Last Sunday evening I remembered that I had a pork tenderloin sitting in the fridge. I had taken it out of the freezer two days before, and was suddenly gripped with anxiety over it going bad before I had a chance to cook and eat it. I had been planning to bop over to SF Market to grab some shio koji to marinate it in, but I had not done that, and (more importantly) I did not want to leave my home.
Luckily, I had some red miso (that is, soy bean paste that had been fermented with shio koji). Unluckily, I did not have mirin or sake, the other two ingredients required to make this excellent traditional Japanese marinade. Frustrated by my pathetic pantry, but still unwilling to leave my home, I smeared the undiluted miso paste all over the pork, plunked in a small sheet cake pan, and set it in the fridge, uncovered, for 24 hours.
The next evening, I wiped the miso off of the pork, placed it in a shallow baking pan, and slow-roasted it an oven set to 250℉ to for 50 minutes, until it reached a temp of 130℉. I finished it in a hot pan full of foaming, sputtering butter, which brought the temp to around 145℉, which is right where I like it. (You may recognize this sequence of events as “the reverse sear,” which is my favorite way to cook pork.)
It was, as one might expect, good, despite the effects being slightly less nuanced than the other two marinades. The miso lightly cured the pork, drawing out moisture, intensifying the pork’s flavor, and infusing it with a salty fermented flavor. It didn’t have the subtly sweet and sour notes of the miso-mirin-sake combination, and it wasn’t as funky as the pork I had marinated in shio koji, but it was incredibly tender, with a slightly nutty, intensely savory flavor that required no additional seasoning.
Obviously, I am not the first person to encase something in miso and notice its delicious effects—Japanese people have been doing it for a very long time. But it was a nice reminder that this ingredient has so much to offer all on its own, and I was surprised by how effective and delicious it was without any other ingredients. I used red miso, but I suspect other colors would have similarly delightful effects, though keep in mind that the darker ones will bring a saltier, more intense flavor to your meat.
There’s no need to measure, just smear it on a piece of meat until the whole thing is coated in about an 1/8th inch of paste, set it in the fridge for five hours (or up to 24), then wipe it off and cook it as usual. The longer your meat sits in miso, the more “cured” it will taste, so start light with more delicate proteins. For a pork tenderloin, however, I recommend the full 24 hours. That thing was good.