June 12, 2011

Some Notes on Making Nukadoko/ぬか床作りに関する注意点

Here are some notes on making nukadoko (rice bran pickling bed).

1.  Rice bran:  Of the six sites explaining how to make nukazuke (rice bran pickles) that I referred to, only one recommends fresh (un-roasted) rice bran.  Another site says that fresh (un-roasted) rice bran will be fermented quickly, can spoil easily, can get wormy, and will be difficult to maintain.
If you cannot get pre-roasted rice bran, roast fresh rice bran at 75C for 1-2 min. (according to one site) or 70C for 15 min. (according to another).  To roast it evenly, you are recommended to roast a small amount (say, 300 g) at a time.

2.  Salt:  Almost all sites I referred to recommend coarse salt (but I used cheap refined salt).

3.  Rice bran-to-salt ratio:  One site explicitly says that the salt should be 13% of the rice bran (200 g coarse salt for 1.5 kg fresh (un-roasted) rice bran).
The following lists the amounts of rice bran, salt, and water that are given on the six sites:
  1.  1 kg 140 g 1.2 liters
  2.  1.5 kg 200 g 1.5 liters
  3.  2 kg 400 g 2 liters
  4.  3 kg 500 g 2 liters
  5.  2 kg 300 g 2.7 liters
  6.  1 kg 200-250 g 1-1.5 liters
In summary, the salt should be 13-20% of the rice bran, and the water should be equal to the rice bran in weight.
Anyway, the nukadoko should be slightly less moist than miso.

4.  Container:  For 1-kg rice bran, for example, use a container (enamel, glass, ceramic, or plastic one) with a capacity of 3.5 to 4 liters.  For easy mixing, the container should be twice as high as the nukadoko.  As you can see, my container is a bad example.

5.  Whether to add bread, beer, yogurt, etc.:  Some sites recommend adding them to quicken the fermentation, while others doubt their effectiveness.  (I didn't add any of them.)
If you know by any chance someone who already has nukadoko, ask them to give you about 100 g of their nukadoko and add it to your nukadoko to quicken the fermentation.

6.  Salt concentration of the nukadoko
2.15%:  Bacteria other than lactic acid bacteria will grow, so you can't make nukazuke.
4.3% or higher:  Lactic acid bacteria will multiply proliferously.
8.6% or higher:  Even lactic acid bacteria cannot multiply proliferously.
The salt concentration of nukadoko should be kept at round 7%.


Mix the nukadoko twice a day in the summer and once a day in the winter.  When mixing the nukadoko, make sure that you turn it upside down.  After mixing, pat the nukadoko until flat to release air.
Reason:  Film yeasts, which are aerobic, will grow around the top of the nukadoko, whereas butyric acid bacteria, which are anaerobic, will grow around the bottom, so it is important to turn the nukadoko upside down.  Film yeasts smell of paint thinner, while butyric acid bacteria smell of damp socks.

Replenish the nukadoko as appropriate with rice bran containing 7% salt (100 g plus 7 g salt).

Keep the nukadoko at 20-25C, suitable for the growth of lactic acid bacteria.  At higher temperatures, the nukadoko will turn sour.  A common remedy for such sour nukadoko is to add karashi (Japanese mustard) powder, 1-2 tbsp of it per 1 kg rice bran and mix thoroughly, or add egg shell (membrane removed, and sterilized by boiling).

To be continued.

Edited to add on Oct. 8, 2011:
According to this site (Japanese only),
vegetable lactic acid bacteria differ from animal lactic acid bacteria in many respects. For example, the former can coexist with various microbes, while the latter cannot, and the former can survive in high salt concentration, while the latter cannot.
I don't think that adding yogurt, which contain animal lactic acid bacteria, to nukadoko will speed up the fermentation.

According to this site,
adding bread to nukadoko in the early stages of fermentation will not make any significance difference.


In summary, in maintaining nukadoko, it is important to control the temperature (20-25C, moisture (slightly less moist than miso), and salt concentration (around 7%).
I think that salt concentration is the most difficult to control because you can't tell the exact concentration unless you have a concentration meter. You may have to guess the concentration by tasting the resultant nukazuke.


