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Importance of Gas Exchange ( updated: April 15, 2008, at 10:11 AM ) dead link reports, comments and suggestions welcome any time

When mushrooms digest a substrate, they produce carbon dioxide(CO₂), and consume oxygen(O₂).
This is a fairly important factor determining success or demise of a growth attempt.

I prepared a few plastic containers with ¹/₂ pint content with my standard substrate I use for PF tek jars. The plastic containers have a lid, that completely seals the container, so there is no gas exchange.

When I use the same substrate in jars with an aluminum foil lid, like described in the PF-Tek for Simple Minds I get full colonization in 8-12 days.

The spores germinated after 2 days and the colonization went fairly fast for another 3 days, then it suddenly stopped.

I left is then another week, and the colonization barely moved on.
Then I opened the container in font of a flow hood for a few seconds to provide some air.
The colonization again started, and again halted after a few days....
I repeated this another 2 times, and after 1 month into colonization, the substrate is still not completely colonized.
You can see at the pictures how the mycelium has a different appearance in some areas and it shows the different growth and stall phases.

The inoculation was at the sides and one inoculation point at the top of substrate. There is no vermiculite seal, but a thin vermiculite bottom layer.

TEST II :
This time I took the same plastic containers, but fitted them with a polyfill filter.
This is day 6 of colonization, look what a difference the air exchange makes!

One has to love polyfill !
Day 8:

I hereby declare this cake colonized.

FAQ

Why couldn't I put a few heat loving plants in my incubator at night to help with the exchange
Plants convert CO₂ and water into oxygen and sugars....when they have light. This process is called photosynthesis.
The incubator shouldn't have light. So this woudn't really work well.
Plants need some oxygen for themselves too, btw.
Read
http://www.mcps.k12.md.us/departments/eventscience/EBS.OS1_RS~DF.html
http://www.hsv.k12.al.us/schools/middle/wtms/student/cell/cell_energy.html
http://www.saburchill.com/chapters/summary02.html

Besides, the point is not that the oxygen isn't available, it is there , in the normal air, to more than 20%, the problem is that it has to get to the mycelium, and it can't get there, if the jar is sealed.

I've found that the most tightly closed casings during regrow, turned out the best
In the post casing - pre pinning phase the CO₂ levels should be high. This is best achieved by simply covering the casing container with aluminum foil or similar.
It will get some air exchange(same as the jars with the aluminum foil lid), but the CO₂ level will be high. That's what you want to achieve.

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