A Homemade Incubator and Inquiry Labs

Homemade Incubator

Week two of our study on bacteria continues swimmingly.  Out of the eight plates grown from around the house, the boys chose two with robust colonies to transfer to new plates for tests of various household cleaners.  Keeping colonies at the proper temperature and humidity challenged them last time, so my son’s friend designed an incubator for this and further experiments.   

Inside the incubator


 A styrofoam cooler serves as the body, with a notch on the side for a nightlight attached to an extension cord, which is hot-glue-gunned on the outside of the cooler.  On the other side is a candy thermometer.  The device maintains a steady 92 degree atmosphere with ample humidity (our plates in the box on the heat duct dried out significantly).  Inside, plastic racks allow petri dishes to be separated, allowing room for air circulation.  The bacteria are thriving in this simple, inexpensive incubator.  This child has also offered to create a centrifuge.  I’m taking him up on it.  

This week, we’re discussing antibiotics and antibiotic resistance.  They’ll design an experiment with some samples (which we’ll bleach down afterward — we don’t want to contribute to any resistance problems).  While I have them do some labs that are of the “follow the directions and see what happens” type, I’ve worked in several inquiry labs, where they design the lab with minimal guidance and learn as they go.  Both boys are much more interested in chemistry than biology, and they really froze up when asked to think of ways to, for example, explore enzyme activity, without a script.  Interest level in the topic was key to their effort.  I’m seeing improvement in the quality of their lab designs as they become more comfortable with the material, and I’ve learned to give them a bit more information before designing a lab than I did at the start of the year.  

Stay tuned as they attempt to make their own growth medium using a pressure cooker (not the homemade variety).  Stand back, we’re going to learn!


14 thoughts on “A Homemade Incubator and Inquiry Labs

  1. What were the exact steps and materials used to make it? This would save me a TON of money and a large amount of time in comparison to buying a professional-grade incubator. Thank you!

    • My son’s friend started with a small styrofoam cooler. He cut a hole near the bottom big enough for a nightlight bulb, then sealed the rest of the hole with a caulk/foam material. He used a few plastic racks inside for shelves (not sure what they were from), and created a hole in the top for a thermometer, sealing that as well. There was no thermostat, but the single bulb seemed to keep the temp in the upper 90s F, which worked for our experiments. He’s an amazing kid, and he’s created plenty of other handy items for our chemistry study. I’m due to post more about those. Hope that helps!

    • It works wonderfully. A word of warning when grown bacteria at home: you are likely to grow some pathogens in your petri dishes. Keep the dishes closed until it is time to disposed of them. When it’s time to dispose of them, a solution of one part bleach and four parts water can be added to each plate, allowed to sit overnight, making the plates safe for disposal. An autoclave would also do the trick, but so far, we’ve not made one of those for home use.

  2. What kind of lamp did you guys use? What kind of light bulb would you recommend to reach a temperature about 100 Degrees F inside the incubator?

  3. Hi, I’m trying to make a homemade incubator. I have a styrofoam cooler, and I put two 4 watt nightlights in there and a thermometer, However, the temperature won’t get any higher than 34C….are there any suggestions you would have to raise the temperatures?

    • Are they incandescent bulbs? When this was built, traditional (rather hot) night light bulbs were easily available. That may not be so anymore. If not, you may need to add another bulb. Before you do that, assure that your system is without leaks of heat, especially around the bulbs. I suppose you could try a higher wattage bulb, too.

  4. This is an EXCELLENT idea for an incubator. I’m going to start breeding yeast cultures for my husband’s homebrew beer soon and I needed a cheap incubator. All I need to do is get some racks along with disposable plates. This is going to be fantastic!

  5. This is super helpful for the incubator I am trying to put together. But I have a lot of petri dishes… Is it safe to stack them on top of each other or do they all have to be on the same level?

  6. Hello,

    we built an incubator like this, but would the constant light bother the petri dishes? Should I cover up the light? Thank you!

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