Tuesday, July 4, 2017

Two Fermemtation Heat Sources Compared

In have tried using different heating methods to keep the fermentation temperature at an optimum. I like to use the oven as my fermentation vessel because I can scale up production when I want to share natto with friends. So for me, the heating source has to be strong enough to heat the inside of an oven and I do not want to manually manage the temperature.

I have tried using a yutanpo (japanese water bottle heater), pet heating pad and oven warm setting. They all lacked the control I was looking for. 

So I bought a Single Burner Electrical Coil along with a Digital Controller Thermostat. This turned out to be the two most important pieces of equipment to give me a reliable fermentation regardless of the season or ambient temperature. I have been using this setup for more than three years. (Note: This is not the proper use of the single burner electrical coil so use at your own risk).

Single Burner Electrical Coil and Digital Controller Thermostat

I recently found a 150 watt Ceramic Infrared Heat Emitter online (plus the white socket power plug) and was curious to see if it would be powerful enough to heat the inside of an oven up to 98F (37C) needed to ferment natto. (Note: Again, this is not the proper use of the ceramic infrared heat emitter so use at your own risk)

150W Ceramic Infrared Heat Emitter, Socket with plug, and Digital Controller Thermostat

In order to test the two heating sources, I used a temperature data logger (Elitech GSP-6 Temp Logger) to follow the two heating sources. I charted this over some time measured in minutes.

Set Temp: 98F (37C)

Single burner
Max: 108F (42.4C)
Min: 95F (34.9C)
Avg: 101F (38.3C)

Ceramic Emitter
Max:  103F (39.4C)
Min: 94F (34.5C)
Avg.: 98F (36.8C)

The set temp for the digital controller thermostat was 98F (36.7C) for both runs. The ambient temp was around 80F (27C). It can be seen that the Single Burner Electrical Coil (Red line) had a higher peak temperature and it took longer to cool. This is because the particular single burner I use has a solid metal plate instead of a metal coil found in most. One disadvantage is that the dial is getting finicky and I have to jiggle it until it switches on. 

In contrast, the 150 watt Ceramic Infrared Heat Emitter had shorter On/Off cycle and had a lower max temp. It is simpler in design so there are fewer things that can break compared to the single burner. 

Both of them are great heat sources in conjunction with a digital controller thermostat. I use a glass baking pan as the fermenting vessel so the higher max temp of the single burner is not much of an issue.

The 150W Ceramic Infrared Heat Emitter is a new addition so I will be using this to test it out. Moving forward, my recommendation will be for the 150 watt Ceramic Emitter. I will post any new info if my recommendation changes.

If you have any questions, please "Contact Me" instead of leaving a comment.

Natto Dad

Wednesday, April 15, 2015

Two Frozen Natto Starters Compared

  I have been using packaged frozen natto as the starter for a long time. I did this by saving a portion of the freshly made natto and freezing it. When this became low, I saved a portion again and successfully did it until the third generation when it suddenly became unstringy. This was probably due to contamination or due to prolonged freezing killing the natto. I will never know the reason and for many batches after that, I tried to use the third generation starter to see if I could change the fermentation conditions to make stringy natto again.

After a while, I got tired of eating unstringy natto and gave up using my third generation starter. This was hard to do as I initially thought that I would be able to keep a starter culture indefinitely. To start over, I went to the Japanese market and got 3 packaged natto. The first two that I tried were, Tokyo Natto and Okame Natto. I forget what the third was... So I fermemted two batches side by side to see how the natto would turn out.

On the left is Tokyo Natto. I randomly picked this so there is no logical reason for this choice. On the right, Okame natto. A widely distributed long seller that is one of the most common natto brands.

These packages are kept in the freezer at all times. When frozen, I cut them into 12 small frozen pieces per package. So a 3 pack will yield 36 frozen natto starter cubes. I plop a cube into the steamed soybeans and mix it in. For full instructions refer to the Homemade Natto Recipe.

