KITAKYUSHU-KOKURA Nuka-Doko Nuka-Daki KENKYUKAI

北九州小倉・糠床糠炊き研究会
The Research society for beds of rice-bran (Nuka-Doko, 400
year history), fermented by lactic acid bacteria and yeast
fungus, used for pickling vegetables (Nuka-Zuke) and flavoringboiled blue-backed fish (sardine, mackerel : Nuka-Daki) as
healthy traditional dishes in Kokura, Kitakyushu-City, Japan糠床糠漬け (upper : Nuka-Zuke)糠炊き (lower : Nuka-Daki)(Nuka-Dokos)

2018.7.10

Nuka-Doko and Nuka-Zuke
Pickling vegetables in Nuka-Doko
One of the Japanese traditional food culture
Kitakyushu-Kokura Nuka-Doko, Nuka-Daki Kenkyukai

Hiroshi Kimura

Nuka-DokoNuka-Zuke

What is Nuka-Doko ?
A Nuka-Doko, a bed of rice-bran, is composed of rice-bran as a main starting
material, mixed with appropriate amount of water and salt, and preferably with ahigh-quality starter which is fully fermented and aged rice-bran by the combinationof lactic acid bacteria and yeast fungus, used for pickling vegetables. By repeatedpickling of various vegetables in a Nuka-Doko a t a n appropriate temperature (20-25
C) and by taking out pickled ones, lactic acid bacteria and yeast fungus in addition
to enzymes in vegetables ferment sugar (glucose), oils (rice-bran oil) and amino acids
to produce special flavor which is absorbed in pickled vegetables to be Nuka-Zuke.
This is rare fermented food in the world.

Nuka-Zuke
Nuka-Dokos

Nuka-Daki
MacherelSardineRoots of a Nuka-Doko in Japan
There is a historical description (as letters) inhistory books edited by Tokyo Univ on the Hosokawa
family in Kokura castle. Tadaoki Hosokawa was aruler of the northern area of Kyushu. In the oldletters between Tadaoki and his son, Tadatoshi (in1626 and 1628), there is a description that a NukaZuke of eggplant was sent to Tadaoki in a different
place by his son, and his father satisfied with the
Nuka-Zuke very much. Therefore, it wasdemonstrated that Nuka-Doko was already existed
early in the 17 th century in Japan.

Nuka-Zuke & Pickles
Nuka-Zuke once may be taken as preserved vegetable food
like piclkes in US. But at present, it’s not. Because it is eaten
up in one or two days after taking them out of a Nuka-Doko.
In Kitakyushu-City, especially in Kokura district,comparatively many family own their Nuka-Doko, and they
pickle seasonal vegetables with Nuka-Doko. Nuka-Zuke iseaten as a side dish for breakfast and supper.

Nuka-Doko at present time
However, at present, Nuka-Doko is not so popular among
younger generations, 20s and 30s. One of the Japasese
traditional fermented food is getting forgotten . This is thesame phenomenon as in other traditional food in Japan.
This is why we, the research group, have been handing down
the expertise and skills on Nuka-Doko by setting public
lectures and training sessions for adults and children.

Kokura Castle
Kitakyushu City Hall

In order to overcome the present stagnant situation,
new approaches and challenges were presented
by Kitakyushu City itself
to reactivate the traditional food culture of Nuka-Doko andto propose modern and new fashion for the foodculture.

Challenges、“HAKKO JAPAN in KYUSHU 2015”(fermentation)

Hiroshi

Teaching how to make Nuka-Daki in TV

Promotion girls for the Nuka-Doko cultureHiroshi

Opening tape-cut for the big event

A competitive showfor new proposals using
Nuka-Doko & Nuka-Daki

A variety of new cooking was
proposed by students, general
citizens and professional cooks
for the competition.
Judges for the new cuisine using Nuka-Doko & Nuka-Daki

Bagna Cauda as Grand Prix by a restaurant owner

Visit the related site

http://hakkou-japan.com/

New waysof takingNuka-Doko&Nuka-DakiHiroshiHealth checkup of Nuka-Dokosof the visitors in the event.
pH, NaCℓ％ 、 odor, taste, andmoisture of their Nuka-Dokos
were checked by specialists.

