koji rice in bowl

Have you ever heard of koji? Many people haven’t, yet chances are you’ve had at least one food that owes its flavor to it. Miso, soy sauce, sweet rice vinegar, and sake- to name a few- all contain koji. So what is it?Koji’s considered a hallmark of Japanese cuisine and is found in many different foods. Elizabeth Andoh, the director of the Taste of Culture culinary arts program in Tokyo, calls koji a “fermenting agent of change.” The name koji can be referring to either a mold or a food ingredient.  Tane koji, which translates to “seed koji”, are the actual spores from either the Aspergillus oryzae or Monascus purpureus molds, although the Aspergillus is the more commonly used species. The ingredient known as koji is made by adding the mold to steamed grains and allowing it to cultivate. The mold releases enzymes that break down the starches, proteins, and fats, resulting in foods that are more tender and flavorful. In English, we tend to refer to all types of koji-inoculated grains collectively as koji; in cultures like Japan, where it’s commonly used, there are names and distinctions made between the different kinds. With sake, for example, koji used in regular versus premium sake is considered distinct; the difference lies in the type of rice that is initially inoculated with the koji seeds.

hand holding some koji seeds

The first step in making foods containing koji is to add the Aspergillus culture to steamed grains. The mix is placed in a warm, humid area for up to 50 hours, and during that time the Aspergillus feeds on the grains and breaks them down. After the culture has had a chance to grow, it’s then added to larger quantities of grains and mixed with brine or alcohols and allowed to ferment.

jar of koji rice

Sake is one of the most well koji products. When making sake, rice is mixed with koji, allowed to sit while the koji breaks down carbohydrates and sugars, and then fermented with yeast. Koji, for sake, is said to be the equivalent of what malt is to beer; both break starches down into sugars, allowing the sugars to ferment into alcohol. Rice, barley, and soybean kojis are all used to make different types of misos.  Whole soybean koji is used to make traditional Chinese soy sauce and fermented black soybeans (also known as Hamanatto or Daitokuji natto). One of the most common uses of koji among chefs outside of Japan is utilizing koji as a tenderizing agent for meat. The meat is rubbed down with the koji-inoculated grains and left to sit in the fridge for 48  hours or so, creating a dry cured meat that is similar to traditional salt-cured meats that can take as many as 45 days to cure. Koji-cured meats are said to have a distinct, semi-sweet, miso-like flavor. One of the great things about koji-curing is that you can take a cheap piece of meat, cure it, and then have meat that tastes like a much more expensive cut! Some other uses are adding koji to marinades, sauces, dressings, and pickles. The flavor is said to be uniquely umami, although the taste differs depending on the kind of grain or legume used.

bowl of ground koji rice

We decided koji sounded so intriguing that we decided to experiment with it ourselves. I found some at Asiana Market in Cotati, in the refrigerated section alongside kimchee, pickles and other fermented foods. I brought it home, opened the container, and was surprised to see that the rice looked fairly normal, just very dry and very white. It didn’t have much of a smell either; just a faint aroma that smelled slightly different than normal dry rice. Now that I had some, the hard part was deciding how I was going to use it! I decided to try dry curing some meat, as I’ve done this with just salt in the past, and was curious to see how it differed.

steak dusted with ground koji rice

 When trying to find information on how to koji dry-cure meat, I discovered that it appears to be fairly experimental still; as such, it was hard to find a consensus on the exact process. I patted the excess moisture off one rib eye steak with paper towels, and then rubbed approximately 1/2 cup of ground koji rice powder all over it, making sure to cover the meat well. I then sprinkled 1/8 tsp of salt between both sides of the meat, set on a rack, and left it in the fridge for 48 hours.

Steak after aging 24 Hours steak after aging 48 hours

The meat definitely changed a lot over those 2 days! The first photo above was after 24 hours; the second photo was after 48 hours. It became darker red in color and had dried out spots that looked a lot like a meat that had been curing for longer. After the two days of waiting were up, I took the beef out of the fridge and washed the koji powder off; if you don’t do this, the koji will burn and your meat won’t cook. The meat was very dark red, and the marbling was more visible than it was originally.

48 hour aged steak with koji rice washed off

I patted the moisture off the beef, and then cooked it in a saute pan on medium heat in canola oil, for about 4-5 minutes per side. The meat turned very grayish white, which was a little intimidating, to say the least.

steak after cooking   steak after cooking, side view

After letting the steak rest for about 5 minutes, it was time for the moment of truth! I cut into the meat and took a bite… wow. The texture of the meat was super tender and incredibly juicy. The flavor was strangely buttery; my husband said it tasted like someone had boiled a steak in movie theater popcorn butter, which to be honest, wasn’t far off. It was incredibly flavorful, enough so that it was hard to believe there were no additional seasonings added. Needless to say, we ate it all! I could see this flavor working really well with other meats also. Final thoughts: I would certainly try this again, and I look forward to experimenting more with koji in the future! Have you done any experimenting with koji? Let us know in the comments!

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