Later On

A blog written for those whose interests more or less match mine.

Tempeh incubator box version 1.0 complete

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Origin of the incubator

In my previous apartment I routinely produced batches of excellent tempeh. In my new apartment I had a string of failures, and I finally decided that the cause was too high a temperature. [That may or may not have contributed, but cooking the beans with a little added baking soda certainly was a problem. The beans were then alkaline, and the tempeh mold requires an acidic environment. – LG] As the post at the link notes, tempeh is best cultivated at 88ºF. The oven in the old apartment was large and with the door ajar maintained a temperature that produced good batches of tempeh. The new apartment’s oven is smaller and, with the light on, hotter — and I thought that heat might be the source of the problem. (Modern ovens often have a “proofing” setting for making bread, and that would work; my oven is not so modern.)

So I decided to make a tempeh incubation box. There were various suggested DIY videos on YouTube. Those offered some good ideas, and this post describes the route I went. I decided to start with a cardboard box, which (unlike a styrofoam cooler) can be folded flat and easily stored in the back of the closet when not in use.

Incubator construction – Version 1

Update after two batches in this version 1 box: Making Version 2.
After some experience with this first box, I used what I had learned from experience (Poor Richard’s Almanack: “Experience keeps a dear school, but fools will learn in no other…”) to make a better box: cheaper, stronger, not affected by humidity, better insulation, easier to build. See this post for details. The first box was a failure./update

The Version 1 incubator box is now complete. I found a good-sized box — 18″ x 12″ x 12″ — at Staples for $1.79, and above you see it wrapped in closed-cell insulating foam (just 1/8″ thick, but that should be ample). The sides and top are covered with foam, and you can see some double layers when I covered places where cardboard was still exposed after the initial application. The bottom is not insulated: heat rises, so not much will escape from the bottom. [But see version 2 of the box – LG]

A half-sheet rack fits easily into the box and allows good air circulation. The foam I used comes in a sheet 12″ wide and 48″ long, and I bought two of them: 96″ total, 12″ wide. The 12″ width is perfect for the box; the sides took two 30″ strips: a length 12″ + 18″ that’s 12″ wide covers one end and one side. So with 60″ all sides can be covered, and the top can be covered with an 18″ strip that’s 12″ wide. That leaves 18″ for narrow strips to cover exposed edges.

The first step was to cover the sides. I put the box flat and cut off one strip of foam at a 30″ length. That covered one side and one end. Then I flipped the box over and used another 30″ strip for the other side and end. (Thus two of the vertical corner edges required an additional strip of foam to cover the exposed cardboard.)

The top took an 18″ strip: I applied it intact and then used a knife to cut down the middle to free the two flaps. The total used was 78″ of the 96″ I had. I used the remaining 18″ to in relatively narrow strips of foam to cover exposed edges.

The box will be folded flat when not in use, so the flaps for top and bottom and not secured. The heavy book is to keep the top closed. I will in fact use my heavy terrycloth robe folded on the top — that will hold the lid closed while adding more insulation to where the heat tries most to leave.

Result: Excellent temperature control

The thermostat in the photo shows the inside temperature as the box is heating up — 73.7ºF at the time of the photo — and the “heating” indicator is on. if I push the “set” button I can see the target temperature (for tempeh: 88ºF). The box did warm up to target temperature and stabilized, staying within a degree of the target with no problems.

This from an earlier post is interesting:

If the inoculated beans reach a temperature above 92°F (33.3°C), conditions are no longer ideal for Rhizopus spores but are ripe for a different set of organisms such as those of the Bacillus group. Rhizopus can be severely damaged by heat of over 92°F ( 33.3°C).

As a point of interest: I used the new digital thermostat I bought for the incubator to measure my oven temperature with door closed and light on. It was 94ºF — well above 92ºF — so building my tempeh incubator was indeed a good call. But that alone did not solve the problem.

First batch in new incubator: Another failure

I was quite pleased with the box, and was expecting to be even more pleased when it worked. I cooked a couple of cups of soybeans, drained and dried them, and mixed in vinegar and tempeh starter culture. I then bagged some in a Ziploc produce bag and some in a bag I perforated myself and put those on the rack in the box. I used one of these racks. The rack’s legs hold the tempeh well above the heating mat. Because it’s a rack rather than a (solid) baking sheet, air flow within the box is unhindered. The free flow of air should help the temperature within the box to be even (with no hot spots or cold spots).

As you can see in photo at the right, Ziploc produce bags are pre-perforated (click photo to enlarge). Here are the two bags of the first batch. That phot was taken after one day — but after three days the culture had died and I had another failure.

At least this time I knew the problem wasn’t due to the temperature.

One more step to solve the problem

It occured to me, as I listed out exactly what I was doing, that I recently — just about the time I moved into this apartments — started cooking dried beans in water in which I dissolved 1/2 teaspoon baking soda (sodium bicarbonate) per cup of dried beans. That results in much quicker cooking and nice tender beans. But I realized that the beans then are, unfortunately, toxic to tempeh mold.

I knew that baking soda was alkaline, but I assumed that the vinegar I added (1 tablespoon per cup of dried beans) after the cooked beans were drained and dried would be enough to offset the alkalinity.

Since the baking soda was the sole remaining potential cause, I cooked a batch without any baking soda (and used my tempeh incubator). Cooking the beans in plain water did take onsiderably longer for the beans to become, but the culture was (at last) a great success.

Update: Lid problem.

After the first use, the two insulated lid flaps started to cave in a bit. I’ve figured out what I’m going to do to reinforce them, and I’ll post photos when I’ve done it. 

Update: After a couple more batches, the incubator showed itself to be unsatisfactory. I abandoned it as a learning experience and moved on to make a much better (and so far totally satisfactory) incubator box as described in this post.

Written by Leisureguy

9 October 2020 at 1:29 pm

Posted in Daily life, Food, Non-animal diet

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