Might be hard to see, but Tokyo natto is a little bit weak visible by the shinnier appearance and thinner natto growth on the bean. Also when the cling wrap was pulled, stringyness was not too visible. As for the Okame natto, the natto growth was much stronger and stringyness was seen when the cling wrap was pulled back.

This to me is the moment of truth when the natto is stirred with chopsticks. Here, the difference in natto is obvious. Tokyo natto on the left is very loose compared to Okame natto which is thick and almost gummy in texture.

Adding liquid seasoning such as shoyu or mentsuyu is the ultimate stringiness test as the weaker natto will decrease in stringiness when seasoning is added (left). Okame natto is going strong with the liquid seasoning added and becomes almost frothy when stirred vigorously.

On the pull test, the weaker Tokyo natto has a loose appearance and the strings do not hold the beans. In comparison, the Okame natto has strong thick strings which hold the beans.

Okame natto is the winner!

Concluding thoughts:
After running this side-by-side fermemtation, it is apparent that the natto starter used will have a big impact on the finished natto. Furthermore, the existence of "Niowa Natto", or low smelling natto tells me that there are different strains of natto used by the natto manufacturers. My assumption would be that older strains would be more stinky and may be linked to more stringiness. Okame Natto, which has been around for decades may be using an older, more traditional strain of natto that is more stringy and more stinky. This being based on my assumptions concocted by my perceptions are more for discussion than to inform you.

The other possible explanation is that the Okame natto package that I happen to pick up was fresher thus had a stronger livelier population of natto-kin.

The take home message to fellow natto makers is to weigh-in more on the natto starter if you have perfected the cooking conditions and are still getting poor results. As of now, my working hierarchy of making good natto in descending order of importance is:

1) Proper soaking of soybeans: At least 12 hours in the summer with a preference towards 16 hours, up to 22 hours in the winter. 
There are two test that can be done to check full hydration. First, split the soybean in half. The two halves should not have a gap in the middle. When fully hydrated, the two halves will touch in the middle. Second, foam will start to appear on the surface of the water. Probably due to respiration of the soybean getting ready to germinate.
When not properly soaked, the natto will turn hard when finished fermemting.

2) Proper steaming of soybeans: The soybeans should be steamed under pressure with a pressure cooker for 40 minutes. You can steam them in a regular pot, but expect up to 6 hours of steaming to achieve what can be done in 40 minutes steamed under pressure. By cutting corners here, the natto will turn hard when finished fermenting. The natto-kin might also have a hard time getting nutrients. I do not recommend boiling soybeans as the flavors will leach out into the water and the natto will lack flavor.

3) Fermenting Temperature: The standard is to ferment at 40C or 104F at least for the first 6-8 hours, when the natto start growing vigorously. You can tell that they are starting to grow by the pleasant nutty fermenting aroma. After this critical period, the natto will start to generate heat by its metabolism and you can be more relaxed about temperature on the last 10-12 hours of fermentation.

4) Natto starter: If you have the top three conditions under control and you are still not getting good results, this will more than likely be the culprit. I have used Mitoku Natto Starter in the powder form, but I have never made a stringy batch using it. Use frozen packaged natto, and try different brands if available as the results will vary as shown above.

5) More trivial, non-crucial matters: 
-Moisture and aeration. I usually use enough water from the bottom of the pressure cooker to wet cooked soybeans so water does not pool in the fermenting vat (about 3 spoonfuls). Having said that, I have forgotten to put the water and it still comes out fine. I have read online that natto needs lots of air, but I have found that this is not true. When the fermenting natto is exposed to air, the surface will start to dry out and harden and will look dark brown. I recommend the poked double cling method explained on the Homemade Natto Recipe.
-Adding sugar and/or salt: I have also seen this where sugar is added to make the natto happy. I have never used sugar and I get consistently good results. Same is true with salt.

I went a little longer than intended, but if this helps a fellow natto maker out there, my mission is accomplished.

Happy natto making and cheers to you for improving your well-being by eating natto!