1. 米ぬか: 参照した、ぬか床の作り方を説明する六つのサイトのうち、煎ってない米ぬかを薦めるのは一つだけでした。他の或るサイトでは、生の米ぬかは発酵が早く、腐りやすく、虫がわくことがあり、また維持が大変だそうです。
煎りぬかが手に入らない場合は、生ぬかを(或るサイトでは)75Cで1~2分間または(別のサイトでは)70Cで15分間、煎って下さい。むらなく煎るには、少量づつ(例えば、300 gづつ)煎ったほうがいいです。

2. 塩: ほぼどのサイトも、荒塩を薦めています(私は安い精製塩を使いました)。

3. ぬかと塩の割合: 或るサイトでは、塩は米ぬかの13%とする(生ぬか1.5キロに対して荒塩200 g)とはっきり書いてありました。
1. 1キロ 140 g 1.2リットル
2. 1.5キロ 200 g 1.5リットル
3. 2キロ 400 g 2リットル
4. 3キロ 500 g 2リットル
5. 2キロ 300 g 2.7リットル
6. 1キロ 200-250 g 1-1.5リットル

4. 容器: 例えば、米ぬか1キロに対して、容量3.5~4リットルの容器(ホウロウ、ガラス、陶器、プラスチック製)を使います。簡単に混ぜられるよう、容器の高さはぬか床の二倍は必要です。ご覧の通り、私の容器は悪い例です。

5. パン、ビール、ヨーグルトなどを入れるべきか?: 発酵を早めるため、入れることを薦めるサイトもありますが、その効果を疑問視するサイトもあります(私はどれも入れませんでした)。
もし、ぬか床を既に持っている人を知っていれば、そのぬか床を100 g程度くれるよう、頼んでみて下さい。ぬか床に入れれば、発酵が早まります。

6. ぬか床の塩分濃度
2.15%: 乳酸菌以外の細菌も繁殖するので、ぬか漬けはできない。
4.3%以上: 乳酸菌が繁殖する。
8.6%以上: 乳酸菌でさえ繁殖できない。


理由: 産膜酵母(さんまくこうぼ)は好気性(酸素が好き)なので、ぬか床の上部で繁殖し、一方、酪酸菌は嫌気性(酸素が嫌い)なので、底のほうで繁殖します。ですから、ぬか床を上下逆さにすることが重要です。産膜酵母はシンナーの臭い、酪酸菌は濡れた靴下の臭いがします。

ぬか床は、7%の塩を含む米ぬか(ぬか100 gに塩7 g)を適宜、足します。








Sissi said...

Thank you, Hiroyuki, for this detailed nukadoko guide. I feel I am ready to start next week!

Fräulein Trude said...

Very helpful! Thank you so much for your hard work! This is really contagious...


Hiroyuki said...

Sissi and Kiki: The notes are not exhaustive; there are many others, and I will mentioned them later.
I find this site the most useful:
Sorry, Japanese only, but I hope you can get some understanding from the photos.

If you find nukazuke hard to make, I would recommend making yogurt zuke.
(Japanese only)
450 g yogurt
22 g salt (5%)
Vegetables of your choice such as 1-2 cucumbers and carrots

Mix yogurt and salt, add vegetables, and put in the fridge overnight or 2-3 nights.
If you prefer nukazuke flavor, add 1.5 slices of bread.

Very easy, isn't it?

muskrat said...

ひろゆきさん、ありがとう!ブーラグ がすきです!わたしわ アメリカジん です。My grandmother kept a nukadoko bed, and made nukka pickles often. I started making nukka pickles last year and love them. (My grandmother was from Sapporo.) I enjoy reading your blog very much. I'm studying Japanese and reading your blog is good practice for me.

Hiroyuki said...

muskrat: Thanks! So, your nukadoko is one year old!?

Fräulein Trude said...

Hiroyuki-san: I just put together the joghurt version (Thx). I hope the bread will do. http://fraeuleintrudeskochversuche.blogspot.com/2011/06/japanese-style-joghurt-pickles.html


muskrat said...

ひろゆきさん、I kept nukadoko for several months, but I started classes again and did not have time to tend it and it went bad. After reading your blog, I think I will try again!

Hiroyuki said...

muskrat: Mine is nearly one month old, and I'm going to write about it pretty soon.