Since first trying tsukemono (漬物) nearly 20 years ago, I’ve been infatuated with Japanese pickles. In the U.S., we’re accustomed to a very limited range of pickles - usually cucumbers pickled in a vinegar solution with or without dill. Not so in Japanese cuisine where the variety of pickling techniques is amazing.
One of the most intriguing varieties of tsukemono are the nukazuke (糠漬け) which are vegetables that are preserved by burying them in a bed of fermented rice bran (糠). The resultant pickles are crisp, salty and tangy; but the process of preparing the nukadoko or nukamiso (ぬかみそ | 糠味噌) is not easy. I started my own nuka bed 4 weeks ago and it is just now starting to develop the complex character of a mature nukamiso.
The base of the bed is made of rice bran that is toasted over a medium flame in small batches with constant stirring to prevent scorching. You must stir it quickly and very vigorously as the color deepens. The goal is to toast it until it becomes a few shades darker. I used Bob’s Red Mill stabilized rice bran. I’m not sure what effect “stabilization” has on the product; but everything seems to be working. After completing the toasting of the entire bag in small batches, I carefully weighed the toasted bran. You need to get the exact weight because the amount of salt must be adjusted according to a strict proportion.
I added Korean sea salt, the sort that I use for kimchi. If the ambient temperature is cooler, you can get by with about 13% salt or less. Warmer climates need about 15% salt by weight. I split the difference and adjusted the salt to 14%. The salt must use no additives such as iodine. Sea salt is best.
Next, I dried the peel of two apples and one very ripe persimmon. I used a food dehydrator to accelerate the process. I added the dried peels and several pieces of dried kombu (昆布) to the toasted nuka and added just enough distilled water to make a slightly pasty mash. The amount of water is hard to specify; but it needs to be like wet sand. Under no circumstances should it pool in the bottom of the container. Finally, you must add starter vegetables to the mix. They stay in for a day, then are removed and discarded. The idea is to see the bed with the bacterial flora that it needs. Ideally, these are species of the genus Lactobacillus but I’m told that under certain circumstances - too little salt, too much water, too much warmth, too little airflow - that yeast can become prominent. This upsets the balance of microbial flora and can set up alcoholic fermentation. Of course, this is undesirable. By restoring some of the ideal factors, you can apparently reset the microbial balance; but who really knows?
Speaking of containers, I used shallow glass square container; but it is not ideal. Traditionally, wooden fermentation vessels would be used. Almost anything works. Most importantly, there has to be some airflow. I cover it only with a dish towel. It must be mixed with clean hands every day forever. I’m told you came get by with putting it in the refrigerator for a week or so if you’re away.
It took a little over two weeks to discern that anything was going on. The bed begins to take on a nutty, sweet aromatic smell about then; and the color begins to darken still more. Between three and four weeks, I added a little more toasted nuka to supply fresh unfermented material to the mix, to increase its volume somewhat and to dilute the salt somewhat based on my early tasting. After the bed matures about 4-6 weeks, it is ready to start pickling. Most vegetables can sit covered in the nuka for anywhere from a few hours to a day or so.