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How to Koji Muro

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it is best to sand as you cut your peices. In the pics i show how to tighten up the gaps with your last pieces, so use caution when sanding that you don’t take off your factory crisp edges. I also have a pic of the stainless steel nails that i used (ring shanked). So upon completion of constructing the cedar box. Its best to give a light sanding to touch to anything you want on the outside, it will clean off easier and without floating onto your rice. I then soaked a rag in sodium metabisulfate and water, and wiped (soaked) every crevice with this to kill sanitize and clean the wood of sawdust or any other debris etc… I did this about 3 times.( I tend to be excessive) I made removable stackable shelves, I dipped them in" io star" . Ss nails again here as rust isn’t appealing in the koji muro. Hmmmmmmm. Oh I bought one indoor outdoor thermostat with humidity. Nail that on the inside to give me stats with the remote sensor in the rice I can get both box temps and rice temps. But being a cheaper model humidity was on the unit so I only get box humidity. There was more but not all coming to me at once.

The rice has proved to be difficult compared to a 5g bucket that I was using. I had two mini crockpots, that do great one in a cooler or bucket holds temp almost perfect and gives off the water safely in its porcelain construction. The two together wassnt giving off enough moisture and temp in the larger box. I upgraded to a med sized electric flattop with a aluminium food tray. It regulates temp great “if your room is regulated half decent.”. Mines not I keep it in the fire room so the rice temp bounces 95-105 which for me is fine I’m only trying to propogate kojikin for now. Before setting the rice in a aluminum pan on one of the shelves I soak the walls with a spray bottle on heavy mist. And get the box up to temp. I have found that I needed to raise my rice pan about 12"from the heater + pan, that way I can crank the heater up alittle and get more moisture. Because even at “99”% humidity supposedly according to the digital gauge my rice still drieing out. Though I have been using previously frozen koji rice from a supplier. Which I try to soak alittle now before growing on. I bought this instead of koji kin in a packet, as my first starter. Umm lately I have been getting better at % of kojikin coverage but I still get some spots that dry out more and dont spore.

Some crappy phone pics

Notice the uneven growth kinda like moss growing on the north side of a tree. I have tried covered and uncovered even spraying with a mist occaisionally

Good job on building yourself a koji muro :slight_smile:

On future posts, try to add some space (hit the enter key), as this makes your posts a lot more enticing. I’ll just comment as I remember things, so not in a chronological order (sorry).

Your rice looks a bit greenish. I don’t remember my koji looking green, you should probably check out for possible infections.

Rice are really good at soaking a lot of water out of the air, so a lot of moist is required. Either way, there is not really any reason that your moisture sensor says 100%, while your rice is dry - maybe return it?

I would try to use a different material for containing a water source, as your current material is terrible for transferring heat (with a different material, you should experience a huge increase in moisture).

I would love some higher res pictures, also if you have from the entire building process.

Keep up the good work and remember to share it :wink:

Things are kinda out of order here but I can’t remember all at once. I used 100% cedar , white cedar for the uprights and supports cause it came as 2"x1" boards, (home depot sells them at 8’ for 4.30$ but in their cull or bent wood area its .50c per 4’ section.) :wink: and red cedar tongue and groove for the door floor and backing. I will say that cedar is great with watery areas, but has huge expansion and twist when wet. So I can show you where to accomodate for this. If you have a plainer it is advised to use this on your cull board “sides” to create better sealing edges. If u don’t , don’t worry. You just have to follow more closely to my pics on wedging in your last boards to hold back the twist.

Mr nillson was right about my aluminum pan for the water but because the aluminum on the inside and outside started to oxidize (rust) and make a mess on my flattop (heater). I probably will go back to using a ceramic container/pot.

First, awesome mini muro. Your post inspired me to join the forum. Are you still working on the project?

Your enclosure may be mini by muro standards, but it’s huge really. How much do you make at a time?

I built a part cedar koji box that is 12in/24in/12in or so, and I grow 11lb at a time in there. You could probably make loads and loads of koji in that space.

I like your tiered system a lot. I find runaway-temps challenging with mine, maybe I need to redesign. It’s always improving.

What kind of temperatures are you seeing in the rice mass?

Anyway, lets hear an update on your project!

Here is a pic of mine. I plumb in warm moist air and cover the top with some glass.

Sorry it took me so long to get back to you. Most people here post in weeks and months not day I have tried to liven it up a bit, to no avail. But great muro idea yourself , I like the pipe in temp idea. My temps are pretty consistent with a probed temp digital from Walmart. I have a pic somewhere around here. I’ll try to look back alittle more often again to respond more. My project went on hold after a few failed batches come to find out my water sucks so bad it kept killing my koji slowly. It was fighting to hard for its life. Then with the wood swellling and contracting from moisture and temps it needed some repairs. What kinda metal is that your using? Ss or aluminum. I imagine I could do 30lb a wack but I’m trying to perfect the process first using some small 1-2 lb batches. And i need to build some trays. Got the.cedar not the time.

Hey kojikin,

30 lbs, nice. It is stainless, I encounter a lot of shiny, unwanted stainless on jobsites. Thats an expandable exhaust hood shroud and a cradle I bent from some sort of commercial kitchen grille. The end caps are t&g cedar.

The basket really ensures condensation is shed without touching the koji. And once I was able to let my koji breathe from below, the process became much easier. The rough-side of the cedar facing inward helps wick away moisture too. Plumbing in moisture ensures it is always available, and condensation management ensures there is never too much.

I like this design because it can be taken completely apart and cleaned. When I grow ~10 lb it about fills that box, I find with a forced air system I can stack the rice deeper than usual, but i’ve hit a wall.

I think I may take the climate control apparatus and put it to use on an enclosure like yours. You may find your environment is significantly different when you increase the amount of koji in there. I’d like to hear your results when you do step up the poundage.


How exactly do you plumb in moisture to such a large container? And I found that air acces from bottom in my case created a koji “mat” green and thick on the bottom. You get that?

I have 1" copper pipe that runs the length of the container and has perforations. A couple feet away is a mass of copper pipe and sketchy looking electrical stuff that heats water and fan forces that air up the copper. A pid controller similar to what is used in kilns controls the temp, and since the box is uninsulated, the unit runs a few times a minute.

The rice mass stays white and relatively dry, without any grain matting. I could pour my koji. I do 12 hour mixings until the rising temps in the core demand mixings every few hours.

Do you ever let your koji go to spore? If so have you run into any issues or do anything special?

It keeps bugging me I’m trying to figure out, could you post a larger pic of what your using for your profile pic.

My hops are coming in (chinook crowns) once I get them in the ground im going to try again withbottled water ,(mine has tons of iron and other baddies) and some wood ash. Repairs are complete I used this waterproof np1 sealant. It great stuff. Expands and contracts without letting go of either side, seals and hopefully will lesten the amount of moisture/heat loss and damage from expansion. Also now that the wood stove is down for hopefully till next winter I will have more steady temps. O yeah and I’m going to be running temps of 105f like I have seen from some big time brewers.

I have never tried taking koji to spore, though it may have happened inadvertently in the past. I recall early attempts having some prominent mycelia and dark spots.

My profile pic is the fermenter, during construction when I was wrapping it in copper for glycol. Its been a few years since that pic. I had a nipple welded to the bottom for a ball valve and it has a tilting frame so I can tip the tank for cleaning and whatnot. It’s a little taller than me with the frame. heh.

The highest temp I’ve had koji get was 136F before I was able to let it cool, and it turned out fine. Are you going to keep yours at 105 the whole time for koji kin?

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