Nihon Chomiryo Tabi
Shoyu koji and shio koji, side by side
- The koji underneath is the same. The difference is whether salt or shoyu goes in with it.
- Shio koji is rice koji with salt and water. Saltiness and the soft sweetness of koji lead, which makes it something like salt, one level up.
- Shoyu koji is rice koji with shoyu. On top of the saltiness come the body of shoyu and the savor of glutamic acid.
- Taste a little of each and shoyu koji has the sharper outline.
Shio koji has been on Japanese tables for some years now. What about shoyu koji? Plenty of people have heard the name, but few could say plainly how it differs from shio koji.
The koji underneath the two is in fact the same. The difference lies in what is added to it.
The split: salt in, or shoyu in
Shio koji is a seasoning made by fermenting rice koji with salt and water. Saltiness leads, with the soft sweetness koji produces behind it. It draws moisture out of an ingredient while seasoning it, and gets used as something like salt, one level up.
Shoyu koji, on the other hand, ferments rice koji with shoyu (soy sauce). Because shoyu goes in where salt would, it brings not only saltiness but the body of the shoyu and the savor of glutamic acid. Taste a little of each and shoyu koji has the sharper outline.
Which to choose depends on the job. Shio koji if you want the color and taste of the ingredient to stay light; shoyu koji if you want to add savor and body in earnest.
How koji makes sweetness and savor
For both shio koji and shoyu koji, the source of the flavor is the enzymes of koji (the fermentation culture Aspergillus oryzae) living in the rice koji. Amylase turns starch into sugar; protease breaks protein down into savory compounds. Over days of aging, these enzymes keep quietly working, drawing out sweetness and savor.
That is why a spoonful, poured on with no cooking at all, changes the taste of a dish. A koji seasoning is a seasoning that borrows the power of fermentation to make the ingredient itself taste better, and that is what makes it interesting.
From Ono, a shoyu brewing town: Yamato Shoyu Miso's Shoyu Koji
A good bottle for getting to know shoyu koji is made in the port quarter of Ono (大野) in Kanazawa, Ishikawa Prefecture.
Ono has been a shoyu brewing town since the Edo period. Soybeans and wheat carried in by the kitamaebune trading ships, groundwater from Mount Haku (白山), and a damp sea wind. The character of this place has supported the work of koji for a long time. Yamato Shoyu Miso, founded in 1911 (Meiji 44), carries on passing along fermented food culture under the phrase "ichiju issai ni ikkoji" (一汁一菜に一糀), a koji with every simple meal.
This "Shoyu Koji" is a fermented seasoning combining the brewery's own honjozo shoyu with rice koji from domestic rice. The deep sweetness the koji enzymes create dissolves into the body of the shoyu. A teaspoon over rice with a raw egg. That alone opens up a full, lingering finish that shoyu on its own cannot reach.
Ways to enjoy shoyu koji
- Rice with a raw egg: just a teaspoon poured over. Start here
- Chilled tofu, natto, sashimi: straight, in place of shoyu
- Cucumber salad: toss it with chopped cucumber and you have a dish in a minute
- Marinating meat or fish: the koji enzymes tenderize and draw out savor
Know the difference between shio koji and shoyu koji, use each for its own job, and the ingredients you already cook with go up a step.
Frequently asked questions
What is the difference between shoyu koji and shio koji?
The rice koji at the base is the same; what gets added differs. Shio koji ferments rice koji with salt and water, and saltiness with a soft sweetness leads. Shoyu koji ferments rice koji with shoyu, so the body of the shoyu and the savor of glutamic acid come with it. If shio koji stands in for salt, shoyu koji stands in for shoyu.
What can I use shoyu koji in?
A teaspoon over rice with a raw egg is the standard move. Use it straight on chilled tofu, natto, or sashimi, and tossed with cucumber it becomes a dish on its own. Marinate meat or fish in it and the enzymes in the koji break down protein and leave it tender.
Which shoyu koji should I buy first?
We would point you to "Shoyu Koji" from Yamato Shoyu Miso in Ono, Kanazawa, Ishikawa Prefecture. A brewery founded in 1911 (Meiji 44) makes this fermented seasoning by combining its own honjozo shoyu with rice koji from domestic rice, and it is a good one to try first over rice with an egg, where the sweetness and body of the koji show.