Training session for Nuka-Dokoby Hiroshi’s wife

Pickling processes using Nuka-Doko in Japan
Pickling of various vegetables using a Nuka-Doko is performed batchwise in every home as well as in Nuka-Zuke shops in Kitakyushu-city
Japan. A continuous pickling process is not applicable because a NokaDoko is a mud-like composition and because several kinds of vegetables are
pickled all at once. A Nuka-Zuke taken out of a Nuka-Doko is adhered by
Nuka-Doko (or called Nuka-Miso) Therefore, it is removed by washing
before eating. These processes are different from those for “Pickles” in US.
Recently, a Nuka-Doko in a liquid phase has been developed andcommercialized. However, the flavor typical to fermented Nuka-Doko has
not been fully reproduced. Therefore, Nuka-Zuke produced by using a
conventional Nuka-Doko is preferred by consumers who know the real taste
and flavor of Nuka-Doko and Nuka-Zuke.

Nuka-Dokos to prepare Nuka-Zuke
I have seven Nuka-Dos below for experiment, three rice-bran based andfour not rice-bran based. My wife’s are larger rice-bran based ones.

Hiroshi’s Nuka-Dokos(for experiment)
Net content :1Kg, 1kg (left), 3Kg(right)
1Kg(left), 3Kg(right)
2Kg(left), 2Kg(right)(not rice-bran based)

My wife’s Nuka-Dokos
Hiroshi’s Nuka-Dokos

In Hiroshi’s

My wife’s Nuka-Doko
Net content :12Kg(left), 6Kg(right)

Preparation of vegetables before pickling(in case of root vegetables)

Cucumber and carrot are washed and adhered water is removed withpaper towel. Carrots are peeled totally, and cucumbers peeled as shown in
the right figure (two lines). Rub very small amount of salt on the peeledsurface of the vegetables to promote pickling.

If vegetables are weighed before and after pickling, water flown out fromvegetables divided by the original weight can be an index of picklingdegree. But it depends on the kinds of vegetables.

Pickling vegetables (cucumber and carrot)

Push vegetables completely inside the Nuka-Dokos

Pickling time of vegetables at 20-25℃
Cucumbers 8hrs
Carrots
10hrs(depends on preference of people)

Vegetables used for Nuka-Zuke
Spring bamboo shoots, bracken, broccoli, cabbage,
asparagus
Summer eggplant, cucumber, Japanese ginger, okra,
green soybeans, paprika, Konjac, celery,
tomato, spaghetti squash,. pumpkin
Autumn/Winter Japanese white radish, turnip,
carrot, lotus root, yam, chayote,
Italy (peel)

Delicacy

avocado, banana

Degree of pickling
Quick pickled(Asa-Zuke*)slightSour
pickling time, hr
5-6
20-25
Temp, ℃
weight loss, %～8
taste
taste bland
like vegetable salad

Well-pickled(Furu-Zuke**)very sour
10-24
20-25
＞10
dark taste*vegetables lightly preserved in salt**st ir fry cut Nuka-Zuke with little oil, and red pepper isadded to be a very nice dish when drinking.

Asa-Zuke

Stir fry of Nuka-Zuke

Nuka-Zuke cuisine by the Japaneserestaurant, “Ajidokoro-Yano”, owned by“Sumico”, a popular jazz singer(She is one of the advisers for our research group,and her sensory taste and smell are extremely sensitive)Preparation of a Nuka-Doko by Kimura
Materials①rice-bran (raw and fresh)
1000g②salt (natural)
140g③water (natural)
1400-1600g④starter (high quality fermented rice150g
bran)
200g
⑤cucumber (grated）
5g⑥kelp （chopped)
2.5g⑦red pepper (chopped)
Into a plastic container (5ℓ), 1600g of water and 140g of salt are charged,
and agitate the mixture to make a homogeneou s solution.
Then, 1000g of rice-bran is charged and mix the content to make a ricebran suspension. Then, a starter, grated cucumber, chopped kelp and red
pepper are charged, and mix the content homogeneously.
Then, the final mixture is filled in a transparent tapperware (5-ℓ).
The reason why a transparent container is used is to observe theinitiation of the fermentation and aging processes. Dramatic change instate of a Nuka-Doko is observed during the initial fermentation and aging
processes.

