Custom Koji Incubator

Hello All,

I am new to the forums and new to homebrewing. My first batch of Sake is nearly ready for bottling and for the upcoming summer i am ready to start brewing another batch; you see i wanted a trial run.

I was thinking to myself if the koji is one of the most important ingredients i want to make sure i produce it as well as i can. My first attempt went alright but i feel as though it could of been produced better results. I started looking into how it was produced commercially and historically (for smaller batch production) and found that in some cases a couple people over in Japan had made though own Koji Incubators probably for producing miso and shoyu.

I looked at everything i possibly could and drew some plans up of my own; i am currently in the process of drawing up everything as well as developing my idea so that it takes every aspect of koji making into considerations.

The reason for this post is to show you what i have got so far and take in any suggestions about what could make it better. Hopefully by the end i will have some descent plans that could be used by all if people are interested (I do hope you are).

This is an early concept drawing. There has been a few more things that i have taken into consideration but not drawn up yet including:

Natural Stack Ventilation: Vents at the top and bottom that can be manually opened and closed to allow fresh air and humidity to be controlled.

Control Box: Sit on the top of the incubator and includes the thermostat, two thermometers (each shelve then has its temperature measured and the transformer for the kotatsu heater (Japanese table heater)

Things that i also think i need to take into consideration:

Humidity measuring device
What type of insulation to use?
Should I use PVA (wood glue) to make sure construction is solid?

I don;t mind answering any queries so feel free to ask away. All ideas welcome; explanation of why i would need it and where you would put it would be useful.

I am not much of a builder myself, but it definently looks like a good initiative. You should be selling those things on ebay if you ever got around to making a good copy :slight_smile:

Good luck, and keep us updated.

Thanks for the reply Claes. I will stick to the designing and developing process for a bit before i start actually building because of cost of parts etc I don’t want to make something that hasn’t had every little thing thought about.

I might think about making one for people if there is interest there but it would cost quite a bit due to labor and parts and plus would only want people to pick it up in northern England. I am though hoping to make a pretty extensive guide so anyone can build one and have no queries of what to do. I want to make sure the community has the knowledge to build one; i want to give back as so many people have helped me through free knowledge.

Anyway onto the update. The control box that will go somewhere on the main body

  1. The plug from the Kotatsu heater that plugs into the thermostat.
  2. Thermometer (2 to make sure each shelve has its temperature measured)

Does anyone think anything else needs to be added? That quite a large space free due to the size of the transformer (approximate size) in which i just added vents over to ventilate all of the electronics so thy don’t overheat.

In late May i should be able to get better designs drawn up as i have a lot of work on at the moment.

Thanks for viewing.

Looks great!

I’m in the middle of building my box. Its about 46 inches tall, and 30 inches square. 3/4 inch laminated board. Working out a chest freezer type of door. Insulating the inside with silver bubble-wrap stuff for water heaters. Looking for wire shelving like oven racks-ish.

Plan on having a digital temp controller attached to a firmwrap heater on the bottom. I will mount computer fans inside for circulation. Placing a tin of water on the heater for the first 24-30 hrs will supply the moisture.

My hope is to have the air temperature warmed to 98-104, but monitor the temp of the growing koji. My problem in the past has been making the koji warm, but not surrounding area. This causes the rice to dry out. The mold should be taking the moisture out the kernal, not the air.

I wanted the box to be air-neutral or at least supply a deep aquarium pump / hepa filter to allow for slight positive pressure out. The kind that supplies air to wort for brewing beer.

How many watts is the heater you are going to use? I would be careful about that as if you’re going to use the firmwrap heater that i’ve seen (a demijohn one) it’s only 40W and we not be suitable for heater up that internal volume to the desired temperature. I used a 100W heat-pad to heat up a small cooler box and that was not sufficient. For this project i am using a 510W kotatsu heater so you want to make sure you get something similar or get the same.

