overheated koji

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overheated koji

Postby orangebird on Wed Nov 03, 2010 9:10 am

first time making koji, day 1....well, it all looked good when i went to bed, gave my hot water bottles a little bump up to get them through the night, and when i woke up 8 hours later, the koji temperature was at 116! way above the recommended range. does it produce its own heat at this stage, like tempeh? and, more importantly, is it dead? i cooled it off and put it back in, but no point in continuing if i've killed it. any ideas?
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Re: overheated koji

Postby Tim Hall on Wed Nov 03, 2010 12:02 pm

It definitely produces it's own heat. I've only made koji a few times, so I have limited experience, but the information I have says don't let it go over 104F.

Personally I would keep it going and see how it turns out. Some enzymes and proteins denature (breakdown from heat) rapidly, but some can tolerate their maximum temperature for quite a while before serious damage is done. 116F is over the ideal limit, but it's not extreme in terms of killing fungi, yeast, bacteria, etc. I wouldn't toss it on speculation...wait and see.

If it starts to grow mold or turns mushy/runny in spots, you'll know the koji is dead.
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Re: overheated koji

Postby Tim Hall on Wed Nov 03, 2010 12:11 pm

According to Shurtleff the ideal ambient temperature range is from about 80-86F with your koji well wrapped/insulated. It wouldn't take many hot water bottles inside an ice chest to go over this range.

I've resolved to go the hi-tech route with temperature-critical ferments. This is a somewhat pricey solution compared to using hot water bottles, but I use a RANCO thermostatic controller (about $100) with a low-wattage light bulb inside an ice chest or old freezer/fridge for things like this.

The RANCO unit I have has two stages, meaning I can control heating and cooling at the same time. So I can actually plug in both a light bulb and a refrigerator to the controller, place the light bulb inside the fridge, set the temperature range, and control the temperature of any ferment within about 3-degrees accuracy.

A cheap rheostat or dimmer switch and light bulb inside an ice chest will also work well, but you'll have to monitor the temperatures, and adjust the rheostat manually to get what you want.

Another hack would be using an aquarium heater in a pot of water. I once saw someone made a "heat bomb" by placing an aquarium heater inside a water-filled plastic bottle...basically an eletronic hot-water bottle. I'm always on the lookout for stuff to hack on craigslist and ebay.
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Re: overheated koji

Postby orangebird on Wed Nov 03, 2010 12:29 pm

thanks tim! i was also leaning toward the theory it could survive its own heat for a while--just wish i knew what happened overnight. it's still producing heat, so we'll see how it goes...
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Re: overheated koji

Postby Aliyanna on Thu Mar 17, 2011 2:12 pm

What I am trying is a roaster that I got at Walmart that goes really low.

I can set the temp way low but the big problem I was having it even set pretty low the temp was goin way high.

Why is koji so hard to make??? We go thru soooooo much miso that I really need to find a way to do this!!

thanks!!
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