Natto Dad

Wednesday, May 14, 2014

Natto: Essential fermenting conditions

We will look at the natto fermentation from the perspective of our main character, Bacillus subtilis natto. It is a bacteria commonly found in nature and for this reason is also referred to as hay bacillus or grass bacillus. The relation to hay goes back to 1086 AD in Japan when soybeans spontaneously fermented when wrapped in hay (Natto, wikipedia). Due to this spontaneous nature, I am sure that the origin of natto fermetation goes back even further.

Natto is unique in its fermentation as it does not produce acids when fermenting with lactobacillus ie. yogurt and pickles. It also does not produce alcohol as is the case with yeast fermentation. Natto produces stringyness, which comes from long-chain polysaccharides. The stringiness is very unique to fermented products and is what makes natto so cool!

The essential conditions to produce this wonderful stringiness are as follows,
-Properly soaked and cooked beans.
Soybeans have a really tough skin and take a long time to cook. The natto-kin (natto bacteria) has to penetrate to skin in order to get to the nutrients inside. I do not know if the natto-kin actually grow into the soybean or if they absorb the nutrients and grow on the surface, but the result is the same. The nutrients have to be available for the natto-kin and in order to do this, the soybeans have to be soaked long enough for full hydration. I soak the beans for 10-12 hours in the summer and 20-24 hours in the winter time. A good way to tell is to split the soybean in half to see if the two halves touch in the middle. If there is a gap, they need to be soaked longer for full hydration. 
Boiling the soybeans is usually the first method people try for its ease. The disadvantage is that the flavors leach out of the bean and the amount of time it takes, 4-6 hours. The next solution is to steam the beans over boiling water. This will make tastier natto, but it also takes hours to cook. Then there is boiling the soybeans under pressure. This will take 40 minutes, but again one runs into the problem of leaching flavors out of the bean. The best method and the only method I use now is to steam to soybeans under pressure. This solves both problems of time and flavor. Steaming under pressure will retain the flavors and take 40 minutes. From the natto-kin perspective, this is important because more flavor equals more food for them and softness of the beans means that nutrients will be easier to access from within the bean.

-Optimum Temperature
Natto-kin is interesting that although it is tolerant to extreme conditions, it grows slowly and is vulnerable to other bacteria in the initial stages of growth. I have not experienced this personally, but there are anecdotes of contamination in the fermentation. To favor ideal growth conditions, natto should be fermented at a higher temperature when compared to a lactic fermentation. I usually shoot for 95F-108F (34C-42C). It is important to keep this temperature the initial 6 hours of fermentation to establish a strong natto-kin population. After 12 hours, the natto-kin start to generate heat and so one can be more relaxed about maintaining temperature. 

-Moisture and Air
This relationship was really difficult to maintain as there is an inverse relationship. Many natto makers stress the importance of having good ventilation so the natto-kin can breath. This makes absolute sense, as B. subtilis is classified as an obligate aerobe, meaning it needs air to grow. Unfortunately, moisture is impossible to maintain if you keep the fermentation container open. The surface of the natto would become dehydrated and brown and the growth of the natto-kin would decrease. I took a hint from packaged natto which is packaged in a styrofoam container. On top of that, the natto is covered directly with a plastic sheet with small holes. This is how I came up with the double cling-wrap method. I put a cling-wrap with small holes, poked with a tooth pick, directly over the soybeans and another with holes on the baking sheet. Having a cling-wrap directly over the soybeans really helps to prevent drying of the surface. The air gap formed between the sheets also helps slow down evaporation.

The intial 6 hours as mentioned above are very crucial to establish a healthy population of natto-kin. Not much is visible, but the natto-kin is busy getting settled in, absorbing nutrients and later starting to multiply. Then in the 6-12 hours of fermentation, the bacteria go through a population explosion and you can start smelling the aromas coming from the fermentation. After 12 hours of so, the natto start to generate heat from metabolism and will continue fermenting until they start to slow down due to overcrowding and depletion of nutrients at around 18-20 hours. From experience, I have found that under ideal conditions, the fermentation will be done in 18 hours.

Not mentioned here is about the starter used and this deserves a post of its own.