October 6, 2011

Microbes in your nukadoko/ぬか床の中の微生物たち

When you keep your nukadoko, it is very important to keep in mind the characteristics of the microbes you want to grow in it, as well as those of the ones you don't want to.

Here is a summary.

1. Vegetable lactic acid bacteria
Facultative anaerobic, meaning that they like an environment with a little oxygen.
Can survive in high salt concentration, unlike animal lactic acid bacteria.
Eat sugar to produce lactic acid and amino acid.

2. Yeast
Facultative anaerobic, meaning that it likes an environment with a little oxygen.
Eats sugar to produce alcohol, among others.
Ester is produced from alcohol, giving aroma to nukazuke.

3. Butyric acid bacteria
Obligate anaerobic, meaning that they absolutely hate oxygen.
Unwanted but harmless (used in some antiflatulents).
If you fail to mix your nukadoko regularly, butyric acid bacteria will start growing at the bottom of your nukadoko, giving off the smell of damp socks.

4. Film yeast
Obligate aerobic, meaning that it absolutely likes oxygen.
Unwanted but harmless (used in the production of sherry)
If you fail to mix your nukadoko regularly, film yeast will start growing on the surface of your nukadoko, producing ethyl acetate (thereby giving off a smell like paint thinner).
When mixed inside your nukakodo, it will start alcohol fermentation.

5. Other unwanted bacteria and fungi
Most of them are obligate anaerobic, meaning that they absolutely hate oxygen.
If you fail to mix your nukadoko regularly, you may let butyric acid bacteria to grow, possibly enabling other unwanted bacteria and fungi to grow. If this happens, it will be difficult to recover your nukadoko.

***
ぬか床を管理する際、ぬか床で繁殖させたい微生物の特徴、ならびに繁殖させたくない微生物の特徴を覚えておくことがとても重要です。

下記にまとめます。

1. 植物性乳酸菌
通性嫌気性(酸素が少ない環境が好き、ということ)。
動物性乳酸菌と異なり、高塩分濃度でも生存できる。
糖分を食べ、乳酸やアミノ酸を作る。

2. 酵母
通性嫌気性(酸素が少ない環境が好き、ということ)。
糖分を食べ、アルコールなどを作る。
アルコールからエステルが作られ、ぬか漬けに香りを与える。

3. 酪酸菌
偏性嫌気性(酸素が大嫌い、ということ)。
不要だが無毒(整腸剤に使われる)。
ぬか床を定期的にかき混ぜないと、ぬか床の底で繁殖し始め、濡れた靴下の臭いを出す。

4. 産膜酵母
偏性好気性(酸素が大好き、ということ)。
不要だが無毒(シェリー酒の製造に使われる)。
ぬか床を定期的にかき混ぜないと、ぬか床の表面で繁殖し始め、酢酸エチルを作る(従って、シンナーのような臭いを出す)。
ぬか床に混ぜ込めば、アルコール発酵を始める。

5. 他の雑菌、かび
大半は偏性嫌気性(酸素が大嫌い、ということ)。
ぬか床を定期的にかき混ぜないと、酪酸菌が繁殖し、他の雑菌やかびの繁殖を許してしまうことがある。こうなると、ぬか床の修復は難しい。

Reference/参照:
http://macrobi.livedoor.biz/archives/51429430.html
(Japanese only)

7 comments:

muskrat said...

Very Helpful! Thank you!

Hiroyuki said...

muskrat: Are you ready to start?

I recommend not adding yogurt, bread, or other "contaminants".

Yogurt contains animal lactic acid bacteria, which are not resistant to salt.
And, I found this paper last night:
http://ci.nii.ac.jp/naid/110001170912
Bread has no favorable effect on nukadoko.

muskrat said...

Yes, I'm on vacation next week... the last time I made nukadoko, I didn't use bread, beer, yogurt or any of the other commonly recommended 'starters'. I just toasted the nuka, added dried peppers, garlic, kombu, a little bonito, and some well cooked, ground eggshell. Any suggestions on these ingredients?

Hiroyuki said...

muskrat: I think that roasted rice bran, water, and salt are the only indispensable ingredients for nukadoko. Red peppers and kombu are well-tried ingredients, so I added them to my nukadoko.

I personaly refrain from adding anything of animal origin, such as dried bonito shavings. Don't ask me why; I just don't want to add them.

Eggshell is often used to recover overly fermented, sour nukadoko, because the calcium in the eggshell will neutralize the acidity (karashi (Japanese mustard) powder is also often used), but I don't think it's used to start nukadoko.

muskrat said...

Thanks - I'd read that the egg shells add calcium to the pickle.

Sissi said...

Thank you for such an informative and detailed post. Your blog becomes a nukadoko bible :-)

Hiroyuki said...

Siss: Thanks for your compliment.

I updated a previous post on nukadoko:
http://hiro-shio.blogspot.com/2011/06/some-notes-on-making-nukadoko.html

I refrained from posting about the carrot nukazuke because that would be quite redundant. The carrot nukazuke was tasty enough, so was the daikon nukazuke. My nukadoko is in good condition.