Tuesday, June 4, 2013

Troubleshooting Guide for Homemade Natto

I have made many bad batches of natto. Hopefully this troubleshooting guide will help homemade natto makers out there make better natto. If you have any questions that are not listed here, please email me at "Contact Me" or directly at my email if you want to attach pics.

Before going through the Q&A, here are the most basic requirements to make good natto.

1. Fully hydrate soybeans. 16-20 hours for Summer time and 20-24 hours for Winter time.

2. Cook beans by steaming under pressure. This means putting beans in a basket and steaming them in a pressure cooker. The cooked beans should be soft enough to squish with your thumb and pinky and should have the consistency of a thick paste. 

3. Use frozen packaged natto as starter. (I place this as a requirement as I have not figured out how to make stringy natto with Mitoku spore starter).

4. Ferment beans at 38C (100F) for 18-22 hours.

Q: My natto is not stringy, what's up?

A: This one is the hardest question and probably deserves its own post. From past experiences, the best short answer might be that the starter is not doing its job. I have used Mitoku natto spore starter and it is very fussy. I have not isolated what the problem is and would love to hear from a fellow natto maker. I have switched to using frozen packaged natto which produces stringy natto every time. I keep it in the freezer cut up into cubes ready to use.

A: Low temperature will result in the natto not growing properly. It is important to shoot for 38C - 40C (100F-104F) for 18-22 hours.

A: The soybeans were not cooked long enough. The cooked beans should be easily squished with the thumb and pinky and have a creamy texture. Steamed under pressure takes 40 minutes to reach this with soybeans.

A: Another possibility noted on some natto blogs is that the fermentation temperature is too high. I have not experienced this personally but it sounds reasonable.

A: I used to think that overcooking the soybeans somehow destroyed a nutrient to make the silky threads, but this is not the case. Overcooking should not be a concern from what I have seen. As a note, I have noticed that boiling soybeans will make the natto have a non-stringy rubbery growth on the beans.

Q: My natto looks white and leathery.

A: This is related to the question above. When the natto is not stringy, it usually turns out leathery and white. This might be related to lower fermenting temps.

Theories:  One working theory is that the initial concentration when using natto spore starter is too high. Having said that I have used one tiny spoonful, the one that comes with the Mitoku starter, diluted in about 100 mls of water. Then I use 5 soup spoonfuls of diluted starter and it still turned out white and leathery. Another theory is that the natto spore starter is old, has gone evil and/or is contaminated. The band-aid solution is to use frozen packaged natto.

Q: My natto stinks of ammonia.

A: I associate this with temperature problems. One of my earlier batches smelled strongly of ammonia and the natto was not stringy. If I remember correctly this was because the temperature was too low and I left the natto batch fermenting for 24 hours waiting for the stringyness to appear.

Q: My natto does not have flavor.

A: Boiling the soybeans is the reason why natto turns out flavorless. Boiling them in a regular pot or boiling them under pressure will do this. Curiously the skin of the soybean will come off when boiled. To resolve this, you must cook the soybeans in a steamer basket or strainer above the boiling water. I use a small glass bowl to suspend the steamer basket over the boiling water.

Q: My boiled soybeans are soft, but the natto is hard.

A: The reason is that the soybeans were not cooked long enough. This is hard to accept when you spend 4-6 hours of your valuable time to steam the soybeans. I have done this and there is that transitional stage when they are almost soft enough, but not quite. The soybeans should be a dark beige color and not yellow. Also, when eaten, it should have an almost creamy texture. I recommend steaming them under pressure which only takes 40 minutes.

Q: My natto is dry.

A: I initially thought that natto needed a lot of ventilation for the natto to breathe and to blow off the ammonia produced in the fermentation. So I covered the natto with paper towels and newspaper and then put it in a paper bag. This was a very long path to a dead end which led to not so tasty dry natto. Turns out that natto does not need that much air. So now I use the Double Cling Wrap Method (scroll down to the middle of the post). I poke holes on the cling wrap with a tooth pick so there is a hole every 1-2 cm (1/2" to 1") apart. This is tedious, but I enjoy this mindless repetitive work.

Q: My natto tastes like boiled soybeans and not natto.

A: The temperature of the fermentation was too low.

A: I do not have a vendetta against the Mitoku Natto Spore Starter, but the spore starter has given me this result. So for now with the Mitoku Natto Spore Starter, I either make leathery white natto or unfermented natto that tastes like cooked beans. Use packaged frozen natto as the starter.

A: Packaged frozen natto starter was weak. Try a different brand of packaged frozen natto if available.  

Q: How much packaged natto starter should I add?

A: When I use the frozen packaged natto, I chop up the package into 9 cubes. For Okame Natto, one package is 50 grams, so one cube is 5-6 grams. One cube will easily ferment 400 grams of dry soybeans (a little less than 1 lb). So a 3-pack of 150 grams will yield 27 cubes, or 27 batches of natto!

Q: What is the conversion rate of Dry soybeans to fully hydrated soybeans (after 18 hours). 

A: For soybeans, I use x2 as the conversion factor. So 400 grams of dry soybeans will become 800 grams of fully hydrated soybeans.

Note: Please use the "Contact Me" or email me directly at nattodad[at]gmail.com if you want direct replies.