Wednesday, March 19, 2014

Testing My Incubator

I did a trial of making tempeh in homemade incubator. I ordered my tempeh starter from Cultures for Health. I'm very happy with the results and I highly recommend them. I followed their tempeh recipe.

For my first tempeh trial I used a 40W bulb in my incubator with the door slightly open (to keep it from getting too hot and killing the spores). It was in the incubator for about 3 or 4 hours, then I transferred it to my oven with the light on overnight. I didn't see any growth on the soybeans at that time. I didn't want to leave my incubator turned on overnight unattended as I have a crazy cat that likes to run around the house during the night.

I checked on the tempeh in the morning, and I still couldn't see much growth. I got a little bummed out, thinking that my incubator was too hot and killed the spores. I left it in the oven though, since I knew that has worked for me before. Sure enough, later in the day I could see the white mycelium forming on it. Except for one spot.


The non-white spot on the left bag was directly under the light in my incubator. I assume that the light made it too hot and killed the fungus. But I guess I transferred it to the oven before more was killed.

I got a little too excited, and I should have done more temperature tests before making tempeh. So this means....

Science time! (Yay!!!)

I want to use this incubator, so I need to do some trials and figure out how to use it. As I mentioned in my previous post, there are 3 ways to control the temperature of my incubator:
  1. using a different wattage light bulb
  2. opening the door to let some of the heat out
  3. turning the light on and off
The first one is the easiest. A 40W bulb might be too hot for tempeh, so I purchased a 25W light bulb. I did trials with both of these light bulbs. Ideally, I don't want to be turning the light on and off to control the temperature. I'd rather just set it up, then check on it every now and then to make sure it's ok. These trials were done with only changing the bulbs and adjusting the opening of the door.

I also decided to re-position the light for when I make tempeh. I measured the light bulb (when attached near the top of the door) being about 3 inches from the tempeh. This was probably too close, especially with a light that may have been too hot. Also, maybe the temperature is too hot that close to the heat source, but is fine in the rest of the incubator. I decided to move the light bulb to the bottom of the door. I measured this light as being 4 inches away from where the tempeh would be. Not much of a difference, but using a lower wattage too will hopefully help.


I think that when I culture yogurt I should be able to put the light at the top of the door. The yogurt will be in glass jars and can sit directly in the incubator. I do not need the wire rack for it and can take it out.

Results:

The following 5 tables show data using the 25W light bulb.

Trial with 25W Temp. Tempeh
85°F - 91°F
Yogurt
108°F - 112°F
Door open 0.25 inch for 1 hour100°FNo (too hot)No (too cool)
Door open 0.25 inch for 2 hours105°FNo (too hot)No (too cool)
Door open 0.25 inch for 3 hours110°FNo (too hot)Yes (perfect)
Door open 0.25 inch for 4 hours115°FNo (too hot)No (too hot)

Trial with 25W Temp. Tempeh
85°F - 91°F
Yogurt
108°F - 112°F
Door open 1 inch for 1 hour92°FNo (too hot)No (too cool)
Door open 1 inch for 2 hours92°FNo (too hot)No (too cool)
Door open 1 inch for 3 hours93°FNo (too hot)No (too cool)

Trial with 25W Temp. Tempeh
85°F - 91°F
Yogurt
108°F - 112°F
Door open 1.5 inches for 1 hour90°FYesNo (too cool)
Door open 1.5 inches for 2 hours90°FYesNo (too cool)
Door open 1.5 inches for 3 hours90°FYesNo (too cool)

Trial with 25W Temp. Tempeh
85°F - 91°F
Yogurt
108°F - 112°F
Door open 1.75 inches for 1 hour88°FYes (perfect)No (too cool)
Door open 1.75 inches for 2 hours88°FYes (perfect)No (too cool)
Door open 1.75 inches for 3 hours88°FYes (perfect)No (too cool)

Trial with 25W Temp. Tempeh
85°F - 91°F
Yogurt
108°F - 112°F
Door open 2 inches for 1 hour85°FYesNo (too cool)
Door open 2 inches for 2 hours85°FYesNo (too cool)
Door open 2 inches for 3 hours85°FYesNo (too cool)


The following 3 tables show data using a 40W light bulb.

