GROWING GOURMET - Anto2ni.it

The best one can hope is that contaminants in
the sawdust have been reduced to a level as to
not be a problem, i. e. within the normal time
frame needed for the mushroom mycelium to
achieve thorough colonization.Again, the time
period needed is approximately two weeks.
Should colonization not be complete in two
weeks, the development of contaminants elsewhere
in the substrate is not unusual Of
course, by increasing the spawn rate, colonization
is accelerated, and the window of
opportunity favors the mushroom mycelium.
The recommended sterilization times for various
media are described in Chapters 15—17.
Badham (1988) found that sterilization of
supplemented sawdust under pressure for 4
hours at 19 psi was functionally similar (in
terms of contamination reduction, growth rate,
and yield of Shiitake) to high temperature pasteurization
(190-194° F. or 88-90° C.) for 14
hours at atmospheric pressure (1 psi). Remote
sensing thermometers, placed at a variety of
depths, are used to determine a temperature
profile. When the coolest probe reads 190° F.
(88° C.), steam is continuously supplied for a
minimum of 12 hours, preferably 14-16 hours
depending on substrate mass.
Since heat penetration varies with each substrate
material's density, and is co-dependent
on the moisture content, the use of sterilization
indicator strips is recommended to confirm
that sterilization has actually occurred.
Yet another limiting factor is that media biochemically
changes, potentially generating
toxins to mycelial growth. Should malt agar be
cooked for 2-3 hours at 18 psi, the resulting
media changes into a clear, amber liquid as
sugars have been reduced. Under these conditions,
cultivators say the media has
"caramelized" and generally discard the media
and make up a new batch. Contaminants won't
THE SIX VECTORS OF CONTAMINATION 79
Figure 59. Heat-sensitive sterilization indicator
strips showing no sterilization, partial sterilization,
and complete sterilization.
grow on this media; nor does most mushroom
mycelia. The cultivator is constantly faced
with such dilemmas. What makes a good cultivator
is one who seeks the compromises which
lead most quickly to colonization and
fruitbody production.
4. The Tools: In this category, all tools of the
trade are included from the scalpel to the pressure
cooker to the media vessels. Insufficient
sterilization of the tools can be a direct vector
since contact with the media is immediate.
Flame-sterilizing scalpels is the preferred method
over topical disinfection with alcohol or
bleach. However, the latter is used widely by
the plant tissue culture industry with few problems.
If you are using a pressure cooker for sterilizing
media and other tools, many forget that
although the interior of the vessel has been
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