Nukadoko or nukamiso is Japanese fermented picking bed made from rice bran. Pickles made in nukadoko is called nukazuke. Nutrient rich bran-pickled-vegetables have been supplemented important vitamins and minerals to Japanese diet from hundreds of years ago.
This is a very deep and complicated subject. You can think of nukamiso pickling bed just like other fermented food, such as active yogurt or sauerkraut. In the same sense yogurt is alive, pickling bed is alive and active lactic acid and other living organisms has to be taken care of every day.
In Japan, you can get fresh unprocessed rice bran at rice processing stations very cheaply. Unprocessed rice bran is rich in nutrients, which are essential to the pickling bed, but highly perishable. In order to extend the shelf life, packaged rice bran in Japanese markets are processed by heat. Some people don’t like toasty smell coming from heat processed rice bran.
In the United States, rice bran sold at health food stores. I understand that for a longer shelf live, U.S. manufacturers stabilize rice bran by extracting oil without heating it.
Raw, unprocessed, and not stabilized rice bran is the best to make active nukadoko quickly. But most of us don’t have access to it. I used to buy processed nuka from a Japanese market, but I switched American made stabilized rice bran.
From my experience, cold processed American rice bran is more suitable than Japanese processed rice brans to make pickling bed.
There are important notes about nuka pickling bed. You need to keep it somewhere around 77°F and mix it thoroughly every day with your clean hand, in order to encourage the growth of lactic acid and yeast. If you will be away for a while or your kitchen gets too hot in summer, keep it in a refrigerator. Refrigeration delays fermentation process, but you can avoid spoilage. Nuka bed gets over fermented or spoiled, if it is kept in over 85°F temperature.
I usually keep my nuka bed in a refrigerator. It takes a little longer to pickle, but I will not fail in that way.
Healthy nukadoko smells little sour, as other fermented food does. If your nuka bed smells overly sour, bitter, or emit other unpleasant smell, you may need to fix it, or in the worst case you may need to discard it and start a new batch.
Daikon, white turnips, carrots, cucumbers, cabbage and eggplants are the most typical vegetables to be pickled. But okuras, broccoli stalks, inner white part of watermelon rind are also tasty. If you want strong smelling vegetables such as celery stalks or onions, you need to make a different pickling bed batch in a different container as pickling bed absorbs the strong odor.
To start making your own nukazuke pickling bed, you need a large enough container to put picking bed and vegetables. The size of the container has to be large enough to put whole cucumbers or carrots.