Tuesday, July 4, 2017

Two Fermentation Heat Sources Compared

I 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 the 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 due to the insulating properties of glass.

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


  1. Use two bricks to accumulate the heat

  2. What is the brand and model# for the thermastst ? I want one just like that. millarlarry@gmail.com

  3. Thank you, Natto Dad, for sharing your knowledge and experience. I think the information about the variation in temperature is very useful. I recently started using an egg incubator (with the egg trays removed) for fermenting. It works very well, but I don't know if it is more or less stable than the oven methods that you use. I will try to find a way to measure the temperature over time, as you did, and post my results. (It may take a while to get the data.)

    Thank you, again, for sharing your findings.

    North Carolina

  4. Very nice! I'm wondering if an insulated cooler of some kind would be more efficient that the oven.

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  6. I just made a batch using a 60 watt ceramic heater in my oven. With one chopstick in the door, temperature maintained at a constant 99 degrees and the natto turned out pretty well. I let it ferment for 24 hours, but it looks like it could have used a few more hours as it was not as stringy as I had anticipated.

  7. I just made my first batch of natto according to natto dad’s instructions. I used a Johnson Controls A419 digital thermostat with a temperature probe. I used a ceramic heater that has a fan inside a wooden box with a lid. I put two sleeping bags on the box to insulate. It seemed to work well. After I got the setup fine tuned it seems the temperature was mostly 98-101. Ambient temperature in my garage was about 50.

    It has been 25 hours since i put the natto in the refrigerator and I just sampled it. Nice and stringy and Super slimy. Tastes good with soy sauce.

  8. Hell Natto Dad. THank you for your wonderful videos on making Natto. I am new to making Natto, never made it before, and I'm wondering have you connect the Ceramic Emitter. Do you plug it in and run the cord through the over door and leave the door open I have a small convection oven 10"L x 20"W. Hoping you answer my questions. Cana't wait to get start. Please keep up the good work. ER

  9. Sorry for typo's. 'how you connect', 'oven door'and 'Can't wait".

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