The function of each material for a Nuka-Doko①Ricebran④astarter⑤
cucumber
⑥kelp

⑦red
pepper⑧
Sansho⑨a resource of glucose and related sugars, andinitial lactic acid bacteria source.
fermented and aged Nuka-Doko to promote thefermentation of a newly prepared Nuka-Doko.
a supply source for glucose and lipoxygenasea supply source for sodium glutamate as astarting material for propionic acid as a majorfermented odor of a Nuka-Doko. It is also a
supply source for taste. In Japan, Rausu kelp
has the highest content of gultamate. Its price istwice or three times higher than general kelps.
capsaicin is antibacterial and promotes lactic
acid fermentation
fruit of Japanese pepper, sanshol also functions
as red pepper
citron pericarp is often used as additional flavor

(1) Observation of fermentation of a newly
prepared Nuka-Doko without using a starter(2)About 2-3 months are required for the completionof the fermentation as shown in Fig 1.

(2) Observation of fermentation of a newly
prepared Nuka-Doko with using a starter.
Only two weeks are required for the completion of
the fermentation followed by the primary aging, asshown in Fig 2. A significant decrease in pH bypromoted fermentation due to the addition ofa starter was clearly observed.

Fig 1 Fermentation of a Nuka-Dokowithout using a promoter

A starter is “a fermented and aged
Nuka-Doko with high quality”
maintained by continued careful dailycare of a Nuka-Doko.
It is mixed with raw rice-bran when
preparing a new Nuka-Doko to promotefermentation and to attain the same
flora of a starter for a newly preparedone.
suitable pH region for Nuka-Zuke
After the initial two weeks, pickling offavorite vegetables can be performed toprepare Nuka-Zuke. And red pepper,
Sansho (Japanuse pepper), pericarp,
and kelp are added further depending on
preference of a owner of Nuka-Dokos.

Fig 2 Effects of a promoter on thefermentation of a newly prepared Nuka-Doko

(3 ) Comparison of starters
Comparison of fermentation processes of newly prepared Nuka-Dokos
promoted by three different starters from Dr. Iai’s and two advisers, Ms.
Hatano and Ms. Yano for our research group was performed as shown in
Fig 3 and following pictures of Nuka-Dokos. Dr. Imai, who was the top
adviser for our research group, revealed the versatility of the fermentation
process of Nuka-Dokos for the first time in 1980s by detailed experiments.
He was a pioneering top scientist in the science of Nuka-Doko fermentation.

Dr. Imai’s Nuka-Doko, 150 years oldthen, highly aged with high quality .

Dr. Imai, Hiroshi and Ms. Yano
After his lecture in the university.

Fig. 1 pH change after the preparation of NukaDokos using three persons’ different starters(I indicates Dr. Imai’s, Nuka-Doko, 150 years at 1995)

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2015.9.15 5:32:04 (8165)

2015.9.15 5:32:12 (8166)

Day 1.5

Day 1.5

Day 0.5

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2015.9.15 5:33:12 (8168)

2015.9.15 5:33:26 (8169)

Day 2.0

Day 1.0
Day 2.0

2015.9.15 17:42:16 (8179)

2015.9.15 17:43:00 (8181)

2015.9.15 17:43:36 (8183)

Day 1.5

2015.9.15 17:42:30 (8180)

2015.9.15 17:43:10 (8182)

2015.9.16 04:10:50 (8184)

Expansion of Nuka-Dokos by thje generation of CO2
proceeded greatly, and a water phase (depth: 15-20mm) is
observed at the bottom of Nuka-Dokos.

Day 2.5
2015.9.16 04:12:32 (8186)

Day 2.5
2015.9.16 04:13:06 (8187)

Day 1.5
2015.9.16 04:11:50 (8185)

The expansion almost completed at Day
2.5, and then contraction proceeded.

Day 2.5

2015.9.16 04:33:42 (8191)
Growth of white film yeast isobserved at the upper edge ofthe container.

