> I'm interested in dealing with pure H2O2 because, I happen to have
> found a shop that sells it for almost nothing. And I was unable to
> find Hydrogen peroxide food grade, all I found had other chemicals in
> it, which I certainly don't want to put in my substrate. You might
> want to argue about how dangerous such a small amount of those
> chemicals may be, but hey, I don't. I like to be as precise as
Okay. I'm not really interested in arguing, but I am curious.
I've never seen H2O2 sold as anything but pure (diluted with
H20, of course). Nor have I ever seen "food grade" peroxide.
What country are you in?
> My problem with the websites, is that I'm not sure if they know what
> they're talking about, one website talks about a spoon of 3% H2O2,
> while the other talks about 1/3 of a cup of unknown concentration. I
> just cannot base myself on these values and I'm sure you understand.
In the United States, you have to go to some effort to get anything
but 3% or 6% concentrations (i.e., visit a specialty store of some
kind), and 3% is by far the more common. If the website author
doesn't specify, he almost surely means 3%.
If you're worried about the imprecision of the measurements, you
have a point. On the other hand, 3% is only the nominal
concentration; it's not realistic to expect better than 0.1%
accuracy without great effort. Dr. Wayne spends a good number
of pages in his first book talking about how to work out the
real peroxide concentration from your storebought bottle. I've
never bothered; P. cubensis is forgiving enough that that
level of precision isn't necessary. I've never had a problem
assuming that a bottle of "3% Hydrogen Peroxide" is precisely
I've poured lots of agar plates at 0.02% in open air, with
no problems. I've also tried instant brown rice (the kind
that's pre-cooked and freeze-dried; destroys lots of peroxide-
decomposing enzymes) soaked in a 0.3% solution. Most of
the brown rice jars colonized without contamination (remarkable,
since I didn't even bother to filter their air supply), but
the end product was kinda goopy. I think I had too much water
in there. Might work better mixed with verm or something.
(There's no typo in that 0.02%--very little H2O2 is needed
to protect agar. I was measuring it out with an eyedropper.)
The contamination resistance of the brown rice+peroxide is
interesting, and might be a useful technique with any grain,
as long as you do it in addition to pressure-cooking, and
not as a replacement. Say, after you take the jars out of
the pressure cooker, splash enough in to get in the .1% to .3%
range. Since I put the glove box together, contaminated
jars haven't been a problem for me, so I've never experimented
That's it. I'm totally tapped out. There's a couple of numbers
for you to extract out of all that verbiage; if you need more,
you'll need to find a better source. Good luck with your project.