How to Build a Fermentation Chamber
Building a fermentation chamber for growing koji is easier than you’d think. In fact, it only takes 5 minutes and requires no technical skills.
In this post, I share the exact setup and equipment I use to grow koji.
This is a fool-proof guide for building a fermentation chamber, which is a temperature-controlled and humidity-controlled environment for growing koji or proofing bread.
But before I start, it’s worth noting that The Noma Guide to Fermentation is the best koji guide on the market. I highly recommend it. Still, the Noma Guide can be a bit overwhelming, and some of the equipment pictured in the guide doesn’t work in the suggested manner without modifications. This guide, meanwhile, was designed to remove all the guesswork to make the setup as easy as possible. Let’s go.
GOAL
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GOODS
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PROCESS
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GOAL 〰️ GOODS 〰️ PROCESS 〰️
THE GOAL
What We’re Going For
Here’s my setup.
Notice that:
The chamber is built from a styrofoam cooler with a swing top.
On one side, there is a thermostat (for controlling temperature), humidistat (for controlling humidity), and humidifier (for adding humidity). The thermostat and humidistat are each secured with a screw.
On the other side, there is a heating pad and 4 screws about 5 inches from the top of the cooler.
When it’s time to grow koji, I add a perforated hotel pan lined in a kitchen towel.
Notice that:
The screws serve to keep the hotel pan from touching the bottom of the cooler. This is essential to maintain adequate airflow in your chamber. Otherwise, the koji will overheat and die before it grows enough.
There is still sufficient room (around 5 inches) between the substrate (in this case, barley) and the top of the cooler.
Now that you know what we’re going to build, let’s get to building it.
GOAL
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GOODS
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PROCESS
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GOAL 〰️ GOODS 〰️ PROCESS 〰️
THE GOODS
This is the exact fermentation chamber equipment I use to grow koji for my ramen and ceviche pop-ups in San Francisco. This setup is perfect for making koji in batches of 500g of uncooked barley at a time.
1. Styrofoam cooler.
This one is great for a few reasons. It’s not as tall as others, and it can fold up when not in use, so it takes up less space. The flip-top is great for allowing in just the right amount of air necessary for the koji to do its thing.
2. Half-sized hotel pan
This is what your koji will rest in. The holes provide airflow to prevent the koji from overheating.
3. Humidifier
This is the hardest to find piece of equipment in this guide. Why? Because you specifically need a humidifier that turns on when it receives power. Most humidifiers need you to press “on” for it to turn on, and that won’t work with the humidistat. Even the humidifier pictured in the Guide will not work! But this one does.
4. Humidistat
The humidistat turns off the humidifier when the fermentation chamber has enough humidity and turns on the humidifier when it needs more humidity.
5. Heating pad
This is for keeping the koji at 86f. My preferred heating pad is bigger than it needs to be, but it folds in half and fits perfectly.
6. Thermostat
The thermostat turns on the heating pan when the temperature is too low and turns off the heating pad when the temperature is too high.
7. Kitchen towels
You need 2 kitchen towels, preferably 2 you don’t use for anything else. I use these. Be sure to wash them before using them for the first time.
8. Long nails or screws
You need 6 nails or screws to keep the hotel pan, humidistat, and thermostat in place. I use narrow screws that are approximately 3 inches long.
GOAL
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GOODS
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PROCESS
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GOAL 〰️ GOODS 〰️ PROCESS 〰️
PROCESS
1. Clean the styrofoam cooler with a wet cloth. Better safe than sorry.
2. Insert 4 nails/screws through the cooler to elevate your hotel pan. Koji often overheats, killing itself in the process. By elevating your hotel pan about 4 inches from the bottom of the cooler, you will encourage airflow that prevents the koji from overheating. I recommend placing the holes like I did here, where there are two holes on each long side of the cooler. The holes are approximately 5 inches from the top of the cooler. On each side, one hole is 3 inches from the side, and the other hole is 14 inches from the side. You might need to adjust these measurements if your hotel pan or cooler is different than mine, so test with the hotel pan before making the holes.
3. Place the hotel pan on top of the nails. Ensure that the hotel pan remains elevated and you can close the lid. If at this point you realize that the holes are in the wrong place, no worries! The fermentation chamber doesn’t need to be airtight, so you can just make new holes and not worry about your mess-ups.
4. With 2 nails/screws, attach the thermostat and humidistat to the short side of the cooler opposite the hotel pan. The placement of these is less critical, so feel free to place them elsewhere if it is more convenient for your home setup.
5. Fold the heating pad in half and place it under the hotel pan. Plug the heating pad into the thermostat.
6. Place the humidifier in the cooler. Plug the humidifier into the humidistat.
And that’s it! Before you grow your koji, you’ll have to program the thermostat and humidistat to regulate for the right temperature and humidity. I recommend testing the setup before you try it with koji to ensure that you’ve set that part up correctly.
