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How To Make A DIY Incubator

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Fermented foods are an ancient form of food preservation that is gaining popularity in the modern world. For some fermented foods, a DIY incubator can make a big difference, especially in colder seasons and regions.

Fermented foods that require incubation include koji, natto, tempeh, and yogurt, among many others. The microbes and enzymes that make these fermented products require elevated temperatures for a certain period of time. Luckily, DIY incubators are easy to make, and you may even already have one.

In this article we will discuss a few different approaches to making a DIY incubator, including a perfectly serviceable approach that may not cost you anything.

The Ironic ‘Cooler as DIY Incubator’

With some moderately-priced components, this cooler can keep your ferment nice and warm for days.

This design draws heavily from plans in the excellent book Koji Alchemy, by Rich Shih and Jeremy Umansky. With an aquarium pump and a few inches of water, you can create a humid DIY incubation chamber in your cooler that can hold temperatures in the 80s and low 90s (26-32 Celcius). Add an aquarium pump to keep the water moving and evenly heated. To use, just place four equally sized items in the cooler to stand your substrate on. These can be bricks, Mason jars, coffee mugs, or whatever you have that’s handy. I use this style of DIY incubator for koji and have had uniformly excellent results.

Drawbacks: Not many. Obviously, it takes up some space, but in between uses, all components tuck neatly inside and out of the way.

Sous Vide It!

A sous vide immersion circulator can give you pinpoint temperature control and can be a great option for higher-temperature fermented foods like amazake, the Japanese sweet rice beverage.

Slightly higher up on the cost spectrum, a sous vide immersion circulator is a great kitchen tool to have that can double as a DIY incubator. The most straightforward approach with sous vide is to use its water bath with the contents you’re incubating in a jar. This is great for things like Japanese amazake and Chinese jiu niang (both fermented rice beverages or porridge) as well as yogurt, but isn’t a great option for ferments that need a steady amount of air exchange, like koji, tempeh, and natto.

I have experimented with using my sous vide cooker in a cooler, but found it wasted water. There are other options, including mounting the sous vide circulator onto something inside a cooler, or perhaps just getting the largest size sous vide water bath container you can find.

One non-fermentation application where sous vide really shines is in mycology. You can store sterilized agar in the hot water bath to keep it liquid until you’re ready to use it. Just take the jar from the pressure cooker and put it into a pre-heated 200F/93C sous vide bath. Drop the temperature to 135F/57C or so, and it’ll be ready when you are.

Drawbacks: Tricky to mount on hardware that’s not specific for sous vide. If you get past that, it’s an excellent way to get high humidity and precise temperature, even very high temperatures.

Light Up Your Oven

If your oven has an interior light, you may already have a DIY incubator.

The oven in your kitchen can work as a DIY incubator, especially if it has a light you can switch on inside it. That’s often as much as you need to incubate tempeh, natto, koji, or yogurt. Even if your oven doesn’t have a light, it’s easy enough to set up a clamp lamp with a 60 or 100 watt bulb in the oven to provide the necessary temperatures. You can generate humidity by pouring boiling water into a tray in the oven every few hours.

Drawback: Inevitably, a family member will forget you’re incubating something and start to pre-heat the oven. Good signage can save you from a lot of misery.

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