Wednesday, May 15, 2013

Natto Making Overview

Natto making, no matter what the scale, follows this basic steps:

1) Soaking
2) Cooking
3) Fermentation
4) Maturation
5) Eat

1) Soaking of the soybeans takes anywhere from 20+ hours in the winter to as little as 12 hours in the summer. This relates to the soaking time of the bean hydrates the soybeams. From what I gather germination happens in 3 steps: Step 1) Imbibition of water (aka hydration), Step 2) Saturation of water, enzyme activity, Step 3) Visible growth and axis elongation. I makes sense to me that for natto making you want to stop on step two. Some people have commented that a good indication of when the soybeans are fully hydrated is to look for bubbles on the water surface. The presence of bubble indicates respiration due to enzymatic and metabollic activity signaling a fully awake soybean. At this time, look for soybeans that did not hydrate and discard them.

2) Cooking the soybeans can be done either by boiling the soybeans or steaming them. After my initial failure of boiling the beans, I realized that this is not ideal. Boiling the soybeans takes too long and the flavors leach out into the boiling water. The second method is to steam them in a regular pot. This can be done by putting a steamer in the pot and suspending it above the boiling water. The flavors will not leach out, but this too will take time. You can boil the soybeans in a pressure cooker which is faster, but will leach out the flavor in the boiling water. So the most ideal way to cook them is to steam them with a pressure cooker. This cuts the cooking time down to 40 minutes from 4-6 hours and they will turn out very soft with an almost creamy texture. The pressure cooked soybeans will have a nice light caramel color and will be slightly sweet in taste.

3) Fermentation temperature needs to be controlled so it remains around 38C (100F) to 42C (108F). Popular heat sources include a yutanpo, oven light, and lamps. I have tried to use an area heater used for small pets and also a single-coil range. Moisture also needs to be kept so the soybeans don't dry out during the fermentation. Most suggest to ferment the beans for 18 to 24 hours. I have seen different containers used for this purpose. One can use a styrofoam box or cooler or use the oven as a fermentation box.

For the inoculant, you can use Dry natto spores and store bought natto packs.

4) Maturation can take place at room temperature or in the refrigerator. To achieve the best flavor, it is recommended to leave the natto maturing anywhere from 1-7 days. I have found that maturing them for a day at room temperature and then storing natto in the fridge for another 3-5 days produces the best flavor. After that, I will store natto in small containers and freeze them. They should taste good for a few weeks if it does not get freezer burn or get that funky freezer smell.

5) Eating is the best part! This is when you get to taste the fruit of your labor. I usually pour a combination of shoyu, mentsuyu and and a little bit of sugar and mix it until it is well combined. I have put some olive oil at times because of some trivial health benefit that was mentioned by a doctor on a Japanese show.

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