Trial with 40W Temp. Tempeh
85°F - 91°F
Yogurt
108°F - 112°F
Door open 0.25 inch for 1 hour115°FNo (too hot)No (too hot)
Door open 0.25 inch for 2 hours130°FNo (too hot)No (too hot)

Trial with 40W Temp. Tempeh
85°F - 91°F
Yogurt
108°F - 112°F
Door open 0.75 inch for 1 hour105°FNo (too hot)No (too cool)
Door open 0.75 inch for 2 hours108°FNo (too hot)Yes
Door open 0.75 inch for 3 hours110°FNo (too hot)Yes (perfect)
Door open 0.75 inch for 4 hours110°FNo (too hot)Yes (perfect)

Trial with 40W Temp. Tempeh
85°F - 91°F
Yogurt
108°F - 112°F
Door open 1 inch for 1 hour100°FNo (too hot)No (too cool)
Door open 1 inch for 2 hours105°FNo (too hot)No (too cool)
Door open 1 inch for 3 hours105°FNo (too hot)No (too cool)
Door open 1 inch for 4 hours105°FNo (too hot)No (too cool)

Clarifications:

I checked the temperature after the stated time using a candy thermometer. It can read as low as 75°F. If the temperature started to remain constant, or got too hot, I ended the testing.

The ideal ambient temperature for fermenting tempeh is 88°F (with a range of 85°F - 91°F). The ideal ambient temperature for culturing yogurt is 110°F (with a range of 108°F - 112°F). If the temperature is too low, the fungus/bacteria won't grow. If the temperature is too high, the fungus/bacteria is killed. 

The ambient temperature of our house (outside of the incubator) is currently 68°F. I feel like this should be taken into account as the incubator is never fully sealed, and the greater the temperature difference, the more heat that will be lost inside the incubator. If I perform these trials over the summer (when our house is about 80°F), I will probably get different results. It may not be a huge difference, but I will need to test it before I use it to make tempeh or yogurt in the summer. The temperature range for making these foods is pretty small, so I want to make sure my incubator is still in the correct range.

Results Analysis:

The temperature of the incubator rose too quickly while the door was open 0.25 inch (just enough for the light cord) with both light bulbs. The temperature became too hot for tempeh or yogurt, so I will not be using those results in my analysis.

I've determined that it is best to use the 25W light bulb for fermenting tempeh, and to use the 40W light bulb for culturing yogurt.

The following is a graph of the results with the 25W light bulb. The light grey area on the graph is the ideal temperature range for fermenting tempeh.


I will start out with the door open 1.75 inches. Once the tempeh starts to generate its own heat (after about 12 hours) I will open the door to about 2 inches to help keep the temperature from getting too hot.

The following is a graph of the results with the 40W light bulb. The light grey area on the graph is the ideal temperature range for culturing soy yogurt.


The temperature of the incubator took a little while to level off. I will probably turn the incubator on while I'm preparing the yogurt to start to get it heated. Keeping the door open at 0.75 inch, it leveled off directly in the middle of the ideal temperature range - 110°F.

Further Modifications to the Incubator

I've determined the best wattage and door opening for making tempeh and yogurt. Since I don't want to deal with checking to make sure the door is open to the correct spot, or have the door accidentally be knocked closed, I made little spacers. I already had a bag of these little wood rectangles (I used some to make mini tables for my husband's D&D group). I didn't even have to cut them - they were already at some of the sizes I needed - 0.75 in, 1.5 in, 2 in. I glued them together using Elmer's and hot glue.


There was no rectangle that had a size of 1.75 inches on a side (which I would need for tempeh). Instead of cutting a rectangle to that size, I decided to made an add-on spacer. I glued three rectangles together, which is 0.25 inch wide. I then glued a piece of string around it so I can tie it to a spacer. I plan to use this to make small adjustments to my spacers, rather than make new spacers if I need a new size.

Here is the add-on spacer show by itself and tied to the 1.5 inch spacer (to give it a width of 1.75 inches).


And here is what a spacer looks like in the fridge:


This will prevent the door from being accidentally closed while I'm using it.

I feel like a super nerd for doing all these tests (and graphing them) and making little spacers for it. But it was fun! I plan to try making yogurt soon. I'll let you know how it goes!