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Category: Contams & Troubleshooting

My incubator with spawn jars was overheated

Overheated incubator for spawn jars
High heat in incubation box, 105F for a few hours. Original photo by D!NGO on Shroomok Discord

Will mycelium survive if my incubator accidentally overheated

A real case that can happen to every mushroom grower

D!NGO: So my thermometer fell out of the box while I was away at work… I'm screwed on this, aren't I? Is it possible they survived at 105°F (40°C)? That would be such a life saver! It's B+ strain btw, if that means anything

Answer from Shroomok: Temperature is one of the most critical factors in mushroom cultivation for any kind of fungi as it affects survival overall, growth rate, time of fruiting, yields, molecular changes in protein structure and even mushroom morphology.

The survival of fungi is determined by temperature, but also exposure time.

Mycelium perishes at high temperatures around 113°F (45°C). However, prolonged exposure at temperatures above 95°F (35°C) more than 3-4 hours can also destroy mycelium cells and eventually kill mycelium.

It was shown in researches and experiments with shiitake and warm-weather species by Tokimoto and Komatsu (1978, 1982)

D!NGO: This is very helpful! Thank you. I haven't thrown anything away yet so fingers crossed

Shroomok: Let's hope for the best 🤞 Keep us updated please!

D!NGO: Dito! I be sure to document everything and go from there!

Notes to consider for other growers:

  1. If you are using a thermostat aka temperature controller, make sure to place the temperature sensor inside the box.
  2. Temperature controller is optional, but very helpful device. It turns on/off the heating element (i.g. heat mat) within required temperature range (typically we need around 75-80F).
  3. If you don't have thermostat, test the box (temperature inside for a few hours) before using it as an incubation box for jars/bags. Use at least simple thermometer inside the box.

Useful stuff on Amazon:

  • Digital Thermometer, Hygrometer with Remote App $12.99 - you'll receive an alert once the temp. is out of its preset range
  • Reptile Heat Mat 9" x 16" $10.99 - budget option, with manual temperature regulator, but w/o thermostat.
  • Inkbird Digital Temperature Controller $35.00 - good quality thermostat w/o heating mat
  • VIVOSUN Heat Mat 10"x 20.75" with Digital Thermostat $30.99 - 2-in-1 Combo Set

Some time later…

Shroomok: Hey D!NGO! Do you remember when you accidentally left spawn jars at 105°F? Did the jars survive? Any updates?

D!NGO: They did not unfortunately. They ended up dying off after a few days. Apparently it was left at that temperature for a few hours

Shroomok: All the jars dead? And mycelium was already there, right?

D!NGO: Yeah they all turned black and just stayed that way. I kept them 3 weeks to see if anything would change and it didn't. And yeah... They were about 1/8th colonized

Shroomok: You're not alone with this case. Thank you for update!

One more case later:

Hey guys, quick one, stupidly left my heater on for about an hour and a half and the room got to 120°Fahrenheit (49°C). Will the jars be ok? It’s cooled down now. Quite a lot of condensation in the jars but they seemed to have cooled off

What do you think happened next? :(

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