GROWING GOURMET - Anto2ni.it

170
GROWING GOURMET MUSHROOMS ON ENRICHED SAWDUST
by the cold mass. (This causes considerable
condensation within the autoclave.) Thennal inertia
is soon overcome, and Boyle's Law becomes
operative.
Many autoclaves not only have a combined
pressure/temperature gauge but also sport a
separate, remote bulb sensor that records temperature
deep within the autoclaved mass. This
combination enables the laboratory personnel
to compare readings between the two gauges.
The duration of the autoclave run should not be
timed until these differentials have been largely
eliminated. (A differential of 100 F. should be
considered negligible.) In real terms, the differential
is normally eliminated within two hours
of start-up. Obviously smaller vessels have reduced
differentials while the most massive
autoclaves have substantial contradictions between
pressure and temperature readings.
Since the duration of "sterilization" is critical,
careful consideration of these temperature
trends can not be underemphasiZed. Cultivators
often mistakenly believe that the mass has
been autoclaved sufficiently when only partial
sterilization has been effected. Discarding several
hundred bags due to insufficient sterilization is a
strong incentive forcultivators to understand the
nuances of autoclave cycling. Redundant
gauges are recommended since devices fail
over time.
When the steam supply to the autoclave is
cut off, pressure and temperature precipitously
decline. Ideally, your autoclave should achieve
a vacuum as it cools. If your autoclave or steam
box does not have a tight seal, and can not form
a vacuum, provisions must be made so that the
air drawn in is free of airborne contamination.
This usually means the timely opening of the
autoclave into the clean room air just as atmo-
spheric pressure is attained. Commonly, an autoclave
can swing in pressure from 20 psi to -20
psi within several hours after steam injection
has stopped. This radical fluctuation in pres-
sure further enhances the quality of the
sterilization cycle. A 40-psi pressure swing is
devastating at the cellular level, disabling any
bacteria or conidia of
surviving endo spores of
contaminating molds.
Unloading the Autoclave
Once the autoclave has achieved a vacuum,
the pressure must be returned to atmospheric
before the door can be opened. Ideally, a gate
valve has been installed on the clean room side,
on a pipe connected to the combination pressure/vacuum
gauge. A microporous filter
canister can be attached for further insurance
that the rush of air into the autoclave does not
introduce contaminant spores. (See Figure
137). When the pressure has equalized, the
next step is to open the drain valve to draw off
excess condensate. Several gallons of condensate
is common. After a few minutes, the
autoclave door on the clean room side can be
opened.
If the mass has just been autoclaved, the containers
will be too hot to unload by hand unless
protective gloves are worn. With the door ajar,
several hours of cooling are necessary before
the bags can be handled freely. Bear in mind
that, as the mass cools, air is being drawn in. If
that air is full of dust, contamination is likely. I
like to thoroughly clean my laboratory while
the autoclave is running. I remove any suspicious
cultures, vacuum and mop the floors, and
wipe the countertopS with alcohol. In a separate
pressure cooker, I autoclave towels, extra
water, and other equipment essential to the impending
inoculation cycle. Selected personnel
for laboratory work wear laboratory garments
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