Are you using cedar in your project or just laminated board?
As for making sure the koji doesn’t dry out i would wrap it in some material such as muslin cloth; i will be purchasing this for my project so i will have a piece of cloth for every draw. You should consider this to as this is what you do in baking to make sure the dough doesn’t dry out. Most saké breweries do this therefor i think it’s a tried and tested method.

I was thinking about possible having fans to ventilate it properly but just thought through natural stack ventilation

you would get a similar effect without the extra stuff. This would also have the effect of pushing air out like the pump you said you might acquire. Therefor you would be killing two birds with one stone. I will upload designs of my manually operated vents later on for this process.

Hope this helps.

Because the inner volume is relatively small, I didn’t see the need for cedar. Cedar has a great property in holding and releasing moisture without warping and resistant to mold. This box of mine will be lined essentially in a plastic barrier of sorts. I will wrap the rice in cloth. Even then I was getting dried out rice kernals. The inner air temp was colder than the rice, so moisture was pulled out.

Thanks for the heads up on the heater. I may have to use a small ceramic heater with fan. Will prob. use both. At least the firmwrap will heat up the water tray. I want to keep it a closed system if I can. The ‘box’ will be nice on the outside so it can reside in the living room, maybe a lamp ontop. That way I can grow koji and keep the wife happy.

finished my second semester now so should be on with finalizing my design for the build. The heater has cost me an arm and a leg but i know it should definitely work efficiently. I have imported one from Japan that cost about £75 and the transformer cost me roughly £50 so it was a big investment (i will however probably be using it on another project). To make Koji Rice in Japan they normally put the inoculated rice under their kotatsu table if making from home for such things as miso therefor i think will be an extremely good choice. I will also probably be lining mine with a VCL (vapour control layer) so that moisture does not penetrate through the cedar.

Dray: hows things going? Have you started your build yet? what finishes extras are you thinking about putting on your finalized incubator: paint or stain, wheels or legs?

Some Pics

The door was re-done and it was stained, added a seal around the door frame as well as adding some insulation to the back of the door. Going to add shelving and some access ports on the bottom. The whole thing is on casters.

I need to figure out how to bypass the thermostat on the ceramic heater so I can use the temp controller.

Nice, looks like it’s coming together nicely. Just a couple questions about fabrication; what joints did you use (miter i presume) and how are they fixed together (pins, glue etc)? How did you cut the sheets? do you have your own cutting equipment or did you get it cut at a shop? I’m drawing up some plans now and am trying to get my head around what joints I’m going to use to make it as stable as possible.

Thank you!

My Dad and I worked on the ‘box’. We cut the sheets of supposed oak laminated board… it had to been pine, as the door was oak and hickory. We used a dado blade and grooved the boards so they locked in. Wood clue and air-nailed. Added a frame and the door attaches to it. Hickory will bust your blades and drill bits.

The board is 3/4 inch thick. Dado channel was cut about 1/2 inch deep. The back has all 4 edges dado cut. The sides are dado cut at the top and bottom. The open frame is dado cut and angle cut to lock in and become fairly square. Adding wood glue and air-hammering in nails all down the center of the dado insert, the box ends up very strong and sturdy. The box itself weighs about 70 pounds. We filled in the nail holes and sanded everything down.

We silicon caulked all the inside joints. Added 2 sided tape, and used the silver bubble wrap insulator that goes around water heaters and pipes. I stapled the insulation into the box as well.

We used a circular saw table to cut the wood.

I want to say its something like 2 feet wide by 2 1/2 feet deep by 4 feet tall or so.

It took a small miracle to make everything square.

I’ll post some more pictures, but we are planning to put some wood rails in to allow either trays to slide in and out or I’m going to put wood runners and grove them so 3/4 inch dowels can run across as shelving. This would allow me to hang my moromi in bags above a bucket inside to allow a clean area for the Sake to drip filter.

Trying to work out a way to add some peltier coolers.

