After I posted salt koji recipe a couple of weeks ago, I found out koji is literally a miracle condiments. This is the easiest thing to make, as long as you can find koji (usually at the Japanese grocery store), and the result is super-tacular. Marinate meat, even chicken breast, and it will never go dry. If you marinate it for even 30 minutes, the result is completely awesome.
It does have a distinct flavor, similar to miso or sake. Some people marinate (or pickle) vegetables in it, but I feel it imparts too much of the koji flavor this way. But using it as base marinade for meat and fish is awesome.
You can use soy sauce instead of salt and water to make shoyu koji (soy sauce koji). This is even simpler than salt koji. All you need is koji and shoyu. The ratio is 1 part koji, 1.5 part shoyu.
Mix everything together and leave it in room temperature for a week to 10 days. After a day or so, the koji will soak up all the liquid, and you want to add more soy sauce so that all the koji is covered in soy sauce again. After a week, it will smell like senbei (rice crackers), a mixture of rice and soy sauce, which is very nostalgic for me. This mixture is best to be used as a substitute to soy sauce, rather than using it as marinade. You can put a bit on top of silky tofu, or in anything you normally use soy sauce. It tastes like something in between soy sauce and miso -- it's versatile.
Miso, made out of soy beans, salt and koji, can be improved by adding koji and other goodies, to make miso koji.
From left, ginger, garlic and scallions. Chop them up (about 2tbsp each, or you can adjust to your likings).
Add about 1/3 ratio of warm water (about 120˚F degrees). If you are using 200 grams of koji, 60ml of warm water.
What I didn't do (ended up with not so great product) is to rest this, wrapped in towel to keep the temperature around 120˚F degrees for about two hours. This process will make sure koji will puff up.
Then add miso:
Then mix in ginger/garlic/scallions:
This is also better to use as condiments than marinade. I marinated aji (spanish mackerel).
Top two are marinated in miso koji, below is marinated in shoyu koji.
The miso one was definitely better. Shoyu was a bit too salty. As I said earlier, it may be better to use these as condiments, or sauce, rather than marinade.
Koji is awesome. How it tenderizes meat is beyond belief. You can only realize its greatness when you use this. Find koji now, and try it.