sake (needs strong amylatic power) and soy sauce (needs lots of proteases), you are best off buying two strains. If you want to make rice miso and amazake, you are served well by just buying one strain.

I am sure can grow barley koji on rice too – might be worth an experiment!

The 9 strains explained

Which of the 9 kojis you should choose really depends on what you are planning to make.

Strains for miso:

Light Rice Koji

This is the strain to get if you plan to make short term sweet misos, amazake and/or sake. Sweet misos are misos which don’t ferment for very long (from 2 weeks to two months) with a relatively low percentage of salt.

This strain has strong amylatic power.

Red Rice Koji

This strain has been bred to best suit long term rice misos, also called red rice misos. These misos ferment from 6 to 12 months and contain more salt.

Compared to the light rice koji, this one has stronger proteatic power but less amylatic power. The strong proteatic power helps to make the miso as delicious as possible.

Barley Koji

This strain is probably my favourite to make. It just smells so good! Incidentally barley miso (also called mugi miso) is my favourite miso, too. It ferments from 4-12 months.

As the name says it is best suited for barley, which is a more “difficult” (for the fungus) substrate than rice. So this strain has been bred to grow easily on pearled barley.

Amylatic and proteatic power are both at a similar level.

If you’d ask me which strain you should buy if you just want to buy one – I’d say either this one or red rice koji, depending on which miso you like better.

Soy Koji

Some misos are made exclusively with soy beans – a difficult substrate for the fungus. These misos also take the longest to ferment, from 12 to 24 months. This strain has been bred to fulfill the needs of this application, it grows best on soy beans and has strong proteatic and medium amylatic power.

Strains for soy sauce:

Soy sauce Koji

If you are planning to make soy sauce, I really recommend getting this strain.

Soy sauce is made by toasting wheat, breaking it up, mixing it with steamed soy beans and then growing koji on it. Needless to say that is not an easy substrate for the fungus, but this strain has been bred to grow best on a substrate like that within a considerable time.

My supplier has this strain running under the name “three-dia”, because it takes only three days to grow, other than the usual four days for such an application.

With soy sauce there are more factors in what is needed from a strain. Low sugar consumption is wanted – to leave more in the final sauce/for yeasts. Also high proteatic power is needed, so suppliers breed specifically for these needs.

Mild Soy Sauce Koji

The normal soy sauce strain can be really vigorous, and for that reason it is prone to overheating. This strain grows more slowly, which is why beginners might find it easier to use. This is the reason it is called “mild”. The soy sauces you make with this strain will be no less strong than the ones you make with the normal strain.

A. Sojae

This is actually a different species, called Aspergillus Sojae. I provide this strain for people who want to change it up a bit. It is traditionally used for pale soy sauces and is said to have a different characteristic smell and taste.

If you are making soy sauces – try it! If you are starting out and want to make miso it may be better to stick to other strains. However it might be an interesting experiment to make miso with this one.

Other strains:

White Koji

This is a strain that is primarily meant for Amazake. I think of all the Koji strains I offer, this one smells best: flowery and mushroomy. While this strain is primarily for Amazake, I have made miso with it as well and it was good, too!

Black Koji

This is not A. Oryzae, but A. awamori. Traditionally this fungus is used for making shochu, a distilled drink either made from rice, barley or sweet potato. Unlike regular Koji, it produces citric acid. The acid helps to lower pH to make the amylases more effictive (their optimum is between 4.2 – 4.8 or so).

So this strain is for you if you want to make shochu, or if you want to experiment with a strain that has a black color and produces citric acid.


I hope this article helped to make your choice! If you have any questions, ask away :)