2015.9.16 04:14:20 (8188)

Day 3.0

Day 3.01015.9.17 04:37:30 8194

1015.9.17 04:38:18 8195

Day 2.01015.9.17 04:38:54 8196

1015.9.17 04:39:36 8197

1015.9.17 04:39:48 8198

1015.9.17 04:40:02 8199

The growth of white film yeast over the upper surface of Nuka-Dokos proceeded
greatly first for the left Nuka-Doko started by Hatano-Doko. Hatano-Dokogenerates excellent fermentation odor. produced by yeast. Within four days after
the preparation of Nuka-Dokos, a pH of a Nuka-Doko decreased to less than 4.

Day 4.0

Day 4.0

Day 3.01015.9.18 04:47:20 8205

1015.9.18 04:48:26 8207

1015.9.18 04:49:22 8209

1015.9.18 04:47:40 8206

1015.9.18 04:48:40 8208

1015.9.18 04:49:36 8210

Dramatic expansion of a Nuka-Doko due to CO2 generation, followed , by thegrowth of white film yeast, was completed within 4-5 days after the preparation ofa Nuka-Doko. But it depends on temperatures . Foam sound by the generation of
CO2 was also listened.

Influence of accumulated water by repeatedpickling of vegetables on the fermentation of
Nuka-Dokos, and corresponding treatments
Addition of salt as well as rice-bran should be performed in
the daily use of a Nuka-Doko. Because water liberated byrepeated pickling accumulates in a Nuka-Doko, resulting in adecrease in a concentration of salt of a Nuka-Doko and anincrease in moisture of Nuka-Dokos .
These additional treatment, especially addition of salt isvery important to keep the health of a Nuka-Doko.

If the additional treatment is ignored, an acid %of a NukaDoko rapidly decreases (●) to deteriorate a Nuka-Dokoresulting in unpleasant order and taste. This is because
unnecessary microorganisms (●) producing unpleasant odor
and taste increase rapidly from Day 7 as shown in Fig 4.

9good t aste

salty

s al t shor tage, bitter

acid

75

8

8

3.0

7

microorganis log(N)
5
6
7

2.5

moist ure

2.0

70

6
s alt

numberof4

unnec cessa ry
micro organis
m

4

1.0

65

1.5

5

salt

％

0
acid ％

moisture％

60

3
1

2

3

4

5

6

7

8

9

10 11

Repeated pickling days
（one pickling / day）

Fig. 4 Influence of repeated pickling on a Nuka-Doko
M. Imai, Nippon Nougeikagaku kaishi, 57 (11), 1105-1112 (1983).
The original figure was remade as Fig 4.

Nuka-Zuke
Shop 2

ProposedNuka-DokoNuka-Zuke
Shop 1No
fermentation

water
shortage

Effect of moisture %of a Nuka-Doko on
the fermentation of Nuka-Dokos

moisture %50

54 55 Tough Doko 60 61
most home in
Kitakyushu

65

70Softer Doko (soggy or mushy)
Water layer over a Nuka-Doko

Softer Doko : easy fermentation and pickling;
deteriorate at higher temperatures than 35℃

Aroma is different between the two types of NukaDokos.

Flavor produced in a Nuka-Doko
Flavor typical of fermented Nuka-Doko is produced by the series of
enzyme reactions based on yeast starting from sodium glutamate. Kelp is amajor resource for the amino acid. Details about the flavor produced in a
Nuka-Doko was reported by Dr. Imai in 1980s. He revealed theuniversality of the fermentation of a Nuka-Doko for the first time in 1980s.

M. Imai, Nippon Nougeikagaku Kaishi, 57 (11), 1105-1112 (1983).
The content of flavor compounds in a fermented and aged Nuka-Doko isless than 100 ppm. Most of them are oil-soluble and are existed with ricebran containing rice-bran oil which is also a source for γ-lactones (mainly
C9, peach like odor) as an important aroma in aged Nuka-Doko.
Therefore, separation of fermented rice-bran from a Nuka-Doko forincreased productivity for Nuka-Zuke degrades the quality of it significantly.
Nuka-Zuke greatly. Because oil-suluble falavor are lost. The higher the
productivity for Nuka-Zuke is, the lower the quality of Nuka-Zuke is.
Volatile lower carboxylic acids constitute 75% of the flavor of a Nuka-Doko,among which a content of propionic acid (CH3CH2COOH) is 54 ppm asshown in Fig 5.

