Minokamo’s Natto Koji: Doubly Delicious Thanks to Fermentation by Two Different Microbes
Feb 08,2024
Many people find it difficult to stay healthy as winter gives way to spring. It’s time for some trusty fermented foods that are simple to eat.
This installment is devoted to natto koji, which can easily be made with two Japanese fermented staples, natto (fermented soybeans) and rice koji (malt). Nagao Akiko, who travels all over Japan and shares meal ideas showcasing local culinary cultures and ingredients under the name “Minokamo,” explains what makes natto koji so great and how to prepare it. She tells us about how she pickles vegetables in a barrel with a weight or two on top. And she suggests a way to have fun while they’re fermenting away.
A combo of two fermented powerhouses for your daily meals
The Tohoku region in northeast Honshu is home to various local foods pairing natto with rice koji. Akiko first came across natto koji on a visit to Sendai in Miyagi, when she bought it at the store and gave it a try. She was amazed at how good this fermented food combo tasted.
“It has a mellower aroma and flavor than plain natto, with a more complex umami. It’s a more profound taste experience. I was also impressed at how you can just mix in some rice koji and eat it in abundance. So I started making it myself.”
Natto is rich in nutrients like protein and fiber, and the natto bacilli in it maintain intestinal health. Rice koji is rich in enzymes that break down nutrients and aid digestion. Eating this combination of both has to be good for you. “Adding vegetables gives it a dash of color and makes it more nutritionally balanced.”
Simply mix koji and natto with ordinary seasonings.
Another appealing thing about natto koji, says Akiko, is its simplicity. It can be prepared with ingredients available in any kitchen. “Add carrots, soy sauce, and ginger to some boiling hot sake and mirin (sweetened sake). Then after letting it cool a little, add some rice koji. Once it cools a bit more, mix in some natto, let it sit in the fridge for two or three days, and it’s ready to eat. It’s so simple, right? It’s just a matter of mixing a few ingredients.”
A handy formula to keep in mind is to use equal amounts of natto and rice koji. “That said, the amount of natto in a container varies considerably, right? Even with slightly less natto than koji, the stuff still turns out great. Try making it with however much you have at hand.”
It’s also fun to experiment with different combinations of natto and rice koji until you find the flavor and texture right for you. “I like the beans in my natto firm. Today, I’ve tried making natto koji with a pack of domestically grown medium-sized Kawaguchi Natto beans produced in Miyagi.”
“The rice koji grains retain their shape,” notes Akiko. “Their nice chewy texture accentuates the flavor.”
Recipe for natto koji
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- Ingredients (for an easy-to-make amount)
- 80–100g natto
- 100g rice koji
- 1 carrot (100g net)
- ½ knob ginger
- 60ml each sake, mirin (sweetened sake), and soy sauce
- 5×5cm sheet of kombu (kelp) if available
This natto koji was made with dried rice koji, but fresh koji works equally well. For the kelp, you can use sliced kombu. Also delicious with chili peppers.
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- Instructions
- 1. Cut the carrot into thin strips. Mince the ginger without removing the skin. Cut the kombu into easy-to-eat pieces with scissors.
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2. Put the mirin and sake in a pan and heat over medium heat. Once they come to the boil, turn off the heat. While still hot, add the carrots and stir in. Then add the soy sauce, ginger, and kombu, in that order, and stir in.
Adding the carrots while the sake and mirin are still boiling hot gives them a softer texture. Adding the soy sauce later ensures that it retains its full aroma and flavor.
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3. When the liquid from Step 2 cools to about 40˚C, add the rice koji while crumbling it with your hands and mix in. After it cools a bit more, add the natto and stir in.
To determine when to add the rice koji, just stick in your finger. The liquid should be the temperature of a hot bath. It cools instantly as you add the vegetables and soy sauce, especially during the cold months, so be nimble.
Finally, when the mixture has cooled, add the natto and mix in well.
- 4. Transfer the mixture from Step 3 to a clean storage container or jar. Let sit in the fridge for 2-3 days. During that time, take out and give it a stir once a day. Once the rice koji is soft, it’s ready to eat. It will keep in the fridge for about a month.
The natto koji at the top of this article is exactly six days old.
Handy serving suggestions for using natto koji as a flavoring
Natto koji makes the perfect rice accompaniment at breakfast time. Akiko also uses it extensively as a flavoring. She loves to pour it on or mix it into her food.
“To make an instant treat, just dish up some on a block of tofu, some yams or other vegetables, or a plate of sashimi. These are great quick snacks to enjoy with a drink. I’d also recommend pouring it over fish fritters or other deep-fried foods.”
You can also mix it into udon, pasta, or other noodles for a surefire treat. “Natto koji is a great thing to have on hand for lunch on a hectic day or a late-night meal.”
When not making miso, I pickle napa cabbage in the barrel.
The most eye-catching thing in and around Akiko’s kitchen is her magnificent miso barrel. She makes her own miso in it every year. “When you make miso in a wooden barrel, just the right amount of moisture escapes, resulting in a richer taste.”
Miso making isn’t all she has fun doing. After she’s used up all the miso she’s made and before she prepares a new batch the next winter, she uses the now-empty barrel to pickle napa cabbage. It’s become a yearly routine. It brings back memories of her grandmother.
“As I’m pickling away, I remember how delicious the pickles were at my grandmother’s place when I was a little girl. They were slowly fermented in this pickling shed she had. The natural fermentation process constantly varies, so I adapt to it while having fun watching the changes that occur from day to day. I sometime make kirizuke (cut pickles) with daikon, red turnips, carrots and whatnot. I love sneaking a mouthful while it’s fermenting as I check how it’s coming along [laughs].”
Akiko’s miso barrel is made by Okemitsu, a cooper on Fukuejima, one of the Goto Islands in Nagasaki Prefecture. She’s also fond of their rice tubs.
A way to have fun while your vegetables are pickling away
Last year, Akiko started putting weights on top when pickling vegetables. “I came across a jar and two pickling weights at the back of the house in Gifu where my grandmother used to live. They’re the ones she once used. One of the women in the neighborhood told me that the best-tasting pickles are those fermented in a jar. I wanted to give it a try myself, so I promptly stuffed them in my backpack and took them home with me to Tokyo [laughs].”
First she puts on both weights to squeeze out the moisture. Once the vegetables are compacted, she uses a single weight. “That gives the pickles a wonderful lingering taste, I guess because they’re pickled so well.”
And they’re not just delicious either. Akiko has noticed another fun thing as well. “When the napa cabbage is pickling, the weights gradually sink down as the water escapes. I like to watch how the appearance changes. It gets me excited with anticipation about how good the pickles are going to taste.”
A smooth stone weight of just the right size. The cover has sunk in considerably, telling you that the napa cabbage is slowly pickling away.
“Using a barrel and weights may sound a bit daunting. But there’s an easier way to enjoy the pickling process. Lightly massage some vegetables with salt and place them in a small glass jar. Then put a small rock on top so they’re immersed in the liquid.”
A small rock can be washed clean and used as a weight for a jar of pickles. Akiko is fond of this rock she found on the beach in Noto, Ishikawa. It also creates a treat for the eyes.
