The nukadoko needs to be mixed at least daily. Hotter and more humid climates require more mixing – sometimes twice or three times daily. If the nukadoko is kept in a wooden tub or porcelain container (i.e. not airtight) then it will also require more mixing.
Results of not mixing the nukadoko enough-
Bugs or small flies may gather and lay eggs.
The nukadoko may turn sour.
Clean and dry hands thoroughly, try not to use a soap with heavy fragrance or lotions.
Mix nukadoko by hand thoroughly. Take care to mix from the the bottom of the container. Remember, the main point of mixing is to aerate the nukadoko.
After mixing thoroughly, pat the surface of the nukadoko to make sure it is flat. Make sure any vegetables are completely covered, and that you do not compress the nukadoko, simply flatten it. Compressing the nukadoko will remove the air that was just mixed in.
Wipe the walls inside of container with a clean terrycloth towel or a lint-free paper product to ensure there are no stray bits of nukadoko.
Close container and store in a cool, dark place.
Wash vegetables is clean water.
Cut daikon and nasu in half. Do not cut cucumbers. Nappa cabbage can be cut into quarters.
Rub salt onto vegetables. If the vegetables are dry, use wet hands to rub the salt on the vegetables.
Bury vegetables in the nukadoko.
Vegetables buried deeper in container will pickle faster.
Lay longer vegetables flat so that they pickle evenly.
Flatten the surface of the nukadoko, wipe walls, close and store in a dry, dark place. Flatten the surface but do not compress it. Increased pressure on it will increase the speed of fermenting but may very well suffocate nukadoko, causing it to stall or sour.
Find and remove the vegetables to a plate. Generally speaking, don’t worry about wiping the excess nukadoko from the vegetable.
After removing the vegetables, mix, flatten, wipe walls, close and store the nukadoko.
Wash vegetables in cold water.
Cut and serve, or store in Tupperware in the refrigerator.
Twice a month or so, you’ll probably have to add nuka. Nuka, salt, togarashi, and konbu should be added. Sometimes, some people would recommend that some of the old nukadoko be discarded during this procedure to allow for more new nuka. This depends on the total volume of the nukadoko, and the water content. Nuka that is added can be toasted or untoasted, but must be tepid.
When the nukadoko gets wet…
Wet nukadoko can suffocate the fermentation process, and cause it to sour. To decrease water level, design a device with some combination of sieve and paper towels to soak up extra moisture. Alternatively, remove old nuka and add fresh, dry nuka. I usually do this, as it is easier.
Try adding some combination of eggshells, Japanese mustard, or togarashi peppers. Depending on your climate, try leaving the lid off a little or mixing 3+ times per day. Also, add some salt to slow down the process.
Too little air (not enough mixing)
Chemicals from soaps or lotions on hands
Bacteria from unwashed hands or vegetables.
Personally, I’m using a large plastic Tupperware-style box with an air-tight rubber seal. I've seen people use plastic bags, Tupperware, ceramic urns, and cedar tubs. In my opinion, wood seems to be the best because it allows some air through and adds flavor. Used sake "taru" are supposed to be quite good. Also, since one wants to lay the vegetables flat, remember that the container should be as wide as the largest vegetables are long.
Dealing With Your Nukadoko When You Travel
If you are leaving for a few days, give it a good mix cover the top of the nukadoko with salt. Seal the container well and place in the back of your refrigerator. Upon returning, throw away the top layer of nukadoko. If your trip is longer than a few days, then you will need to leave the nukadoko with a caretaker. It will be imperative that the nukadoko is stirred regularly by hygienic hands during this time.
Materials commonly added to Nukadoko
Nails - The iron in the nails prevents eggplant surfaces from oxidizing and turning brown. Iron paperweight sized products are available which do the same thing.
Garlic - Garlic adds flavor and aroma.
Katsuobushi - Katsuobushi is the shaved dried mackerel used to make lots of Japanese dishes. Pieces chip off of a block can be inserted into the nukadoko. They add a nice woody flavor.
Japanese Mustard - Helps control the fermentation of nukadoko and adds flavor and aroma.
Dried Shiitake Mushrooms - Adds flavor and aroma.
Bread Crumbs - Helps fermentation and adds flavor.
Beer - Helps fermentation and adds flavor.
Chili Peppers -Helps control fermentation, adds flavor.
Dashi Konbu - Dried kelp. Adds flavor and depth to the nukadoko, as well as maintains its health.
Salt - Salt is the single most important part of the nukadoko. Too much kills the flavor, too little lets the fermentation get out of control. The balance of the salt on the vegetable is essential for the final saltiness of the pickle.
There are many things that affect the character of nukadoko. I have friends who add beer, bread, garlic, konbu and togarashi, as well as eggs, fruit rinds, and other scraps. One friend in Fukuoka uses only broken pieces of dried katsuo, konbu, and whole chili peppers. My nukadoko is a getting older everyday, and the flavor is ever-evolving and becoming more complex. Everyone seems to agree that one you use bare hands wen mixing and andling the nukadoko. Mixing frequently, above all else, is the most important thing. When the mixture is health a pleasure to mix and to smell. On the other hand, bad nukadoko can smell like garbage. Also, it is important to feed the nuka even if there are is no need to pickle anything. Feeding the nukadoko vegetables that will be discarded will help keep it healthy and maintain its flavor.