Aroma produced in a fermented Nuka-Doko

Imai, J. Japan Association of Food Preservation Science, 21 (3), 161-178 (1995)..
Imai, Shokuno Senmon Zasshi, 107(1), 41-45 (2013).
Pro pionic acid 54.5 ppm, acetic acid 3,2 ppm, Butyric acid 1.1 ppm
1.7 ppm
C9 γ-lactone

Sensory test & Principal Component Analysis
for Nuka-Zuke
Estimation items
1. fermentation and aged flavor of Nuka-Dokos
2. sour taste
3. flavor of vegetables (freshness)
4. sweetness
5. bitterness
6. irritation
7. good to eat or no good
8. requested preference for the Nuka-Zuke samples

Pickling of sliced cucumber and its sensory test
(picking time, 20 mins at 25 ℃)

1
2
3
4

5
6
7
8
9

NaCI％

pH

3. 5
4. 8
6. 0
6. 9
2. 4
2. 7
1. 1
1. 6

4. 1
4. 3
6. 4
5. 7
6. 1
5. 9
6. 0
4. 1
0

0

7.0
6.5
6.0
5.5
p H 5.0
4.5
4.0
3.5
3.0

s h ortageo f s altn o fetrmentation

suitabler e gion

0

1

2

3

4

5

NaCℓ％

6

7

8

Health check of Nuka-Dokosof the visitors to HAKKO Japan 2015
〇 in the square is no good because excess Shansho was added resulting
in deterioration of her Nuka-Doko (no fermentation odor)● is the best Nuka-Doko. She was a housewife of a large family. She
picked large amount of vegetables resulting in a significant decreasein NaCℓ%. I told her to add salt and rice-bran as fast as possible.

6.0

4
8

7

1

酸 味 なし

5.5

2

5.0

3
4

3

pH

2

弱 い 酸味
1

4.5

6

5

10

程 良 い酸 味

4.0
3.5

9

5

13

6

11

7

12

8

強 い酸味

9
10

3.0

3

4

5

6

7

8

11
12

NaCℓ％

13

塩分

ｐH

4. 5
5. 2
3. 4
4. 1
6. 0
4. 0
6. 5
4. 1
7. 6
4. 6
4. 7
4. 8
5. 0

4. 7
5. 2
4. 8
5. 9
4. 2
4. 4
5. 9
5. 9
4. 3
4. 2
3. 9
3. 7
4. 1

Health check of Nuka-Dokos of the members of ourresearch group including the two advisers, Ms Hatanoand Ms Yano (Nuka-Zuke shop owners)

Training session for Nuka-Dokos
Kitakyushu Kokura Nuka-Doko, Nuka-Daki Kenkyukai
http://www.nukaken.jp

Materials of NukaDoko andtheirfunction

Bodily sensationof fermentation ofa Nuka-Doko

White film yeast
Don’t throw away

Pickle seasonal
vegetables

For maintenancefor healthof aNuka-DokoHi !
Which is mackerel used for Nukla-Daki ?

meckerel

SardineNuka-Dokos are basis
for Nuka-Zuke and Nuka-DakiMy research targets
1. To reproduce the taste of the Nuka-Daki which my aunt
used to prepare for us (more than 60 years ago) . She has alarge Nuka-Doko then. Recently, taste of Nuka-Dakidrastically degraded due to shortage of fermented NukaDoko and use of excess amount of seasoning such as Shoyu,
Mirin, sugar and Japanese Sake. Traditional real taste of
Nuka-Daki was already lost in the related markets. Recent
younger generation do not know the taste of Nuka-Daki
2. To develop high quality Nuka-Dokos with highest
productivity by fastest fermentation.
3. To improve texture or mouth-feel of Nuka-Daki of mackerel
4. To commercialize non-rice bran based Nuka-Doko

1951

1968

My aunt and me

Dr. Imai, Hiroshi and Ms. Yano after the second lecture
by Dr. Imai at the University of Kitakyushu in 2014.

Hiroshi

Ms YanoMs Hatano