Updated Pics

Updated pics of my koji box. A few with my Wife and children. I added (not pictured) a power strip at the bottom-back inside and the shelving.

I have a ceramic heater, but not sure if that will work. Its pretty air-tight. I definitely need some cpu fans in a few places to circulate the air.

Looking into a 24(or 12)VDC aux. power supply to power a few peltier devices.

Working on a really bad cooling system :slight_smile: I’m working a way to mount a few peltier devices directly onto a 1 product cold plate with large heat sinks and fans on them. The peltier’s hot side would be on the cold plate and air would blow across the topside heat sinks. I would then plumb a water supply to circulate the heat out of the cold plate and allowing me to cool down the box. Would be interesting to see what would happen…

Dray, that looks awesome!
I just had a look at the photo’s you posted and I was impressed I must say.
I mean, it has a very “clean” look to it but you managed to also give it a sort of “wooden” look.
Very nice.

Personally I’m tinkering with the thought of either trying another batch or giving up on the sake-projekt altogether, and this construction of yours just might have persuaded me into giving it another try. . .

Ty! Its been fun making it. I am about to load it up in the van and take it home. After stain, we put some semi-gloss protective sealant on it.

dray, what timber did you use in the end? I am planning to re-design my incubator this summer as my degree finishes at the end of this year. I have bought all the components (just need to make it). Are you thinking about modifying anything now that you have made it?

A plan on releasing plans and diagrams once i have made it.

The wood was supposed to be oak vainer plywood, but we figured it was just 3/4 plywood. The edging around the door is hickory (box and door) with an oak panel for the door. The wood for the shelving ended up being stock 2x6 pine I think, stripped up.

Used interlocking joints, wood glue and nails. Stained the outside and added semi-transparent gloss finish. Used water-heater bubble insulation on the inside.

I have more pictures on the album. A 200Watt ceramic simple on/off heater will bring the entire box up to 122-125F easily. Added 2 fans to force hot air down from the top and draw pooling air from the bottom.

When under a humidity load, the door being thinner will condense a lot more. Walls have some condensation, even though the air is maintained inside the box at temperature. Around 85% humidity, the slightest temp difference makes for water to form.

A fancy heater that would pull air from the middle and shoot the hot air up along the walls would help, or use of a few ceramic infrared bulbs shining on the walls would help as well I think.

The door should be just a thick as the box.

Box works quite well. Making it smaller would be good too, as I have enough capacity to make 4-6x koji at one sitting that I need to.

Some other plans is to add the ability to cool the box down as well.

Makes great tempeh as well.

I’m loving all the koji boxes on this forum. I had no idea so many people were getting elaborate with their koji.

Marshall I can’t wait to see your finished design, I love a good set of drawings.

Dray, yours looks great, nice woodwork. Are you still cranking out the koji? What about the peltier incororation?

You said you can make 4-6x the koji you need; how much is that? I think I am maxed out with my system. Anything more that the 11lb I do now and the runaway temps are extreme.

I could make 6 double batches easily in the box I made. Working on a course cloth ‘bag’ to hold the rice on top the wood shelving. I need the rice to be about 2 inches thick, block like. Once it starts to grow, I can spread it out into a baking tin. A batch makes 6 cups of finished koji.

And thank you :slight_smile:

I’m not going with a peltier device. I figure (and it will be not efficient) I will get a very small fridge, a diaphragm pump and something to hold water (water/glycol?) in the fridge. I have 2 transmission cooling radiators. I would put the radiators in with fans blowing through them and circulate coolant into the box. Figure I could get the box to 50 maybe? If this works, I could also ferment in the box as well :slight_smile:

Ah, well, I was curious about the peltier; the ability to cool the box without introducing dry air has been a challenge. I messed around with an ultrasonic humidifier, but gave it up.

That’d be cool if you could also ferment in there. Dual-duty any equipment you can, hehe, lest your pile be as unruly as mine.