Pickles made with rice bran (nuka). ぬかずけ、糠漬け。
A typical sort of tsukemono, pickled vegetables ("preserved vegetables"). Vegetables are buried in a bed of ricebran (nukadoko) where they undergo lactic acid fermentation. Any vegetable may be used, but the most popular ones are radish, eggplant, cucumber and cabbage.
The nuka-bed is traditionally kept in a wooden barrel but today ceramic tubs or plastic buckets are more common. Rice bran (the white powder that is obtained when polishing rice; sometimes it is first roasted) is mixed in a barrel with saline water. Also konbu and miso as well as chilies may be added. The resulting mash, called nukadoko, looks like wet sand.
Starter vegetables and fruit peels are added to the nuka-doko. It is a good idea to "seed" a new nukadoko with some seasoned nuka from an older batch to get the fermenting culture of lactobacilli and yeast started. In the past, upon marriage, daughters used to take some of their mother's nukadoko to their new home (that was in the good old times that families still made their own pickles - now there are at most some farmers and hobbyists doing that).
Once fermentation has started and the nukadoko exudes a particular earthy or yeasty aroma, the starter vegetables are exchanged for the pickling vegetables. These are usually buried in the nukadoko for about a month, although periods of several months also are known if one wants to obtain a strong flavor. Pickling in a new bed also takes more time.
The nukadoko contains live organisms, so tastes vary considerably, depending on the season, the region, etc. When the pickles are ready, they are washed, sliced and eaten.
Once the bed has become active, new vegetables can be added at any time. To keep it in good order, and prevent it from becoming moldy, it has to be stirred every day; now and then, additional rice bran and salt have to be added.
The most famous type of nukazuke is takuan, pickled daikon radish (see photo below). The radish is colored yellow by adding turmeric (ukon; unfortunately, mass produced takuan rely on food coloring). Named after a famous priest of Daitokuji in Kyoto who purportedly invented this type of pickle.
Nukazuke are healthy when eaten with white rice as they have obtained Vitamin B1 from the rice bran, thereby reconstituting a vitamin that is lacking in the polished rice itself.