The nukazuke method of pickling vegetables in a fermented rice bran bed called a nukadoko was developed in the 17th century. Since vegetables pickled in a nukadoko absorb Vitamin B1 from the rice bran, they helped to prevent beriberi, an illness stemming from a lack of the vitamin that was so prevalent in Edo (present-day Tokyo) that it was called “the Edo disease.”

These days, nukazuke pickles are back in the nutritional spotlight as a probiotic food, a great source of gut-friendly microorganisms.

Nukazuke pickles are usually eaten after being in the nukadoko for one or two days, while they are still fresh and crisp yet packed with salty-sour, sweet umami-rich flavor. The longer the vegetables are left in the nukadoko the stronger the flavor they will develop. The most famous type of preserved nukazuke is takuan, which is made with dried daikon.

Making a new nukadoko is simple — all you need are rice bran, salt and water. You can also add various flavor-enhancing ingredients to the mix such as sansho peppercorns, red chili peppers, konbu seaweed and yuzu citrus peel. A new nukadoko must then be encouraged to ferment by adding vegetable scraps to it daily, which facilitates the growth of beneficial yeast and lactobacilli. The scraps are removed daily and fresh scraps are added. You can use almost any vegetable scraps, but be sure not to use anything that’s dirty or going bad in any way.

Repeat this sutezuke (throwaway pickling) process until the nukadoko develops a slightly sour, fermented odor, which means it’s starting to produce lactic acid. You can also buy or ask a friend to give you a small amount of mature nukadoko get the culture going. This passing of the bacteria torch will speed up the maturation process considerably. On a side note: Some nukadoko are more than 100 years old and are passed on from mother to daughter.

The keys to creating and maintaining a healthy, well-balanced nukadoko are temperature, maintenance and hygiene. The type of organisms you want in a good nukadoko love temperatures between 20 to 25 C; anything above 30 C will encourage the types of organisms that will make the nukadoko smell alcoholic or turn moldy.

It’s also possible, however, for a nukadoko to mature at lower temperatures such as those found in a refrigerator, though it will happen at a slower rate. If you’re starting a new nukadoko at an ideal room temperature you can expect it to become ready to use in a week to 10 days, while it may take two to three weeks in the refrigerator. It’s also important to stir up the nukadoko regularly, at least twice a day at room temperature, once a day if refrigerated. This redistributes the aerobic and anaerobic enzymes in a way that encourages a healthy, tasty, low-pH (slightly sour) nukadoko.

Last but not least, keep everything that comes in contact with the nukadoko impeccably clean — utensils, your hands and, of course, the vegetables. This will prevent any undesirable organisms from storming the keep of your precious nukadoko.

You can pickle any vegetables you like in a mature nukadoko. Besides the classics like eggplant and cucumber, my favorites are zucchini, cherry tomatoes and radishes.

Rub any vegetables with a skin, such as cucumber and eggplant, with salt before putting them in the nukadoko. This speeds up the pickling process by drawing out the water from the vegetables. If a nukadoko gets too wet, mix in some fresh dry rice bran with about 13 percent of its total weight in salt. I keep a well-matured nukadoko in the refrigerator, where it will keep even without stirring for a few days. If you’re taking an extended break from making nukazuke, freeze some of your nukadoko to use as a starter for a new batch.

My basic formula for a new nukadoko uses dried roasted rice bran (irinuka), which is widely available. If you can get fresh rice bran (namanuka) by all means use that instead.

How to make a healthy nukadoko

1 kg roasted rice bran (irinuka) or dried rice bran
1,000ml (1 liter) water
130 – 150g salt (13% to 15% of the rice bran)
2 dried red chili peppers
1 10-cm-square piece dried konbu seaweed
1 tablespoon sansho pepper berries
Vegetable scraps such as torn cabbage leaves or radish tops

Suggested equipment: A large, deep, noncorrosive, clean container (heat-proof glass, enamel, ceramic or plastic) with a lid; a clean spoon or other stirring implement; and a room thermometer.

Bring the water to a boil. Put the hot water in the prepared container and add the salt. Stir until the salt is dissolved, and leave to cool down to room temperature.

Add the rice bran gradually, stirring well between additions. Once all the rice bran is added, the mixture should have the consistency of moist sand. Mix the chili peppers, konbu seaweed and sansho pepper berries into the moist rice bran. This is the basic nukadoko (rice bran pickling bed). Add your first batch of vegetable scraps, push them in well, and smooth out the surface.

Put the container in a dark place where the ambient temperature is between 20 C and 25 C if possible, and certainly no higher than 30 C. If you don’t have a place with this temperature, put the container in the refrigerator.

Follow the instructions in the article for fermenting and maturing the nukadoko.

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